Hkkjrh; ekud IS 732 : 2019

Indian Standard

fo|qfr;h ok;fjax vf/"Bkiuksa osQ

fy, jhfr lafgrk

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
( pkSFkk iqujh{k.k )

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Code of Practice for Electrical
Wiring Installations
( Fourth Revision )

ICS 91.140.50

© BIS 2019

Hkkjrh; ekud C;wjks

BUREAU OF INDIAN STANDARDS
ekud Hkou] 9 cgknqj'kkg T+kiQj ekxZ] ubZ fnYyh&110002
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI-110002
www.bis.org.in www.standardsbis.in

February 2019 Price ` 2720 .00

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 CONTENTS
Page

Foreword ................................................................................................................................................................ v
1 Scope ............................................................................................................................................................... 1
2 References ....................................................................................................................................................... 2
3 Terminology .................................................................................................................................................... 6
4 Fundamental Principles, Assessment of General Characteristics .................................................................. 15
4.1 Protection for Safety .............................................................................................................................. 15

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
4.2 Protection for Safety—Protection against Electric Shock ..................................................................... 35
4.3 Protection for Safety — Protection Against Thermal Effects ............................................................... 45
4.4 Protection for Safety — Protection Against Overcurrent ....................................................................... 50
4.5 Protection for Safety — Protection Against Voltage Disturbance and Electromagnetic Disturbance .... 55
5 Selection and Erection of Electrical Equipment ............................................................................................ 83

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

5.1 Common Rules ....................................................................................................................................... 83
5.2 Selection and Erection of Electrical Equipment — Wiring Systems ..................................................... 94
5.3 Selection and Erection of Electrical Equipment— Isolation, Switching and Control .......................... 104
5.4 Selection and Erection of Electrical Equipment —Earthing Arrangements and Protective
Conductors ........................................................................................................................................... 116
5.5 Selection and Erection of Electrical Equipment — Other Equipment ................................................. 122
5.6 Selection and Erection of Electrical Equipment — Safety Services .................................................... 128
6 Verification .................................................................................................................................................. 132
6.1 Void ...................................................................................................................................................... 132
6.2 Initial Verification ................................................................................................................................ 132
6.3 Periodic Verification ............................................................................................................................. 136

ANNEXURES
Annex A Provisions for Basic Protection ....................................................................................................... 138
Annex B Obstacles and Placing Out of Reach ............................................................................................... 139
Annex C Protective Measures for Application Only When the Installation is Controlled or Under the
Supervision of Skilled or Instructed Persons ................................................................................... 140
Annex D Protection of Conductors in Parallel Against Overcurrent ........................................................ 141
Annex E Conditions 1 and 2 of 4.4.4.1 .......................................................................................................... 144
Annex F Position or Omission of Devices for Overload Protection .............................................................. 145
Annex G Position or Omission of Devices for Short-circuit Protection ......................................................... 147
Annex H Explanatory Notes Concerning 4.4.5.1 and 4.4.5.2 ......................................................................... 149
Annex J Guidance for Overvoltage Control by SPDs Applied to Overhead Lines ....................................... 150
Annex K Determination of the Conventional Length, D ............................................................................ 151
Annex L Concise List of External Influences ................................................................................................. 153
Annex M Interdependence of Air Temperature, Relative Air Humidity and Absolute Air Humidity .............. 154
Annex N Classification of Mechanical Conditions ......................................................................................... 163
Annex P Classification of Macro-Environments ............................................................................................ 164
Annex Q Permissible Protective Conductor Currents for Equipment............................................................. 164
Annex R Methods of Installations .................................................................................................................. 166
Annex S Current-Carrying Capacities ............................................................................................................ 173
Annex T Example of a Method of Simplification of the Tables of 5.2.6 ....................................................... 199

( iii )
IS 732 : 2019

Page
Annex U Formulae to Express Current-Carrying Capacities .......................................................................... 201
Annex V Effect of Harmonic Currents on Balanced Three-Phase Systems .................................................... 204
Annex W Selection of Conduit Systems .......................................................................................................... 205
Annex Y Voltage Drop in Consumers’ Installations ....................................................................................... 206
Annex Z Examples of Configurations of Parallel Cables ............................................................................... 207
Annex AA Installation of Surge Protective Devices in TN Systems ................................................................. 209
Annex BB Installation of Surge Protective Devices in TT Systems ................................................................. 210
Annex CC Installation of Surge Protective Devices in IT Systems .................................................................. 212

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Annex DD Installation of Class I, II and III Tested SPDs, for Example in TN-C-S Systems ........................... 213
Annex EE Method for Deriving the Factor K in 5.4.3.1.2 (see also IEC 60724 and IEC 60949) .................... 214
Annex FF Example of Earthing Arrangements and Protective Conductors ..................................................... 217

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Annex GG Explanation of Symbols Used in Luminaires, in Controlgear for Luminaires and in the
Installation of the Luminaires .......................................................................................................... 219
Annex HH Guidance for Emergency Lighting................................................................................................... 221
Annex JJ Guidance for Fire Protection Equipment ......................................................................................... 222
Annex KK Methods for Measuring the Insulation Resistance/ Impedance of Floors and Walls to Earth or
to the Protective Conductor ............................................................................................................. 223
Annex LL Method LL1, LL2 and LL3 ............................................................................................................. 225
Annex MM Guidance on the Application of the Rules of Clause 6.2 Initial Verification ................................... 227
Annex NN Example of a Diagram Suitable for the Evaluation of the Voltage Drop ......................................... 230
Annex PP Recommendation for Electrical Equipment, Which is Being Re-Used in Electrical Installations . 231
Annex QQ Description of the Installation for Verification ................................................................................ 231
Annex RR Form for Inspection of Electrical Installations ................................................................................ 233
Annex SS Report of Verification ...................................................................................................................... 237
Annex TT Extracts from Central Electrictty Authority Notification, New Delhi, the 20th September, 2010 .. 239

( iv )
FOREWORD

This Indian Standard (Fourth Revision) was adopted by the Bureau of Indian Standards, after the draft finalized
by the Electrical Installation Sectional Committee had been approved by Electrotechnical Division Council.
This standard was first published in 1958 to guide and govern installation of electrical wiring in buildings with
particular reference to safety and good engineering practice.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The second revision of this standard was brought out in 1982 in 3 parts. Soon after the publication of the second
revision, work on the preparation of National Electric Code (NEC) began. NEC was published in 1985. NEC,
besides drawing assistance from IS 732, further elaborates the stipulations on wiring practice with reference to
specific occupancies.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Soon after the publication, major revision of IS 732 was carried out in order to align with the modified pattern of
power consumption and advance technology in installation design. There was also a strong need to align the Code
with international level, namely at the level of IEC/TC 64 ‘Electrical Installation of Building’. The third revision
was published in 1989.
Since publication of IS 732: 1989, lot of changes have taken place in Indian Electrical scenario. Due to increase
of population and rapid urbanization over last few decades there has been significant increase in residential,
commercial and other buildings in all major cities in India. This has led to a significant rise in the installation of
electrical wiring and electrical services in all types of buildings in urban, semi-urban and rural areas.
NEC 2011 has since been published taking into account many of the changes mentioned above. Central Electricity
Authority has also brought out regulations for “Measures relating to safety and electric supply”.
The work of fourth revision of IS 732 started almost simultaneously with preparation of NEC 2011. Initially,
Committee was working to align this standard completely with IEC Standard and planning to make this standard
as IS/IEC 60364 series ‘Low-voltage Electrical Installation’. However, further study revealed that many significant
changes are required to ensure that this standard is in line with NEC 2011, CEA Regulations, 2010 and present
Indian environment and power supply conditions.
This version of IS 732 is largely based on the following standards:
IEC 60364-1 : 2005 Low-voltage electrical installations — Part 1: Fundamental principles,
assessment of general characteristics, definitions
IEC 60364-4-41 : 2005 Low-voltage electrical installations — Part 4-41: Protection for safety —
Protection against electric shock
IEC 60364-4-42 : 2010 Low-voltage electrical installations — Part 4-42: Protection for safety —
Protection against thermal effects
IEC 60364-4-43 : 2008 Low-voltage electrical installations — Part 4-43: Protection for safety —
Protection against over current
IEC 60364-4-44 : 2007 Low-voltage electrical installations — Part 4-44: Protection for safety —
Voltage disturbance and electromagnetic disturbance
IEC 60364-5-51 : 2005 Electric installations of buildings — Part 5-51: Selection and erection of
electrical equipment — Common rules
IEC 60364-5-52 : 2009 Electric installations of buildings — Part 5-52: Selection and erection of
electrical equipment — Wiring systems
IEC 60364-5-53 : 2015 Electric installations of buildings — Part 5-53: Selection and erection of
electrical equipment — Isolation switching and control

(v)
 IEC 60364-5-54 : 2011 Electric installations of buildings — Part 5-54: Selection and erection of
electrical equipment — Earthing arrangements and protective conductors
IEC 60364-5-55 : 2016 Electric installations of buildings — Part 5-55: Selection and erection of
electrical equipment — Other equipment
IEC 60364-5-56 : 2009 Electric installations of buildings — Part 5-56: Selection and erection of
electrical equipment — Safety services
IEC 60364-6 : 2016 Low voltage electrical installations — Part 6: Verification
Necessary changes have been made to ensure that the above mentioned points are taken care of. Whenever necessary,
provision of this code shall be read in conjunction with other codes such as those on earthing, lightning protection
and the National Electrical Code.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The major deviations from the IEC standards are listed below. These differences are mainly because the revision
takes into account the National Electric Code and CEA notification dated 20th September 2010 for ‘Measures
relating to Safety and Electric supply’:
a) All country specific comments and notes for special applications mentioned in IEC 60364 have not been

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

incorporated in this standard.
b) CEA Rule 42 – Earth leakage protection: To align with CEA Rule 42 and the National Electrical Code,
the provisions given in IEC standards have been modified to ensure uniform application of RCD for
protection in this standard.
c) CEA Rule 41 % Connection with Earth: To align with CEA Rule 41 and National Electric Code, earthing
systems have been modified. For example as per CEA and National Electric Code 2011, for 415 V
systems, double earthing is mandatory. Also a section on earthing will follow in the National Electric
Code and IS 3043.
d) IEC 60364 -5- 52 wiring Installation: Minimum nominal cross-sectional area of Conductors has been
changed as per National Electric Code in this standard.
The provisions of IEC 60364-7 ‘Requirements for special installations or locations’ is not included in the
requirements of IS 732 as it shall be incorporated in National Electric Code during its revision.

( vi )
 IS 732 : 2019

Indian Standard
CODE OF PRACTICE FOR ELECTRICAL WIRING
INSTALLATIONS
( Fourth Revision )
1 SCOPE 1.2.1 This standard applies to items of electrical
equipment only, so far as, its selection and application
This Code gives the rules for the design, erection, and
in the building electrical installation are concerned. The

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
verification of electrical installations. The rules are
rules in this standard do not deal with the requirements
intended to provide for the safety of persons, livestock
for the factory-built construction of electrical equipment,
and property against dangers and damage which may
namely, type tested (TT) and partially type tested (PTT),
arise in the reasonable use of electrical installations
Switchgear and Controlgear Assemblies, Distribution
and to provide for the proper functioning of those

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Boards, Fuse Distribution Boards, Circuit Breaker
installations.
Distribution Boards, Bus-bar Trunking Systems (bus-
1.1 General ways), electric supply track systems for luminaries,
power track system intended for wall and ceiling
This standard applies to the design, erection and mounting, boxes and enclosures for electrical accessories
verification of electrical installations such as those of: for house-hold and similar fixed electrical installations,
a) residential premises, electricity control units known as Consumer Units or
b) commercial premises, Consumer Control Units. The factory-built assemblies
c) public premises, of these electrical equipment are required to comply with
IS 8623 (all parts), IS 14772, BSEN 60439-1, BSEN
d) industrial premises,
60439-2, BSEN 60439-3. BSEN 60439-4, BSEN 60570,
e) agricultural and horticultural premises,
BSEN 60570-2-1, BSEN 60670-1, BSEN 60670-22,
f) photovoltaic systems, and IEC 60670-21, BSEN 61534-21 and other relevant
g) low-voltage generating sets. Indian Standards/IEC Standards.
NOTE — “premises” covers the land and all facilities including
buildings belonging to it.
1.2.2 This standard does not apply to the following
electrical installations:
1.2 This standard include requirements for:
a) construction sites, exhibitions, shows,
a) circuits supplied at normal voltage upto and fairgrounds and other installations for
including 1 000V a.c. or 1 500V d.c. For a.c., temporary purposes including professional
the preferred frequencies which are taken into stage and broadcast applications;
account in this standard are 50 Hz, 60 Hz and b) marinas;
400 Hz.The use of other frequencies for c) external lighting and similar installations;
special purposes is not excluded.
d) mobile or transportable units;
b) circuits, other than the internal wiring of e) highway equipment and street furniture;
equipment, operating at voltage exceeding
f) medical locations;
1 000 V a.c., for example discharge lighting,
g) operating and maintenance gangways;
electro static precipitator, X-ray and scanning
apparatus, high voltage electrode boilers. h) pre-fabricated building;
j) systems for the distribution of electricity to
c) wiring systems and cables not specifically
the public by Electricity Distribution
covered by the standards for appliances,
Companies governed by the Central Electricity
namely product standards.
Authority Regulations made under the
d) all consumer installations external to buildings. Electricity Act, 2003;
e) fixed wiring for information and communication k) power generation and transmission for such
technology, signalling, control and the like distribution system in (a);
(excluding internal wiring of equipment). m) railway traction equipment, rolling stock and
f) any extension, namely, additions and alteration signalling equipment;
to installations and also parts of the existing n) electrical equipment of motor vehicles, except
installation affected by an addition or alteration. those to which the requirements of the regulation

1
IS 732 : 2019

concerning mobile units are applicable; regulations made by the appropriate Electricity
p) electrical equipment on board ships; Regulatory Commission shall prevail. The Electricity
q) electrical equipment of mobile and fixed off- Regulatory Commissions in the Supply Code and
shore installations; Distribution Code made by them generally include a
r) electrical equipment in aircraft; deeming provision that the statutory requirements in
s) those aspects of mines and quarries which are Supply Code and Distribution Code are duly observed
specially covered by statutory Regulation by users and consumers of electricity, if the electrical
under Mines Act, 1952 (35 of 1952); installation owned by them are constructed, installed,
t) radio interference suppression equipment, protected, inspected, tested, operated, worked and
except so far as, it affects safety of the maintained according to this Indian Standard besides,
electrical installation; complying with the provisions of sub regulation (1),
(3) and (4) of the Central Electricity Authority

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
u) external lighting protection systems (LPS)
(Measures Relating to Safety and Electric Supply)
for buildings and structures covered under
Regulations, 2010 and all other applicable statutory
IS/IEC 62305;
regulations made under the Electricity Act, 2003.
v) safety machinery and electric equipment of
machinery covered under Factory Act, 1948 2 REFERENCES

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

and other Special Publications of BIS;
The standards given below contain provisions which,
w) those aspects of lift installations which are
through reference in this text, constitute provisions of
covered under relevant parts of statutory Rules
this standard. At the time of publication, the editions
made under Helps Act framed by various states
indicated were valid. All standards are subject to
in India and also covered by the various Indian
revision, and parties to agreements based on this
Standards on Lifts and Escalators formulated
standard are encouraged to investigate the possibility
by BIS;
of applying the most recent editions of these standards.
x) electric fences covered by relevant Indian
Standard relating to Electrical safety in IS No./ Title
consumer’s appliances; and International
y) public street-lighting installation which are Standards
part of distribution system by Public utility 1293 : 2005 Plugs and socket — outlets of
under the Electricity Act, 2003. rated voltage up to and including
250 volts and rated current up to
1.3 Installation of Premises Subject to Licensing 16 amperes
For installation of premises over which a licensing or 1885 Electrotechnical vocabulary:
other authority exercises a statutory control, the (Part 37) : 1993 Part 37 Tariffs for Electricity
requirements of that authority shall be as ascertained (first revision)
and complied with in the design and execution of the (Part 70) : 1993/ Generation, transmission and
installation. IEC 60050 (604) : distribution of electricity —
1987 Operation
1.3.1 The relationship with the Central Electricity 8130 : 2013 Conductors for insulated electric
Authority (Measure Relating to Safety and Electric cables and flexible cords (second
Supply) Regulations 2010, and Regulations made by revision)
appropriate Electricity Regulatory Commission under 8623 (Part 1) : 1993/ Low-voltage switchgear and
Electrically Act, 2003 is as given below: IEC 60439-1(1985) and controlgear assemblies:
Part 1 Type-tested and partially
The legal status of this standard, including other Codes of
type-tested assemblies
Practice Standards of the Bureau of Indian Standard or
8623 (Part 2) : 1993/ Low-voltage switchgear and
National Electrical Code, is explained in sub-regulation
IEC 60439-2 (1987) controlgear assemblies: Part 2
(2) of Regulation 12 of the Central Electricity Authority
Particular requirements for
(Measure Relating to Safety and Electric Supply) busbar trunking systems
Regulations, 2010. Hence, these Rules may be used to (busways)
satisfy any statutory approving authority under the 9000 (Part 11) : 1983 Basic environmental testing
Electricity Act, 2003 or in any Court of Law in evidence procedures for electronic and
to claim compliance with a statutory requirement. electrical items: Part 11 Salt mist
The rules in this Code, however, are intended to test
supplement the Statutory Regulations made by the 9537 (All Parts) Conduits for electrical
appropriate Electricity Regulatory Commission and in installations — Specification
the event of any inconsistency; the provisions of those 10322 (All Parts) Luminaires
2
 IS 732 : 2019

IS No./ Title IS No./ Title

International International
Standards Standards

11731 (All Parts) Methods of test for determi- (Part 6/Sec 1) : Generic standards, Section 1:
nation of the flammability of 2008 Immunity for residential,
solid electrical insulating commercial and light-industrial
materials when exposed to an environments
igniting source (Part 6/Sec 2) : Generic standards, Section 2
12032 (All Parts) Graphical symbols for use on 2008 Immunity for industrial
equipment environments
12360 : 1988 Voltage bands for electrical (Part 6/Sec 3) : Generic standards, Section 3

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
installations including preferred 2002 Emission standard for
voltages and frequency residential, commercial and
13234 (Part 0) : 2016 Short-circuit currents in three- light-industrial environments
phase a.c. systems: Part 0 14772 : 2000 Enclosures for accessories for
Calculation of currents (first household and similar fixed

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

revision) electrical installations
13252 (Part 1) : 2010/ Information technology equip- 14927 (All Parts) Cable trunking and ducting
IEC 60950-1 : 2005 ment — Safety: Part 1 General systems for electrical installations
requirements 14930 (All Parts) Conduit systems for electrical
13703 Low voltage fuses for voltages installations
not exceeding 1 000 V ac or 15382 (Part 1) : 2014 Insulation co-ordination for
1 500 V d.c.: equipment within low-voltage
(Part 2/Sec 1) : Fuses for use by authorized systems: Part 1 Principles,
1993 persons, Section 1 Supple- requirements and tests
mentary requirements 15697 Capacitors for use in tubular
(Part 4) : 1993 Supplementary requirements for fluorescent and other discharge
fuse-links for the protection of lamp circuits:
semiconductor devices (Part 1) : 2013 Safety requirements
13736 (All Parts) Classification of environmental (Part 2) : 2013 Performance requirements
conditions 16242 Uninterruptible power systems
14700 Electromagnetic compatibility (UPS):
(EMC): (Part 1) : 2014 General and safety requirements
(Part 4/Sec 2) : Testing and measurement (Part 3) : 2014/ Method of specifying the
2008 techniques, Section 2 IEC 62040-3 : 2011 performance and test requirements
Electrostatic discharge immunity 16463 (Part 12) : Surge-protective device
test 2016/IEC 61643-12 : connected to low-voltage power
(Part 4/Sec 3) : Testing and measurement 2008 distribution systems: Part 12
2008 techniques, Section 3 Radiated, Performance requirements and
radio-frequency, electro- testing methods
magnetic field immunity test IEC 60050-195 International Electrotechnical
(Part 4/Sec 4) : Testing and measurement Vocabulary — Part 195:
2008 techniques, Section 4 Electrical Earthing and protection against
fast transient/burst immunity test electric shock
(Part 4/Sec 6) : Testing and measurement IEC 60050-826 International Electrotechnical
2016 techniques, Section 6 Immunity Vocabulary — Part 826:
to conducted disturbances, Electrical installations
induced by radio-frequency fields IEC 60073 : 1996 Basic and safety principles for
(Part 4/Sec 8) : Testing and measurement man-machine interface, marking
2008 techniques, Section 8 Power and identification — Coding
frequency magnetic field principles for indication devices
immunity test and actuators
(Part 4/Sec 12) : Testing and measurement IS/IEC 60079 Electrical apparatus for
2008 techniques, Section 12 (All Parts) explosive gas atmospheres
Oscillatory waves immunity test IEC 60245-3 Rubber insulated cables —
Rated voltages up to and

3
IS 732 : 2019

IS No./ Title IS No./ Title

International International
Standards Standards
including 450/750 V — Part 3: IEC 60446 Basic and safety principles for
Heat resistant silicone insulated man-machine interface, marking
cables and identification —
IEC 60255-22-1 : Electrical relays — Part 22: Identification of conductors by
1988 Electrical disturbance tests for colours or numerals
measuring relays and protection IEC 60447 : 1993 Man-machine interface (MMI)
equipment, Section 1: 1 MHz — Actuating principles
burst disturbance tests IEC 60449 Voltage bands for electrical
IEC 60269-3 Low-voltage fuses — Part 3:

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
installations of buildings
Supplementary requirements for IS/IEC 60479-1 : Effects of current on human
fuses for use by unskilled persons 2005 beings and livestock — Part 1:
(fuses mainly for household and General aspects
similar applications) — IEC 60502 (All Parts) Power cables with extruded
Examples of standardized

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

insulation and their accessories
systems of fuses A to F for rated voltages from 1 kV
IEC 60287 (All Parts) Electric cables — Calculation of (U m = 1.2 kV) up to 30 kV
the current rating (Um = 36 kV)
IEC 60331 (All Parts) Tests for electric cables under IS/IEC 60529 Degrees of protection provided
fire conditions — Circuit by enclosures (IP Code)
integrity IEC 60570 Electrical supply track systems
IEC 60331-11 Tests for electric cables under for luminaires
fire conditions — Circuit IEC 60598-2-13 : Luminaires — Part 2-13:
integrity — Part 11: Apparatus 2006 Particular requirements —
— Fire alone at a flame Ground recessed luminaires
temperature of at least 750 °C IEC 60598-2-22 : Luminaires — Part 2-22:
IEC 60331-21 Tests for electric cables under 1997 Particular requirements —
fire conditions — Circuit Luminaires for emergency
integrity — Part 21: Procedures lighting
and requirements — Cables of IEC 60598-2-24 Luminaires — Part 2-24:
rated voltage up to and including Particular requirements —
0.6/1.0 kV Luminaires with limited surface
IEC 60332 (All Parts) Tests on electric and optical fiber temperatures
cables under fire conditions IEC 60670-21 Boxes and enclosures for
IEC 60332-1-1 Tests on electric and optical fibre electrical accessories for
cables under fire conditions — household and similar fixed
Part 1-1: Test for vertical flame electrical installations — Part
propagation for a single 21: Particular requirements for
insulated wire or cable — boxes and enclosures with
Apparatus provision for suspension means
IEC 60332-1-2 Tests on electric and optical fibre IEC 60702 (All Parts) Mineral insulated cables and
cables under fire conditions — their terminations with a rated
Part 1-2: Test for vertical flame voltage not exceeding 750 V
propagation for a single insulated IEC 60724 Short-circuit temperature limits
wire or cable — Procedure for 1 of electric cables with rated
kW pre-mixed flame voltages of 1 kV (Um = 1.2 kV)
IEC 60364 (All parts) Low-voltage electric installations and 3 kV (Um = 3.6 kV)
IEC 60445 Basic and safety principles for IS/IEC 60898 Electrical accessories — Circuit-
man-machine interface, marking (All Parts) breakers for overcurrent
and identification — protection for household and
Identification of equipment similar installations
terminals and of terminations of IS/IEC 60947-2 Low-voltage switchgear and
certain designated conductors,
controlgear — Part 2: Circuit-
including general rules for an
breakers
alphanumeric system

4
 IS 732 : 2019

IS No./ Title IS No./ Title

International International
Standards Standards

IS/IEC 60947-3 Low-voltage switchgear and IEC 61439-1 Low-voltage switchgear and
controlgear — Part 3: Switches, controlgear assemblies — Part 1:
disconnectors, switch- General rules
disconnectors and fuse- IEC 61439-2 Low-voltage switchgear and
combination units controlgear assemblies — Part 2:
IEC 60947-6-2 Low-voltage switchgear and Power switchgear and
controlgear — Part 6-2: Multiple controlgear assemblies
function equipment — Control IEC 61534 (All Parts) Power track systems

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
and protective switching devices IEC 61535 Installation couplers intended for
(or equipment) (CPS) permanent connection in fixed
IEC 60947-7 Low-voltage switchgear and installations
(All Parts) controlgear — Part 7: Ancillary IEC 61537 Cable management — Cable
equipment tray systems and cable ladder

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

IEC 60949 Calculation of thermally systems
permissible short-circuit IS/IEC 61557-1 : Electrical safety in low voltage
currents, taking into account 2007 distribution systems up to
non-adiabatic heating effects 1 000 V a.c. and 1 500 V d.c. —
IEC 60998 (All Parts) Connecting devices for low- Equipment for testing,
voltage circuits for household measuring or monitoring of
and similar purposes — Part 1: protective measures: Part 1
General requirements General requirements
IEC 61000-2 Electromagnetic compatibility IS/IEC 61557-2 : Electrical safety in low voltage
(All Parts) (EMC) — Part 2: Environment 2007 distribution systems up to
IEC 61009 (All Parts) Residual current operated 1 000 V a.c. and 1 500 v d.c. —
circuit-breakers with integral Equipment for testing,
overcurrent protection for measuring or monitoring of
household and similar uses protective measures: Part 2
(RCBOs) Insulation resistance
IEC 61024-1 : 1990 Protection of structures against IEC 61577-6 Electrical safety in low voltage
lightning — Part 1: General distribution systems up to
principles 1 000 V a.c. and 1 500 V d.c. —
IEC 61082 (All Parts) Preparation of documents used Equipment for testing,
in electrotechnology measuring or monitoring of
IEC 61140 Protection against electric shock protective measures — Part 6:
— Common aspects for Residual current devices (RCD)
installation and equipment in TT and TN systems
IEC 61312-1 : 1995 Protection against lightning IEC 61558-2-1 Safety of power transformers,
electromagnetic impulse — Part power supplies, reactors and
1: General principles similar products — Part 2-1:
IEC/TS 61312-2 : Protection against lightning Particular requirements for tests
1999 electromagnetic impulse for separating transformers and
(LEMP) — Part 2: Shielding of power supplies incorporating
structures, bonding inside separating transformers for
structures and earthing general applications
IEC/TS 61312-3 : Protection against lightning IEC 61558-2-4 Safety of power transformers,
2000 electromagnetic impulse — power supply units and similar
Part 3: Requirements of surge Part 2-4: Particular requirements
protective devices (SPDs) for isolating transformers for
IEC 61346-1 : 1996 Industrial systems, installations general use
and equipment and industrial IS/IEC 61558-2-6 : Safety of power transformers,
products — Structuring principles 1997 power supply units and similar
and reference designations — — Part 2-6: Particular
Part 1: Basic rules requirements for safety isolating
transformers for general use
5
IS 732 : 2019

IS No./ Title 3.3 Ambient Temperature — The temperature of the

International air or other medium where the equipment is to be used.
Standards
3.4 Appliance — An item of current-using equipment
IEC 61558-2-15 Safety of power transformers, other than a luminaire or an independent motor.
power supply units and similar
3.5 Arm’s Reach — A zone extending from any point
— Part 2-15: Particular
on a surface where persons usually stand or move about,
requirements for isolating
to the limits which a person can reach with the hand in
transformers for the supply of
any direction without assistance.
medical locations
IEC 61643 (All Parts) Low-voltage surge protective NOTE — This space is by convention, limited as shown in
devices Fig. 1.
IEC 61643-1 : 1998 Surge-protective device

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
connected to low-voltage power
distribution systems — Part 1:
Performance requirements and
testing methods
IEC 61936-1 Power installations exceeding 1

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

kV a.c. — Part 1: Common rules
IEC 61995 (All Parts) Devices for the connection of
luminaires for household and
similar purposes
IEC Guide 104 The preparation of safety
publications and the use of basic
safety publications and group
safety publications
IS/IEC 62305-1 : Protection against lightning —
2010 Part 1: General principles
IS/IEC 62305-3 : Protection against lightning —
2010 Part 3: Physical damage to
structures and life hazard
IS/IEC 62305-4 : Protection against lightning —
2010 Part 4: Electrical and electronic
systems within structures
IS/ISO 834 Fire-resistance tests — Elements
FIG. 1 ARM’S REACH
of building construction
IS/ISO 8528-12 : Reciprocating internal 3.6 Back-up Protection — Protection which is
1997 combustion engine driven intended to operate when a system fault is not cleared
alternating current generating or abnormal condition not detected in the required time,
sets — Part 12: Emergency because of failure or inability of other protection to
power supply to safety services operate or failure of appropriate circuit-breaker to trip.
ISO 30061 : 2007 Emergency lighting
3.7 Barrier V— A part providing a defined degree of
3 TERMINOLOGY protection against contact with live parts, from any
usual direction of access.
For the purposes of this standard, the following
definitions shall apply. As far as possible, the definitions 3.8 Basic Insulation — Insulation applied to live parts
below are aligned with IS 1885 and the fundamental to provide basic protection against electric shock and
International vocabulary IEC 60050-826. which does not necessarily include insulation used
exclusively for functional purpose.
3.1 Accessory — A device, other than current-using
equipment, associated with such equipment or with the 3.9 Basic Protection — Protection against electric
wiring of an installation. shock under fault-free condition.
NOTE — For low voltage installations, systems and equipment,
3.2 Agricultural and Horticultural Premises —
basic protection generally corresponds to protection against
Rooms, location or areas where live stocks are kept; direct contact that is “contact of persons or live parts”.
feed, fertilizers, vegetable and animal products are
produced, stored, prepared or processed; plants are 3.10 Basin of Fountain — A basin not intended to be
grown, such as greenhouse. occupied by persons and which cannot be accessed

6
 IS 732 : 2019

(reached by persons) without the use of ladders or or in the ground, open or ventilated or closed, and
similar means. For basins of fountains which may be having dimensions which do not permit the access of
occupied by persons, the requirement of swimming persons but allow access to the conductor and/or cables
pools applies. throughout their length during and after installation.
3.11 Bonding Conductor — A protective conductor NOTE — A cable channel may or may not form part of the
building construction.
providing equipotential bonding.
3.12 Bonding Network (BN) — A set of 3.22 Cable Cleat — A component of a support system
interconnected conductive parts that provide a path for which consists of elements spread at intervals along
current at frequencies from direct current (d.c.) to radio the length of the cable or conduits and which
frequency (RF) intended to divert, block or impede the mechanically retains the cable or conduit.
passage of electromagnetic energy. 3.23 Cable Bracket — A cable support consisting of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3.13 Bonding Ring Conductor (BRC) —A bus single devices fixed to elements of building or plant
earthing conductor in the form of a closed ring. construction.

NOTE — Normally the bonding ring conductor, as part of the 3.24 Cable Coupler — A means enabling the
bonding network, has multiple connections to the common connection, at will, of two flexible cables. It consists

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

bonding network (CBN) that improves its performance. of a connector and a plug.
3.14 Booth — Non-stationary unit intended to 3.25 Cable Ducting — A manufactured enclosure of
accommodate equipment generally for pleasure or metal or insulating material, other than conduit or cable
demonstration purpose. trunking, intended for the protection of cables which
3.15 Building Voids, Accessible — Space within the are drawn-in after erection of the ducting, but which
structure or the components of a building accessible is not specifically intended to form part of a building
only at certain points. structure.
NOTES 3.26 Cable Trunking — A factory made closed support
1 Examples are: Space within partitions, suspended floors, and protection system into which conductors and/or
ceilings and certain types of window frame, door frame and cables are laid after removal of the cover.
architraves.
2 Specially formed building voids are also as ducts. 3.27 Cable Tunnel — An enclosure (corridor)
containing supporting structures for conductors and/or
3.16 Building Void, Non-accessible — A space within cables and joints and whose dimensions allow free
the structure or the components of building which has access to persons throughout the entire length.
no ready means of access.
3.28 Cable Tray — A cable support consisting of a
3.17 Buried Direct — A cable laid in the ground in continuous base with raised edges and no covering. A
intimate contact with the soil. cable tray is considered to be non-perforated, where
3.18 Bunched — Cables are said to be bunched when less than 30 percent of the material is removed from
two or more cables are contained within a single the base.
conduit, duct, ducting, or trunking or, if not enclosed, 3.29 Cable Ladder — A cable support occupying less
are not separated from each other. than 10 percent of the plan area and consisting of a
3.19 Busbar Trunking System — A type-tested series of supporting elements rigidly fixed to each
assembly, in the form of an enclosed conductor system other or to a main supporting member or members.
comprising solid conductors separated by insulating 3.30 Circuit —An assembly of electrical equipment
materials. The assembly may consist of units such as: supplied from the same origin and protected against
a) Busbur trunking units, with or without tap-off overcurrent by the same protective devices. Certain
facilities; types of circuit are categorised as follows:
b) Tap-off units where applicable; and a) Category 1 Circuit — A circuit (other than a
c) Phase-transposition, expansion, building- fire alarm or emergency lighting circuit)
movement, flexible, end-feeder and adaptor operating at low voltage and supplied directly
units. from a mains supply system.
3.20 Bypass Equipotential Bonding Conductor — b) Category 2 Circuit — With the exception of
Bonding conductor connected in parallel with the fire alarm and emergency lighting circuits, any
screens of cables. circuit for telecommunication (for example,
radio, telephone, sound distribution, intruder
3.21 Cable Channel — An enclosure situated above alarm, bell, call and data transmission circuits)

7
IS 732 : 2019

which is supplied from a safety source. 3.40 Competent Person —A person who possesses
c) Category 3 Circuit — A fire alarm circuit or sufficient technical knowledge, relevant practical skill
an emergency lighting circuit. and experience for the nature of the electrical work
undertaken and is able at all the time to prevent danger
3.31 Cartridge Fuse Link — A device comprising a and, where appropriate, injury to him/herself and others.
fuse element or several fuse elements connected in
parallel enclosed in a cartridge usually filled with an 3.41 Conduit —A part of a closed wiring system a
arc-extinguishing medium and connected to circular or non-circular cross-section for conductors
terminations. The fuse link is the part of a fuse which and/or cables in electrical installations, allowing them
requires replacing after the fuse has operated. to be drawn in and/or replaced. Conduits should be
sufficiently closed-jointed so that the conductors can
3.32 Circuit Breaker — A mechanical switching only be drawn in and not inserted laterally.
device capable of making, carrying and breaking

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
currents under normal circuit conditions and also of 3.42 Confined Conductive Location — Allocation
making, carrying for as specified, and breaking currents having surfaces which are mainly composed of
under specified abnormal circuit conditions such as extraneous conductive parts and which are of such
those of short circuit. dimensions that movement is restricted to such an extent
that contact with surfaces is difficult to avoid (for

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — A circuit breaker is usually intended to operate example in a boiler).
infrequently, although some types are suitable for frequent
operation. 3.43 Connector — The part of a cable coupler or of
3.33 Circuit Breaker Linked— A circuit breaker the an appliance coupler which is provided with female
contacts of which are so arranged as to make or break contact and is intended to be attached to the flexible
all poles simultaneously or in a definite sequence. cable connected to the supply.

3.34 Class I Equipment — Equipment in which 3.44 Consumer Unit (may also be known as a
protection against electric shock does not rely on basic consumer control unit or electricity control unit) — A
insulation only, but which includes an additional safety particular type of distribution board comprising a type-
precaution in such a way that means are provided for tested co-ordinated assembly for the control and
the connection of exposed conductive parts to a distribution of electrical energy, principally in domestic
protective conductor in the fixed wiring of installation premises, incorporating manual means of double-pole
in such a way that accessible conductive parts may not isolation on the incoming circuit(s) and an assembly of
become live in the event of a failure of basic installation. one or more fuses, circuit-breakers, residual current
operated devices or signalling and other devices proven
NOTE — For information on classification of equipment with during the type-test of the assembly as suitable for such
regard to means provided for protection against electric shock,
see IEC 61140.
use.

3.35 Class II Equipment — Equipment in which 3.45 Continuous Operating Voltage (Uc) —
protection against electric shock does not rely on basic Maximum r.m.s voltage which may be continuously
insulation only, but in which additional safety applied to an SPD’s mode of protection. This is equal
precautions, such as double or reinforced insulation are to rated voltage.
provided, there being no provision for the connection 3.46 Conventional Impulse Withstand Voltage —
of exposed metal work of the equipment to a protective The peak value of an impulse test voltage at which
conductor, and no reliance upon precautions to be taken insulation does not show any disruptive discharge, when
in the fixed wiring of the installation. subjected to a specified number of applications of
impulses of this value, under specified condition.
3.36 Class III Equipment — Equipment in which
protection against electric shock relies on supply at 3.47 Conventional Touch Voltage Limit —
SELV and in which voltages higher than those of SELV Maximum value of the touch voltage which is permitted
are not generated. to be maintained indefinitely in specified conditions
of external influences.
3.37 Cold Tail — The interface between the fixed
installation and a heating unit. 3.48 Conventional Operating Current (of a
Protective Device) — A specified value of the current
3.38 Combustible — Capable of burning. which causes the protective device to operate within a
3.39 Common Equipotential Bonding System, specified time, designated conventional time.
Common Bonding Network — Equipotential bonding NOTES
system providing both protective equipotential bonding 1 For fuses this current is called the conventional fusing current.
and functional equipotential bonding. For circuit breakers this current is called the conventional
operating current.

8
 IS 732 : 2019

2 The conventional operating current is greater than the rated 3.62 Earth Fault Current — A current resulting from
current or current setting of the device and the conventional
a fault of negligible impedance between a line
time varies according to the type and rated current of the
protective device. conductor and an exposed conductive part or a
protective conductor.
3.49 Current Carrying Capacity of a Conductor —
The maximum current which can be carried by a 3.63 Earth Electrode Resistance — The resistance
conductor under specified conditions without its steady of an earth electrode to earth.
state temperature exceeding a specified value. 3.64 Earth Fault Loop Impedance — The impedance
3.50 Current Using Equipment — Equipment which of the earth fault current loop (phase to earth loop)
converts electrical energy into another form of energy, starting and ending at the point of earth fault. This
such as light, heat, or motive power. impedance is denoted by the symbol Z. The earth fault
loop comprises the following, starting at the point of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3.51 Danger — Danger to health or danger to life or fault:
limb from shock, burn or injury from mechanical
movement to persons (and livestock where present), or a) the circuit protective conductor;
from fire attendant upon the use of electrical energy. b) the consumer’s earthing terminal and earthing
conductor, and for TN systems, the metallic
3.52 Design Current (of a Circuit) — The magnitude

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

return path;
of the current intended to be carried by the circuit in
normal service. c) for TT and IT systems, the earth return path;
d) the path through the earth neutral point of the
3.53 Direct Contact — Contact of persons or transformer;
livestock with live parts which may result in electric
e) the transformer winding; and
shock.
f) the line conductor from the transformer to
3.54 Disconnector — A mechanical switching device the point of fault.
which, in the open position, complies with the
requirements specified for the isolation function. 3.65 Earth Leakage Current — A current which flows
to earth, or to extraneous conductive parts, in a circuit
NOTES which is electrically sound.
1 A disconnector is otherwise known as isolator.
2 A disconnector is capable of opening and closing a circuit NOTE — This current may have a capacitive component
when either a negligible current is broken or made, or when no including that resulting from the deliberate use of capacitors.
significant change in the voltage across the terminals of each
3.66 Earthing — Connection of the exposed
pole of the disconnector occurs. It is also capable of carrying
currents under normal circuit conditions and carrying for a conductive parts of an installation to the main earthing
specified time, current under abnormal conditions such as those terminal of that installation.
of short-circuit.
3.67 Earthing Resistance, Total — The resistance
3.55 Discrimination — Ability of a protective device
between the main earthing terminal and the earth.
to operate in preference to another protective device in
series. 3.68 Earthed Concentric Wiring — A wiring system
in which one or more insulated conductors are
3.56 Distribution Circuit (of Buildings) — A circuit
completely surrounded throughout their length by a
supplying a distributing board.
conductor, for example a sheath, which acts as a PEN
3.57 Double Insulation —Insulation comprising both conductor.
basic insulation and supplementary insulation.
3.69 Earthing Conductor — A protective conductor
3.58 Duct — A closed passage way formed under connecting the main earth terminal (or equipotential
ground or in a structure and intended to receive one or bonding conductor of an installation when there is no
more cables which may be drawn in. earth bus) to an earth electrode or to other means of
earthing.
3.59 Ducting (see 3.25)
3.70 Electric Shock — A dangerous patho-
3.60 Earth — The conductive mass of the earth, whose
physiological effect resulting from the passing of an
electric potential at any point is conventionally taken
electric current through a human body or an animal.
as zero.
3.71 Electrical Equipment (abb: Equipment) — Any
3.61 Earth Electrode Network — Part of an earthing
item for such purposes as generation, conversion,
arrangement comprising only the earth electrodes and
transmission, distribution or utilization of electrical
their interconnections.
energy, such as machines, transformers, apparatus,
measuring instruments, protective devices, wiring

9
IS 732 : 2019

materials, accessories, and appliances. 3.82 Extraneous Conductive Part — A conductive

part got forming part of the electrical installation and
3.72 Electrical Installation (of a Building) — An
liable to introduce a potential, generally the earth
assembly of associated electrical equipment to fulfil a
potential.
specific purpose or purposes and having coordinated
characteristics. 3.83 Factory Built Assembly (of LV Switchgear and
Controlgear) — See IS 8623 (Part 1).
3.73 Electrically Independent Earth Electrodes —
Earth electrodes located at such a distance from one 3.84 Fault — A circuit condition in which current flows
another that the maximum current likely to flow through through an abnormal or unintended path. This may
one of them does not significantly affect the potential result from an insulation failure or a bridging of
of the other(s). insulation. Conventionally the impedance between live
conductors or between lives conductors and exposed

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3.74 Electrical Source for Safety Services —
or extraneous conductive parts at the fault position is
Electrical source intended to be used as part of an
considered negligible.
electrical supply system for safety services.
3.85 Fault Current — A current resulting from a fault.
3.75 Electrical Supply System for Safety Services —
A supply system intended to maintain the operation of 3.86 Fault Protection — Protection against electric

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

essential parts of an electrical installation and shock under single fault conditions.
equipment: NOTE — For low voltage installation, systems and equipment,
fault protection generally corresponds to protection against in
a) For health and safety of persons and livestock,
direct contact, mainly with regards to failure of basic insulation.
and Indirect contact is “contact of persons or livestock with exposed-
b) To avoid damage to the environment and to conductive parts which have become live under fault
other equipment. conditions.”

NOTE — The supply system includes the source and the 3.87 Final Circuit — A circuit connected directly to
circuit(s) up to the terminals of the electrical equipment. current using equipment, or to socket outlets or other
outlet points for the connection of such equipment.
3.76 Electrode Boiler (or Electrode Water Heater)
— Equipment for the electrical heating of water or 3.88 Fire
electrolyte by the passage of an electric current between
electrodes immersed in the water or electrolyte. a) A process of combustion characterized by the
emission of heat and effluent accompanied by
3.77 Emergency Switching — Rapid cutting off of smoke, and/or flame and/or glowing.
electrical energy to remove any hazard to persons,
b) Rapid combustion spreading uncontrolled in
livestock, or property which may occur unexpectedly.
time and space.
3.78 Enclosure — A part providing protection of
3.89 Fixed Equipment — Equipment fastened to a
equipment against certain external influences and, in
support or otherwise secured.
any direction, protection against direct contact.
3.90 Flammability — Ability of a material or product
3.79 Equipotential Bonding — Electrical connection
to burn with a flame under specified test condition.
putting various exposed conductive parts and
extraneous conductive parts at a substantially equal 3.91 Functional Bonding Conductor — Conductor
potential. provided for functional equipotential bonding.
NOTE — In a building installation equipotential bonding 3.92 Functional Earthing — Connection to earth
conductors shall interconnect the following conductive parts: necessary for proper functioning of electrical
a) Protective conductor, equipment.
b) Earth continuity conductor, and
c) Risers of air-conditioning system and heating systems (if 3.93 Functional Extra-low Voltage (FELV) — An
any). extra-low voltage system in which not all of the
3.80 Exposed Conductive Part — A conductive part protective measures required for SELV or PELV have
of electrical equipment, which can be touched and been applied.
which is not normally live, but which may become live 3.94 Fuse — A device which, by melting of one or
under fault conditions. more of its specially designed and proportioned
3.81 External Influence — Any influence external to components, opens the circuit in which it is inserted by
an electrical installation which affects the design and breaking the current when this exceeds a given value
safe operation of that installation. for a sufficient time. The fuse comprises all the parts
that form the complete device.

10
 IS 732 : 2019

3.95 Fuse Carrier — The movable part of a fuse enclosing surrounding or supporting a conductor.
designed to carry a fuse link. NOTE — See also the definitions for basic insulation, double
insu lation , rein forced insulation and sup p lemen tary
3.96 Fuse Element — A part of a fuse designed to
insulation.
melt when the fuse operates.
3.110 Insulation Co-ordination — The selection of
3.97 Fuse Link — A part of fuse, including the fuse the electric strength of equipment in relation to the
element(s), which requires replacement by a new or voltages which can appear on the system for which the
renewable fuse link after the fuse has operated and equipment is intended, taking into account the service
before the fuse is put back into service. environment and the characteristics of the available
3.98 Gas Installation Pipe — Any pipe, not being a protective devices.
service pipe or pipe comprised in a gas appliance, for 3.111 Isolation — Cutting off an electrical installation,

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
conveying gas for a particular consumer and including a circuit, or an item of equipment from every source of
any associated valve or other gas fitting. electrical energy.
3.99 Hand-Held Equipment — Portable equipment 3.112 Isolator — A mechanical switching device which,
intended to be held in the hand during normal use, in in the open position, complies with the requirements
which the motor, if any, forms an integral part of the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

specified for the isolating function. An isolator is
equipment. otherwise known as a disconnector.
NOTE — A hand held equipment is an item of equipment, the
functioning of which requires constant manual support or 3.113 Leakage Current — Electric current in an
guidance. unwanted conductive path under normal operating
conditions.
3.100 Hazardous-Live Part — A live part which can
give, under certain condition of external influence, an 3.114 Lighting Protection Zone — Zone where the
electric shock. lightning electromagnetic environment is defined.
3.101 Impulse Current — A parameter used for the 3.115 Line Conductor — A conductor of an a.c. system
classification test for SPDs; it is defined by three for the transmission of electrical energy other than a
elements, a current peak value, a charge Q and a specific neutral conductor or a PEN conductor. This also means
energy W/R. the equivalent conductor of a d.c. system unless
otherwise specified in the Regulations.
3.102 Impulse Withstand Voltage— The highest peak
value of impulse voltage of prescribed form and polarity 3.116 Live Part — A conductor or conductive part
which does not cause breakdown of insulation under intended to be energized in normal use including a
specified condition. neutral conductor but, by convention, not a PEN
conductor.
3.103 Indirect Contact — Contact of persons or
livestock with exposed conductive parts made live by 3.117 Low Voltage (see 3.187).
a fault and which may result in electric shock.
3.118 Luminaire — Equipment which distributes,
3.104 Ignitability — Measure of the ease with which filters or transforms the light from one or more lamps,
a specimen can be ignited due to the influence of an and which includes any parts necessary for supporting,
external source, under specified test condition. fixing and protecting the lamps, but not the lamps
themselves, and, where necessary, circuit auxiliaries
3.105 Ignition — Initiation of combustion.
together with the means for connecting them to the
3.106 Installations (see 3.72). supply
3.107 Overcurrent — A current exceeding the rated NOTE — For the purposes of this code a batten lampholder, or
a lampholder suspended by flexible cord, is a luminaire.
value. For conductors, the rated value is the current
carrying capacity. 3.119 Luminaire Supporting Coupler (LSC) — A
3.108 Overcurrent Detection —A method of means comprises of LSC outlet and an LSC connector,
establishing that the value of current in a circuit (or providing mechanical support for a luminaire and the
wall) such that in the event of direct contact exceeds a electrical connection to and disconnection from a fixed
predetermined value for a specified time with a live wiring installation.
part, a person standing on the floor (or touching the 3.120 Low-Voltage Switchgear and Controlgear
wall) cannot be traversed by a shock current flowing Assembly —A combination of one or more low voltage
to the floor (or wall). switching devices together with associated control,
3.109 Insulation — Suitable non-conductive material measuring, signalling, protective, regulating equipment,

11
IS 732 : 2019

etc, completely assembled under the responsibility of NOTE — An electrical installation may have more than one
origin.
the manufacturer with all the internal electrical and
mechanical inter-connections and structural parts. The 3.132 Overcurrent — A current exceeding the rated
components of the assembly may be electromechanical value. For conductors the rated value is the current
or electronic. carrying capacity.
3.121 Main Earthing Terminal — The terminal or 3.133 Overcurrent Detection — A method of
bar which is the equipotential bonding conductor of establishing that the value of current in a circuit exceeds
protective conductors, and conductors for functional a predetermined value for a specified length of time.
earthing, if any, to the means of earthing.
3.134 Overload Current (of a Circuit) — An
3.122 Mechanical Maintenance — The replacement, overcurrent occurring in a circuit in the absence of an
refurbishment or cleaning of lamps and non-electrical electrical fault.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
parts of equipment, plant and machinery.
3.135 PEL Conductor —A conductor combining the
3.123 Meshed Bonding Network (MESH-BN) — function of both a protective earthing and a line
Bonding network in which all associated equipment conductor.
frames, racks and cabinets and usually the d.c. power
3.136 PELV (Protective Extra-low Voltage) — An

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

return conductor are bonded together as well as at
multiple points to the CBN and may have the form of a extra-low voltage system which is not electrically
mesh. separated from earth, but which otherwise satisfies all
the requirements for SELV.
3.124 Minimum Illumination — Illumination for
emergency lighting at the end of rated operating time. 3.137 PEM Conductor — A conductor combining the
function of both a protective earthing conductor and a
3.125 Minor Works — Additions and alterations to midpoint conductor.
an installation that do not extend to the provision of a
new circuit. 3.138 PEN Conductor — A conductor combining the
functions of both protective conductor and neutral
3.126 Mobile Equipment — Electrical equipment conductor.
which is moved while in operation or which can be
easily moved from one place to another while connected 3.139 Phase Conductor — A conductor of an a.c.
to the supply. system for the transmission of electrical energy, other
than a neutral conductor.
3.127 Monitoring — Observation of the operation of
NOTE — The term also means the equivalent conductor of a
a system or part of a system to verify correct functioning d.c. system unless otherwise specified in this code.
or detect incorrect functioning by measuring system
variables and comparing the measured value with the 3.140 Plug — A device, provided with contact pins,
specified value. which is intended to be attached to a flexible cable,
and which can be engaged with a socket outlet or with
3.128 Neutral Conductor (Symbol N) — A conductor a connector.
connected to the neutral point of a system and capable
of contributing to the transmission of electrical energy. 3.141 Point (in Wiring) — A termination of the fixed
wiring intended for the connection of current using
The term also means the equivalent conductor of an IT equipment.
or d.c. system unless otherwise specified in the
regulations and also identifies either the mid-wire of a 3.142 Portable Equipment — Equipment which is
three-wire d.c. circuit or the earthed conductor of a two- moved while in operation or which can easily be moved
wire earthed d.c. circuit. from one place to another while connected to the supply.

3.129 Non-flame Propagating Component — 3.143 Powertrack — A system component, which is

Component which is liable to ignite, as a result of an generally a linear assembly of spaced and supported
applied flame, but in which the flame does not busbars, providing electrical connection of accessories.
propagate and which extinguishes itself within a limited 3.144 Powertrack System (PT System) — An
time after the flame is removed. assembly of system components including a powertrack
3.130 Obstacle — A part preventing unintentional contact by which accessories may be connected to an electrical
with live parts but not preventing deliberate contact. supply at one or more points (predetermined or
otherwise) along the powertrack.
3.131 Origin of an Electrical Installation — The
NOTE — The maximum current rating of a powertrack system
point at which electrical energy is delivered to an is 63A.
installation.

12
 IS 732 : 2019

3.145 Prospective Fault Current (Ipf) — The value insulation under the conditions specified in the relevant
of overcurrent at a given point in a circuit resulting standard.
from a fault of negligible impedance between live NOTE — The term ‘single insulation’ does not imply that
conductor having a difference of potential under normal the insulation must be one-homogeneous piece. It may comprise
operating conditions, or between a live conductor and several layers which cannot be tested singly as supplementary
an exposed conductive part. or basic insulation.

3.146 Prospective Touch Voltage — The highest touch 3.156 Residual Current — The algebraic sum of the
voltage liable to appear in the event of a fault of instantaneous values of current flowing through all live
negligible impedance in the electrical installation. conductors of a circuit at a point of the electrical
installation.
3.147 Protective Conductor — A conductor used for
some measures of protection against electric shock and 3.157 Residual Current Device (RCD) — A

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
intended for connecting together any of the following mechanical switching device or association of devices
parts: intended to cause the opening of the contacts when the
residual current attains a given value under specified
a) Exposed conductive parts, conditions.
b) Extraneous conductive parts,
3.158 Residual Current Operated Circuit-Breaker

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

c) The main earthing terminal, and with Integral Overcurent Protection (RCBO) —A
d) The earthed point of the source, or an artificial residual current operated switching device designed to
neutral. perform the functions of protection against overload
3.148 Protective Conductor Current —Electric and/or short-circuit.
current appearing in a protective conductor, such as 3.159 Residual Current Operated Circuit-Breaker
leakage current or electric current resulting from an without Integral Overcurrent Protection (RCCB)
insulation fault. —A residual current operated switching device not
3.149 Protective Earthing —Earthing of a point or designed to perform the functions of protection against
points in a system or in equivalent for the purposes of overload and/or short-circuit.
safety. 3.160 Residual Operating Current — Residual
3.150 Protective Euqipotential Bonding — current which causes the residual current device to
Equipotential bonding for the purpose of safety. operate under specified conditions.

3.151 Protective Multiple Earthing (PME) —An 3.161 Resistance Area (for an Earth Electrode only)
earthing arrangement, found in TN-C-S systems, in — The surface area of ground (around an earth
which the supply neutral conductor is used to connect electrode) on which a significant voltage gradient may
the earthing conductor of an installation with Earth. exist.

3.152 Protective Separation — Separation of one 3.162 Response Time —The time that elapses between
electric circuit from another by means of: the failure of the normal power supply and the of the
auxiliary power supply to energize the equipment
a) Double insulation,
3.163 Ring Final Circuit —A final circuit arranged
b) Basic insulation and electrically protective
in the form of a ring and connected to a single point of
screening (shielding), or
supply.
c) Reinforced insulation.
3.164 Safety Service —An electrical system for
3.153 Rated Current —Value of current used for electrical equipment provided to protect or warn
specification purposes, established for a specified set persons in the event of a hazard, or essential to their
of operating conditions of a component, device, evacuation from a location.
equipment or system.
3.165 SELV (Separated Extra Low-Voltage) — An
3.154 Rated Impulse Withstand Voltage Level (Uw) extra low-voltage system which is electrically separated
—The level of impulse withstand voltage assigned by from earth and from other system in such a way that a
the manufacturer to the equipment, or to part of it, single fault cannot give rise to the risk of electric shock.
characterizing the specified withstand capability of its
insulation against overvoltages. 3.166 Shock Current —A current passing through the
body of a person or an animal and having
3.155 Reinforced Insulation — Single insulation characteristics likely to cause dangerous patho-
applied to live parts, which provides a degree of physiological effects.
protection against electric shock equivalent to double

13
IS 732 : 2019

3.167 Short-Circuit Current — An overcurrent handle and having such a mass that it cannot easily be
resulting from a fault of negligible impedance between moved.
live conductors having a difference in potential under
3.176 Supplementary Insulation — Independent
normal operating conditions.
insulation applied in addition to basic insulation in
3.168 Simple Separation —Separation between order to provide protection against electric shock in
circuits or between a circuit and earth by means of basic the event of a failure of basic insulation.
insulation.
3.177 Surge Current — A transient wave appearing
3.169 Simultaneously Accessible Parts — Conductors as an overcurrent caused by a lightning electromagnetic
or conductive parts which can be touched impulse.
simultaneously by a person or, where applicable by 3.178 Surge Protective Devices (SPD) — A device
livestock. that is intended to limit transient overvoltages and divert

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTE — In the context of protection against direct contacts a surge currents. It contains at least one non-linear
live part may be accessible with: component.
a) another live part, or
b) an exposed conductive part, or 3.179 Switch — A mechanical switching device
c) an extraneous conductive part, or capable of making, carrying and breaking current under

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

d) a protective conductor. normal circuit conditions, which may include specified
operating overload conditions, and also of carrying
The following may constitute simultaneously accessible parts
in the context of protection against indirect contacts: for a specified time currents under specified abnormal
a) Exposed conductive parts, circuit conditions such as those of short circuit.
b) Extraneous conductive parts, and NOTE — A switch may also be capable of making, but not
c) Protective conductors. breaking, short-circuit currents.
It should be noted that the word touched signifies any contact
3.180 Switch, Linked — A switch, the contacts of
with any part of the body (hand, foot, head, etc).
which are so arranged as to make or break all poles
3.170 Skilled Person —A person with technical simultaneously or in a definite sequence.
knowledge or sufficient experience to enable him/her
3.181 Switch-disconnector — A switch which, in the
to avoid dangers which electricity may create.
open position, satisfies the isolating requirements
3.171 Socket Outlet — A device, provided with female specified for a disconnector.
contacts, which is intended to be installed with the fixed NOTE — A switch-disconnector is otherwise known as an
wiring, and intended to receive a plug. isolating switch.
NOTE — A luminaire track system is not regarded as a socket 3.182 Switchboard — An assembly of switchgear with
outlet system.
or without instruments, but the term does not apply to
3.172 Space Factor — The ratio (expressed as a a group of local switches in a final circuit.
percentage) of the sum of the overall cross-sectional NOTE — The term ‘switchboard’ includes a distribution
areas of cables (including insulation and sheath) to the board.
internal cross-sectional area of the conduit or other
3.183 Switchgear — An assembly of main and
cable enclosure in which they are installed. The
auxiliary switching apparatus for operation,
effective overall cross-sectional area of a non-circular
regulation, protection or other control of electrical
cable is taken as that of a circle of diameter equal to
installations.
the major axis of the cable.
3.184 System — An electrical system consisting of a
3.173 Spur — A branch cable connected to a ring or
single source or multiple sources running in parallel of
radial final circuit.
electrical energy and an installation. Types of system
3.174 Standby Supply System —A system intended are identified as follows, depending upon the
to maintain supply to the installation or part thereof, in relationship of the source, and of exposed-conductive
case of interruption of the normal supply, for reasons parts of the installation, to Earth:
other than safety of persons.
a) TN system — A system having one or more
NOTE — Standby supplies are necessary, for example, to avoid points of the source of energy directly earthed,
interruption of continuous industrial processes or data the exposed conductive-parts of the
processing.
installation being connected to that point by
3.175 Stationary Equipment — Either fixed protective conductors.
equipment or equipment not provided with a carrying b) TN-C system — A system in which neutral

14
 IS 732 : 2019

and protective conductors are combined in a in the reasonable use of electrical installations. The
single conductor throughout the system. requirements to provide for the safety of livestock are
c) TN-S system — A system having separate applicable in locations intended for them.
neutral and protective conductor throughout NOTE — In electrical installations, the following hazards may
the system. arise:
d) TN-C-S system — A system in which neutral a) shock currents;
and protective conductors are combined in a b) excessive temperatures likely to cause burns, fires and other
injurious effects;
single conductor in part of the system.
c) ignition of a potentially explosive atmosphere;
e) TT system — A system having one point of d) undervoltages, overvoltages and electromagnetic influences
the source of energy directly earthed, the likely to cause or result in injury or damage;
exposed-conductive-parts of the installation e) power supply interruptions and/or interruption of safety

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
being connected to the earth electrodes services;
electrically independent of the earth electrodes f) arcing, likely to cause blinding effects, excessive pressure,
and/or toxic gases; and
of the source.
g) mechanical movement of electrically activated equipment.
f) IT system — A system having no direct
connection between live parts and Earth, the 4.1.2 Protection Against Electric Shock

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

exposed-conductive-parts of the electrical 4.1.2.1 Basic protection (protection against direct
installation being earthed. contact)
NOTE — The types of systems depending upon the relationship
NOTE — For low-voltage installations, systems and equipment,
to the source and of the exposed conductive parts of the
basic protection generally corresponds to protection against
installation to earth are defined in IS 3043.
direct contact.
3.185 Temporary Overvoltage (UTOV) — A Protection shall be provided against dangers that may arise from
fundamental frequency overvoltage occurring on the contact with live parts of the installation by persons or livestock.
network at a given location, of relatively long duration. This protection can be achieved by one of the following
methods:
NOTES a) preventing a current from passing through the body of any
1 TOVS may be caused by faults inside the LV system or inside person or any livestock; and
the HV system. b) limiting the current which can pass through a body to a non-
2 Temporary overvoltages, typically lasting up to several hazardous value.
seconds, usually originate from switching operations or faults
(for example, sudden load rejection, single-phase faults, etc.) 4.1.2.2 Fault protection (protection against indirect
and/or from non-linearity (ferroresonance effects, harmonics, contact)
etc).
NOTE — For low-voltage installations, systems and equipment,
3.186 Touch Voltage — The potential difference fault protection generally corresponds to protection against
between the ground potential rise (GPR) of a grounded indirect contact, mainly with regard to failure of basic
insulation.
metallic structure and the surface potential at the point
Protection shall be provided against dangers that may arise from
where a person could be standing while at the same contact with exposed - conductive-parts of the installation by
time having a hand in contact with the grounded metallic persons or livestock.
structure. Touch voltage measurements can be “open This protection can be achieved by one of the following
circuit”(without the equivalent body resistance included methods:
in the measurement circuit) or “closed circuit” ( with a) preventing a current resulting from a fault from passing
the equivalent body resistance included in the through the body of any person or any livestock;
measurement circuit) voltage by which an installation b) limiting the magnitude of a current resulting from a fault,
which can pass through a body, to a non-hazardous value; and
or part of an installation is designated.
c) limiting the duration of a current resulting from a fault, which
3.187 Voltage Nominal (of an Installation) — Voltage can pass through a body, to a non-hazardous time period.
by which an installation or part of an installation is 4.1.2.3 Protection against thermal effects
designated.
The electrical installation shall be so arranged to
4 FUNDAMENTAL PRINCIPLES, ASSESSMENT minimize the risk of damage or ignition of flammable
OF GENERAL CHARACTERISTICS materials due to high temperature or electric arc. In
4.1 Protection for Safety addition, during normal operation of the electrical
equipment, there shall be no risk of persons or livestock
4.1.1 General suffering burns.
The requirements stated in 4.1.1 to 4.1.5 are intended 4.1.2.4 Protection against overcurrent
to provide for the safety of persons, livestock and
property against dangers and damage which may arise Persons and livestock shall be protected against injury

15
IS 732 : 2019

and property shall be protected against damage due to following factors shall be taken into account to provide:
excessive temperatures or electromechanical stresses
a) the protection of persons, livestock and
caused by any overcurrents likely to arise in conductors.
property in accordance with 4.1.
Protection can be achieved by limiting the overcurrent b) the proper functioning of the electrical
to a safe value or duration. installation for the intended use.
4.1.2.5 Protection against fault currents The information required as a basis for design is listed
Conductors, other than live conductors, and any other in 4.1.3.2 to 4.1.3.5. The requirements with which the
parts intended to carry a fault current shall be capable design shall comply are stated in 4.1.3.6 and 4.1.3.7.
of carrying that current without attaining an excessive 4.1.3.2 Characteristics of available supply or supplies
temperature. Electrical equipment, including
When designing electrical installations in accordance

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
conductors shall be provided with mechanical
protection against electromechanical stresses of fault with this standard it is necessary to know the
currents as necessary to prevent injury or damage to characteristics of the supply. Relevant information from
persons, livestock or property. the network operator is necessary to design a safe
installation according to this standard. The
Live conductors shall be protected against over currents characteristics of the power supply should be included

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

arising from faults by the methods given in 4.1.2.4. in the documentation to show conformity with this
NOTE — Attention should particular be given to PE conductor standard. If the network operator changes the
and earthing conductor currents. characteristics of the power supply this may affect the
safety of the installation.
4.1.2.6 Protection against voltage disturbances and
measures against electromagnetic influences 4.1.3.2.1 Nature of current — a.c. and/or d.c.
4.1.2.6.1 Persons and livestock shall be protected 4.1.3.2.2 Function of conductors
against injury and property shall be protected against
a) for a.c.:
any harmful effects as a consequence of a fault between
live parts of circuits supplied at different voltages. 1) line conductor(s);
2) neutral conductor;
4.1.2.6.2 Persons and livestock shall be protected
3) protective conductor.
against injury and property shall be protected against
damage as a consequence of overvoltages such as those b) for d.c.:
originating from atmospheric events or from switching. 1) line conductor(s);
NOTE — For protection against direct lightning strikes, see 2) midpoint conductor;
IS/IEC 62305 series.
3) protective conductor.
4.1.2.6.3 Persons and livestock shall be protected NOTE — The function of some conductors may be
against injury and property shall be protected against combined in a single conductor.
damage as a consequence of undervoltage and any
4.1.3.2.3 Values and tolerances
subsequent voltage recovery.
a) voltage and voltage tolerances;
4.1.2.6.4 The installation shall have an adequate level
of immunity against electromagnetic disturbances so b) voltage interruptions, voltage fluctuations and
as to function correctly in the specified environment. voltage dips;
The installation design shall take into consideration the c) frequency and frequency tolerances;
anticipated electromagnetic emissions, generated by the d) maximum current allowable;
installation or the installed equipment, which shall be e) earth fault loop impedance upstream of the
suitable for the current-using equipment used with, or origin of the installation; and
connected to, the installation. f) prospective short-circuit currents.
4.1.2.7 Protection against power supply interruption For standard voltages and frequencies, see IS 12360.
Where danger or damage is expected to arise due to an 4.1.3.2.4 Protective provisions inherent in the supply,
interruption of supply, suitable provisions shall be made for example, system earthing or mid-point earthing.
in the installation or installed equipment.
4.1.3.2.5 Particular requirements of the supply
4.1.3 Design undertaking.
4.1.3.1 General 4.1.3.3 Nature of demand
For the design of the electrical installation, the The number and type of circuits required for lighting,

16
 IS 732 : 2019

heating, power, control, signalling, information and g) other stresses to which the wiring can be
communication technology, etc shall be determined by: subjected during the erection of the electrical
a) location of points of power demand; installation or in service.
b) loads to be expected on the various circuits; 4.1.3.8 Protective equipment
c) daily and yearly variation of demand;
The characteristics of protective equipment shall be
d) any special conditions such as harmonics; determined with respect to their function which may
e) requirements for control, signalling, be, for example, protection against the effects of:
information and communication technology,
etc; and a) overcurrent (overload, short-circuit),
f) anticipated future demand if specified. b) earth fault current,
4.1.3.4 Electric supply systems for safety services or c) overvoltage, and

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
standby electric supply systems d) undervoltage and no voltage.
a) Source of supply (nature, characteristics). The protective devices shall operate at values of current,
b) Circuits to be supplied by the electric source voltage and time which are suitably related to the
for safety services or the standby electrical characteristics of the circuits and to the possibilities of

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

source. danger.
4.1.3.5 Environmental conditions 4.1.3.9 Emergency control
The design of the electrical installation shall take into Where, in case of danger, there is the necessity for the
account the environmental conditions to which it will immediate interruption of supply, an interrupting device
be subjected [see 5.1 and IS 13736 (All Parts)]. shall be installed in such a way that it can be easily
4.1.3.6 Cross-sectional area of conductors recognized and effectively and rapidly operated.

The cross-sectional area of conductors shall be 4.1.3.10 Disconnecting devices

determined for both normal operating conditions and Disconnecting devices shall be provided so as to permit
for fault conditions according to: switching and/or isolation of the electrical installation,
a) their admissible maximum temperature; circuits or individual items of apparatus as required
b) the admissible voltage drop; for operation, inspection and fault detection, testing,
c) the electromechanical stresses likely to occur maintenance and repair.
due to earth fault and short-circuit currents; 4.1.3.11 Prevention of mutual detrimental influence
d) other mechanical stresses to which the
conductors can be subjected; The electrical installation shall be arranged in such a
e) the maximum impedance with respect to the way that no mutual detrimental influence will occur
functioning of the protection against fault between electrical installations and non-electrical
currents; and installations.
f) the method of installation. 4.1.3.12 Accessibility of electrical equipment
NOTE — The items listed above concern primarily the safety The electrical equipment shall be arranged so as to
of electrical installations. Cross-sectional areas greater than afford as may be necessary:
those required for safety may be desirable for economic
operation. a) sufficient space for the initial installation and
later replacement of individual items of
4.1.3.7 Type of wiring and methods of installation
electrical equipment; and
For the choice of the type of wiring and the methods of b) accessibility for operation, inspection and
installation the following shall be taken into account: fault detection, testing, maintenance and
a) the nature of the locations; repair.
b) the nature of the walls or other parts of the 4.1.3.13 Documentation for the electrical installation
building supporting the wiring;
c) accessibility of wiring to persons and Every electrical installation shall be provided with
livestock; appropriate documentation.
d) voltage; 4.1.4 Selection of Electrical Equipment
e) the electromagnetic stresses likely to occur
4.1.4.1 General
due to earth fault and short-circuit currents;
f) electromagnetic interference; and Every item of electrical equipment used in electrical

17
IS 732 : 2019

installations shall comply with such Indian Standards c) asymmetrical load;

as are appropriate. Where there are no applicable d) harmonics; and
standards, the item of equipment concerned shall be e) transient overvoltages generated by equipment
selected by special agreement between the person in the installation.
specifying the installation and the installer.
4.1.5 Erection and Verification of Electrical
4.1.4.2 Characteristics Installations
Every item of electrical equipment selected shall have 4.1.5.1 Erection
suitable characteristics appropriate to the values and
conditions on which the design of the electrical 4.1.5.1.1 Good workmanship by competent persons and
installation (see 4.1.3) is based and shall, in particular, proper materials shall be used in the erection of the
fulfil the following requirements: electrical installation. Electrical equipment shall be

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
installed in accordance with the instructions provided
a) Voltage — Electrical equipment shall be by the manufacturer of the equipment.
suitable with respect to the maximum steady-
state voltage (r.m.s. value for a.c.) likely to be 4.1.5.1.2 The characteristics of the electrical equipment,
applied, as well as overvoltages likely to occur. as determined in accordance with 4.1.4.2, shall not be
impaired during erection.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — For certain equipment, it may be necessary to
take account of the lowest voltage likely to occur.
4.1.5.1.3 Conductors shall be identified in accordance
b) Current — All electrical equipment shall be with IEC 60446. Where identification of terminals is
selected with respect to the maximum steady- necessary, they shall be identified in accordance with
state current (r.m.s. value for a.c.) which it has IEC 60445.
to carry in normal service, and with respect to
the current likely to be carried in abnormal 4.1.5.1.4 Connections between conductors and between
conditions and the period (for example, conductors and other electrical equipment shall be made
operating time of protective devices, if any) in such a way that safe and reliable contact is ensured.
during which it may be expected to flow. 4.1.5.1.5 All electrical equipment shall be installed in
c) Frequency — If frequency has an influence such a manner that the designed heat dissipation
on the characteristics of electrical equipment, conditions are not impaired.
the rated frequency of the equipment shall
correspond to the frequency likely to occur in 4.1.5.1.6 All electrical equipment likely to cause high
the circuit. temperatures or electric arcs shall be placed or guarded
d) Load factor — All electrical equipment which so as to minimize the risk of ignition of flammable
is selected on the basis of its power materials. Where the temperature of any exposed parts
characteristics shall be suitable for the duty of electrical equipment is likely to cause injury to
demanded of the equipment taking into persons, those parts shall be so located or guarded as
account the design service conditions. to prevent accidental contact therewith.

4.1.4.3 Conditions of installation 4.1.5.1.7 Where necessary for safety purposes, suitable
warning signs and/or notices shall be provided.
All electrical equipment shall be selected so as to
withstand safely the stresses and the environmental 4.1.5.1.8 Where an installation is erected by using new
conditions (see 4.1.3.5) characteristic of its location materials, inventions or methods leading to deviations
and to which it may be subjected. If, however, an item from the rules of this standard, the resulting degree of
of equipment does not have by design the properties safety of the installation shall not be less than that
corresponding to its location, it may be used on obtained by compliance with this standard.
condition that adequate additional protection is
4.1.5.1.9 In the case of an addition or alteration to an
provided as part of the completed electrical installation.
existing installation, it shall be determined that the
4.1.4.4 Prevention of harmful effects rating and condition of existing equipment, which will
have to carry any additional load, is adequate for the
All electrical equipment shall be selected so that it will
not cause harmful effects on other equipment or impair altered circumstances. Furthermore, the earthing and
the supply during normal service including switching bonding arrangements, if necessary for the protective
operations. In this context, the factors which can have measure applied for the safety of the addition or
an influence include, for example: alteration, shall be adequate.

a) power factor; 4.1.5.2 Initial verification

b) inrush current; Electrical installations shall be verified before being

18
 IS 732 : 2019

placed in service and after any important modification under normal operating conditions; and
to confirm proper execution of the work in accordance b) types of system earthing.
with this standard.
4.1.5.8.1 Current-carrying conductors depending on
4.1.5.3 Periodic verification kind of current
It is recommended that every electrical installation is The following arrangements of current-carrying
subjected to periodic verification. conductors under normal operating conditions are taken
4.1.5.4 Void into account in this standard:
NOTE — The conductor arrangements described in this clause
4.1.5.5 Assessment of general characteristics are not exhaustive. They are included as examples of typical
arrangements.
An assessment shall be made of the following

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
characteristics of the installation in accordance with a) Current carrying conductors in a.c. circuits
the clauses indicated: (see Fig. 2 to Fig. 6).
a) the purposes for which the installation is
intended to be used, its general structure and
its supplies (4.1.5.9, 4.1.5.14 and 4.1.5.15);

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

b) the external influences to which it is to be
exposed (4.1.5.11);
c) the compatibility of its equipment (4.1.5.12);
and
d) its maintainability (4.1.5.13). * Numbering of conductors optional
Those characteristics shall be taken into account in the FIG. 2 SINGLE-P HASE 2-W IRE
choice of methods of protection for safety (see 4.2
to 4.5) and the selection and erection of equipment
(see 5.1 to 5.5).
4.1.5.6 Purposes, supplies and structure
4.1.5.6.1 Maximum demand and diversity
For economic and reliable design of an installation
within thermal and voltage drop limits, a determination
of maximum demand is essential. In determining the
maximum demand of an installation, or part thereof,
diversity may be taken into account.
4.1.5.7 Void
4.1.5.8 Conductor arrangement and system earthing
The following characteristics shall be assessed: Phase angle 0°
* Numbering of conductors optional
a) arrangements of current-carrying conductors FIG. 3 SINGLE-P HASE 3-W IRE

* Numbering of conductors optional

FIG. 4 T WO-P HASE 3-W IRE

19
IS 732 : 2019

FIG. 5 T HREE-P HASE 3-W IRE

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 6 T HREE-P HASE 4-WIRE (see Note 3)

NOTES 2 In installations with all loads connected between phases, the

1 In case of a single-phase 2-wire arrangement which is derived installation of the neutral conductor may not be necessary.
from a three-phase 4-wire arrangement, the two conductors are 3 Three-phase, 4-wire with neutral conductor or PEN
either two line conductors or a line conductor and a neutral conductor. By definition, the PEN is not a live conductor but a
conductor or a line conductor and a PEN conductor. conductor carrying an operating current.

b) Current-carrying conductors in d.c. circuits — See Fig. 7 and Fig. 8.

FIG. 7 2-WIRE FIG. 8 3-WIRE

NOTE — PEL and PEM conductors are not live conductors of this standard. For this case, the figures may be completely
although they carry operating current. Therefore, the designation shown in solid lines.
2-wire arrangement or 3-wire arrangement applies. 4 The codes used have the following meanings:
4.1.5.8.2 Types of system earthing First letter — Relationship of the power system to earth:
T = direct connection of one point to earth; and
The following types of system earthing are taken into I = all live parts isolated from earth, or one point
account in this standard. connected to earth through a high impedance.
Second letter — Relationship of the exposed-conductive-parts
NOTES
of the installation to earth:
1 Figure 9 to Fig. 21 show examples of commonly used three- T = direct electrical connection of exposed-conductive-
phase systems. Figure 22 to Fig. 26 show examples of commonly parts to earth, independently of the earthing of any
used d.c. systems. point of the power system; and
2 The dotted lines indicate the parts of the system that are not N = direct electrical connection of the exposed-
covered by the scope of the standard, whereas the solid lines conductive-parts to the earthed point of the power
indicate the part that is covered by the standard. system (in a.c. systems, the earthed point of the
3 For private systems, the source and/or the distribution system power system is normally the neutral point or, if a
may be considered as part of the installation within the meaning neutral point is not available, a line conductor).

20
 IS 732 : 2019

Subsequent letter(s) (if any)— Arrangement of neutral and 4.1.5.8.2.1 TN systems

protective conductors:
S = protective function provided by a conductor separate a) Single source systems
from the neutral conductor or from the earthed line
(or, in a.c. systems, earthed phase) conductor. TN power systems have one point directly earthed at
C = neutral and protective functions combined in a single the source, the exposed conductive parts of the
conductor (PEN conductor). installation being connected to that point by protective
conductors. Three types of TN system are considered
Explanation of symbols for Fig. 9 to Fig. 26 according to the arrangement of neutral and protective
according to IS 12032 (all parts) conductors, as follows:

Neutral conductor (N); 1) TN-S system in which, throughout the system, a

separate protective conductor is used (see Fig. 9 to
mid-point conductor (M)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Fig. 11).
Protective conductor (PE) NOTE — For symbols, see explanation given in 4.1.5.8.2.

Combined protective and

neutral conductor (PEN)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 9 TN-S SYSTEM WITH SEPARATE NEUTRAL CONDUCTOR AND

P ROTECTIVE CONDUCTOR T HROUGHOUT THE SYSTEM

21
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the distribution and in the installation must be provided.

FIG. 10 TN-S SYSTEM WITH SEPARATE EARTHED LINE CONDUCTOR AND

P ROTECTIVE CONDUCTOR T HROUGHOUT THE SYSTEM

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 11 TN-S SYSTEM WITH EARTHED PROTECTIVE CONDUCTOR AND NO DISTRIBUTED NEUTRAL
CONDUCTOR T HROUGHOUT THE SYSTEM

22
 IS 732 : 2019

2) TN-C-S system in which neutral and protective conductor functions are combined in a single conductor in a
part of the system (see Fig. 12 to Fig. 14).
NOTE — For symbols, see explanation given in 4.1.3.2.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PEN or PE in the installation must be provided.

FIG. 12 TN-C-S SYSTEM 3-P HASE, 4-W IRE, WHERE PEN IS SEPARATED INTO PE AND N
ELSEWHERE IN THE INSTALLATION

NOTE — Additional earthing of the PEN in the distribution and of the PE in the installation must be provided.

FIG. 13 TN-C-S SYSTEM 3-P HASE, 4-W IRE, WHERE PEN IS SEPARATED INTO
PE AND N AT THE ORIGIN OF THE INSTALLATION
23
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PEN in the distribution and of the PE in the installation must be provided.

FIG. 14 TN-C-S SYSTEM SINGLE-P HASE, 2-W IRE , WHERE THE PEN IS SEPARATED INTO
PE AND N AT THE ORIGIN OF THE INSTALLATION
3) TN-C system in which neutral and protective conductor functions are combined in a single conductor throughout
the system (see Fig. 15).
NOTE — For symbols, see explanation given in 4.1.5.8.2.

NOTE — Additional earthing of the PEN in the installation must be provided.

FIG. 15 TN-C WITH NEUTRAL AND PROTECTIVE CONDUCTOR FUNCTIONS COMBINED IN A SINGLE CONDUCTOR
T HROUGHOUT THE SYSTEM

24
 IS 732 : 2019

b) Multiple source systems unintended paths. The essential design rules shown in
NOTE — The multiple source system is shown for the TN
Fig. 16 from a) to d) are given in the legend below
system with the unique aim of providing EMC. The multiple Fig. 16.
source system is not shown for IT and TT systems because these
systems are generally compatible with regard to EMC. The marking of the PE conductor shall be in accordance
with IEC 60446.
In the case of an inappropriate design of an installation
forming part of a TN system with multiple sources some Any extension of the system shall be taken into account
of the operating current may flow through unintended with regard to the proper functioning of the protective
paths. These currents may cause measures.

a) fire; In industrial plants with only 2-phase loads and 3-phase

b) corrosion; and loads between line conductors, it is not necessary to

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
provide a neutral conductor (see Fig. 17). In this case,
c) electromagnetic interference.
the protective conductor should have multiple
The system shown in Fig. 16 is a system where minor connections to earth.
partial operating currents flow as currents through

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Key
a) — No direct connection from either the transformer neutral point or the generator star point to earth is permitted.
b) — The interconnection conductor between either the neutral points of the transformers or the generator star points shall be insulated.
The function of this conductor is like a PEN; however, it shall not be connected to current-using equipment.
c) — Only one connection between the interconnected neutral points of the sources and the PE shall be provided. This connection shall
be located inside the main switchgear assembly.
d) — Additional earthing of the PE in the installation must be provided.

FIG. 16 TN-C-S MULTIPLE SOURCE SYSTEM WITH SEPARATE P ROTECTIVE CONDUCTOR AND
NEUTRAL CONDUCTOR TO CURRENT USING E QUIPMENT

25
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
Key
a) — No direct connection from either the transformer neutral point or the generator star point to earth is permitted.
b) — The interconnection conductor between either the neutral points of the transformers or the generator star points shall be insulated.
The function of this conductor is like a PEN; however, it shall not be connectedto current-using equipment.
c) — Only one connection between the interconnected neutral points of the sources and the PE shall be provided. This connection shall
be located inside the main switchgear assembly.
d) — Additional earthing of the PE in the installation must be provided.

FIG. 17 TN-C-S MULTIPLE SOURCE SYSTEM WITH P ROTECTIVE CONDUCTOR AND NO NEUTRAL CONDUCTOR
T HROUGHOUT THE SYSTEM FOR 2- OR 3-P HASE LOAD

4.1.5.8.2.2 TT system collectively or to the earthing of the system according

to 4.2.11.6 (see Fig. 20 and Fig. 21).
The TT system has only one point directly earthed and
the exposed-conductive-parts of the installation are 4.1.5.8.2.4 d.c. systems
connected to earth electrodes electrically independent
Type of system earthing for direct current (d.c.) systems.
of the earth electrode of the supply system (see Fig. 18
and Fig. 19). Where the following Fig. 22 to Fig. 26 show earthing
of a specific pole of a two-wire d.c. system, the
4.1.5.8.2.3 IT system
decision whether to earth the positive or the negative
The IT power system has all live parts isolated from pole shall be based upon operational circumstances
earth or one point connected to earth through an or other considerations, for example, avoidance of
impedance. The exposed-conductive-parts of the corrosion effects on line conductors and earthing
electrical installation are earthed independently or arrangements.

26
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 18 TT SYSTEM WITH SEPARATE NEUTRAL CONDUCTOR AND P ROTECTIVE CONDUCTOR T HROUGHOUT THE
INSTALLATION

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 19 TT SYSTEM WITH EARTHED PROTECTIVE AND NO DISTRIBUTED NEUTRAL

CONDUCTOR T HROUGHOUT THE INSTALLATION

27
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the installation must be provided.
a) The system may be connected to earth via a sufficiently high impedance. This connection may be made, for example, at the
neutral point, artificial neutral point, or a line conductor.
b) The neutral conductor may or may not be distributed.

FIG. 20 IT SYSTEM WITH ALL EXPOSED -CONDUCTIVE-P ARTS I NTERCONNECTED BY A P ROTECTIVE

CONDUCTOR WHICH IS COLLECTIVELY EARTHED

NOTE — Additional earthing of the PE in the installation must be provided.

a) The system may be connected to earth via a sufficiently high impedance.
b) The neutral conductor may or may not be distributed.

FIG. 21 IT SYSTEM WITH EXPOSED-CONDUCTIVE-P ARTS EARTHED IN G ROUPS OR INDIVIDUALLY

28
 IS 732 : 2019

4.1.5.8.2.4.1 TN-S-system or the earthed mid-point conductor M in type (b) is

separated from the protective conductor throughout the
The earthed line conductor for example L– in type (a)
installation.

Type a)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the installation must be provided.

Type b)

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 22 TN-S d.c. SYSTEM

29
IS 732 : 2019

4.1.5.8.2.4.2 TN-C-system combined in one single conductor PEL throughout the

installation, or the earthed mid-point conductor M and
The functions of the earthed line conductor for example
the protective conductor are combined in type (b) in
L– and of the protective conductor are in type (a)
one single conductor PEM throughout the installation.

Type a)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PEL in the installation must be provided.

Type b)

NOTE — Additional earthing of the PEM in the installation must be provided.

FIG. 23 TN-C d.c. SYSTEM

30
 IS 732 : 2019

4.1.5.8.2.4.3 TN-C-S-system combined in one single conductor PEL in a part of the

installation, or the earthed mid-wire conductor M in
The functions of the earthed line conductor for example
type (b) and the protective conductor are combined in
L–in type (a) and of the protective conductor are
one single conductor PEM in a part of the installation.

Type a)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the installation must be provided.

Type b)

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 24 TN-C-S d.c. SYSTEM

31
IS 732 : 2019

4.1.5.8.2.4.4 TT-system
Type a)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — Additional earthing of the PE in the installation must be provided.

Type b)

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 25 TT d.c. SYSTEM

32
 IS 732 : 2019

4.1.5.8.2.4.5 IT-system
Type a)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
1) — The system may be connected to earth via a sufficiently high impedance.
NOTE — Additional earthing of the PE in the installation must be provided.

Type b)

1) — The system may be connected to earth via a sufficiently high impedance.

NOTE — Additional earthing of the PE in the installation must be provided.

FIG. 26 IT d.c. SYSTEM

33
IS 732 : 2019

4.1.5.9 Supplies not due to a fault;

4.1.5.9.1 General e) mitigate the effects of EMI;
f) prevent the indirect energizing of a circuit
4.1.5.9.1.1 The following characteristics of the supply intended to be isolated.
or supplies, from whatever source, and the normal range
of those characteristics where appropriate, shall be 4.1.5.10.2 Separate distribution circuits shall be
determined by calculation, measurement, enquiry or provided for parts of the installation which need to be
inspection: separately controlled, in such a way that those circuits
are not affected by the failure of other circuits.
a) the nominal voltage(s);
b) the nature of the current and frequency; 4.1.5.11 Classification of external influences
c) the prospective short-circuit current at the NOTE — This clause has been transferred to 5.1.2.2.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
origin of the installation; 4.1.5.12 Compatibility
d) the earth fault loop impedance of that part of
the system external to the installation; 4.1.5.12.1 Compatibility of characteristics
e) the suitability for the requirements of the An assessment shall be made of any characteristics of
installation, including the maximum demand; equipment likely to have harmful effects upon other

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

and electrical equipment or other services or likely to impair
f) the type and rating of the overcurrent the supply, for example, for coordination with
protective device acting at the origin of the concerned parties. Those characteristics include, for
installation. example:

These characteristics shall be ascertained for an external a) transient overvoltages;

supply and shall be determined for a private source. b) undervoltage;
These requirements are equally applicable to main c) unbalanced loads;
supplies and to safety services and standby supplies. d) rapidly fluctuating loads;
4.1.5.9.2 Supplies for safety services and standby e) starting currents;
systems f) harmonic currents;
Where the provision of safety services is required, for g) d.c. feedback;
example, by the authorities concerned with fire h) high-frequency oscillations;
precautions and other conditions for emergency j) earth leakage currents;
evacuation of the premises, and/or where the provision k) necessity for additional connections to earth;
of standby supplies is required by the person specifying and
the installation, the characteristics of the sources of
m) excessive PE conductor currents not due to a
supply for safety services and/or standby systems shall
fault.
be separately assessed. Such supplies shall have
adequate capacity, reliability and rating and appropriate 4.1.5.12.2 Electromagnetic compatibility
change-over time for the operation specified.
All electrical equipment shall meet the appropriate
For further requirements for supplies for safety services, electromagnetic compatibility (EMC) requirements,
see 4.1.5.14 hereafter and 5.6. For standby systems, and shall be in accordance with the relevant EMC
there are no particular requirements in this standard. standards.
4.1.5.10 Division of installation Consideration shall be given by the planner and
designer of the electrical installations to measures
4.1.5.10.1 Every installation shall be divided into
reducing the effect of induced voltage disturbances and
circuits, as necessary, to
electromagnetic interferences (EMI).
a) avoid danger and minimize inconvenience in
Measures are given in 4.5.
the event of a fault;
b) facilitate safe inspection, testing and 4.1.5.13 Maintainability
maintenance (see also 5.3); An assessment shall be made of the frequency and
c) take account of danger that may arise from quality of maintenance, the installation can reasonably
the failure of a single circuit such as a lighting be expected to receive during its intended life. Where
circuit; an authority is responsible for the operation of the
d) reduce the possibility of unwanted tripping of installation, that authority shall be consulted. Those
RCDs due to excessive PE conductor currents characteristics are to be taken into account in applying

34
 IS 732 : 2019

the requirements of 4 to 6 so that, having regard to the e) long break: an automatic supply available in
frequency and quality of maintenance expected: more than 15 s.
a) any periodic inspection and testing, 4.1.5.15 Continuity of service
maintenance and repairs likely to be necessary
An assessment shall be made for each circuit of any
during the intended life can be readily and
need for continuity of service considered necessary
safely carried out;
during the intended life of the installation. The
b) the effectiveness of the protective measures following characteristics should be considered:
for safety during the intended life shall remain,
and a) selection of the system earthing,
c) the reliability of equipment for proper b) selection of the protective device in order to
functioning of the installation is appropriate achieve discrimination,

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
to the intended life. c) number of circuits,
4.1.5.14 Safety services d) multiple power supplies, and;
e) use of monitoring devices.
4.1.5.14.1 General
4.2 Protection for Safety—Protection against

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTES Electric Shock
1 The need for safety services and their nature are frequently
regulated by statutoryauthorities whose requirementshave to This clause deals with protection against electric shock
be observed. as applied to electrical installations. It is based on
2 Examples of safety services are: emergency escape lighting, IEC 61140 which is a basic safety standard that applies
fire alarm systems, installations for fire pumps, firebrigade lifts, to the protection of persons and livestock. IEC 61140
smoke and heat extraction equipment.
is intended to give fundamental principles and
The following sources for safety services are requirements that are common to electrical installations
recognized: and equipment or are necessary for their co-ordination.
a) storage batteries; The fundamental rule of protection against electric
b) primary cells; shock, according to IEC 61140, is that hazardous live
parts must not be accessible and accessible conductive
c) generator sets independent of the normal
parts must not be hazardous live, neither under normal
supply; and
conditions nor under single fault conditions.
d) a separate feeder of the supply network
effectively independent of the normal feeder The protection under normal conditions is provided by
(see 5.6.4). basic protective provisions and protection under single
fault conditions is provided by fault protective
4.1.5.14.2 Classification provisions. Alternatively, protection against electric
A safety service is either: shock is provided by an enhanced protective provision,
which provides protection under normal conditions and
– a non-automatic supply, the starting of which under single fault conditions.
is initiated by an operator, or
4.2.1 In this standard the following specification of
– an automatic-supply, the starting of which is voltages is intended unless otherwise stated:
independent of an operator.
a) a.c. voltages are r.m.s.; and
An automatic supply is classified as follows according
b) d.c. voltages are ripple-free.
to change-over time:
Ripple-free is conventionally defined as an r.m.s. ripple
a) no-break: an automatic supply which can
voltage of not more than 10 percent of the d.c.
ensure a continuous supply within specified
component.
conditions during the period of transition, for
example as regards variations in voltage and 4.2.2 A protective measure shall consist of:
frequency;
a) an appropriate combination of a provision for
b) very short break: an automatic supply basic protection and an independent provision
available within 0.15 s; for fault protection, or
c) short break: an automatic supply available b) an enhanced protective provision which
within 0.5 s; provides both basic protection and fault
d) medium break: an automatic supply available protection.
within 15 s; and

35
IS 732 : 2019

Additional protection is specified as part of a protective installation or part of an installation or within equipment
measure under certain conditions of external influences shall have no influence on each other such that failure
and in certain special locations (see IEC 60364-7). of one protective measure could impair the other
protective measures.
NOTES
1 For special applications, protective measures which do not 4.2.10 The provision for fault protection (protection
follow this concept are permitted (see 4.2.6 and 4.2.7). against indirect contact) may be omitted for the
2 An example of an enhanced protective measure is reinforced following equipment:
insulation.

4.2.3 In each part of an installation one or more a) metal supports of overhead line insulators
protective measures shall be applied, taking into which are attached to the building and are
placed out of arm’s reach;
account of the conditions of external influence.
b) steel reinforced concrete poles of overhead

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The following protective measures generally are lines in which the steel reinforcement is not
permitted: accessible;
a) automatic disconnection of supply (4.2.11), c) exposed conductive parts which, owing to
b) double or reinforced insulation (4.2.12), their reduced dimensions (approximately 50
c) electrical separation for the supply of one item mm × 50 mm) or their disposition cannot be

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

of current-using equipment (4.2.13), and gripped or come into significant contact with
a part of the human body and provided that
d) extra-low-voltage (SELV and PELV) (4.2.14).
connection with a protective conductor could
4.2.4 The protective measures applied in the installation only be made with difficulty or would be
shall be considered in the selection and erection of unreliable; and
equipment. NOTE —This exemption applies, for example, to bolts,
rivets, nameplates and cable clips.
For particular installations see 4.2.5 to 4.2.10. d) metal tubes or other metal enclosures
NOTE — In electrical installations the most commonly used protecting equipment in accordance
protective measure is automatic disconnection of supply. with 4.2.12.
4.2.5 For special installations or locations, the particular 4.2.11 Protective Measure: Automatic Disconnection
protective measures given in IEC 60364-7 shall be of Supply
applied.
4.2.11.1 General
4.2.6 The protective measures, specified in Annex B,
that is., the use of obstacles and placing out of reach, Automatic disconnection of supply is a protective
shall only be used in installations accessible to: measure in which:
a) skilled or instructed persons, or a) basic protection is provided by basic
b) persons under the supervision of skilled or insulation of live parts or by barriers or
instructed persons. enclosures, in accordance with Annex A; and
b) fault protection is provided by protective
4.2.7 The protective measures, specified in Annex C, equipotential bonding and automatic
that is, disconnection in case of a fault in accordance
a) non-conducting location, with 4.2.11.3 to 4.2.11.6.
b) earth-free local equipotential bonding, and NOTE —Where this protective measure is applied, Class
II equipment may also be used.
c) electrical separation for the supply of more
than one item of current-using equipment, Where specified, additional protection is provided by
may be applied only when the installation is under the a residual current protective device (RCD) with rated
supervision of skilled or instructed persons so that residual operating current not exceeding 30 mA, in
unauthorized changes cannot be made. accordance with 4.2.15.1. System Voltage Independent
RCD shall be used for domestic and similar application.
4.2.8 If certain conditions of a protective measure
NOTE — Residual current monitors (RCMs) are not protective
cannot be met, supplementary provisions shall be devices but they may be used to monitor residual currents in
applied so that the protective provisions together electrical installations. RCMs produce an audible or audible
achieve the same degree of safety. and visual signal when a preselected value of residual current
is exceeded.
NOTE —An example of the application of this rule is given
in 4.2.11.7. 4.2.11.2 Requirements for basic protection
4.2.9 Different protective measures applied to the same All electrical equipment shall comply with one of the

36
 IS 732 : 2019

provisions for basic protection (protection against direct Conductors for protective equipotential bonding shall
contact) described in Annex A or, where appropriate, comply with 5.4 and IS 3043.
Annex B.
Any metallic sheath of telecommunication cables shall
4.2.11.3 Requirements for fault protection be connected to the protective equipotential bonding,
taking account of the requirements of the owners or
4.2.11.3.1 Protective earthing and protective
operators of these cables.
equipotential bonding
4.2.11.3.2 Automatic disconnection in case of a fault
4.2.11.3.1.1 Protective earthing
4.2.11.3.2.1 Except as provided by 4.2.11.3.2.5
Exposed conductive parts shall be connected to a
and 4.2.11.3.2.6, a protective device shall automatically
protective conductor under the specific conditions for
interrupt the supply to the line conductor of a circuit or
each type of system earthing as specified in 4.2.11.4

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
equipment in the event of a fault of negligible
to 4.2.11.6.
impedance between the line conductor and an exposed-
Simultaneously accessible exposed conductive parts conductive-part or a protective conductor in the circuit
shall be connected to the same earthing system or equipment within the disconnection time required
individually, in groups or collectively. in 4.2.11.3.2.2, 4.2.11.3.2.3 or 4.2.11.3.2.4.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Conductors for protective earthing shall comply NOTES
with 5.4 and IS 3043. 1 Higher values of disconnection time than those required in
this sub-clause may be admitted in systems for electricity
Each circuit shall have available a protective conductor distribution to the public and power generation and transmission
connected to the relevant earthing terminal. for such systems.
2 Lower values of disconnection time may be required for
4.2.11.3.1.2 Protective equipotential bonding special installations or locations according to the IEC 60364-7.
3 For IT systems, automatic disconnection is not usually
In each building the earthing conductor, the main required on the occurrence of a first fault (see 4.2.11.6.1). For
earthing terminal and the following conductive parts the requirements for disconnection after the first fault
shall be connected to the protective equipotential see 4.2.11.6.4.
bonding: 4.2.11.3.2.2 The maximum disconnection time stated
a) metallic pipes supplying services into the in Table 1 shall be applied to final circuits.
building, for example, gas, water; 4.2.11.3.2.3 In TN systems, a disconnection time not
b) structural extraneous conductive parts, if exceeding 5s is permitted for distribution circuits, and
accessible in normal use, metallic central for circuits not covered by 4.2.11.3.2.2.
heating and air-conditioning systems; and
4.2.11.3.2.4 In TT systems, a disconnection time not
c) metallic reinforcements of constructional
exceeding 1s is permitted for distribution circuits and
reinforced concrete, if reasonably practicable.
for circuits not covered by 4.2.11.3.2.2.
Where such conductive parts originate outside the
4.2.11.3.2.5 If automatic disconnection according
building, they shall be bonded as close as practicable
to 4.2.11.3.2.1 cannot be achieved in the time required
to their point of entry within the building.

Table 1 Maximum Disconnection Times

(Clause 4.2.11.3.2.2)

System 50 V <Uo < 120 V 120 V <Uo < 230 V 230 V <Uo < 400 V Uo > 400 V
s s s s
a.c. d.c. a.c. d.c. a.c. d.c. a.c. d.c.
(1) (2) (3) (4) (5) (6) (7) (8) (9)
TN 0.8 Note 1 0.4 5 0.2 0.4 0.1 0.1
TT 0.3 Note 1 0.2 0.4 0.07 0.2 0.04 0.1
Where in TT systems the disconnection is achieved by an overcurrent protective device and the protective equipotential bonding is
connected with all extraneous-conductive-parts within the installation, the maximum disconnection times applicable to TN systems may
be used.
Uo is the nominal a.c. or d.c. line to earth voltage.
NOTES
1 Disconnection may be required for reasons other than protection against electric shock.
2 Where disconnection is provided by an RCD see Note to 4.2.11.4.4, Note 4 to 4.2.11.5.3 and Note to 4.2.11.6.4.

37
IS 732 : 2019

by 4.2.11.3.2.2, 4.2.11.3.2.3, or 4.2.11.3.2.4 as that the protective conductors also be connected to such points
wherever possible. Earthing at additional points, distributed as
appropriate, supplementary protective equipotential
evenly as possible, may be necessary to ensure that the potentials
bonding shall be provided in accordance with 4.2.15.2. of protective conductors remain, in case of a fault, as near as
possible to that of earth. In large buildings such as h i g h - ri s e
4.2.11.3.3 Additional protection buildings, additional earthing of protective conductors is not
possible for practical reasons. In such buildings protective-
In a.c. systems, additional protection by means of a
equipotential-bonding between protective conductors and
residual current protective device (RCD) in accordance extraneous-conductive-parts has, however, a similar function.
with 4.2.15.1 shall be provided for: 2 It is recommended that protective conductors (PE and PEN)
should be earthed where they enter any buildings or premises
a) at the incomer of every sub-distribution board taking account of any diverted neutral currents.
having one or more outgoing circuits with
fixed installation and socket-outlets to ensure 4.2.11.4.3 In fixed installations, a single conductor may
serve both as a protective conductor and as a neutral

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
safety of user from earth leakage, and
b) mobile equipment. conductor (PEN conductor) provided that the
requirements of 5.4.3.4 are satisfied. No switching or
System voltages independent RCD not exceeding isolating device shall be inserted in the PEN conductor.
30 mA shall be used for domestic and similar
application of a particular item of equipment. 4.2.11.4.4 The characteristics of the protective devices

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(see 4.2.11.4.5) and the circuit impedances shall fulfil
NOTE — An exemption may be made for:
the following requirement:
a) Socket-outlets for use under the supervision of skilled or
instructed persons, for example, in some commercial or Zs × Ia < Uo
industrial locations, or
b) A specific socket-outlet provided for connection. where
Zs = the impedance in ohms (Ω) of the fault loop
4.2.11.4 TN system
comprising
4.2.11.4.1 In TN systems the integrity of the earthing – the source,
of the installation depends on the reliable and effective
– the line conductor up to the point of the
connection of the PEN or PE conductors to earth.
fault, and
Where the earthing is provided from a public or other
supply system, compliance with the necessary – the protective conductor between the point
conditions external to the installation is the of the fault and the source;
responsibility of the supply network operator. Ia = the current in amperes (A) causing the
NOTE — Examples of conditions include:
automatic operation of the disconnecting
device within the time specified
a) the PEN is connected to earth at a number of points and is
in 4.2.11.3.2.2 or 4.2.11.3.2.3. When a
installed in such a way as to minimize the risk of a break in the
PEN conductor; residual current protective device (RCD) is
b) RB/RE < 50/(Uo – 50) used this current is the residual operating
where current providing disconnection in the time
RB= earth electrode resistance, in ohms, of all earth electrodes specified in 4.2.11.3.2.2 or 4.2.11.3.2.3.
in parallel; Uo = the nominal a.c. or d.c. line to earth voltage
R E= minimum contact resistance with earth, in ohms, of
in volts (V).
extraneous-conductive-parts not connected to a protective
conductor, through which a fault between line and earth may NOTE — Where compliance with this sub-clause is
occur; and provided by an RCD, the disconnecting times in
Uo = nominal a.c. r.m.s. voltage to earth, in volts. accordance with Table 1 relate to prospective residual
fault currents significantly higher than the rated
4.2.11.4.2 The neutral point or the midpoint of the residual operatingcurrent of theRCD(typically5I∆n).
power supply system shall be earthed. If a neutral point
4.2.11.4.5 In TN systems, the following protective
or midpoint is not available or not accessible, a line
devices may be used for fault protection (protection
conductor shall be earthed.
against indirect contact):
Exposed conductive parts of the installation shall be
– overcurrent protective devices;
connected by a protective conductor to the main
earthing terminal of the installation which shall be – residual current protective devices (RCDs).
connected to the earthed point of the power supply NOTE — Where an RCD is used for fault protection the circuit
system. should also be protected by an overcurrent protective device in
accordance with 4.4.
NOTES
1 If other effective earth connections exist, it is recommended A residual current protective device (RCD) shall not

38
 IS 732 : 2019

be used in TN-C systems. high impedance. This connection may be made either
at the neutral point or mid-point of the system or at an
Where an RCD is used in a TN-C-S system, a PEN
artificial neutral point. The latter may be connected
conductor shall not be used on the load side. The
directly to earth if the resulting impedance to earth is
connection of the protective conductor to the PEN
sufficiently high at the system frequency. Where no
conductor shall be made on the source side of the RCD.
neutral point or mid-point exists, a line conductor may
NOTE — Where discrimination between RCDs is necessary, be connected to earth through a high impedance.
see 5.3.6.3.
The fault current is then low in the event of a single
4.2.11.5 TT system fault to an exposed conductive part or to earth and
4.2.11.5.1 All exposed conductive parts collectively automatic disconnection in accordance with 4.2.11.3.2
protected by the same protective device shall be is not imperative provided the condition in 4.2.11.6.2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
connected by the protective conductors to an earth is fulfilled. Provisions shall be taken, however, to avoid
electrode common to all those parts. Where several risk of harmful patho-physiological effects on a person
protective devices are utilized in series, this requirement in contact with simultaneously accessible exposed
applies separately to all the exposed-conductive-parts conductive parts in the event of two faults existing
protected by each device. simultaneously.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

The neutral point or the mid-point of the power supply NOTE — To reduce overvoltage or to damp voltage oscillation,
it may be necessary to provide earthing through impedances or
system shall be earthed. If a neutral point or mid-point artificial neutral points, and the characteristics of these should
is not available or not accessible, a line conductor shall be appropriate to the requirements of the installation.
be earthed.
4.2.11.6.2 Exposed conductive parts shall be earthed
4.2.11.5.2 Generally in TT systems, RCDs shall be used individually, in groups, or collectively.
for fault protection.
The following condition shall be fulfilled:
NOTES
1 Where an RCD is used for fault protection the circuit should – in a.c. systems RA× Id < 120 V
also be protected by an overcurrent protective device in – in d.c. systems RA× Id < 120 V
accordance with 4.4.
where
2 The use of fault-voltage operated protective devices is not
covered by this standard. RA = the sum of the resistance in W of the earth
electrode and protective conductor for the
4.2.11.5.3 Where a residual current protective device
exposed conductive parts; and
(RCD) is used for fault protection, the following
conditions shall be fulfilled: Id = the fault current in A of the first fault of
negligible impedance between a line
a) the disconnection time as required by conductor and an exposed conductive part.
4.2.11.3.2.2 or 4.2.11.3.2.4, and The value of Id takes account of leakage
b) RA×I∆n ≤ 50 V currents and the total earthing impedance of
the electrical installation.
where
RA = the sum of the resistance (in Ω) of the earth 4.2.11.6.3 In IT systems the following monitoring
electrode and the protective conductor for devices and protective devices may be used:
the exposed conductive-parts, and a) insulation monitoring devices (IMDs);
I∆n = the rated residual operating current of the b) residual current monitoring devices (RCMs);
RCD. c) insulation fault location systems;
NOTES
d) overcurrent protective devices; and
1 Fault protection is provided in this case also if the fault
impedance is not negligible. e) residual current protective devices (RCDs).
2 Where discrimination between RCDs is necessary, see 5.3.6.3. NOTE — Where a residual current operating device
3 Where RA is not known, it may be replaced by ZS. (RCD) is used, tripping of the RCD in event of a first
4 The disconnection times in accordance with Table 1 relate to fault cannot be excluded due to capacitive leakage
prospective residual fault currents significantly higher than the currents.
rated residual operating current of the RCD (typically 5 I∆n). 4.2.11.6.3.1 In cases where an IT system is used for
4.2.11.6 IT system reasons of continuity of supply, an insulation monitoring
device shall be provided to indicate the occurrence of
4.2.11.6.1 In IT systems live parts shall be insulated a first fault from a live part to exposed conductive parts
from earth or connected to earth through a sufficiently or to earth. This device shall initiate an audible and/or

39
IS 732 : 2019

visual signal which shall continue as long as the fault protective device within the time required
persists. in 4.2.11.3.2.2 for TN systems
or 4.2.11.3.2.3.
If there are both audible and visible signals, it is
NOTES
permissible for the audible signal to be cancelled.
1 The time stated in Table 1 of 4.2.11.3.2.2 for the TN
NOTE — It is recommended that a first fault be eliminated system is applicable to IT systems with a distributed or
with the shortest practicable delay. non-distributed neutral conductor or mid-point
conductor.
4.2.11.6.3.2 Except where a protective device is 2 The factor 2 in both formulas takes into account that
installed to interrupt the supply in the event of the first in the event of the simultaneous occurrence of two faults,
earth fault, an RCM or an insulation fault location the faults may exist in different circuits.
system may be provided to indicate the occurrence of 3 For fault loop impedance, the most severe case should
a first fault from a live part to exposed conductive parts be taken into account, for example, a fault on the line

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
conductor at the source and simultaneously another fault
or to earth. This device shall initiate an audible and/or on the neutral conductor of a current-using equipment
visual signal, which shall continue as long as the fault of the circuit considered.
persists. b) Where the exposed-conductive-parts are
If there are both audible and visual signals it is earthed in groups or individually, the
following condition applies:

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

permissible for the audible signal to be cancelled, but
the visual alarm shall continue as long as the fault RA× Ia < 50 V
persists.
where
NOTE — It is recommended that a first fault be eliminated
with the shortest practicable delay. RA = the sum of the resistances of the earth
electrode and the protective conductor to the
4.2.11.6.4 After the occurrence of a first fault, exposed conductive parts,
conditions for automatic disconnection of supply in the
event of a second fault occurring on a different live Ia = the current causing automatic disconnection
conductor shall be as follows: of the disconnection device in a time
complying to that for TT systems in Table 1
a) Where exposed conductive parts are of 4.2.11.3.2.2 or in a time complying
interconnected by a protective conductor to 4.2.11.3.2.4.
collectively earthed to the same earthing NOTE — If compliance to the requirements of (b) is
system, the conditions similar to a TN system provided by a residual current protective device (RCD)
apply and the following conditions shall be compliance with the disconnection times required for
TT systems in Table 1 may require residual currents
fulfilled where the neutral conductor is not
significantly higher than the rated residual operatin g
distributed in a.c. systems and in d.c. systems current I∆n of the RCD applied (typically 5 I∆n).
where the mid-point conductor is not
distributed: 4.2.11.7 Functional extra-low voltage (FELV)

2IaZs < U 4.2.11.7.1 General

or where the neutral conductor or mid-point Where, for functional reasons, a nominal voltage not
conductor respectively is distributed: exceeding 50 V a.c. or 120 V d.c. is used but all the
requirements of 4.2.14 relating to SELV or to PELV
2IaZ's < Uo are not fulfilled, and where SELV or PELV is not
where necessary, the supplementary provisions described
in 4.2.11.7.2 and 4.2.11.7.3 shall be taken to ensure
Uo = the nominal a.c. or d.c. voltage, in V, between
basic protection and fault protection. This combination
line conductor and neutral conductor or mid-
of provisions is known as FELV.
point conductor, as appropriate;
U = the nominal a.c. or d.c. voltage in V between NOTE — Such conditions may, for example, be encountered
when the circuit contains equipment (such as transformers,
line conductors; relays, remote-control switches, contactors) insufficiently
Zs = the impedance in Ω of the fault loop insulated with respect to circuits at higher voltage.
comprising the line conductor and the 4.2.11.7.2 Requirements for basic protection
protective conductor of the circuit;
Basic protection shall be provided by either,
Z's = the impedance in Ω of the fault loop
comprising the neutral conductor and the a) basic insulation according to A-1
protective conductor of the circuit; and corresponding to the nominal voltage of the
Ia = the current in A causing operation of the primary circuit of the source, or

40
 IS 732 : 2019

b) barriers or enclosures in accordance equipment with double insulation or reinforced

with A-2. insulation), it shall be verified that the installation or
circuit concerned will be under effective supervision
4.2.11.7.3 Requirements for fault protection
in normal use so that no change is made that would
The exposed conductive parts of the equipment of the impair the effectiveness of the protective measure. This
FELV circuit shall be connected to the protective protective measure shall not, therefore, be applied to
conductor of the primary circuit of the source, provided any circuit that includes a socket-outlet or where a user
that the primary circuit is subject to protection by may change items of equipment without authorization.
automatic disconnection of supply described in 4.2.11.3
4.2.12.2 Requirements for basic protection and fault
to 4.2.11.6.
protection
4.2.11.7.4 Sources
4.2.12.2.1 Electrical equipment

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The source of the FELV system shall be either a
Where the protective measure, using double or
transformer with at least simple separation between
reinforced insulation, is used for the complete
windings or shall comply with 4.2.14.3.
installation or part of the installation, electrical
NOTE — If the system is supplied from a higher voltage system equipment shall comply with one of the following sub-
by equipment which does not provide at least simple separation

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

clauses:
between that system and the FELV system, such as
autotransformers, potentiometers, semiconductor devices, etc., – 4.2.12.2.1.1; or
the output circuit is deemed to be an extension of the input
circuit and should be protected by the protective measure – 4.2.12.2.1.2 and 4.2.12.2.2; or
applied in the input circuit. – 4.2.12.2.1.3 and 4.2.12.2.2.
4.2.11.7.5 Plugs and socket-outlets 4.2.12.2.1.1 Electrical equipment shall be of the
Plugs and socket-outlets for FELV systems shall comply following types, and type tested and marked to the
with all the following requirements: relevant standards:

a) plugs shall not be able to enter socket-outlets a) electrical equipment having double or
of other voltage systems, reinforced insulation (Class II equipment);
b) socket-outlets shall not admit plugs of other b) electrical equipment declared in the relevant
voltage systems, and product standard as equivalent to Class II, such
as assemblies of electrical equipment having
c) socket-outlets shall have a protective
total insulation [see IS 8623 (Part 1)].
conductor contact.
NOTE — This equipment is identified by the symbol
4.2.12 Protective Measure: Double or Reinforced
see IS 12032.
Insulation
4.2.12.1 General 4.2.12.2.1.2 Electrical equipment having basic
insulation only shall have supplementary insulation
4.2.12.1.1 Double or reinforced insulation is a applied in the process of erecting the electrical
protective measure in which, installation, providing a degree of safety equivalent to
a) basic protection is provided by basic electrical equipment according to 4.2.12.2.1.1 and
insulation, and fault protection is provided by complying with 4.2.12.2.2.1 to 4.2.12.2.2.3.
supplementary insulation, or NOTE — The symbol should be fixed in a visible position
b) basic and fault protection is provided by on the exterior and interior of the enclosure [see IEC 60417-
reinforced insulation between live parts and 5019 (DB: 2002-10) : Protective earth (ground)].
accessible parts. 4.2.12.2.1.3 Electrical equipment having uninsulated
NOTE — This protective measure is intended to prevent live parts shall have reinforced insulation applied in
the appearance of dangerous voltage on the accessible the process of erecting the electrical installation,
parts of electrical equipment through a fault in the basic
insulation. providing a degree of safety equivalent to electrical
equipment according to 4.2.12.2.1.1 and complying
4.2.12.1.2 The protective measure by double or with 4.2.12.2.2.2 and 4.2.12.2.2.3; such insulation
reinforced insulation is applicable in all situations, being recognized only where constructional features
unless some limitations are as given in IEC 60364-7. prevent the application of double insulation.
4.2.12.1.3 Where this protective measure is to be used NOTE — The symbol should be fixed in a visible position
as the sole protective measure (that is, where a whole on the exterior and interior of the enclosure [see IEC 60417-
installation or circuit is intended to consist entirely of 019 (DB: 2002-10): Protective earth (ground)].

41
IS 732 : 2019

4.2.12.2.2 Enclosures shall be effected in such a way as not to impair the

protection afforded in compliance with the equipment
4.2.12.2.2.1 The electrical equipment being ready for
specification.
operation, all conductive parts separated from live parts
by basic insulation only, shall be contained in an 4.2.12.2.3.2 Except where 4.2.12.1.3 applies, a circuit
insulating enclosure affording at least the degree of supplying items of Class II equipment shall have a
protection IPXXB or IP2X. circuit protective conductor run to and terminated at
each point in wiring and at each accessory.
4.2.12.2.2.2 The following requirements apply as
specified: NOTE — This requirement is intended to take account of the
replacement by the user of Class II equipment by Class I
a) the insulating enclosure shall not be traversed equipment.
by conductive parts likely to transmit a 4.2.12.2.4 Wiring systems

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
potential; and
b) the insulating enclosure shall not contain any 4.2.12.2.4.1 Wiring systems installed in accordance
screws or other fixing means of insulating with 5.2 are considered to meet the requirements
material which might need to be removed, or of 4.2.12.2 if:
are likely to be removed, during installation a) the rated voltage of the wiring system shall be

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

and maintenance and whose replacement by not less than the nominal voltage of the system
metallic screws or other fixing means could and at least 300/500 V, and
impair the enclosure’s insulation. b) adequate mechanical protection of the basic
Where the insulating enclosure must be traversed by insulation is provided by one or more of the
mechanical joints or connections (for example, for following:
operating handles of built-in apparatus), these should 1) the non-metallic sheath of the cable, or
be arranged in such a way that protection against shock 2) non-metallic trunking or ducting
in case of a fault is not impaired. complying with IS 14297 (Part 1) and
4.2.12.2.2.3 Where lids or doors in the insulating IS 14927 (Part 2/Section 1), or non-
enclosure can be opened without the use of a tool or metallic conduit complying with either is
key, all conductive parts, which are accessible if the IS 9537 or the IS 14930 (Parts 1 and 2).
lid or door is open, shall be behind an insulating barrier NOTES
(providing a degree of protection not less than IPXXB 1 Cable product standards do not specify impulse
or IP2X) preventing persons from coming withstand capability. However, it is considered that the
insulation of the cabling system is at least equivalent to
unintentionally into contact with those conductive parts.
the requirement in IEC 61140 for reinforced insulation.
This insulating barrier shall be removable only by use
2 Such a wiring system should not be identified by the
of a tool or key. symbol IEC 60417-5172 (DB: 2002-10), not by the
4.2.12.2.2.4 Conductive parts enclosed in the insulating symbol IEC 60417-5019 (DB: 2002-10).
enclosure shall not be connected to a protective
4.2.13 Protective Measure: Electrical Separation
conductor. However, provision may be made for
connecting protective conductors which necessarily run 4.2.13.1 General
through the enclosure in order to serve other items of
4.2.13.1.1 Electrical separation is a protective measure
electrical equipment whose supply circuit also runs
in which,
through the enclosure. Inside the enclosure, any such
conductors and their terminals shall be insulated as a) basic protection is provided by basic
though they were live parts, and their terminals shall insulation of live parts or by barriers and
be marked as PE terminals. enclosures in accordance with Annex A, and
Exposed conductive parts and intermediate parts shall b) fault protection is provided by simple
not be connected to a protective conductor unless separation of the separated circuit from other
specific provision for this is made in the specifications circuits and from earth.
for the equipment concerned. 4.2.13.1.2 Except as permitted by 4.2.13.1.3, this
4.2.12.2.2.5 The enclosure shall not adversely affect protective measure shall be limited to the supply of
the operation of the equipment protected in this way. one item of current-using equipment supplied from one
unearthed source with simple separation.
4.2.12.2.3 Installation
NOTE — When this protective measure is used, it is particularly
4.2.12.2.3.1 The installation of equipment mentioned important to ensure compliance of the basic insulation with
the product standard.
in 4.2.12.2.1 (fixing, connection of conductors, etc)

42
 IS 732 : 2019

4.2.13.1.3 Where more than one item of current-using This protective measure requires:
equipment is supplied from an unearthed source with
a) limitation of voltage in the SELV or PELV
simple separation, the requirements of C-3 shall be met.
system to the upper limit of Voltage Band I,
4.2.13.2 Requirements for basic protection 50 V a.c. or 120 V d.c. [see IS 12360 (Part
2)],
All electrical equipment shall be subject to one of the
basic protective provisions given in Annex A or to the b) protective separation of the SELV or PELV
protective measure in 4.2.12. system from all circuits other than SELV and
PELV circuits, and basic insulation between
4.2.13.3 Requirements for fault protection the SELV or PELV system and other SELV or
4.2.13.3.1 Protection by electrical separation shall be PELV systems; and
ensured by compliance with 4.2.13.3.2 to 4.2.13.3.6. c) for SELV systems only, basic insulation

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
between the SELV system and earth.
4.2.13.3.2 The separated circuit shall be supplied
through a source with at least simple separation, and 4.2.14.1.2 The use of SELV or PELV according
the voltage of the separated circuit shall not exceed to 4.2.14 is considered as a protective measure in all
500 V. situations.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4.2.13.3.3 Live parts of the separated circuit shall not NOTE — In certain cases the standards of the IEC 60364-7
series limit the value of the extra-low voltage to a value lower
be connected at any point to another circuit or to earth than 50 V a.c. or 120 V d.c.
or to a protective conductor.
4.2.14.2 Requirements for basic protection and fault
To ensure electrical separation, arrangements shall be protection
such that basic insulation is achieved between circuits.
Basic protection and fault protection is deemed to be
4.2.13.3.4 Flexible cables and cords shall be visible provided when:
throughout any part of their length liable to mechanical
damage. a) the nominal voltage cannot exceed the upper
limit of Voltage Band I,
4.2.13.3.5 For separated circuits the use of separate b) the supply is from one of the sources listed
wiring systems is recommended. If separated circuits in 4.2.14.3, and
and other circuits are in the same wiring system, multi-
c) the conditions of 4.2.14.4 are fulfilled.
conductor cables without metallic covering, insulated
conductors in insulating conduit, insulated ducting or NOTE — If the system is supplied from a higher voltage
insulated trunking shall be used, provided that system by equipment which provides at least simple
separation between that system and the extra-low-
a) the rated voltage is not less than the highest voltage system, but which does not meet the
requirements for SELV and PELV sources in 4.2.14.3,
nominal voltage, and
the requirements for FELV may be applicable
b) each circuit is protected against overcurrent. (see 4.2.11.7).

4.2.13.3.6 The exposed conductive parts of the 4.2.14.3 Sources for SELV and PELV
separated circuit shall not be connected either to the
protective conductor or exposed conductive parts of The following sources may be used for SELV and PELV
other circuits, or to earth. systems.

NOTE — If the exposed-conductive-parts of the separated circuit 4.2.14.3.1 A safety isolating transformer in accordance
are liable to come into contact, either intentionally or fortuitously, with IEC 61558-2-6.
with the exposed-conductive-parts of other circuits, protection
against electric shock no longer depends solely on protection by 4.2.14.3.2 A source of current providing a degree of
electrical separation but on the protective provisions to which safety equivalent to that of the safety isolating
the latter exposed-conductive-parts are subject. transformer specified in 4.2.14.3.1 (for example, motor
4.2.14 Protective Measure: Extra-Low-Voltage generator with windings providing equivalent
Provided by SELV and PELV isolation).
4.2.14.1 General 4.2.14.3.3 An electrochemical source (for example, a
battery) or another source independent of a higher
4.2.14.1.1 Protection by extra-low-voltage is a voltage circuit (for example, a diesel-driven generator).
protective measure which consists of either of two
different extra-low-voltage systems: 4.2.14.3.4 Certain electronic devices complying with
appropriate standards where provisions have been taken
– SELV; or in order to ensure that, even in the case of an internal
– PELV. fault, the voltage at the outgoing terminals cannot

43
IS 732 : 2019

exceed the values specified in 4.2.14.1.1. Higher c) circuit conductors at voltages higher than
voltages at the outgoing terminals are, however, Band I may be contained in a multi-conductor
permitted if it is ensured that, in case of contact with a cable or other grouping of conductors if the
live part or in the event of a fault between a live part SELV and PELV conductors are insulated for
and an exposed-conductive-part, the voltage at the the highest voltage present;
output terminals is immediately reduced to those values d) the wiring systems of other circuits are in
or less. compliance with 4.2.12.2.4.1; and
NOTES e) physical separation.
1 Examples of such devices include insulation testing equipment
4.2.14.4.3 Plugs and socket-outlets in SELV and PELV
and monitoring devices.
systems shall comply with the following requirements:
2 Where higher voltages exist at the outgoing terminals,
compliance with this clause may be assumed if the voltage at a) plugs shall not be able to enter socket-outlets

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
the outgoing terminals is within the limits specified in 4.2.14.1.1
when measured with a voltmeter having an internal resistance
of other voltage systems;
of at least 3 000 Ω. b) socket-outlets shall not admit plugs of other
voltage systems; and
4.2.14.3.5 Mobile sources supplied at low voltage, for
example, safety isolating transformers or motor c) plugs and socket-outlets in SELV systems shall

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

generators, shall be selected or erected in accordance not have a protective conductor contact.
with the requirements for protection by the use of 4.2.14.4.4 Exposed conductive parts of SELV circuits
double or reinforced insulation (see 4.2.12). shall not be connected to earth, or to protective
4.2.14.4 Requirements for SELV and PELV circuits conductors or exposed conductive parts of another
circuit.
4.2.14.4.1 SELV and PELV circuits shall have:
NOTE — If the exposed-conductive-parts of SELV circuits are
a) basic insulation between live parts and other liable to come into contact, either fortuitously or intentionally,
with the exposed conductive parts of other circuits, protection
SELV or PELV circuits, and against electric shock no longer depends solely on protection
b) protective separation from live parts of circuits by SELV, but also on the protective provisions to which the
not being SELV or PELV, provided by double latter exposed-conductive-parts are subject.
or reinforced insulation or by basic insulation 4.2.14.4.5 If the nominal voltage exceeds 25 V a.c. or
and protective screening for the highest 60 V d.c. or if the equipment is immersed, basic
voltage present. protection shall be provided for SELV and PELV
circuits by:
SELV circuits shall have basic insulation between live
parts and earth. a) insulation in accordance with A-1, or
The PELV circuits and/or exposed conductive parts of b) barriers or enclosures in accordance with A-2.
equipment supplied by the PELV circuits may be Basic protection is generally unnecessary in normal dry
earthed. conditions for:
NOTES a) SELV circuits where the nominal voltage does
1 In particular, protective separation is necessary between the not exceed 25 V a.c. or 60 V d.c.;
live parts of electrical equipment such as relays, contactors,
auxiliary switches, and any part of a higher voltage circuit or a b) PELV circuits where the nominal voltage does
FELV circuit. not exceed 25 V a.c. or 60 V d.c. and exposed
2 The earthing of PELV circuits may be achieved by a conductive parts and/or the live parts are
connection to earth or to an earthed protective conductor connected by a protective conductor to the
within the source itself.
main earthing terminal.
4.2.14.4.2 Protective separation of wiring systems of
In all other cases, basic protection is not required if the
SELV and PELV circuits from the live parts of other
nominal voltage of the SELV or PELV system does not
circuits, which have at least basic insulation, may be
exceed 12 V a.c. or 30 V d.c.
achieved by one of the following arrangements:
4.2.15 Additional Protection
a) SELV and PELV circuit conductors shall be
enclosed in a non-metallic sheath or insulating NOTE — Additional protection may be specified with the
protective measure under certain conditions of external
enclosure in addition to basic insulation; influence and in certain special locations (see IEC 60364-7).
b) SELV and PELV circuit conductors shall be
4.2.15.1 Additional protection: residual current
separated from conductors of circuits at
protective devices (RCDs)
voltages higher than Band I by an earthed
metallic sheath or earthed metallic screen; 4.2.15.1.1 The use of RCDs with a rated residual

44
 IS 732 : 2019

operating current not exceeding 30 mA, is recognized 4.3.1.1 General requirements

in a.c. systems as additional protection in the event of
Persons, livestock and property shall be protected
failure of the provision for basic protection and/or the
against damage or injury caused by heat or fire which
provision for fault protection or carelessness by users.
System voltage Independent RCD not exceeding 30 mA may be generated or propagated in electrical
shall be used for domestic and similar application. installations by taking into account the requirements
of this standard and the instructions of equipment
4.2.15.1.2 The use of such devices is not recognized as manufacturers.
a sole means of protection and does not obviate the
need to apply one of the protective measures specified The heat generated by electrical equipment shall not
in 4.2.11 to 4.2.14. cause danger or harmful effects to adjacent fixed
material or to material which may foreseeable be in
4.2.15.2 Additional protection: supplementary proximity to such equipment. Electrical equipment shall

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
protective equipotential bonding not present a fire hazard to adjacent materials.
NOTES NOTE — Damage, injury or ignition may be caused by effects
1 Supplementary protective equipotential bonding is considered such as
as an addition to fault protection.
i) heat accumulation, heat radiation, hot elements,
2 The use of supplementary protective bonding does not exclude

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

the need to disconnect the supply for other reasons, for example, ii) reduction of the safe function of electrical equipment, e.g.
protection against fire, thermal stresses in equipment, etc. protective devices such as protective switchgear,
3 Supplementary protective bonding may involve the entire thermostats, temperature limiters, seals of cable
installation, a part of the installation, an item of apparatus, penetrations and wiring systems,
or a location. iii) overcurrent,
iv) insulation faults and/or arcs causing interference,
4.2.15.2.1 Supplementary protective equipotential v) harmonic currents,
bonding shall include all simultaneously accessible vi) lightning strikes (see IS/IEC 62305 series),
exposed conductive parts of fixed equipment and vii) overvoltages (see 4.5.3),
extraneous conductive parts including where viii) inappropriate selection or erection of equipment.
practicable the main metallic reinforcement of
constructional reinforced concrete. The equipotential Any relevant manufacturer’s erection instructions shall
bonding system shall be connected to the protective be taken into account in addition to the requirements
conductors of all equipment including those of socket- of this standard.
outlets.
4.3.1.2 Where fixed equipment may attain surface
4.2.15.2.2 Where doubt exists regarding the temperatures which could cause a fire hazard to
effectiveness of supplementary protective equipotential adjacent materials, the equipment shall either
bonding, it shall be confirmed that the resistance R
between simultaneously accessible exposed conductive a) be mounted on or within materials that will
parts and extraneous conductive parts fulfils the withstand such temperatures and are of low
following condition: thermal conductance, or
120V b) be screened from elements of building
R≤ in d.c. systems construction by materials which will withstand
Ia
such temperatures and are of low thermal
50V conductance, or
R≤ in a.c. system
Ia c) be mounted so as to allow safe dissipation of
120V heat at a sufficient distance from any material
R≤ in d.c. systems on which such temperatures could have
Ia
deleterious thermal effects, any means of
where
support being of low thermal conductance.
Ia = the operating current in A of the protective
device 4.3.1.3 Where arcs or sparks may be emitted by
– for residual current protective devices permanently connected equipment in normal service,
(RCDs), I∆n the equipment shall either:
– for overcurrent devices, the 5s operating a) be totally enclosed in arc-resistant material,
current. or
4.3 Protection for Safety — Protection Against b) be screened by arc-resistant material from
Thermal Effects materials on which the emission could have
harmful effects, or
4.3.1 Protection Against Fire Caused by Electrical
c) be mounted so as to allow safe extinction of
Equipment
45
IS 732 : 2019

the emissions at a sufficient distance from erected that its temperature in normal use and
material upon which the emissions could have foreseeable temperature rise during a fault cannot cause
harmful effects. a fire.
Arc-resistant material used for this protective measure These arrangements may be effected by the construction
shall be non-ignitable, of low thermal conductivity, and of equipment or its conditions of installation.
of adequate thickness to provide mechanical stability.
Special measures are not necessary where the
NOTE — For example, a sheet made of fibreglass silicone of temperature of surfaces is unlikely to cause ignition of
20 mm thickness may be considered as arc-resistant.
nearby substances.
4.3.1.4 Fixed equipment causing a concentration of heat 4.3.2.1.3 Thermal cut-out devices shall have manual
shall be at a sufficient distance from any fixed object resetting only.
or building element so that the object or element, in

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
normal conditions, is not subjected to a dangerous 4.3.2.2 Conditions of evacuation in an emergency
temperature. Condition BD2: Low density occupation, difficult
For example, a temperature in excess of its ignition conditions of evacuation
temperature. BD3: High density occupation, easy

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — Any information from the manufacturer of the conditions of evacuation
equipment should be taken into account. BD4: High density occupation, difficult
4.3.1.5 Where electrical equipment in a single location conditions of evacuation (according to
contains flammable liquid in significant quantity, Table 7 of 5.1)
NOTE — Authorities responsible for building construction,
adequate precautions shall be taken to prevent the
public gatherings, fire prevention, etc may specify which BD
spread of liquid, flame and the products of combustion. condition is applicable.
NOTES
4.3.2.2.1 In conditions BD2, BD3 and BD4, wiring
1 Examples of such precautions include:
systems shall not encroach on escape routes unless the
a) a retention pit to collect any leakage of liquid and ensure
extinction in the event of fire;
wiring in the wiring system is provided with sheaths or
b) installation of the equipment in a chamber of adequate
enclosures, provided by the cable management system
fire resistance and the provision of sills or other means of itself or by other means.
preventing liquid spreading to other parts of the building,
such a chamber being ventilated solely to the external Wiring systems encroaching on escape routes shall not
atmosphere. be within arm’s reach unless they are provided with
2 The generally accepted lower limit for a significant quantity protection against mechanical damage likely to occur
is 25 l. during an evacuation.
3 For quantities less than 25 l, it is sufficient to take precautions
to prevent the escape of liquid. Wiring systems in escape routes shall be as short as
4 Products of combustion of liquid are considered to be flame, practicable and shall be non-flame propagating.
smoke and gas.
NOTE — Compliance with this requirement may be achieved
5 It is desirable to switch off the supply at the onset of a fire. by using the following products:
4.3.1.6 The materials of enclosures installed around a) Cables fulfilling tests under fire conditions of IEC 60332-
1-2, and appropriate fire conditions as follows: IEC 60332-
electrical equipment during erection shall withstand the
3-21, IEC 60332-3-22, IEC 60332-3-23, IEC 60332-3-24
highest temperature likely to be produced by the and IEC 60332-3-25;
electrical equipment. b) Conduit systems classified as non-flame propagating
according to IS 14930 (Parts 1 & 2);
Combustible materials are not suitable for the
c) Cable trunking systems classified as non-flame propagating
construction of these enclosures unless preventive according to IS 14297 (Part 1) and IS 14927 (Part 2/
measures against ignition are taken, such as covering Section 1);
with non-combustible or not readily combustible d) Cable tray systems and cable ladder systems classified as
material of low thermal conductivity. non-flame propagating according to IEC 61537; and
e) For powertrack systems: the IEC 61534 series.
4.3.2 Precautions where Particular Risks of Fire Exist
In conditions BD2, BD3 and BD4, wiring systems that
4.3.2.1 General
are supplying safety circuits shall have a resistance to
4.3.2.1.1 Electrical equipment shall be restricted to that fire rating of either the time authorized by regulations
necessary for the use of these locations, except wiring for building elements or 1h in the absence of such a
systems according to 4.3.2.3.5. regulation.
4.3.2.1.2 Electrical equipment shall be so selected and NOTE — For the requirements for maintaining the function of
wiring systems of safety services under fire conditions, see 5.6.

46
 IS 732 : 2019

Wiring within escape routes shall have a limited rate normally flammable surfaces are marked with symbols:
of smoke production.
4.3.2.2.2 In conditions BD2, BD3 and BD4, switchgear and/or
and controlgear devices, except certain devices to
(see N.4 of IEC 60598-1 : 2008 for further
facilitate evacuation, shall be accessible only to
explanations).
authorized persons. If they are placed in passages, they
shall be enclosed in cabinets or boxes constructed of 4.3.2.3.2 Measures shall be taken to prevent an
non-combustible or not readily combustible material. electrical enclosure of equipment such as a heater or
NOTE —This clause does not prohibit plastic enclosures that resistor from exceeding the following temperatures:
are not readily combustible.
a) 90 °C under normal conditions, and
4.3.2.2.3 In conditions BD3 and BD4 and in escape b) 115 °C under fault conditions.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
routes, electrical equipment containing flammable
liquids shall not be installed. Where materials such as dust or fibres sufficient to
cause a fire hazard could accumulate on an enclosure
NOTE — Individual capacitors incorporated in equipment are of electrical equipment, adequate measures shall be
not subject to this requirement. This exception principally
concerns discharge luminaires and capacitors of motor starters.
taken to prevent that enclosure from exceeding the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

temperatures stated above.
4.3.2.3 Locations with risks of fire due to the nature of
NOTE — Luminaires marked in compliance with IS 10322
processed or stored materials are designed to provide limited surface temperature.
Condition BE2: Fire risk (according to Table 7 of 5.1) 4.3.2.3.3 Switchgear for protection, control and
NOTES isolation shall be placed outside locations presenting
1 Quantities of flammable materials or the surface or volume condition BE2, unless it is in an enclosure providing a
of the location may be regulated by national authorities. degree of protection appropriate for such a location of
2 For explosion risks, see IS/ IEC 60079-14. at least IP4X or, in the presence of dust, IP5X or, in the
4.3.2.3.1 Luminaires shall be kept at an adequate presence of conductive dust, IP6X, except where
distance from combustible materials. If no other 4.3.2.3.11 applies.
information is given by manufacturers, spotlights and 4.3.2.3.4 Except where wiring and wiring systems are
projectors shall be installed at the following minimum embedded in non-combustible material, only non-
distances from combustible materials: flame-propagating wiring systems shall be used.
100 W 0.5 m As a minimum, equipment shall be selected in
100 W to 300 W 0.8 m accordance with the following requirements:
300 W to 500 W 1.0 m
a) Cables shall satisfy the test under fire
above 500 W greater distances can be conditions specified in the IEC 60332 series;
necessary. b) Conduit systems shall satisfy the test for
NOTE — In the absence of manufacturers’ instructions, the
resistance to flame propagation specified in
above distances imply all directions.
IS 14930 (Parts 1 and 2);
Lamps and other components of luminaires shall be c) Cable trunking systems and cable ducting
protected against foreseeable mechanical stresses. Such systems shall satisfy the test for resistance to
protective means shall not be fixed on lampholders flame propagation specified in IS 14297
unless they form an integral part of the luminaire. (Part 1) and IS 14297 (Part 2/Section 1);
Modifications to luminaires are not acceptable. d) Cable tray systems and cable ladder systems
A luminaire with a lamp that could eject flammable shall satisfy the test for resistance to flame
materials in case of failure shall be installed with a propagation specified in IEC 61537 series;
safety protective shield for the lamp in accordance with and
the manufacturer’s instructions. e) Powertrack systems shall satisfy the test for
resistance to flame propagation specified in
NOTE — Luminaires suitable for direct mounting on normally
flammable surfaces were earlier marked with the symbol IEC 61534 series.
NOTES
according to IS 10322. 1 Where the risk of flame propagation is high, e.g. in
long vertical runs of bunched cables, cables should meet
With the publication of IEC 60598-1 : 2008, luminaires the flame propagation characteristics of the appropriate
suitable for direct mounting have no special marking part in the IEC 60332-3 series.
and only luminaires not suitable for mounting on 2 Flame propagation tests for cable management systems
are always performed in a vertical configuration.

47
IS 732 : 2019

4.3.2.3.5 Wiring systems which traverse these locations, specified in (a) may be used. In the event of a
but are not necessary for the use of the locations, shall second fault, see 4.2.11 for disconnection
satisfy the following conditions: times.
a) the wiring systems shall meet the requirements Mineral insulated cables and busbar trunking systems
of 4.3.2.3.5; are not considered likely to cause a fire from insulation
faults and therefore need not be protected.
b) they have no connection along the route inside
the locations, unless these connections are NOTE — Cables with metallic coverings are recommended.
The metallic covering should be connected to the protective
placed in fire-resistant enclosures; conductor.
c) they are protected against overcurrent in
accordance with 4.3.2.3.10; and 4.3.2.3.10 Circuits supplying or traversing locations
where condition BE2 applies, shall be protected against
d) bare conductors shall not be used.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
overload and short-circuit by protective devices located
4.3.2.3.6 In forced-air heating installations, the air outside and on the supply side of these locations.
intake shall be outside locations where a presence of Circuits originating inside the locations shall be
combustible dust may be expected. protected against overcurrent by protective devices
located at their origin.
The temperature of the outgoing air shall not be such

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

as to cause fire in the location. 4.3.2.3.11 In circuits supplied at SELV or PELV, live
parts shall be:
4.3.2.3.7 Motors which are automatically or remotely
controlled, or which are not continuously supervised, a) contained in enclosures affording the degree
shall be protected against excessive temperature rise of protection IP2X or IPXXB, or
by temperature responsive devices, unless specifically b) provided with insulation capable of
designed to be inherently heat-limiting. withstanding a test voltage of 500 V d.c. for
1 min regardless of the nominal voltage of the
4.3.2.3.8 Every luminaire shall:
circuit. This is in addition to the requirements
a) be appropriate for the location; of 4.2.14.4.5.
b) be provided with an enclosure providing a 4.3.2.3.12 PEN conductors are not allowed in locations
degree of protection of at least IP4X or, in the where condition BE2 applies, except for circuits
presence of dust, IP5X or, in the presence of traversing such locations and having no connection
conductive dust, IP6X; between their traversing PEN conductor and any
c) have a limited surface temperature in conductive part in the locations.
accordance with IEC 60598-2-24; and
4.3.2.3.13 Every circuit supplying equipment in
d) be of a type that prevents lamp components
locations where condition BE2 applies shall be
from falling from the luminaire.
provided with a means of isolation from all live supply
In locations where there may be fire hazards due to conductors such that no live supply conductor can
dust or fibres, luminaires shall be installed so that dust remain closed when one or more others are open. This
or fibres cannot accumulate in dangerous amounts. may be achieved, for example, by a mechanically linked
NOTE — Luminaires should also comply with relevant parts
switch or a mechanically linked circuit-breaker.
of the IEC 60598 series (see also 5.5.3). NOTE — Provision may be made for isolation of a group of
circuits by a common means, if the service conditions allow
4.3.2.3.9 Final circuits and current-using equipment this.
shall be protected against insulation faults as follows:
4.3.2.4 Locations with combustible constructional
a) In TN and TT systems, RCDs with a rated materials
residual operating current I∆n 300 mA shall be
used. Where resistive faults may cause a fire, Condition CA2: Combustible materials (according to
for example, for overhead heating with heating Table 7 of 5.1).
film elements, the rated residual operating 4.3.2.4.1 Precautions shall be taken to ensure that
current shall be I∆n 30 mA. electrical equipment cannot cause the ignition of walls,
b) In IT systems, insulation monitoring devices floors or ceilings. This can be achieved by proper
monitoring the whole installation or RCMs design, choice and installation of electrical equipment.
(residual current monitoring devices) in the
To avoid the ingress of solid foreign objects, boxes
final circuits, both with audible and visual
and enclosures installed in prefabricated hollow walls
signals, shall be provided. Alternatively, RCDs
liable to be drilled during erection of the wall shall
with a rated residual operating current as
have a degree of protection of at least IP3X.

48
 IS 732 : 2019

4.3.2.4.2 Luminaires shall be kept at an adequate significant value. Examples include: national monuments,
museums and other public buildings. Buildings such as railway
distance from combustible materials. If no other
stations and airports, buildings or facilities such as laboratories,
information is given by manufacturers, spotlights and computer centres and certain industrial and storage facilities.
projectors shall be installed at the following minimum 2 The following measures may be considered:
distances from combustible materials: a) installation of mineral insulated cables according to
IEC 60702-1;
100 W 0.5 m
b) installation of cables with improved fire-resisting
100 W to 300 W 0.8 m characteristics in case of a fire hazard, and complying with
300 W to 500 W 1.0 m IEC 60331-1 or IEC 60331-21 or similar;
c) installation of cables in non-combustible solid walls,
above 500 W greater distances can be ceilings and floors;
necessary. d) installation of cables in areas with constructional partitions
NOTE — In the absence of manufacturers’ instructions, the having a fire-resisting capability for a time of 30 min or 90

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
above distances imply all directions. min, the latter in locations housing staircases and needed
for an emergency escape.
Lamps and other components of luminaires shall be
Where these measures are not practicable, enhanced
protected against foreseeable mechanical stresses. Such
fire protection may be possible by use of reactive fire
protective means shall not be fixed on lampholders,
protection systems.
unless they form an integral part of the luminaire.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4.3.3 Protection against Burns
A luminaire with a lamp that could eject flammable
materials in case of failure shall be installed with a Accessible parts of electrical equipment within arm’s
safety protective shield for the lamp in accordance with reach shall not attain a temperature likely to cause burns
the manufacturer’s instructions. to persons, and shall comply with the appropriate limit
NOTE — Luminaires suitable for direct mounting on normally stated in Table 2. All parts of the installation likely in
normal service to attain, even for short periods,
flammable surfaces were earlier marked with the symbol temperatures exceeding the limits stated in Table 2 shall
according to IS 10322. be guarded so as to prevent any accidental contact.
With the publication of IEC 60598-1 : 2008, luminaires However, the values in Table 2 do not apply to
suitable for direct mounting have no special marking equipment complying with IS standards for the type of
and only luminaires not suitable for mounting on equipment concerned.
normally flammable surfaces are marked with symbols NOTE — Lower temperatures may be applicable where
condition BA2 (children) applies.
and/or
Table 2 Temperature Limits in Normal Service for
(see N.4 of IEC 60598-1 : 2008 for further Accessible Parts of Equipment within Arm’s
explanations). Reach
(Clause 4.3.3)
4.3.2.5 Fire propagating structures
Accessible Parts Material of Maximum
Condition CB2: Propagation of fire (according to Accessible Temperatures
Table 7 of 5.1). Surfaces °C
(1) (2) (3)
4.3.2.5.1 In structures where the shape and dimensions
Hand-held means of Metallic 55
facilitate the spread of fire, precautions shall be taken operation Non-metallic 65
to ensure that the electrical installation cannot propagate Parts intended to be Metallic 70
a fire (for example, chimney effect). touched but not hand-held Non-metallic 80
Parts which need not be Metallic 80
NOTE — Fire detectors may be provided which ensure the touched for normal Non-metallic 90
implementation of measures for preventing propagation of fire, operation
for example, the closing of fire-proof shutters in ducts, building
voids and the like. Boxes and enclosures according to IS 14772
for hollow walls and cables in accordance with the IEC 60332-3 4.3.4 Protection Against Overheating
series can be used. IS 14772 includes marking with the
symbol H for boxes and enclosures for hollow walls. 4.3.4.1 Forced air heating systems

4.3.2.6 Selection and erection of installations in Forced air heating systems shall be such that their
locations with endangering of irreplaceable goods heating elements, other than those of central storage
heaters, cannot be activated until the prescribed air flow
The requirements of 4.3.2.1.2 shall be met. has been established and are deactivated when the air
NOTES flow is less than the prescribed value. In addition, they
1 The locations include buildings or rooms with assets of shall have two temperature limiting devices

49
IS 732 : 2019

independent of each other which prevent permissible appropriate precautions shall be taken.
temperatures from being exceeded in air ducts.
4.4.2.1.2 In a TT or TN system, for a circuit supplied
Supporting parts, frames and enclosures of heating between line conductors and in which the neutral
elements shall be of non-combustible material. conductor is not distributed, overcurrent detection need
not be provided for one of the line conductors, provided
4.3.4.2 Appliances producing hot water or steam
that the following conditions are simultaneously
All appliances producing hot water or steam shall be fulfilled:
protected by design or erection against overheating in
a) there exists, in the same circuit or on the supply
all service conditions. Unless the appliances comply
side, protection intended to detect unbalanced
as a whole with the appropriate Indian standards, the
loads and intended to cause disconnection of
protection shall be by means of an appropriate non-
all the line conductors; and

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
self-resetting device, functioning independently of the
thermostat. b) the neutral conductor is not distributed from
an artificial neutral point of the circuits
If an appliance has no free outlet, it shall also be situated on the load side of the protective
provided with a device which limits the internal water device mentioned in (a).
pressure.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4.4.2.2 Protection of the neutral conductor
4.3.4.3 Space heating appliances
4.4.2.2.1 TT or TN systems
The frame and enclosure of space heating appliances
shall be of non-combustible material. Where the cross-sectional area of the neutral conductor
is at least equivalent to that of the line conductors, and
NOTE — In operating areas with a fire risk, space heating the current in the neutral is expected not to exceed the
appliances may not be operated if the air from these areas is
guided through the appliance. value in the line conductors, it is not necessary to
provide overcurrent detection for the neutral conductor
The side walls of radiant heaters which are not touched or a disconnecting device for that conductor.
by the heat radiation should have a sufficient distance
from flammable parts. In case of a reduction of the Where the cross-sectional area of the neutral conductor
distance by a non-flammable partition, this partition is less than that of the line conductors, it is necessary
should have a distance of at least 1 cm to the enclosure to provide overcurrent detection for the neutral
of the radiant heater and to flammable parts. conductor, appropriate to the cross-sectional area of
that conductor; this detection shall cause the
Unless otherwise declared by the manufacturer, radiant disconnection of the line conductors, but not necessarily
heaters should be mounted so that in the direction of of the neutral conductor.
radiation a safety distance of at least 2 m from
flammable parts is ensured. In both cases the neutral conductor shall be protected
against short-circuit current.
4.4 Protection for Safety — Protection Against
NOTE — This protection may be achieved by the overcurrent
Overcurrent
protective devices in the line conductors. In that case it is not
4.4.1 General Requirements necessary to provide overcurrent protection for the
Protective devices shall be provided to disconnect any neutral conductor or a disconnecting device for that
overcurrent in the circuit conductors before such a conductor.
current could cause danger due to thermal or mechanical Where the current in the neutral conductor is expected
effects detrimental to insulation, joints, terminations to exceed the value in the line conductors, refer
or material surrounding the conductors. to 4.4.2.2.3.
4.4.2 Requirements according to the Nature of the Except for disconnection, the requirements for a neutral
Circuits conductor apply to a PEN conductor.
4.4.2.1 Protection of line conductors 4.4.2.2.2 IT systems
4.4.2.1.1 Detection of overcurrent shall be provided Where the neutral conductor is distributed, it is
for all line conductors, except where 4.4.2.1.2 applies. necessary to provide overcurrent detection for the
It shall cause the disconnection of the conductor in neutral conductor of every circuit. The overcurrent
which the overcurrent is detected but not necessarily detection shall cause the disconnection of all the live
the disconnection of the other live conductors. conductors of the corresponding circuit, including the
If disconnection of a single phase may cause danger, neutral conductor. This measure is not necessary if;
for example in the case of a three-phase motor,
50
 IS 732 : 2019

a) the particular neutral conductor is effectively NOTES

protected against overcurrent by a protective 1 The fuse comprises all the parts that form the complete
protective device.
device placed on the supply side, for example
2 This subclause does not exclude the use of other protective
at the origin of the installation, or devices if the requirements in 4.4.3.1 and 4.4.5.5 are fulfilled.
b) the particular circuit is protected by a residual
current operated protective device with a rated 4.4.3.2 Devices ensuring protection against overload
residual current not exceeding 0.20 times the current only
current-carrying capacity of the corresponding These protective devices shall satisfy the requirements
neutral conductor. This device shall of 4.4 and may have an interrupting capacity below the
disconnect all the live conductors of value of the prospective short-circuit current at the point
the corresponding circuit, including the where the devices are installed.
neutral conductor. The device shall have

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTES
sufficient breaking capacity for all poles.
1 These devices are generally inverse time lag protective devices.
NOTE — In IT systems, it is strongly recommended 2 Fuses type aM do not protect against overload.
that the neutral conductor should not be distributed.
4.4.3.3 Devices ensuring protection against short-
4.4.2.2.3 Harmonic currents circuit current only

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Overload detection shall be provided for the neutral A device providing protection against short-circuit
conductor in a multi-phase circuit where the harmonic current only shall be installed where overload protection
content of the line currents is such that the current in is achieved by other means or where 4.4.4 permits
the neutral conductor is expected to exceed the current- overload protection to be dispensed with. Such a device
carrying capacity of that conductor. The overload shall be capable of breaking, and for a circuit-breaker
detection shall be compatible with the nature of the making, the short-circuit current up to and including
current through the neutral and shall cause the the prospective short-circuit current. Such a device shall
disconnection of the line conductors but not necessarily satisfy the requirements of 4.4.4.
the neutral conductor. Where the neutral is
disconnected, the requirements of 4.4.2.3 apply. Such devices may be:

NOTE — Further requirements regarding protection of neutral a) circuit-breakers with short-circuit release only,
conductors are given in 5.2. and
4.4.2.3 Disconnection and reconnection of the b) fuses with gM, aM type fuse links.
neutral conductor in multi-phase systems 4.4.3.4 Characteristics of protective devices
Where disconnection of the neutral conductor is The operating characteristics of overcurrent protective
required, disconnection and reconnection shall be such devices shall comply with those specified in, for
that the neutral conductor shall not be disconnected example, IS/IEC 60898, IS/IEC 60947-2,
before the line conductors and shall be reconnected at IS/IEC 60947-6-2, IS 12640 (Part 2), IS 13703 (Part 2),
the same time as or before the line conductors. IEC 60269-3, IS 13730 (Part 4) or IS/IEC 60947-3.
4.4.3 Nature of Protective Devices NOTE — The use of other devices is not excluded provided
that their time/current characteristics provide an equivalent level
The protective devices shall be of the appropriate types of protection to that specified in this clause.
indicated by 4.4.2.1 to 4.4.2.3.
4.4.4 Protection Against Overload Current
4.4.3.1 Devices providing protection against both
overload current and short-circuit current 4.4.4.1 Coordination between conductors and overload
protective devices
Except as stated in 4.4.5.5.1, a device providing
protection against both overload and short-circuit The operating characteristics of a device protecting a
current shall be capable of breaking and, for a circuit- cable against overload shall satisfy the two following
breaker, making any overcurrent up to and including conditions:
the prospective short-circuit current at the point where IB < In < IZ ... (1)
the device is installed. Such devices may be: I2 < 1.45 × IZ ... (2)
a) circuit-breakers incorporating overload and where
short-circuit release;
IB = the design current for that circuit;
b) circuit-breakers in conjunction with fuses; and
IZ = the continuous current-carrying capacity of
c) fuses having fuse links with gG characteristics.
the cable (see 5.2.6);

51
IS 732 : 2019

In = the rated current of the protective device; 4.4.4.3 Omission of devices for protection against
NOTE — For adjustable protective devices, the rated overload
current In is the current setting selected.
The various cases stated in this sub-clause shall not be
I2 = the current ensuring effective operation in applied to installations situated in locations presenting
the conventional time of the protective a fire risk or risk of explosion or where the requirements
device. for special installations and locations specify different
The current I2 ensuring effective operation of the conditions.
protective device shall be provided by the manufacturer
4.4.4.3.1 General
or as given in the product standard.
Devices for protection against overload need not be
Protection in accordance with this clause may not
provided:
ensure protection in certain cases, for example where

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
sustained overcurrents less than I2 occur. In such cases, a) for a conductor situated on the load side of a
consideration should be given to selecting a cable with change in cross-sectional area, nature, method
a larger cross-sectional area. of installation or in constitution, that is
NOTES
effectively protected against overload by a
protective device placed on the supply side;

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1 IB is the design current through the line or the permanent
current through neutral in case of a high level of the third b) for a conductor that is not likely to carry
harmonic. overload current, provided that this conductor
2 The current ensuring effective operation in the conventional is protected against short-circuit in accordance
time of protective devices may also be named It or If according
to the product standards. Both It and If are multiples of In and
with the requirements of 4.4.4 and that it has
attention should be given to the correct representation of values neither branch circuits nor socket-outlets;
and indexes. c) at the origin of an installation where the
3 See Annex E for an illustration of conditions (1) and (2) distributor provides an overload device and
of 4.4.4.1.
agrees that it affords protection to the part of
4 Design current IB can be considered as an actual current Ia
after applying correction factors, see 4.1.5.6.1.
the installation between the origin and the
main distribution point of the installation
4.4.4.2 Position of devices for overload protection where further overload protection is provided.
4.4.4.2.1 A device ensuring protection against overload d) for circuits for telecommunications, control,
shall be placed at the point where a change, such as a signalling and the like.
change in cross-sectional area, nature, method of NOTE — For installations according to (a), (b) and
installation or in constitution, causes a reduction in the (d), see Fig. 71.
value of current-carrying capacity of the conductors,
except where 4.4.4.2.2 and 4.4.4.3 apply. 4.4.4.3.2 Position or omission of devices for protection
against overload in IT systems
4.4.4.2.2 The device protecting the conductor against
overload may be placed along the run of that conductor 4.4.4.3.2.1 The provisions in 4.4.4.2.2 and 4.4.4.3.1
if the part of the run between the point where a change for an alternative position or omission of devices for
occurs (in cross-sectional area, nature, method of protection against overload are not applicable to IT
installation or constitution) and the position of the systems unless each circuit not protected against
protective device has neither branch circuits nor socket- overload is protected by one of the following means:
outlet circuits and fulfils at least one of the following a) use of the protective measures described
two conditions: in 4.2.12;
a) it is protected against short-circuit current in b) protection of each circuit by a residual current
accordance with the requirements stated protective device that will operate
in 4.4.5; immediately on a second fault; and
b) its length does not exceed 3 m, it is carried c) for permanently supervised systems only use
out in such a manner as to reduce the risk of of insulation monitoring which either:
short-circuit to a minimum, and it is installed 1) causes the disconnection of the circuit
in such a manner as to reduce to a minimum when the first fault occurs, or
the risk of fire or danger to persons
2) gives a signal indicating the presence of
(see also 4.4.5.2.1).
a fault. The fault shall be rectified
NOTE — For installation according to (a) see Fig. 69. according to the operational requirements
For installation according to (b) see Fig. 70. and recognizing the risk from a second
fault.

52
 IS 732 : 2019

NOTE — It is recommended to install an insulation fault unequal if the difference between any currents is more than 10
location system. With the application of such a system it is percent of the design current for each conductor. Guidance is
possible to given in G-2.

detect and locate the insulation fault without 4.4.5 Protection Against Short-Circuit Currents
interruption of the supply.
This standard only considers the case of short-circuit
4.4.4.3.2.2 In IT systems without a neutral conductor, between conductors belonging to the same circuit.
the overload protective device may be omitted in one
4.4.5.1 Determination of prospective short-circuit
of the phase conductors if a residual current protective
currents
device is installed in each circuit.
The prospective short-circuit current at every relevant
4.4.4.3.3 Cases where omission of devices for overload
point of the installation shall be determined. This may
protection shall be considered for safety reasons
be carried out either by calculation or by measurement.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The omission of devices for protection against overload NOTE — The prospective short-circuit current at the supply
is permitted for circuits supplying current-using point may be obtained from the supply utility.
equipment where unexpected disconnection of the
circuit could cause danger or damage. Examples of such 4.4.5.2 Position of devices for short-circuit protection

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

cases include: A device ensuring protection against short-circuit shall
a) exciter circuits of rotating machines; be placed at the point where a reduction in the cross-
sectional area of the conductors or another change
b) supply circuits of lifting magnets;
causes a change to the current-carrying capacity of the
c) secondary circuits of current transformers; conductors, except where 4.4.5.2.1, 4.4.5.2.2 or 4.4.5.3
d) circuits which supply fire extinguishing applies.
devices; and
4.4.5.2.1 The various cases stated in the following sub
e) circuits supplying safety services (burglar
clause shall not be applied to installations situated in
alarm, gas alarms, etc).
locations presenting a fire risk or risk of explosion and
NOTE — In such cases, consideration should be given where special rules for certain locations specify
to the provision of an overload alarm. different conditions. The device for protection against
4.4.4.4 Overload protection of conductors in parallel short-circuit may be placed other than as specified
in 4.4.4.2, under the following conditions.
Where a single protective device protects several
conductors in parallel, there shall be no branch circuits In the part of the conductor between the point of
or devices for isolation or switching in the parallel reduction of cross-sectional area or other change and
conductors. the position of the protective device there shall be no
branch circuits nor socket-outlet circuits and that part
This subclause does not preclude the use of ring final of the conductor shall:
circuits.
a) not exceed 3 m in length, and
4.4.4.4.1 Equal current sharing between parallel b) be installed in such a manner as to reduce the
conductors risk of a short-circuit to a minimum, and
Where a single device protects conductors in parallel NOTE — This condition may be obtained for example
by reinforcing the protection of the wiring against
sharing currents equally, the value of Iz to be used
external influences (see Fig. 73).
in 4.4.4.1 is the sum of the current-carrying capacities
c) not be placed close to combustible material.
of the various conductors.
4.4.5.2.2 A protective device may be placed on the
It is deemed that current sharing is equal if the
supply side of the reduced cross-sectional area or
requirements of the first indent of 5.2.6.7(a) are
another change made, provided that it possesses an
satisfied.
operating characteristic such that it protects the wiring
4.4.4.4.2 Unequal current sharing between parallel situated on the load side against short-circuit, in
conductors accordance with 4.4.5.5.2.
Where the use of a single conductor, per phase, is NOTE — The requirements of 4.4.4.2.2 may be met by the
impractical and the currents in the parallel conductors method given in Annex G.
are unequal, the design current and requirements for 4.4.5.3 Omission of devices for protection against
overload protection for each conductor shall be short-circuit
considered individually.
Provided that both of the following conditions are
NOTE — Currents in parallel conductors are considered to be

53
IS 732 : 2019

simultaneously fulfilled: Guidance is given in G-3.

– the wiring is installed in such a way as to 4.4.5.5 Characteristics of short-circuit protective
reduce the risk of a short-circuit to a devices
minimum{see item b) of 4.4.5.2.1}, and
Each short-circuit protective device shall meet the
– the wiring is not placed close to combustible requirements given in 4.4.5.5.1.
material, devices for protection against short-
circuit need not be provided for applications 4.4.5.5.1 The rated breaking capacity shall be not less
such as: than the prospective maximum short-circuit current at
a) conductors connecting generators, the place of its installation, except where the following
transformers, rectifiers, accumulator paragraph applies.
batteries to the associated control panels, A lower rated breaking capacity is permitted if another

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
the protective devices being placed in protective device having the necessary breaking
these panels; capacity is installed on the supply side. In that case,
b) circuits where disconnection could cause the characteristics of the devices shall be coordinated
danger for the operation of the so that the energy let through by these two devices does
installations concerned, such as those not exceed that which can be withstood without damage

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

cited in 4.4.4.3.3; by the device on the load side and the conductors
c) certain measuring circuits; protected by these devices.
d) at the origin of an installation where the NOTE — In certain cases other characteristics may need to be
distributor installs one or more devices taken into account such as dynamic stresses and arcing
providing protection against short-circuit energyfor the device on the load side. Details of the
characteristics needing coordination should be obtained from
and agrees that such a device affords
the manufacturers of the devices concerned.
protection to the part of the installation
between the origin and the main 4.4.5.5.2 For cables and insulated conductors, all
distribution point of the installation current caused by a short-circuit occurring at any point
where further short-circuit protection is of the circuit shall be interrupted in a time not exceeding
provided. that which brings the insulation of the conductors to
the permitted limit temperature.
4.4.5.4 Short-circuit protection of conductors in parallel
For operating times of protective devices <0.1 s where
A single protective device may protect conductors in
asymmetry of the current is of importance and for
parallel against the effects of short-circuit provided that
current-limiting devices k2S2 shall be greater than the
the operating characteristics of that device ensures its
value of the let-through energy (I2t) quoted by the
effective operation should a fault occur at the most
manufacturer of the protective device.
onerous position in one of the parallel conductors.
Account shall be taken of the sharing of the short-circuit For short-circuits of duration up to 5 s, the time t, in
currents between the parallel conductors. A fault can which a given short-circuit current will raise the
be fed from both ends of a parallel conductor. insulation of the conductors from the highest
If operation of a single protective device is not effective, permissible temperature in normal duty to the limit
then one or more of the following measures shall be temperature can, as an approximation, be calculated
taken: from the formula:

a) The wiring shall be carried out in such a way t = (k × S/I)2 ... (3)
where
as to reduce to a minimum the risk of a short-
circuit in any parallel conductor, for example, t = the duration, in s;
by protection against mechanical damage, and S = the cross-sectional area, in mm2;
conductors shall be installed in such a manner I = the effective short-circuit current, in A,
as to reduce to a minimum the risk of fire or expressed as an r.m.s. value; and
danger to persons.
k = a factor taking account of the resistivity,
b) For two conductors in parallel, a short-circuit temperature coefficient and heat capacity of
protective device shall be provided at the the conductor material, and the appropriate
supply end of each parallel conductor. initial and final temperatures. For common
c) For more than two conductors in parallel, conductor insulation, the values of k for line
short-circuit protective devices shall be conductors are shown in Table 3.
provided at the supply and load ends of each
parallel conductor.

54
 IS 732 : 2019

Table 3 Values of k for Conductors

(Clause 4.4.5.5.2)

Property/Condition Type of Conductor Insulation

PVC PVC EPR Rubber Mineral
Thermoplastic Thermoplastic XLPE 60 °C
90°C Thermosetting Thermosetting PVC Bare
sheathed unsheathed
Conductor cross-sectional < 300 > 300 < 300 > 300
area mm²
Initial temperature °C 70 90 90 60 70 105
Final temperature °C 160 140 160 140 250 200 160 250

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Conductor material:
Copper 115 103 100 86 143 141 115 135-1151)
Aluminium 76 68 66 57 94 93 – –
Tin-soldered joints in copper 115 – – – – – – –
conductors

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1)
This value shall be used for bare cables exposed to touch.
NOTES
1 Other values of k are under consideration for:
– small conductors (particularly for cross-sectional areas less than 10 mm²);
– other types of joints in conductors;
– bare conductors.
2 The nominal current of the short-circuit protective device may be greater than the current-carrying capacity of the cable.
3 The above factors are based on IEC 60724.
4 See Annex EE (5.4) for the calculation-method of factor k.

4.4.5.5.3 For busbar trunking systems complying with 4.4.6.2 Protection Afforded by Separate Devices
IEC 61439-2 and powertrack complying with the
The requirements of 4.4.4 and 4.4.5 apply, respectively,
IEC 61534 series, one of the following requirements
to the overload protective device and the short-circuit
shall apply:
protective device.
a) The rated short-time withstand current (ICW)
The characteristics of the devices shall be coordinated so
and the rated peak withstand current of a
that the energy let through by the short-circuit protective
busbar trunking or powertrack system shall not
device does not exceed that which can be withstood
be lower than the prospective short-circuit
without damage by the overload protective device.
current r.m.s. value and the prospective short-
circuit peak current value, respectively. The NOTE — This requirement does not exclude the type of
coordination specified in IS/ IEC 60947-4-1.
maximum time for which the ICW is defined
for the busbar trunking or powertrack system 4.4.7 Limitation of overcurrent by characteristics of
shall not be less than the maximum operating supply
time of the protective device.
Conductors are considered to be protected against
b) The rated conditional short-circuit current of
overload and short-circuit currents where they are
the busbar trunking or powertrack system
supplied from a source incapable of supplying a current
associated with a specific protective device,
exceeding the current-carrying capacity of the
shall not be lower than the prospective short-
conductors (for example, certain bell transformers,
circuit current.
certain welding transformers and certain types of
4.4.6 Coordination of Overload and Short-Circuit thermoelectric generating sets).
Protection
4.5 Protection for Safety — Protection Against Voltage
4.4.6.1 Protection afforded by one device Disturbance and Electromagnetic Disturbance
A protective device providing protection against 4.5.1 Void
overload and short-circuit currents shall fulfil the
applicable requirements of 4.4.4 and 4.4.5. 4.5.2 Protection of Low-voltage Installations against
Temporary Overvoltages Due to Earth Faults in the

55
IS 732 : 2019

High-voltage System and Due to Faults in the Low- low-voltage system neutral, for low-voltage
voltage System systems in which the earthing arrangements
of the transformer substation and of the low-
4.5.2.1 Field of application
voltage system neutral are electrically
The rules of this clause provide requirements for the independent.
safety of low-voltage installation in the event of: Uo in TN- and TT-systems: nominal a.c. r.m.s. line
a) a fault between the high-voltage system and voltage to earth
earth in the transformer substation that in IT-systems: nominal a.c. voltage between
supplies the low-voltage installation, line conductor and neutral conductor or
b) a loss of the supply neutral in the low-voltage midpoint conductor, as appropriate.
system, Uf power-frequency fault voltage that appears in

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
c) a short-circuit between a line conductor and the low-voltage system between exposed-
neutral, and conductive-parts and earth for the duration of
the fault.
d) an accidental earthing of a line conductor of a
low-voltage IT-system. U1 power-frequency stress voltage between the
line conductor and the exposed-conductive-

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

The requirements for the earthing arrangement at the parts of the low-voltage equipment of the
transformer substation are given in IEC 61936-1. transformer substation during the fault.
4.5.2.1.1General requirements U2 power-frequency stress voltage between the
line conductor and the exposed-conductive-
As 4.5.2 covers faults between a high-voltage line and parts of the low-voltage equipment of the low-
the earth in the HV/LV substation, it gives rules for the voltage installation during the fault.
designer and installer of the substation. It is necessary NOTE — The power-frequency stress voltage (U1 and
to have the following information concerning the high- U2) is the voltage that appears across the insulation of
voltage system: low-voltage equipment and across surge protective
devices connected to the low-voltage system.
a) quality of the system earthing; The following additional symbols are used in respect
b) maximum level of earth fault current; and of IT-systems in which the exposed conductive parts
c) resistance of the earthing arrangement. of the equipment of the low-voltage installation are
connected to an earthing arrangement that is electrically
The following subclauses consider four situations as
independent of the earthing arrangement of the
proposed in 4.5.2.1, which generally cause the most
transformer substation.
severe temporary overvoltages such as defined in
IS 1885 (Part 70): Ih fault current that flows through the earthing
arrangement of the exposed-conductive-parts
a) fault between the high-voltage system(s) and
of the equipment of the low-voltage
earth (see 4.5.2.2);
installation during a period when there is a
b) loss of the neutral in a low-voltage system high-voltage fault and a first fault in the low-
(see 4.5.2.3); voltage installation (see Table 4).
c) accidental earthing of a low-voltage IT system Id fault current, in accordance with 4.2.11.6.2,
(see 4.5.2.4); and that flows through the earthing arrangement
d) short-circuit in the low-voltage installation of the exposed-conductive-parts of the low-
(see 4.5.2.5). voltage installation during the first fault in a
4.5.2.1.2 Symbols low-voltage system (see Table 4).
Z impedance (for example IMD internal
In 4.5.2 the following symbols are used (see Fig. 27): impedance, artificial neutral impedance)
IE part of the earth fault current in the high- between the low-voltage system and an
voltage system that flows through the earthing earthing arrangement.
arrangement of the transformer substation. NOTE — An earthing arrangement may be considered
electrically independent of another earthing arrangement
RE resistance of the earthing arrangement of the if a rise of potential with respect to earth in one earthing
transformer substation. arrangement does not cause an unacceptable rise of
RA resistance of the earthing arrangement of the potential with respect to earth in the other earthing
arrangement (see IEC 61936-1).
exposed-conductive-parts of the equipment of
the low-voltage installation. 4.5.2.2 Overvoltages in LV-systems during a high-
RB resistance of the earthing arrangement of the voltage earth fault

56
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 27 REPRESENTATIVE SCHEMATIC SKETCH FOR POSSIBLE CONNECTIONS TO EARTHING SUBSTATION AND
LV-INSTALLATION AND OCCURRING OVERVOLTAGES IN CASE OF FAULTS

In case of a fault to earth on the HV-side of the installation between exposed conductive parts and
substation, the following types of overvoltage may earth, shall not exceed the values given for Uf by the
affect the LV-installation: curve of Fig. 28 for the duration of the fault.
a) power frequency fault-voltage (Uf); Normally, the PEN conductor of the low-voltage system
b) power frequency stress-voltages (U1 and U2). is connected to earth at more than one point. In this
case, the total resistance is reduced. For these multiple
Table 4 provides the relevant methods of calculation grounded PEN conductors, Uf can be calculated as:
for the different types of overvoltages.
Uf = 0.5 RE×IE
NOTE — Table 4 deals with IT systems with a neutral point
only. For IT systems with no neutral point, the formulae should NOTE — The curve shown in Fig. 28 is taken from IEC 61936-
be adjusted accordingly. 1. On the basis of probabilistic and statistical evidence this
curve represents a low level of risk for the simple worst case
Where high- and low-voltage earthing systems exist in where the low voltage system neutral conductor is earthed only
proximity to each other, two practices are presently at the transformer substation earthing arrangements.
used:
4.5.2.2.2 Magnitude and duration of power-frequency
— interconnection of all high-voltage (RE) and stress voltages
low-voltage (RB) earthing systems; and
The magnitude and the duration of the power-frequency
— separation of high-voltage (RE) from low- stress voltage (U1 and U2) as calculated in Table 4 of
voltage (RB) earthing systems. the low-voltage equipment in the low-voltage
The general method used is interconnection. The high- installation due to an earth fault in the high-voltage
and low-voltage earthing systems shall be system shall not exceed the requirements given in
interconnected if the low-voltage system is totally Table 5.
confined within the area covered by the high-voltage
earthing system (see IEC 61936-1). 4.5.2.2.3 Requirements for calculation of limits

NOTE — Details of the different types of system earthing (TN, Where required by Table 4, the permissible power-
TT, IT) are shown in National Electrical Code 2011 and IS 3043. frequency stress voltage shall not exceed the value given
in Table 5.
4.5.2.2.1 Magnitude and duration of power-frequency
fault voltage Where required by Table 4, the permissible power-
frequency fault voltage shall not exceed the value given
The magnitude and the duration of the fault voltage Uf
in Table 5.
(as calculated in Table 4) which appears in the LV
57
IS 732 : 2019

Table 4 Power-Frequency Stress Voltages and Power-Frequency Fault Voltage in Low-Voltage System
(Clauses 4.5.2.2 and 4.5.2.2.2).
Types of System Earthing Types of Earth Connections U1 U2 Uf

(1) (2) (3) (4) (5)

RE and RB connected Uo RE× IE+ Uo 0 1)

TT
RE and RB separated RE× IE + Uo Uo1) 0 1)
RE and RB connected Uo1) Uo1) RE× IE2)
TN
RE and RB separated RE× IE + Uo Uo1) 0 1)
RE and Z connected
Uo1) RE × IE + Uo 0 1)
RE and RA separated

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Uo×√3 RE× IE + Uo×√3 RA× Ih

RE and Z connected
Uo1) Uo1) RE×IE
RE and RA interconnected
IT
Uo ×√3 Uo×√3 RE×IE

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

RE and Z separated
RE× IE + Uo Uo1) 01)
RE and RA separated

RE× IE+ Uo×√3 Uo×√3 RA× Id

1)
No consideration needs to be given.
2)
See 4.3.2.2.1 second paragraph.
With existing earth fault in the installation.

NOTES
1 The requirements for U1 and U2 are derived from design criteria for insulation of low-voltage equipment with regard to temporary
power-frequency overvoltage (see also Table 4).
2 In a system whose neutral is connected to the earthing arrangement of the transformer substation, such temporary power-frequency
overvoltage is also to be expected across insulation which is not in an earthed enclosure when the equipment is outside a building.
3 In TT- and TN-systems the statement “connected” and “separated” refers to the electrical connection between RE and RB. For IT-
systems it refers to the electrical connection between RE and Z and the connection between RE and RA.

Table 5 Permissible Power-Frequency Stress Voltage

(Clause 4.5.2.2.2)

Duration of the Earth Fault in the High- Permissible Power-Frequency Stress Voltage on Equipment in Low-Voltage
Voltage System Installations
t U
>5 s Uo + 250 V
5s Uo + 1 200 V
In systems without a neutral conductor, Uo shall be the line-to-line voltage.

NOTES
1 The first line of the table relates to high-voltage systems having long disconnection times, for example, isolated neutral and resonant
earthed high-voltage systems. The second line relates to high-voltage systems having short disconnection times, for example low-
impedance earthed high-voltage systems. Both lines together are relevant design criteria for insulation of low-voltage equipment with
regard to temporary power frequency overvoltage, IS 15382 (Part 1).
2 In a system whose neutral is connected to the earthing arrangement of the transformer substation, such temporary power-frequency
overvoltage is also to be expected across insulation which is not in an earthed enclosure when the equipment is outside a building.

The requirements of 4.3.2.2.2 and 4.3.2.2.3 are deemed necessary. Compliance with the above requirements
to be fulfilled for installations receiving a supply at low- mainly falls into the responsibility of the substation
voltage from a public electricity distribution system. installer/owner/operator who needs also to fulfil
requirements provided by IEC 61936-1. Therefore the
To fulfil the above requirements, coordination between
calculation for U1, U2 and Uf is normally not necessary
the HV-system operator and the LV-system installer is
for the LV system installer.
58
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 28 T OLERABLE FAULT VOLTAGE DUE TO AN EARTH-FAULT IN THE HV SYSTEM

Possible measures to fulfil the above requirements are, of a short-circuit between a line conductor and the
for example neutral conductor
a) separation of earthing arrangement between Consideration shall be given to the fact that if a short-
HV and LV; circuit occurs in the low-voltage installation between a
b) change of LV system earthing; and phase conductor and the neutral conductor, the voltage
between the other line conductors and the neutral
c) reduction of earth resistance RE.
conductor can reach the value of 1.45 ×Uo for a time
4.5.2.3 Power-frequency stress voltage in case of loss up to 5 s.
of the neutral conductor in a TN and TT system
4.5.3 Protection Against Overvoltages of
Consideration shall be given to the fact that, if the Atmospheric Origin or Due to Switching
neutral conductor in a multi-phase system is interrupted,
4.5.3.1 General
basic, double and reinforced insulation as well as
components rated for the voltage between line and This clause deals with protection of electrical
neutral conductors can be temporarily stressed with the installations against transient overvoltages of
line-to-line voltage. The stress voltage can reach up to atmospheric origin transmitted by the supply
U = √3 Uo. distribution system and against switching overvoltages.

4.5.2.4 Power-frequency stress voltage in the event In general, switching overvoltages are lower than
of an earth fault in an IT system with distributed overvoltages of atmospheric origin and, therefore, the
neutral requirements regarding protection against overvoltages
of atmospheric origin normally cover protection against
Consideration shall be given to the fact that, if a line switching overvoltages.
conductor of an IT system is earthed accidentally,
NOTE — Statistical evaluations of measurements have shown
insulation or components rated for the voltage between that there is a low risk of switching overvoltages higher than
line and neutral conductors can be temporarily stressed the level of overvoltage category II (see 4.5.3.2).
with the line-to-line voltage. The stress voltage can
Consideration shall be given to the overvoltages which
reach up to U = √3 Uo.
can appear at the origin of an installation, to the expected
4.5.2.5 Power-frequency stress voltage in the event keraunic level and to the location and characteristics of

59
IS 732 : 2019

surge protective devices, so that the probability of 4.5.3.2.2 Relationship between impulse withstand
incidents due to overvoltage stresses is reduced to an voltages of equipment and overvoltage categories
acceptable level for the safety of persons and property,
Equipment with an impulse withstand voltage
as well as for the continuity of service desired.
corresponding to overvoltage category IV is suitable
The values of transient overvoltages depend on the for use at, or in the proximity of, the origin of the
nature of the supply distribution system (underground installation, for example, upstream of the main
or overhead) and the possible existence of a surge distribution board. Equipment of category IV has a very
protective device upstream of the origin of the high impulse withstand capability providing the
installation and the voltage level of the supply system. required high degree of reliability.
This clause provides guidance where protection against NOTE — Examples of such equipment are electricity meters,
primary overcurrent protection devices and ripple control units.
overvoltages is covered by inherent control or assured

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
by protective control. If the protection according to this Equipment with an impulse withstand voltage
clause is not provided, insulation co-ordination is not corresponding to overvoltage category III is for use in
assured and the risk due to overvoltages shall be the fixed installation downstream of, and including the
evaluated. main distribution board, providing a high degree of
availability.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

This clause does not apply in case of overvoltages due
to direct or nearby lightning. For protection against NOTE — Examples of such equipment are distribution boards,
transient overvoltages due to direct lightning, IS/IEC circuit-breakers, wiring systems (see IEC 60050-826, definition
826-15-01), including cables, bus-bars, junction boxes, switches,
62305-1, IS/IEC 62305-3, IS/IEC 62305-4 and the IS/ socket-outlets) in the fixed installation, and equipment for
IEC 61643 series are applicable. This clause does not industrial use and some other equipment, for example stationary
cover overvoltage through data-transmission systems. motors with permanent connection to the fixed installation.

NOTES Equipment with an impulse withstand voltage

1 As regards transient atmospheric overvoltages, no distinction corresponding to overvoltage category II is suitable for
is made between earthed and unearthed systems. connection to the fixed electrical installation, providing
2 Switching overvoltages generated outside the installation and a normal degree of availability normally required for
transmitted by the supply network are under consideration.
current-using equipment.
4.5.3.2 Classification of impulse withstand voltages
NOTE — Examples of such equipment are household
(overvoltage categories) appliances and similar loads.
4.5.3.2.1Purpose of classification of impulse withstand Equipment with an impulse withstand voltage
voltages (overvoltage categories) corresponding to overvoltage category I is only suitable
NOTES for use in the fixed installation of buildings where
1 Overvoltage categories are defined within electrical protective means are applied outside the equipment –
installations for the purpose of insulation co-ordination and a to limit transient overvoltages to the specified level.
related classification of equipment with impulse withstand
voltages is provided (see Table 6). NOTE — Examples of such equipment are those containing
electronic circuits like computers, appliances with electronic
2 The rated impulse withstand voltage is an impulse withstand
programmes, etc.
voltage assigned by the manufacturer to the equipment or to a
part of it, characterizing the specified withstand capability of Equipment with an impulse withstand voltage
its insulation against overvoltages [in accordance with IS 15382
(Part 1)]. corresponding to overvoltage category I shall not have
direct connection to a public supply system.
The impulse withstand voltage (overvoltage category)
is used to classify equipment energized directly from 4.5.3.3 Arrangements for overvoltage control
the mains. Overvoltage control is arranged in accordance with the
Impulse withstand voltages for equipment selected following requirements.
according to the nominal voltage are provided to 4.5.3.3.1 Inherent overvoltage control
distinguish different levels of availability of equipment
with regard to continuity of service and an acceptable This sub-clause does not apply when a risk assessment
risk of failure. By selection of equipment with a according to 4.5.3.3.2.2 is used.
classified impulse withstand voltage, insulation co- Where an installation is supplied by a completely buried
ordination can be achieved in the whole installation, low-voltage system and does not include overhead lines,
reducing the risk of failure to an acceptable level. the impulse withstand voltage of equipment in
NOTE — Transient overvoltages transmitted by the supply accordance with Table 6 is sufficient and no specific
distribution system are not significantly attenuated down stream protection against overvoltages of atmospheric origin
in most installations. is necessary.
60
 IS 732 : 2019

NOTE — A suspended cable having insulated conductors with example, loss of public services, IT centres,
earthed metallic screen is considered as equivalent to an
museums;
underground cable.
c) consequences to commercial or industrial
Where an installation is supplied by or includes a low- activity, for example, hotels, banks, industries,
voltage overhead line and the keraunic level is lower commercial markets, farms;
than or equal to 25 days per year (AQ 1), no specific
d) consequences to groups of individuals, for
protection against overvoltages of atmospheric origin
example, large residential buildings, churches,
is required.
offices, schools; and
NOTE — Irrespective of the AQ value, protection against e) consequences to individuals, for example,
overvoltages may be necessary in applications where a higher
reliability or higher risks (for example, fire) are expected.
residential buildings, small offices.

In both cases, consideration regarding protection For levels of consequences (a) to (c), protection against

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
against transient overvoltages shall be given to overvoltage shall be provided.
equipment with an impulse withstand voltage according NOTE — There is no need to perform a risk assessment
to overvoltage category I (see 4.5.3.2.2). calculation according to Annex K for levels of consequences
(a) to (c) because this calculation always leads to the result that
4.5.3.3.2 Protective overvoltage control the protection is required.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

In all cases, consideration regarding protection against For levels of consequences (d) and (e), requirement
transient over voltages shall be given to equipment with for protection depends on the result of a calculation.
an impulse withstand voltage according to overvoltage The calculation shall be carried out using the formula
category I (see 4.5.3.2.2). in Annex K for the determination of the length d, which
is based on a convention and called conventional length.
4.5.3.3.2.1 Protective overvoltage control based on
conditions of external influences Protection is required if:
Where an installation is supplied by, or includes, an d > dc
overhead line, and the keraunic level of the location is where
greater than 25 days per year (AQ 2), protection against
overvoltages of atmospheric origin is required. The d = the conventional length in km of the supply
protection level of the protective device shall not be line of the considered structure with a
higher than the level of overvoltage category II, given maximum value of 1 km;
in Table 6. dc = the critical length;
NOTES 1
1 The overvoltage level may be controlled by surge protective dc in km = equal to N for level of consequences (d)
g
devices applied close to the origin of the installation, either in
the overhead lines (see Annex B) or in the building installation. 2
2 According to A.1 of IS/ IEC 62305-3, 25 thunderstorm days and equal to N for level of consequences (e) where
g
per year are equivalent to a value of 2.5 flashes per km2 per
year. This is derived from the formula Ng is the frequency of flashes per km2 per year.
Ng = 0.1 Td If this calculation indicates that an SPD is required,
where the protection level of these protective devices shall
Ng = the frequency of flashes per km2 per year; and not be higher than the level of overvoltage category II,
Td = the number of thunderstorm days per year (keraunic level). given in Table 6.
4.5.3.3.2.2 Protective overvoltage control based on risk 4.5.3.4 Required impulse withstand voltage of
assessment equipment
NOTE — A method of general risk assessment is described in Equipment shall be selected so that its rated impulse
IEC 61662. As far as 4.5.3 is concerned, an essential
simplification of this method has been accepted. It is based on withstand voltage is not less than the required impulse
the critical length dC of the incoming lines and the level of withstand voltage as specified in Table 6. It is the
consequences as described below. responsibility of each product committee to require the
The following are different consequential levels of rated impulse withstand voltage in their relevant
protection: standards according to IEC 60664-1.

a) consequences related to human life, for 4.5.4 Measures Against Electromagnetic Influences
example, safety services, medical equipment 4.5.4.1 General
in hospitals;
The 4.5.4 provides basic recommendations for the
b) consequences related to public services, for
mitigation of electromagnetic disturbances.
61
IS 732 : 2019

Table 6 Required Rated Impulse Withstand Voltage of Equipment

(Clauses 4.5.3.2.1, 4.5.3.3.1, 4.5.3.3.2.1 and 4.5.3.4)

Nominal voltage of the installation1) Required Impulse Withstand Voltage For

V kV3)
Three-phase Single-phase Equipment at the Equipment of Appliances and Specially Protected
Systems2) Systems with Origin of the Distribution and Final Current-using Equipment
Middle Point Installation Circuits (Overvoltage Equipment (Overvoltage
(Overvoltage Category III) (Overvoltage Category I)
Category IV) Category II)
– 120-240 4 2.5 1.5 0.8
230/4002) – 6 4 2.5 1.5
277/4802)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
400/690 – 8 6 4 2.5
1 000 – 12 8 6 4
1)
According to IEC 60038.
2), 3)
This impulse withstand voltage is applied between live conductors and PE.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Electromagnetic Interference (EMI) may disturb or Consideration shall be given by the designer and
damage information technology systems or information installer of the electrical installation to the measures
technology equipment as well as equipment with described below for reducing the electric and magnetic
electronic components or circuits. Currents due to influences on electrical equipment.
lightning, switching operations, short-circuits and other
Only electrical equipment, which meets the
electromagnetic phenomena may cause overvoltages
requirements in the appropriate EMC standards or the
and electromagnetic interference.
EMC requirements of the relevant product standard
These effects are most severe shall be used.
a) where large metal loops exist; and 4.5.4.4.1 Sources of EMI
b) where different electrical wiring systems are Electrical equipment sensitive to electromagnetic
installed in common routes, for example, for influences should not be located close to potential
power supply and for signalling information sources of electromagnetic emission such as:
technology equipment within a building.
a) switching devices for inductive loads,
The value of the induced voltage depends on the rate b) electric motors,
of rise (di/dt) of the interference current, and on the
c) fluorescent lighting,
size of the loop.
d) welding machines,
Power cables carrying large currents with a high rate of e) computers,
rise of current (di/dt) (for example, the starting current f) rectifiers,
of lifts or currents controlled by rectifiers) can induce g) choppers,
overvoltages in cables of information technology h) frequency converters/regulators,
systems, which can influence or damage information
j) lifts,
technology equipment or similar electrical equipment.
k) transformers,
In or near rooms for medical use, electric or magnetic m) switchgear, and
fields associated with electrical installations can n) power distribution busbars.
interfere with medical electrical equipment.
4.5.4.4.2 Measures to reduce EMI
This clause provides information for architects of
buildings and for designers and installers of electrical The following measures reduce electromagnetic
installations of buildings on some installation concepts interference:
that limit electromagnetic influences. Basic a) For electrical equipment sensitive to
considerations are given here to mitigate such electromagnetic influences, surge protection
influences that may result in disturbance. devices and/or filters are recommended to
4.5.4.2 Void improve electromagnetic compatibility with
regard to conducted electromagnetic
4.5.4.3 Definitions (see 3). phenomena.
4.5.4.4 Mitigation of electromagnetic interference b) Metal sheaths of cables should be bonded to
(EMI) the CBN.

62
 IS 732 : 2019

c) Inductive loops should be avoided by selection NOTE — The provision of a by-pass conductor in
proximity to a signal, or data, cable sheath also reduces
of a common route for power, signal and data
the area of the loop associated with equipment, which
circuits wiring. is only connected by a protective conductor to earth.
d) Power and signal cables should be kept This practice considerably reduces the EMC effects of
separate and should, wherever practical, cross lightning electromagnetic pulse (LEMP).
each other at right-angles (see 4.5.4.6.3). k) Where screened signal cables or data cables
e) Use of cables with concentric conductors to are common to several buildings supplied
reduce currents induced into the protective from a TT-system, a by-pass equipotential
conductor. bonding conductor should be used (see
f) Use of symmetrical multicore cables (for Fig. 30), The by-pass conductor shall have a
example, screened cables containing separate minimum cross-sectional area of 16 mm2 Cu
or equivalent. The equivalent cross-sectional

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
protective conductors) for the electrical
connections between convertors and motors, area shall be dimensioned in accordance
which have frequency controlled motor- with 5.4.4.1.
drives. NOTES
1 Where the earthed shield is used as a signal return
g) Use of signal and data cables according to the
path, a double-coaxial cable may be used.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

EMC requirements of the manufacturer’s 2 It is recalled that if the consent according to 4.2.13.1.2
instructions. cannot be obtained, it is the responsibility of the owners
h) Where a lightning protection system is or operators to avoid any danger due to the exclusion of
those cables from the connection to the main
installed,
equipotential bonding.
1) power and signal cables shall be separated 3 The problems of earth differential voltages on large
from the down conductors of lightning public telecommunication networks are the
protection systems (LPS) by either a responsibility of the network operator, who may employ
other methods.
minimum distance or by use of screening.
The minimum distance shall be m) Equipotential bonding connections should
determined by the designer of the LPS in have an impedance as low as possible
accordance with IS/IEC 62305-3; and – by being as short as possible,
2) metallic sheaths or shields of power and – by having a cross-section shape that
signal cables should be bonded in results in low inductive reactance and
accordance with the requirements for impedance per metre of route, for
lightning protection given in IS/ example, a bonding braid with a width to
IEC 62305-3 and IS/IEC 62305-4. thickness ratio of five to one.
j) Where screened signal or data cables are used, n) Where an earthing busbar is intended
care should be taken to limit the fault current (according to 4.5.4.5.7) to support the
from power systems flowing through the equipotential bonding system of a significant
screens and cores of signal cables, or data information technology installation in a
cables, which are earthed. Additional building, it may be installed as a closed ring.
conductors may be necessary, for example, a NOTE — This measure is preferably applied in
by-pass equipotential bonding conductor for buildings of the telecommunications industry.
screen reinforcement (see Fig. 29).

FIG. 29 BY-PASS CONDUCTOR FOR SCREEN REINFORCEMENT TO P ROVIDE A COMMON

EQUIPOTENTIAL BONDING SYSTEM

63
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
FIG. 30 EXAMPLE OF A SUBSTITUTE OR B Y-PASS E QUIPOTENTIAL BONDING CONDUCTOR IN A TT-SYSTEM

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4.5.4.4.3 TN-system be avoided by
To minimize electromagnetic influences, the following a) changing all TN-C parts of the installation
sub-clauses apply. shown in Fig. 33 into TN-S, as shown in
Fig. 31, or
4.5.4.4.3.1 It is recommended that TN-C systems
should not be maintained in existing buildings b) where this change is not possible, by avoiding
containing, or likely to contain, significant amounts of signal and data cable interconnections
information technology equipment. between different parts of the TN-S
installation.
TN-C-systems shall not be used in newly constructed
buildings containing, or likely to contain, significant 4.5.4.4.4 TT system
amounts of information technology equipment. In a TT system, such as that shown in Fig. 34,
NOTE — Any TN-C installation is likely to have load or fault consideration should be given to overvoltages which
current diverted via equipotential bonding into metallic services may exist between live parts and exposed-conductive-
and structures within a building. parts when the exposed-conductive-parts of different
4.5.4.4.3.2 In existing buildings supplied from public buildings are connected to different earth electrodes.
low-voltage networks and which contain, or are likely 4.5.4.4.5 IT system
to contain, significant amounts of information
technology equipment, a TN-S system should be In a three-phase IT system (see Fig. 35), the voltage
installed downstream of the origin of the installation between a healthy line-conductor and an exposed-
(see Fig. 31). conductive-part can rise to the level of the line-to-line
voltage when there is a single insulation fault between
In newly constructed buildings, TN-S systems shall be a line conductor and an exposed-conductive-part; this
installed downstream of the origin of the installation condition should be considered.
(see Fig. 31).
NOTE — Electronic equipment directly supplied between line
NOTE — The effectiveness of a TN-S-system may be enhanced conductor and neutral should be designed to withstand such a
by use of a residual current monitoring device, RCM. voltage between line conductor and exposed-conductive-parts;
see corresponding requirement from IS 13252 (Part 1) for
4.5.4.4.3.3 In existing buildings where the complete information technology equipment.
low-voltage installation including the transformer is
operated only by the user and which contain, or are 4.5.4.4.6 Multiple-source supply
likely to contain, significant amounts of information For multiple-source power supplies, the provisions
technology equipment, TN-S systems should be given in 4.5.4.4.6.1 and 4.5.4.4.6.2 shall be applied.
installed (see Fig. 32).
In the case of single conductor cables, which carry a.c.
4.5.4.4.3.4 Where an existing installation is a TN-C-S current, a circular electromagnetic field is generated
system (see Fig. 33), signal and data cable loops should

64
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) — No voltage drop ∆U along the PE conductor under normal operation conditions.

2) — Loops of limited area formed by signal or data cables.

FIG. 31 AVOIDANCE OF NEUTRAL CONDUCTOR CURRENTS IN A BONDED STRUCTURE BY U SING THE TN-S SYSTEM
FROM THE O RIGIN OF THE P UBLIC S UPPLY UP TO AND I NCLUDING THE FINAL CIRCUIT WITHIN A B UILDING

65
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) — No voltage drop ∆U along the PE conductor under normal operation conditions.

2) — Loops of limited area formed by signal or data cables.

FIG. 32 AVOIDANCE OF NEUTRAL CONDUCTOR CURRENTS IN A B ONDED STRUCTURE BY USING A TN-S SYSTEM
DOWNSTREAM OF A CONSUMER’S PRIVATE SUPPLY T RANSFORMER

66
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) — Voltage drop ∆U along PEN in normal operation.

2) — Loop of limited area formed from signal or data cables.
3) — Extraneous-conductive-part.
NOTE — In a TN-C-S system, the current, which in a TN-S system would flow only through the neutral conductor, flows also through
the screens or reference conductors of signal cables, exposed-conductive-parts, and extraneous- conductive-parts such as structural
metalwork.

FIG. 33 TN-C-S SYSTEM WITHIN AN EXISTING B UILDING INSTALLATION

67
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) — Voltage drop ∆U along PEN in normal operation.

2) — Loop of limited area formed from signal or data cables.

FIG. 34 TT SYSTEM WITHIN A B UILDING I NSTALLATION

68
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) — Voltage drop ∆U along PEN in normal operation.

2) — Loop of limited area formed from signal or data cables.

FIG. 35 IT SYSTEM WITHIN A B UILDING I NSTALLATION

69
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 36 TN MULTIPLE-S OURCE P OWER S UPPLY WITH A NON-SUITABLE M ULTIPLE
CONNECTION BETWEEN PEN AND EARTH

around the core conductor that may interfere with NOTE — Interconnection is only permitted with the consent
of the operator of the external service.
electronic equipment. Harmonic currents produce
similar electromagnetic fields but they attenuate more For EMC reasons, closed building voids housing parts
rapidly than those produced by fundamental currents. of the electrical installation should be exclusively
4.5.4.4.6.1 TN multiple source power supplies reserved for electrical and electronic equipment (such
as monitoring, control or protection devices, connecting
In the case of TN multiple-source power supplies to an devices, etc) and access shall be providedfor their
installation, the star points of the different sources shall, maintenance.
for EMC reasons, be interconnected by an insulated
conductor that is connected to earth centrally at one 4.5.4.4.9 Separate buildings
and the same point (see Fig. 37). Where different buildings have separate equipotential
4.5.4.4.6.2 TT multiple-source power supplies bonding systems, metal-free fibre optic cables or other
non-conducting systems may be used for signal and
In the case of TT multiple-source power supplies to an data transmission, for example, microwave signal
installation, it is recommended that the star points of transformer for isolation in accordance with
the different sources are, for EMC reasons, IEC 61558-2-1, IEC 61558-2-4, IEC 61588-2-6,
interconnected and connected to earth centrally at only IEC 61888-2-15 and IS 13252 (Part 1).
one point (see Fig. 38).
NOTES
4.5.4.4.7 Transfer of supply 1 The problem of earth differential voltages on large public
telecommunication networks is the responsibility of the
In TN systems the transfer from one supply to an network operator, who may employ other methods.
alternative supply shall be by means of a switching 2 In case of non-conducting data-transmission systems, the use
device, which switches the line conductors and the of a by-pass conductor is not necessary.
neutral, if any (see Fig. 39, Fig. 40 and Fig. 41). 4.5.4.4.10 Inside buildings
4.5.4.4.8 Services entering a building Where there are problems in existing building
installations due to electromagnetic influences, the
Metal pipes (for example, for water, gas or district following measures may improve the situation (see
heating) and incoming power and signal cables should Fig. 43):
preferably enter the building at the same place. Metal
pipes and the metal armouring of cables shall be bonded 1) use of metal free fibre optic links for signal
to the main earthing terminal by means of conductors and data circuits (see 4.5.4.4.9);
having low impedance (see Fig. 42). 2) use of Class II equipment; and

70
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
a) — No direct connection from either transformer neutral points or generator star points to earth is permitted.
b) — The conductor interconnecting either the neutral points of transformers, or the star-points of generators, shall be insulated. This
conductor functions as a PEN conductor and it may be marked as such; however, it shall not be connected to current-using-
equipment and a warning notice to that effect shall be attached to it, or placed adjacent to it.
c) — Only one connection between the interconnected neutral points of the sources and the PE shall be provided. This connection
shall be located inside the main switchgear assembly.
d) — Additional earthing of the PE in the installation must be provided.

FIG. 37 TN MULTIPLE SOURCE POWER SUPPLIES TO AN I NSTALLATION WITH CONNECTION TO EARTH OF THE STAR
P OINTS AT ONE AND THE SAME P OINTS

3) use of double winding transformers in 4.5.4.5 Earthing and equipotential bonding

compliance with IEC 61558-2-1 or
4.5.4.5.1 Interconnection of earth electrodes
IEC 61558-2-4 or IS/IEC 61558-2-6 or
IEC 61558-2-15. The secondary circuit should For several buildings, the concept of dedicated and
preferably be connected as a TN-S system but independent earth electrodes connected to an
an IT-system may be used where required for equipotential conductor network may not be adequate
specific applications. where electronic equipment is used for communication
and data exchange between the different buildings for
4.5.4.4.11 Protective devices
the following reasons:
Protective devices with appropriate functionality for
a) a coupling exists between these different earth
avoiding unwanted tripping due to high levels of
electrodes and leads to an uncontrolled
transient currents should be selected, for example, time
increase of voltage to equipment;
delays and filters.
b) interconnected equipment may have different
4.5.4.4.12 Signal cables earth references; and
Shielded cables and/or twisted pair cables should be c) a risk of electric shock exists, specifically in
used for signal cables. case of overvoltages of atmospheric origin.

71
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
a) — No direct connection from either the transformer star points or the generator star points to earth is permitted.
b) — The conductor interconnecting either the star points of transformers, or generator star points, shall be insulated. However, it
shall not be connected to current-using-equipment and a warning notice to that effect shall be attached to it, or placed
adjacent to it.
c) — Only one connection between the interconnected star points of the sources and the PE shall be provided. This connection shall
be located inside the main switchgear assembly.

FIG. 38 TT MULTIPLE-SOURCE P OWER SUPPLIES TO AN INSTALLATION WITH CONNECTION TO E ARTH OF THE STAR
P OINTS AT ONE AND THE SAME P OINT

Therefore, all protective and functional earthing disconnected the connections of all the other conductors
conductors should be connected to one single main remain secured.
earthing terminal. 4.5.4.5.2 Interconnection of incoming networks and
Moreover, all earth electrodes associated with a earthing arrangements
building, for example, protective, functional and Exposed conductive parts of information technology
lightning protection, shall be interconnected (see and electronic equipment within a building are
Fig. 44). interconnected via protective conductors.
In the case of several buildings, where interconnection For dwellings where normally a limited amount of
of the earth electrodes is not possible or practical, it is electronic equipment is in use, a protective conductor
recommended that galvanic separation of network in the form of a star network may be acceptable
communication networks is applied, for instance by the (see Fig. 45).
use of fibre optic links (see also 4.5.4.4.10). For commercial and industrial buildings and similar
buildings containing multiple electronic applications,
Protective and functional bonding conductors shall be a common equipotential bonding system is useful in
connected individually to the main earthing terminal order to comply with the EMC requirements of different
in such a way that if one conductor becomes types of equipment (see Fig. 47).

72
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — This method prevents electromagnetic fields due to stray currents in the main supply system of an installation. The sum of
the currents within one cable must be zero. It ensures that the neutral current flows only in the neutral conductor of the circuit, which
is switched on. The 3rd harmonic (150 Hz) current of the line conductors will be added with the same phase angle to the neutral
conductor current.
FIG. 39 T HREE-P HASE ALTERNATIVE P OWER SUPPLY WITH A 4-P OLE SWITCH

NOTE — A three-phase alternative power supply with an unsuitable 3-pole switch will cause unwanted circulating currents, that will
generate electromagnetic fields.

FIG. 40 NEUTRAL CURRENT FLOW IN A T HREE-P HASE ALTERNATIVE P OWER SUPPLY

WITH AN U NSUITABLE 3-P OLE SWITCH

73
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
NOTE — The earth connection to the secondary circuit of a UPS is not mandatory. If the connection is omitted, the supply inthe UPS-
mode will be in the form of an IT system and, in by-pass mode, it will be the same as the low-voltage supply system.

FIG. 41 SINGLE-P HASE ALTERNATIVE P OWER SUPPLY WITH 2-P OLE SWITCH

MET — Main earthing terminal

I — Induction current
NOTE — A common entry point is preferred, UE” 0 V.

FIG. 42 ARMOURED CABLES AND METAL P IPES ENTERING THE BUILDINGS (E XAMPLES)

74
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
Reference Description of the Illustrated Measures Sub-Clause/
Standard
1) Cables and metal pipes enter the building at the same place 4.5.4.4.8
2) Common route with adequate separations and avoidance of loops 4.5.4.4.2
3) Bonding leads as short as possible, and use of earthed conductor parallel IEC 61000-2-5
to a cable 4.5.4.4.2
4) Signal cables screened and/or conductors twisted pairs 4.5.4.4.12
5) Avoidance of TN-C beyond the incoming supply point 4.5.4.4.3
6) Use of transformers with separate windings 4.5.4.4.10
7) Local horizontal bonding system 4.5.4.5.4
8) Use of class II equipment 4.5.4.4.10

FIG. 43 ILLUSTRATION OF MEASURES IN AN EXISTING BUILDING

75
IS 732 : 2019

FIG. 44 I NTERCONNECTED E ARTH ELECTRODES

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
4.5.4.5.3 Different structures for the network of etc, and from a general point of view to equipment,
equipotential conductors and earthing conductors that is not interconnected by signal cables (see Fig. 45).
The four basic structures described in the following 4.5.4.5.3.3 Multiple meshed bonding star network

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

sub-clauses may be used, depending on the importance
This type of network is applicable to small installations
and vulnerability of equipment.
with different small groups of interconnected
4.5.4.5.3.1 Protective conductors connected to a communicating equipment. It enables the local
bonding-ring conductor dispersion of currents caused by electromagnetic
interference (see Fig. 46).
An equipotential bonding network in the form of a
bonding ring conductor, BRC, is shown in Fig. 48 on 4.5.4.5.3.4 Common meshed bonding star network
the top-floor of the structure. The BRC should
This type of network is applicable to installations with
preferably be made of copper, bare or insulated, and
high density of communicating equipment
installed in such a manner that it remains accessible
corresponding to critical applications (see Fig. 47).
everywhere, for example, by using a cable-tray, metallic
conduit [see IS 14930 (Part 1 and Part 2)], surface A meshed equipotential bonding network is enhanced
mounted method of installation or cable trunking. All by the existing metallic structures of the building. It is
protective and functional earthing conductors may be supplemented by conductors forming the square mesh.
connected to the BRC.
The mesh-size depends on the selected level of
4.5.4.5.3.2 Protective conductors in a star network protection against lightning, on the immunity level of
equipment part of the installation and on frequencies
This type of network is applicable to small installations
used for data transmission.
associated with dwellings, small commercial buildings,

FIG. 45 EXAMPLES OF PROTECTIVE CONDUCTORS IN STAR NETWORK

76
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 46 EXAMPLE OF MULTIPLE MESHED BONDING STAR NETWORK

The area covered by a mesh shall have overall dimensions; the mesh-size refers to the dimensions of square spaces enclosed by the
conductors forming the mesh.

FIG. 47 EXAMPLE OF A COMMON MESHED BONDING STAR NETWORK

Mesh-size shall be adapted to the dimensions of the In some cases, parts of this network may be meshed
installation to be protected, but shall not exceed 2 m × more closely in order to meet specific requirements.
2 m in areas where equipment sensitive to
4.5.4.5.4 Equipotential bonding networks in buildings
electromagnetic interferences is installed.
with several floors
It is suitable for protection of private automatic branch
For buildings with several floors, it is recommended
exchange equipment (PABX) and centralized data
that, on each floor, an equipotential bonding system be
processing systems.
installed (see Fig. 48) for examples of bonding
networks in common use; each floor is a type of

77
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 48 EXAMPLE OF EQUIPOTENTIAL BONDING NETWORKS IN STRUCTURES
W ITHOUT LIGHTNING P ROTECTION S YSTEMS

network. The bonding systems of the different floors 4.5.4.5.6 Commercial or industrial buildings
should be interconnected, at least twice, by conductors. containing significant amounts of information
technology equipment
4.5.4.5.5 Functional earthing conductor
The following additional specifications are intended
Some electronic equipment requires a reference voltage
to reduce the influences of electromagnetic disturbances
at about earth potential in order to function correctly;
on the information technology equipment operation.
this reference voltage is provided by the functional
earthing conductor. In severe electromagnetic environments, it is
recommended that the common meshed bonding star
Conductors for functional earthing may be metallic
network described in 4.5.4.5.3.3 be adopted.
strips, flat braids and cables with circular cross-section.
4.5.4.5.6.1 Equipotential bonding designed as a
For equipment operating at high frequencies, metallic
bonding ring network shall have the following minimum
strips or flat braids are preferred and the connections
dimensions:
shall be kept as short as possible.
a) flat copper cross-section: 30 mm × 2 mm.
No colour is specified for functional earthing
conductors. However, the colours green-and-yellow b) round copper diameter: 8 mm.
specified for earthing conductors shall not be used. It c) as per IS 3043
is recommended that the same colour is used throughout Bare conductors shall be protected against corrosion
the whole installation to mark functional earthing at their supports and on their passage through walls.
conductors at each end.
4.5.4.5.6.2 Parts to be connected to the equipotential
For equipment operating at low frequencies, cross bonding network
sectional areas as indicated in 5.4.4.1 are considered
satisfactory, independent of the conductor shape The following parts shall also be connected to the
[see 4.5.4.4.2 (b) and (k)]. equipotential bonding network:

78
 IS 732 : 2019

a) conductive screens, conductive sheaths or (see 4.2.13 and/or 4.5.4.7.2). Electrical safety and
armouring of data transmission cables or of electromagnetic compatibility require different
information technology equipment; clearances in some cases. Electrical safety always has
b) earthing conductors of antenna systems; the higher priority.
c) earthing conductors of the earthed pole of d.c. Exposed conductive parts of wiring systems, for
supply for information technology equipment; example, sheaths, fittings and barriers, shall be
and protected by requirements for fault protection
d) functional earthing conductors. (see 4.2.13).
4.5.4.5.7 Earthing arrangements and equipotential 4.5.4.6.2 Design guidelines
bonding of information technology installations for
The minimum separation between power cables and
functional purposes

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
information technology cables to avoid disturbance is
4.5.4.5.7.1 Earthing busbar related to many factors such as:
Where an earthing busbar is required for functional a) the immunity level of equipment connected
purposes, the main earthing terminal (MET) of the to the information technology cabling system
building may be extended by using an earthing busbar. to different electromagnetic disturbances

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

This enables information technology installations to be (transients, lightning pulses, bursts, ring wave,
connected to the main earthing terminal by the shortest continuous waves, etc).
practical route from any point in the building. Where b) the connection of equipment to earthing
the earthing busbar is erected to support the systems.
equipotential bonding network of a significant amount c) the local electromagnetic environment
of information technology equipment in a building, it (simultaneous appearance of disturbances, for
may be installed as a bonding ring network; see Fig. 48. example harmonics plus bursts plus
NOTES continuous wave).
1 The earthing busbar may be bare or insulated. d) the electromagnetic frequency spectrum.
2 The earthing busbar should preferably be installed so that it e) the distances that cables are installed in
is accessible throughout its length, e.g. on the surface of parallel routes (coupling zone).
trunking. To prevent corrosion, it may be necessary to protect
bare conductors at supports and where they pass throughout f) the types of cables.
walls. g) the coupling attenuation of the cables.
4.5.4.5.7.2 Cross-sectional area of the earthing busbar h) the quality of the attachment between the
connectors and the cable.
The effectiveness of the earthing busbar depends on j) the type and construction of the cable
the routing and the impedance of the conductor management system.
employed. For installations connected to a supply
having a capacity of 200 A per phase or more, the cross- For the purpose of this standard, it is assumed that the
sectional area of the earthing busbar shall be not less electromagnetic environment has levels of disturbance
than 50 mm2 copper and shall be dimensioned in less than the test levels for conducted and radiated
accordance with 4.5.4.4.2 (k). disturbances contained in IS 14700(Part 4/Sec 1),
IEC 61000-6-2, IS 14700 (Part 4/Sec 3) and IS 14700
NOTE — This statement is valid for frequencies up to 10 MHz.
(Part 4/Sec 4).
Where the earthing busbar is used as part of a d.c. return
For parallel power and information technology cabling,
current path, its cross-sectional area shall be
the following applies (see Fig. 49 and Fig. 50).
dimensioned according to the expected d.c. return
currents. The maximum DC voltage drop along each If the parallel cabling length is equal to or less than
earthing busbar, dedicated as d.c. distribution return 35 m, no separation is required.
conductor, shall be designed to be less than 1 V.
If the parallel cabling length of unscreened cable is
4.5.4.6.1 General greater than 35 m, the separation distances apply to the
full length excluding the final 15 m attached to the
Information technology cables and power supply
outlet.
cables, which share the same cable management system
or the same route, shall be installed according to the NOTE — The separation may be achieved, for example, by a
separation distance in air of 30 mm or a metallic divider installed
requirements of the following sub-clauses. between the cables, see also Fig. 51.
Verification of electrical safety, in accordance with 6.2 If the parallel cabling length of screened cable is greater
and/or 5.1, and electrical separation are required than 35 m, no separation distances are applicable.

79
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
FIG. 49 SEPARATION BETWEEN P OWER AND INFORMATION T ECHNOLOGY
CABLES FOR CABLE ROUTE LENGTHS < 35 m

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Sepration (see Fig. 51)

FIG. 50 SEPARATION BETWEEN P OWER AND INFORMATION T ECHNOLOGY CABLES

FOR CABLE ROUTE LENGTHS > 35 m

4.5.4.6.3 Installation guidelines 4.5.4.7 Cable management systems

The minimum distance between information technology 4.5.4.7.1 General
cables and fluorescent, neon, and mercury vapour (or
Cable management systems are available in metallic
other high-intensity discharge) lamps shall be 130 mm.
and non-metallic forms. Metallic systems offer varying
Electrical wiring assemblies and data wiring assemblies
degrees of enhanced protection to EMI provided that
should preferably be in separate cabinets. Data wiring
they are installed in accordance with 4.5.4.7.3.
racks and electrical equipment should always be
separated. 4.5.4.7.2 Design guidelines
Cables should, wherever practical, cross at right angles. The choice of material and the shape of the cable
Cables for different purposes (for example, mains management system depend on the following
power and information technology cables) should not considerations:
be in the same bundle. Different bundles should be
a) the strength of the electromagnetic fields along
separated electromagnetically from each other
the pathway (proximity of electromagnetic
(see Fig. 51).
conducted and radiated disturbing sources);
80
 IS 732 : 2019

b) the authorised level of conducted and radiated agreed quantity of additional cables to be installed. The
emissions; cable-bundle height shall be lower than the side-walls
c) the type of cabling (screened, twisted, optical of the cable-tray, as shown in Fig. 52. The use of
fibre); overlapping lids improves the cable-tray’s
d) the immunity of the equipment connected to electromagnetic compatibility performance.
the information technology cabling system; For a U-shape cable-tray, the magnetic field decreases
e) the other environment constraints (chemical, near the two corners. For this reason, deep side-walls
mechanical, climatic, fire, etc); are preferred (see Fig. 52).
f) any future information technology cabling NOTE — The depth of the section should be at least twice the
system extension. diameter of the largest cable being considered.

Non-metallic wiring systems are suitable in the 4.5.4.7.3 Installation guidelines

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
following cases:
4.5.4.7.3.1 Metallic or composite cable management
– electromagnetic environment with systems specially designed for electromagnetic
permanently low levels of disturbance; compatibility purposes
– the cabling system has a low emission level; Metallic or composite cable management systems

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

– optical fibre cabling. specially designed for electromagnetic compatibility
For metallic components of cable support systems, the purposes shall always be connected to the local
shape (plane, U-shape, tube, etc), rather than the cross- equipotential bonding system at both ends. For long
section will determine the characteristic impedance of distances, that is, greater than 50 m, additional
the cable management system. Enclosed shapes are best connections to the equipotential bonding system are
as they reduce common mode coupling. recommended. All connections shall be as short as
possible. Where cable management systems are
Usable space within the cable-tray should allow for an constructed from several elements, care should be taken

FIG. 51 SEPARATION OF C ABLES IN W IRING SYSTEMS

FIG. 52 CABLE ARRANGEMENTS IN METAL CABLE-T RAYS

81
IS 732 : 2019

to ensure continuity by effective bonding between recommendations for example, not replacing a metallic
adjacent elements. Preferably, the elements should be conduit by a plastic one.
welded together over their full perimeter. Riveted,
Metallic construction elements of buildings can serve
bolted or screwed joints are allowed, provided that the
electromagnetic compatibility objectives very well.
surfaces in contact are good conductors, that is, they
Steel beams of L-, H-, U-, or T-shape often form a
have no paint or insulating cover, that they are
continuous earthed structure, that contains large cross-
safeguarded against corrosion and that a good electrical
sections and large surfaces with many intermediate
contact between adjacent elements is ensured.
connections to earth. Cables are preferably laid against
The shape of the metallic section should be maintained such beams. Inside corners are preferred to outside
over its full length. All interconnections shall have low surfaces (see Fig. 54).
impedance. A short single-lead connection between two
Covers for metallic cable trays shall meet the same

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
parts of a cable management system will result in a
requirements as the cable trays. A cover with many
high local impedance and, therefore, degradation of its
contacts over the full length is preferred. If that is not
electromagnetic compatibility performance (see
possible, the covers should be connected to the cable
Fig. 53).
tray at least at both ends by short connections less than
From frequencies of a few MHz upwards, a 10 cm long 10 cm, for example, braided or mesh straps.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

mesh strap between two parts of a cable management
When a metallic or composite cable management
system will degrade the shielding effect by more than a
system, specially designed for electromagnetic
factor of 10.
compatibility purposes, is parted in order to cross a
Whenever adjustments or extensions are carried out, it wall, for example, at fire barriers, the two metallic
is vital that work is closely supervised to ensure that it sections shall be bonded with low impedance
complies with the electromagnetic compatibility connections such as braided or mesh straps.

FIG. 53 CONTINUITY OF METALLIC SYSTEM COMPONENTS

FIG. 54 LOCATION OF CABLES INSIDE METALLIC CONSTRUCTION E LEMENTS

82
 IS 732 : 2019

FIG. 55 CONNECTION METALLIC SECTIONS

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
OF

4.5.4.7.3.2 Non-metallic cable management systems 5 SELECTION AND ERECTION OF

Where equipment connected to the cabling system by ELECTRICAL EQUIPMENT

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

unscreened cables are not affected by low frequency 5.1 Common Rules
disturbances, the performance of non-metallic cable
management systems is improved by installing a single Every item of equipment shall be selected and erected
lead within it, as a by-pass equipotential bonding so as to allow compliance with the rules stated in the
conductor. The lead shall be efficiently connected to following clauses and the relevant rules of this standard.
the equipment earthing system at both ends (for example
onto a metal panel of an equipment cabinet). 5.1.1 Compliance with Standards

The by-pass equipotential bonding conductor shall be 5.1.1.1 Every item of equipment shall comply with
designed to withstand large common mode and diverted Indian Standards as are appropriate.
fault currents.
5.1.1.2 Where there are no applicable or Indian
4.5.5 Protection Against Undervoltage Standards, the item of equipment concerned shall be
4.5.5.1 General requirements selected by special agreement between the person
specifying the installation and the installer.
4.5.5.1.1 Where a drop in voltage, or a loss and
subsequent restoration of voltage could imply 5.1.2 Operational Conditions and External Influences
dangerous situations for persons or property, suitable
precautions shall be taken. Also, precautions shall be 5.1.2.1 Operational conditions
taken where a part of the installation or current-using 5.1.2.1.1 Voltage
equipment may be damaged by a drop in voltage.
Equipment shall be suitable for the nominal voltage
An undervoltage protective device is not required if
(r.m.s. value for a.c.) of the installation.
damage to the installation or to current-using equipment
is considered to be an acceptable risk, provided that If, in IT installations, the neutral conductor is
no danger is caused to persons. distributed, equipment connected between phase and
4.5.5.1.2 The operation of undervoltage protective neutral shall be insulated for the voltage between
devices may be delayed if the operation of the appliance phases.
protected allows without danger a brief interruption or NOTE — For certain equipment, it may be necessary to take
loss of voltage. account of the highest and/or lowest voltage likely to occur in
normal service.
4.5.5.1.3 If use is made of contactors, delay in their
opening and reclosing shall not impede instantaneous 5.1.2.1.2 Current
disconnection by control or protective devices.
Equipment shall be selected for the design current
4.5.5.1.4 The characteristics of the undervoltage (r.m.s. value for a.c.) which it has to carry in normal
protective device shall be compatible with the service.
requirements of the IS standards for starting and use
of equipment. Equipment shall also be capable of carrying the currents
4.5.5.1.5 Where the reclosure of a protective device is likely to flow in abnormal conditions for such periods
likely to create a dangerous situation, the reclosure shall of time as are determined by the characteristics of the
not be automatic. protective devices.

83
IS 732 : 2019

5.1.2.1.3 Frequency Utilization and XX1 of each parameter,

construction of buildings except XX2 for the
If frequency has an influence on the characteristics of (B and C) parameter BC
equipment, the rated frequency of the equipment shall 2 The word “normal” appearing in the third column of the table
correspond to the frequency of the current in the circuit signifies that the equipment must generally satisfy applicable
concerned. IS standards.

5.1.2.1.4 Power 5.1.3 Accessibility

Equipment selected for its power characteristics shall 5.1.3.1 General

be suitable for the normal operational conditions taking All equipment, including wiring, shall be arranged so
account of the load factor. as to facilitate its operation, inspection and maintenance
5.1.2.1.5 Compatibility and access to its connections. Such facilities shall not

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
be significantly impaired by mounting equipment in
Unless other suitable precautions are taken during enclosures or compartments.
erection, all equipment shall be selected so that it will
not cause harmful effects on other equipment nor impair 5.1.4 Identification
the supply during normal service, including switching 5.1.4.1 General

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

operations.
Labels or other suitable means of identification shall
5.1.2.2 External influences be provided to indicate the purpose of switchgear and
5.1.2.2.1 Electrical equipment shall be selected and controlgear, unless there is no possibility of confusion.
erected in accordance with the requirements of Table 7, Where the functioning of switchgear and controlgear
which indicates the characteristics of equipment cannot be observed by the operator and where this might
necessary according to the external influences to which cause a danger, a suitable indicator, complying where
the equipment may be subjected. applicable with IEC 60073 and IEC 60447, shall be
Equipment characteristics shall be determined either fixed in a position visible to the operator.
by a degree of protection or by conformity to tests. 5.1.4.2 Wiring systems
5.1.2.2.2 If the equipment does not, by its construction, Wiring shall be so arranged or marked that it can be
have the characteristics relevant to the external identified for inspection, testing, repairs or alteration
influences of its location, it may nevertheless be used of the installation.
on condition that it is provided with appropriate
additional protection in the erection of the installation. 5.1.4.3 Identification of neutral and protective
Such protection shall not adversely affect the operation conductors
of the equipment thus protected. 5.1.4.3.1 The identification of separate neutral and
5.1.2.2.3 When different external influences occur protective conductors shall comply with IEC 60446.
simultaneously, they may have independent or mutual 5.1.4.3.2 PEN conductors, when insulated, shall be
effect and the degree of protection shall be provided marked by one of the following methods:
accordingly.
a) green/yellow throughout their length with, in
5.1.2.2.4 The selection of equipment according to addition, light blue markings at the
external influences is necessary not only for proper terminations, or
functioning, but also to ensure the reliability of the
b) light blue throughout their length with, in
measures of protection for safety complying with the
addition, green/yellow markings at the
rules of this standard generally. Measures of protection
terminations.
afforded by the construction of equipment are valid only
for the given conditions of external influence if the NOTE — The choice of method or methods is made by national
committees.
corresponding equipment specification tests are made
in these conditions of external influence. 5.1.4.4 Protective devices
NOTES The protective devices shall be arranged and identified
1 For the purposes of this standard, the following classes of so that the circuits protected may be easily recognized;
external influences are conventionally regarded as normal:
for this purpose it may be convenient to group them in
AA Ambient temperature AA4
distribution boards.
AB Atmospheric humidity AB4
Other environmental XX1 of each parameter 5.1.4.5 Diagrams
conditions (AC to AR)
5.1.4.5.1 Where appropriate, diagrams, charts or tables

84
IS 732 : 2019

Table 7 Characteristics of External Influences

(Clauses 4.3.2.3, 4.3.2.4 and 5.1.2.2.1)

Code External Influences Characteristics Required Reference

for Selection and Erection
of Equipment

(1) (2) (3) (4)

A Environmental conditions
AA Ambient temperature
The ambient temperature is that of the ambient air

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
where the equipment is to be installed
It is assumed that the ambient temperature includes the
effects of other equipment installed in the same
location
The ambient temperature to be considered for the
equipment is the temperature at the place where the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

equipment is to be installed resulting from the
influence of all other equipment in the same location,
when operating, not taking into account the thermal
contribution of the equipment to be installed
Lower and upper limits of ranges of ambient
temperature:
AA1 –60 °C +5 °C Specially designed IS 13736 (All Parts)
AA2 –40 °C +5 °C equipment or appropriate
arrangements1

AA3 –25 °C +5 °C Normal (in certain cases

AA4 –5 °C +40 °C special precautions may be
necessary)

AA5 +5°C +40 °C Normal

AA6 +5 °C +60 °C Specially designed IS 13736 (All Parts)
equipment or appropriate
arrangements1

AA7 –25 °C +55 °C Specially designed

equipment or appropriate
arrangements1
AA8 –50 °C +40 °C
Ambient temperature classes are applicable only where
humidity has no influence.
The average temperature over a 24 h period must not
exceed 5 °C below the upper limits.
Combination of two ranges to define some
environments may be necessary. Installations subject
to temperatures outside the ranges require special
consideration.
AB Atmospheric humidity
Air Temperature Relative Absolute
°C Humidity Humidity
% g/m3
Low High
Low High
Low High
AB1 –60 +5 3 100 0.003 7 Indoor and outdoor locations IS 13736 (All Parts)
with extremely low ambient
temperatures
Appropriate arrangements
shall be made3
AB2 –40 +5 10 100 0.1 7 Indoor and outdoor locations IS 13736 (All Parts)
with low ambient

85
IS 732 : 2018

Table 7 — (Continued)

Code External Influences Characteristics Required Reference

for Selection and Erection
of Equipment

(1) (2) (3) (4)

temperatures
Appropriate arrangements
shall be made3
Air Temperature Relative Absolute
°C Humidity Humidity
% g/m3

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Low High Low High Low High

AB3 -25 +5 10 100 0.5 7 Indoor and outdoor locations IS 13736 (All Parts)
with low ambient
temperatures
Appropriate arrangements

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

shall be made3
AB4 -5 +40 5 95 1 29 Weather protected locations IS 13736 (All Parts)
having neither temperature
nor humidity control.
Heating may be used to raise
low ambient temperatures
Normal 2
AB5 +5 +40 5 85 1 25 Weather protected locations IS 13736 (All Parts)
with temperature control
Normal 2
AB6 +5 +60 10 100 1 35 Indoor and outdoor locations IS 13736 (All Parts)
with extremely high ambient
temperatures, influence of
cold ambient temperatures is
prevented. Occurrence of
solar and heat radiation
Appropriate arrangements
shall be made 3
AB7 -25 +55 10 100 0.5 29 Indoor weather-protected IS 13736 (All Parts)
locations having neither
temperature nor humidity
control; the locations may
have openings directly to the
open air and be subjected to
solar radiation
Appropriate arrangements
shall be made 3
AB8 -50 +40 15 100 0.04 36 Outdoor and non-weather IS 13736 (All Parts)
protected locations, with low
and high temperatures
Appropriate arrangements
shall be made 3
NOTES
1 All specified values are maximum or limit values which will have a low possibility of being exceeded.
2 The low and high relative humidities are limited by the low and high absolute humidities, so that, for example, for environmental
parameters a and c, or b and d, the limit values given do not occur simultaneously. Therefore, Annex B contains climatograms which
describes the interdependence of air temperature, relative humidity and absolute humidity for the climatic classes specified.
Code External Characteristics Required for Selection Reference
Influences and Erection of Equipment
AC Altitude
AC1 ≤2 000 m Normal2
AC2 >2 000 m May necessitate special precautions such as the application of derating
factors
For some equipment special arrangements may be necessary at
altitudes of 1 000 m and above

86
 IS 732 : 2019

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
AD Presence of water
AD1 Negligible Probability of presence of water is negligible IS 13736 (All Parts)
Location in which the walls do not generally show traces of water but
may do so for short periods, for example in the form of vapour which
good ventilation dries rapidly IS/IEC 60529
IPX0
AD2 Free-falling drops Possibility of vertically falling drops IS 13736 (All Parts)
Location in which water vapour occasionally condenses as drops or
where steam may occasionally be present IS/IEC 60529

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
IPX1 or IPX2
AD3 Sprays Possibility of water falling as a spray at an angle up to 60° from the IS 13736 (All Parts)
vertical
Locations in which sprayed water forms a continuous film on floors
and/or walls IS/IEC 60529

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

IPX3
AD4 Splashes Possibility of splashes from any direction IS 13736 (All Parts)
Locations where equipment may be subjected to splashed water; this
applies, for example, to certain external luminaires, construction site
equipment IS/IEC 60529
IPX4
AD5 Jets Possibility of jets of water from any direction IS 13736 (All Parts)
Locations where hot water is used regularly (yards, car-washing bays)
IPX5 IS/IEC 60529
AD6 Waves Possibility of water waves IS 13736 (All Parts)
Seashore locations such as piers, beaches, quays, etc. IS/IEC 60529
IPX6
AD7 Immersion Possibility of intermittent partial or total covering by water
Locations which may be flooded and/or where the equipment is
immersed as follows:
— Equipment with a height of less than 850 mm is located in such a
way that its lowest point is not more than 1 000 mm below the IS/IEC 60529
surface of the water
— Equipment with a height equal to or greater than 850 mm is
located in such a way that its highest point is not more than 150
mm below the surface of the water
IPX7
AD8 Submersion Possibility of permanent and total covering by water
Locations such as swimming pools where electrical equipment is
permanently and totally covered with water under a pressure greater IS/IEC 60529
than 10 kPa
IPX8
AE Presence of foreign solid bodies or dust
AE1 Negligible The quantity or nature of dust or foreign solid bodies is not IS 13736 (All Parts)
significant IS/IEC 60529
IP0X

AE2 Small objects Presence of foreign solid bodies where the smallest dimension IS 13736 (All Parts)
(2.5 mm) is not less than 2.5 mm IS/IEC 60529
IP3X
Tools and small objects are examples of foreign solid bodies
of which the smallest dimension is at least 2.5 mm

87
IS 732 : 2018

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
AE3 Very small Presence of foreign solid bodies where the smallest dimension IS 13736 (All Parts)
objects (1 mm) is not less than 1 mm IS/IEC 60529
IP4X
Wires are examples of foreign solid bodies of which the
smallest dimension is not less than 1 mm

AE4 Light dust Presence of light deposits of dust: IS 13736 (All Parts)
10<deposit of dust ≤ 35 mg/m² a day IS/IEC 60529

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
IP5X or equipment IP6X if dust should not penetrate
equipment
AE5 Moderate dust Presence of medium deposits of dust: IS 13736 (All Parts)
35 < deposit of dust ≤ 350 mg/m² a day IEC 60529
IP5X or equipment IP6X if dust should not penetrate

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

equipment
AE6 Heavy dust Presence of large deposits of dust: IS 13736 (All Parts)
350 < deposit of dust ≤ 1 000 mg/m² a day IS/IEC 60529
IP6X
AF Presence of corrosive or polluting substances
AF1 Negligible The quantity or nature of corrosive or polluting substances is IS 13736 (All Parts)
not significant
Normal2
AF2 Atmospheric The presence of corrosive or polluting substances of IS 13736 (All Parts)
atmospheric origin is significant
Installations situated by the sea or near industrial zones
producing serious atmospheric pollution, such as chemical
works, cement works; this type of pollution arises especially in
the production of abrasive, insulating or conductive dusts
According to the nature of substances [for example,
satisfaction of salt mist test according to IS 9000 (Part 11)].
AF3 Intermittent or Intermittent or accidental subjection to corrosive or polluting IS 13736 (All Parts)
accidental chemical substances being used or produced
Locations where some chemicals products are handled in small
quantities and where these products may come only
accidentally into contact with electrical equipment; such
conditions are found in factory laboratories, other laboratories
or in locations where hydrocarbons are used (boiler-rooms,
garages, etc)
Protection against corrosion according to equipment
specification
AF4 Continuous Continuously subject to corrosive or polluting chemical IS 13736 (All Parts)
substances in substantial quantity, for example, chemical
works
Equipment specially designed according to the nature of
substances
AG Mechanical shock (see Annex N)
AG1 Low severity Normal, for example, household and similar equipment IS 13736 (All Parts)
AG2 Medium severity Standard industrial equipment, where applicable, or reinforced IS 13736 (All Parts)
protection
AG3 High severity Reinforced protection IS 13736 (All Parts)
AH Vibration (see Annex N)
AH1 Low severity Household and similar conditions where the effects of vibration are IS 13736 (All Parts)
generally negligible

88
 IS 732 : 2019

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
Normal 1
AH2 Medium severity Usual industrial conditions IS 13736 (All Parts)
Specially designed equipment or special arrangements
AH3 High severity Industrial installations subject to severe conditions IS 13736 (All Parts)
Specially designed equipment or special arrangements
AK Presence of flora and/or moulds growth
AK1 No hazard No harmful hazard from flora and/or mould growth. IS 13736 (All Parts)
Normal 4
AK2 Hazard Harmful hazard from flora and/or mould growth. IS 13736 (All Parts)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The hazard depends on local conditions and the nature of flora.
Distinction should be made between harmful growth of vegetation or
conditions for promotion of mould growth
Special protection, such as:
– increased degree of protection (see AE)
– special materials or protective coating of enclosures

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

– arrangements to exclude flora from location
AL Presence of fauna
AL1 No hazard No harmful hazard from fauna IS 13736 (All Parts)
Normal 2
AL2 Hazard Harmful hazard from fauna (insects, birds, small animals) IS 13736 (All Parts)
The hazard depends on the nature of the fauna. Distinction should be
made between:
– presence of insects in harmful quantity or of an aggressive nature;
– presence of small animals or birds in harmful quantity or of an
aggressive nature
Protection may include:
– an appropriate degree of protection against penetration of foreign
solid bodies (see AE);
– sufficient mechanical resistance (see AG);
– precautions to exclude fauna from the location (such as cleanliness,
use of pesticides);
– special equipment or protective coating of enclosures
AM Electromagnetic, electrostatic, or ionising influences [see IEC 61000-2 series and IS 14700 (Part 4 /Section2)]
Low-frequency electromagnetic phenomena (conducted or radiated)
Harmonics, interharmonics
AM1-1 Controlled level Care should be taken that the controlled situation is not impaired

AM1-2 Normal level Complying with Table 1 of

AM1-3 High level Special measures in the design of the installation, for example, filters IEC 61000-2-2
Locally higher than Table 1
of IEC 61000-2-2
Signalling voltages
AM-2-1 Controlled level Possibly: blocking circuits Lower than specified below
AM-2-2 Medium level No additional requirement IEC 61000-2-1 and
AM-2-3 High level Appropriate measures IEC 61000-2-2
Voltage amplitude variations
AM-3-1 Controlled level
AM-3-2 Normal level Compliance with 4.5
AM-4 Voltage unbalance Compliance with
IEC 61000-2-2
AM-5 Power frequency variations 1 Hz according to
IEC 61000-2-2
AM-6 No classification See 4.5 ITU-T
High withstand of signal and control systems of switchgear and
controlgear
AM-7 Direct current in a.c. network
No classification Measures to limit their presence in level and time in the current-using
equipment or their vicinity

89
IS 732 : 2018

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
Radiated magnetic fields
2
AM-8-1 Medium level Normal Level 2 of IS 14700 (Part
4/Section 8)
AM-8-2 High level Protection by appropriate measures, for example, screening and/or Level 4 of IS 14700 (Part
separation 4/Section 8)
Electric fields
2
AM-9-1 Negligible level Normal
AM-9-2 Medium level See IEC 61000-2-5 IEC 61000-2-5

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
AM-9-3 High level See IEC 61000-2-5
AM-9-4 Very high level see IEC 61000-2-5
High-frequency electromagnetic phenomena conducted, induced or radiated (continuous or transient)
Induced oscillatory voltages or currents
2

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

AM-21 No classification Normal IS 14700 (Part 4/Sec 6)
Conducted unidirectional transients of the nanosecond time scale IS 14700 (Part 4/Sec 4)
AM-22-1 Negligible level Protective measures are necessary Level 1
AM-22-2 Medium level Protective measures are necessary (see 5.1.2.2) Level 2
AM-22-3 High level Normal equipment Level 3
AM-22-4 Very high level High immunity equipment Level 4
Conducted unidirectional transients of the microsecond to the millisecond time scale
AM-23-1 Controlled level Impulse withstand of equipment and overvoltage protective means 4.5.4
AM-23-2 Medium level chosen taking into account the nominal supply voltage and the impulse
AM-23-3 High level withstand category according to 4.5 4.5.4

Conducted oscillatory transients

AM-24-1 Medium level see IS 14700 (Part 4/Sec 12) IS 14700 (Part 4/Sec 12)
AM-24-2 High level see IEC 60255-22-1 IEC 60255-22-1
Radiated high-frequency phenomena IS 14700 (Part 4/Sec 3)
AM-25-1 Negligible level Level 1
2
AM-25-2 Medium level Normal Level 2
AM-25-3 High level Reinforced level Level 3
Electrostatic discharges IS 14700 (Part 4/Sec 2)
2
AM-31-1 Small level Normal Level 1
2
AM-31-2 Medium level Normal Level 2
2
AM-31-3 High level Normal Level 3
AM-31-4 Very high level Reinforced Level 4
AM-41-1 Ionization Special protection such as:
No classification – Spacing from source
– Interposition of screens, enclosure by special materials
AN Solar radiation
AN1 Low Intensity ≤ 500 W/m² IS 13736 (Part 3/Sec 3)
2
Normal
AN2 Medium 500 W/m² < intensity ≤ 700 W/m² IS 13736 (Part 3/Sec 3)
Appropriate arrangements shall be made 3
AN3 High 700 W/m² < Intensity ≤ 1 120 W/m² IS 13736 (Part 3/Sec 4)
Appropriate arrangements shall be made 3
Such arrangements could be:
– material resistant to ultra-violet radiation
– special colour coating
– interposition of screens
AP Seismic effects

AP1 Negligible Acceleration ≤ 30 Gal (1Gal = 1cm/s²)

90
 IS 732 : 2019

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
Normal
AP2 Low severity 30 Gal < acceleration ≤ 300 Gal
Under consideration
AP3 Medium severity 300 Gal < acceleration ≤ 600 Gal
under consideration
AP4 High severity 600 Gal < acceleration
Under consideration

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Vibration which may cause the destruction of the building is outside
the classification
Frequency is not taken into account in the classification; however, if
the seismic wave resonates with the building, seismic effects must be
specially considered. In general, the frequency of seismic acceleration
is between 0 Hz and 10 Hz

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

AQ Lightning
AQ1 Negligible ≤ 25 days per year or result of risk assessment in accordance with
4.5.3
Normal
AQ2 Indirect exposure  25 days per year or result of risk assessment in accordance with
4.5.3
Normal
AQ3 Direct exposure Hazard from exposure of equipment
If lightning protection is necessary, it shall be arranged according to
IEC 61024-1
AR Movement of air

AR1 Low Speed ≤ 1 m/s

2
Normal
AR2 Medium 1 m/s < speed ≤ 5 m/s
Appropriate arrangements shall be made 3
AR3 High 5 m/s < speed ≤ 10 m/s
Appropriate arrangements shall be made 3
AS Wind
AS1 Low Speed ≤ 20 m/s
2
Normal
AS2 Medium 20 m/s < speed ≤ 30 m/s
Appropriate arrangements shall be made 3
AS3 High 30 m/s < speed ≤ 50 m/s
Appropriate arrangements shall be made 3
B Utilization
BA Capability of persons
BA1 Ordinary Uninstructed persons
2
Normal
BA2 Children Locations intended for presence of groups of children 5
Nurseries
Equipment of degrees of protection higher than IP2X.
Socket outlets shall be provided with at least IP2X or IPXXB and with
increased protection according to IS 1293
Inaccessibility of equipment with external surface temperature
exceeding 80 °C (60 °C for nurseries and the like)
BA3 Handicapped Persons not in command of all their physical and intellectual abilities

91
IS 732 : 2018

Table 7 — (Continued)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
(sick persons, old persons)
Hospitals
According to the nature of the handicap
BA4 Instructed Persons adequately advised or supervised by skilled persons to enable
them to avoid dangers which electricity may create (operating and
maintenance staff)
Electrical operating areas
BA5 Skilled Persons with technical knowledge or sufficient experience to enable

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
them to avoid danger which electricity may create (engineers and
technicians)
Closed electrical operating areas
BB Electrical resistance of the human body (under consideration)
BC Contact of persons with earth potential

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Class of equipment according to IEC 61140

0-0I I II III

BC1 None Persons in non-conducting situations: 4.2.13.3

A Y A A
BC2 Low Persons who do not in usual conditions make contact with extraneous-
conductive-parts or stand on conducting surfaces:
A A A A
BC3 Frequent Persons who are frequently in touch with extraneouss conductive parts
or stands on conducting surfaces.
Locations with extraneous-conductive-parts either numerous or of
large area
X A A A
A Equipment permitted
X Equipment prohibited
Y Permitted if used as class 0
BC4 Continuous Persons who are immersed in water or in long term permanent contact
with metallic surroundings and for whom the possibility of
interrupting contact is limited
Metallic surroundings such as boilers and tanks
Under consideration
BD Conditions of evacuation in an emergency
BD1 (Low density/easy Low density occupation, easy conditions of evacuation
exit) Buildings of normal or low height used for habitation.
Normal
BD2 (Low Low density occupation, difficult conditions of evacuation
density/difficult High-rise buildings
exit)
BD3 (High density/easy High density occupation, easy conditions of evacuation
exit) Locations open to the public (theatres, cinemas, departments stores, etc)
BD4 (High High density occupation, difficult conditions of evacuation
density/difficult High-rise buildings open to the public (hotels, hospitals, etc)
exit)
BE Nature of processed or stored materials
2
BE1 No significant Normal
risks
BE2 Fire risks Manufacture, processing or storage of flammable materials including 4.3

92
 IS 732 : 2019

Table 7 — (Concluded)

Code External Characteristics Required for Selection Reference

Influences and Erection of Equipment
presence of dust 5.2
Barns, wood-working shops, paper factories
Equipment made of material retarding the spread of flame.
Arrangements such that a significant temperature rise or a spark within
electrical equipment cannot initiate an external fire
BE3 Explosion risks Processing or storage of explosive or low-flash-point materials Under consideration
including presence of explosive dusts
Oil refineries, hydrocarbon stores

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Requirements for electrical apparatus for explosive atmospheres (see
IS/IEC 60079)
BE4 Contamination Presence of unprotected foodstuffs, pharmaceutics, and similar Under consideration
risks products without protection
Foodstuff industries, kitchens:
Certain precautions may be necessary, in the event of fault, to prevent

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

processed materials being contaminated by electrical equipment, for
example, by broken lamps
Appropriate arrangements, such as:
— protection against falling debris from broken lamps
and other fragile objects;
— screens against harmful radiation such as infra-red
or ultra-violet
C Construction of buildings
CA Construction
materials
2
CA1 Non combustible Normal

CA2 Combustible Buildings constructed mainly out of combustible materials 4.3

Wooden buildings
Under consideration
CB Building design
2
CB1 Negligible risks Normal

CB2 Propagation of fire Buildings of which the shape and dimensions facilitates the spread of 4.2 & 4.3
fire (for example, chimney effects)
High-rise buildings. Forced ventilation systems
Equipment made of material retarding the propagation of fire
including fires not originating from the electrical installation. Fire
barriers 6
CB3 Movement Risk due to structural movement (for example, displacement between Contraction or expansion
different parts of a building or between a building and the ground or joints (under consideration)
building foundations 5.2
Buildings of considerable length or erected on unstable ground
Contraction or expansion joints in electrical wiring
CB4 Flexible or Structures which are weak or subject to movement (for example, Flexible wiring (under
unstable oscillation) consideration)
Tents, air-support structures, false ceilings, removable partitions. 5.2
Installations to be structurally self-supporting Under consideration
1 May necessitate certain supplementary precautions (for example, special lubrication).
2 This means that ordinary equipment will operate safely under the described external influences.
3 This means that special arrangements need to be made, for example, between the designer of the installation and the equipment
manufacturer, for example, for specially designed equipment.
4 This means that ordinary equipment will operate safely under the described external influences.
5 This class does not necessarily apply to family dwellings.
6 Fire detectors may be provided.

93
IS 732 : 2019

in accordance with IEC 61346-1 and the IEC 61082 (see Table 7) that can occur when connected and erected
series shall be provided, indicating in particular: as for normal use, and taking into account the intended
level of continuity of service necessary for the
a) the type and composition of circuits (points
application.
of utilization served, number and size of
conductors, type of wiring); and 5.1.5.3.1.2 Equipment shall be chosen with sufficiently
b) the characteristics necessary for the low emission levels so that it cannot cause
identification of the devices performing the electromagnetic interference by electrical conduction
functions of protection, isolation and or propagation in the air with other electrical equipment
switching and their locations. inside or outside the building. If necessary, means of
mitigation shall be installed to minimize the emission
For simple installations the foregoing information may (see 4.5).
be given in a schedule.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5.1.6 Measures Related To Protective Conductor
5.1.4.5.2 The symbols used shall be chosen from the Currents
IS 12032 series.
The protective conductor current generated by electrical
5.1.5 Prevention of Mutual Detrimental Influence equipment under normal conditions of operation and

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

5.1.5.1 Equipment shall be so selected and erected as the design of electrical installations shall be compatible,
to avoid any harmful influence between the electrical in order to provide safety and to assure normal use.
installation and any non-electrical installations. The permissible protective conductor currents for
Equipment not provided with a back plate shall not be equipment are specified in IEC 61140 and reproduced
mounted on a building surface unless the following in Annex Q, and shall be taken into consideration when
requirements are satisfied: information is not available from the manufacturer.

a) a voltage transfer to the building surface is NOTES

1 For the purposes of 5.1.6, a protective conductor current is a
prevented; and
current which flows in the protective conductor when the
b) fire segregation is provided between the equipment is fault-free and operating normally.
equipment and a combustible building surface. 2 For prevention of unwanted tripping of residual current
devices due to protective conductor currents, see 5.3.2.2.1.3.
If the building surface is non-metallic and non- 3 The installer should inform the owner of the installation that
combustible, no additional measures are required. If preferably such equipment should be selected for which the
not, these requirements may be satisfied by one of the manufacturer has provide information concerning the value of
following measures: protective conductor current. Equipment with low values should
be chosen to avoid unwanted tripping.
a) if the building surface is metallic, it shall be 4 For reinforced protective conductors, see 5.4.3.7.
bonded to the protective conductor (PE) or
5.1.6.1 Transformer
to the equipotential bonding conductor of the
installation, in accordance with 4.2.11.3.1.2 Measures may be taken in the electrical installation to
and 5.4; restrict protective conductor currents by supplying
b) if the building surface is combustible, the limited areas with separate winding transformers.
equipment shall be separated from it by a 5.1.6.2 Signalling systems
suitable intermediate layer of insulating
material having a flammability rating as per I The use of any live conductor together with the
c) 1731. protective conductor as a return path for signalling is
not allowed.
5.1.5.2 Where equipment carrying currents of different
NOTE — For the use of d.c. return conductors, see the
types or at different voltages is grouped on a common requirements of 5.4.3.5.
assembly (such as a switchboard, a cubicle or a control
desk or box), all the equipment belonging to any one 5.2 Selection and Erection of Electrical Equipment
type of current or any one voltage shall be effectively — Wiring Systems
segregated wherever necessary to avoid mutual
5.2.1 Void
detrimental influence.
5.2.2 Void
5.1.5.3 Electromagnetic compatibility
5.2.3 General
5.1.5.3.1 Choice of the immunity and emission levels
Consideration shall be given to the application of the
5.1.5.3.1.1 The immunity levels of equipment shall be
fundamental principles of this standard as it applies to:
taken into account the electromagnetic influences

94
 IS 732 : 2019

a) cables and conductors, 5.2.4.6 Conduit systems, cable ducting systems, cable
b) their termination and/or jointing, trunking systems, cable tray systems and cable ladder
c) their associated supports or suspensions, and systems
d) their enclosure or methods of protection Several circuits are allowed in the same conduit system,
against external influences. separated compartment of cable ducting system or cable
trunking system provided all conductors are insulated
5.2.4 Types of Wiring System
for the highest nominal voltage present.
5.2.4.1 The method of installation of a wiring system
Conduit systems shall comply with the IS 14930 series,
(excluding systems covered by 5.2.4.4) in relation to
cable trunking or ducting systems shall comply with
the type of conductor or cable used shall be in
the IS 14297 series and cable tray and cable ladder
accordance with Table 17, provided the external
systems shall comply with IEC 61537.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
influences are taken into account according to 5.2.5.
NOTE — Guidance on the selection of conduit systems is given
5.2.4.2 The method of installation of a wiring system in Annex W.
(excluding systems covered by 5.2.4.4) in relation to
the situation concerned shall be in accordance with 5.2.4.7 Several circuits in one cable
Table 18. Other methods of installation of cables, Several circuits are allowed in the same cable provided

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

conductors and busbars not included in Table 18 are all conductors are insulated for the highest nominal
permitted, provided that they fulfil the requirements of voltage present.
this part.
5.2.4.8 Circuit arrangements
5.2.4.3 Examples of wiring systems (excluding systems
covered by 5.2.4.4) together with reference to the 5.2.4.8.1 Conductors of a circuit shall not be
method of installation to be used to obtain current- distributed over different multi-core cables, conduits,
carrying capacity are shown in Table 19. cable ducting systems or cable trunking systems. This
is not required where a number of multi-core cables,
NOTE — Table 19 gives the reference method of installation forming one circuit, are installed in parallel. Where
where it is considered that the same current-carrying capacities
can safely be used. It is not implied that all these items are
multi-core cables are installed in parallel, each cable
necessarily recognized in national rules of all countries or that shall contain one conductor of each phase and the
other methods of installation are prohibited. neutral, if any.
5.2.4.4 Busbar trunking systems and powertrack 5.2.4.8.2 The use of a common neutral conductor for
systems several main circuits is not permitted. However, single-
Busbar trunking systems shall comply with IS/ phase a.c. final circuits may be formed from one line
IEC 60439-2 and powertrack systems shall comply with conductor and the neutral conductor of one multi-phase
the IEC 61534 series. Busbar trunking systems and a.c. circuit with only one neutral conductor provided
powertrack systems shall be selected and installed in that the arrangement of the circuits remains
accordance with manufacturers’ instructions, taking recognizable. This multi-phase circuit shall be isolated
account of external influences. by means of an isolating device according to 5.3.7.3.2
which isolates all live conductors.
5.2.4.5 a.c. circuits — Electromagnetic effects
NOTE — For the allocation of a common protective conductor
(prevention of eddy current) for several circuits (see 5.3).
5.2.4.5.1 Conductors of a.c. circuits installed in 5.2.4.8.3 Where several circuits are terminated in a
ferromagnetic enclosures shall be arranged so that all single junction box the terminals for each circuit shall
conductors of each circuit, including the protective be separated by insulating partitions, except for
conductor of each circuit, are contained in the same connecting devices in accordance with the IEC 60998
enclosure. Where such conductors enter a ferrous series, and terminal blocks in accordance with
enclosure, they shall be arranged such that the conductor IEC 60947-7.
are only collectively surrounded by ferromagnetic
materials. 5.2.4.9 Use of flexible cables or cords

5.2.4.5.2 Single-core cables armoured with steel wire 5.2.4.9.1 A flexible cable may be used for fixed wiring
or steel tape shall not be used for a.c. circuits. where the provisions of this standard are met.
NOTE — The steel wire or steel tape armour of a single-core 5.2.4.9.2 Equipment that is intended to be moved in
cable is regarded as a ferromagnetic enclosure. For single-core use shall be connected by flexible cables or cords,
wire armoured cables, the use of aluminium armour is except equipment supplied by contact rails.
recommended.

95
IS 732 : 2019

5.2.4.9.3 Stationary equipment which is moved b) from plant, appliances and luminaires,
temporarily for the purpose of connecting, cleaning etc, c) from manufacturing processes,
for example, cookers or flush-mounting units for d) through heat conducting materials, and
installations in false floors, shall be connected with e) from solar gain of the wiring system or its surrounding
medium.
flexible cables or cords.
5.2.4.9.4 Flexible conduit systems may be used to 5.2.5.3 Presence of water (AD) or high humidity (AB)
protect flexible insulated conductors. 5.2.5.3.1 Wiring systems shall be selected and erected
5.2.4.10 Installation of cables so that no damage is caused by condensation or ingress
of water. The completed wiring system shall comply
Insulated conductors (non-sheathed) for fixed wiring with the IP degree of protection relevant to the
shall be enclosed in conduit, cable ducting system or particular location.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
cable trunking system. This requirement does not apply
NOTE — In general, the sheaths and insulation of cables for
to a protective conductor complying with 5.4. fixed installations may be regarded, when intact, as proof against
penetration by moisture. Special considerations apply to cables
5.2.5 Selection and Erection of Wiring Systems in
liable to frequent splashing, immersion or submersion.
Relation to External Influences
5.2.5.3.2 Where water may collect or condensation may

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

The installation method selected shall be such that form in wiring systems, provision shall be made for its
protection against the expected external influences is escape.
ensured in all appropriate parts of the wiring system.
Particular care shall be taken at changes in direction 5.2.5.3.3 Where wiring systems may be subjected to
and where wiring enters into equipment. waves (AD6), protection against mechanical damage
shall be afforded by one or more of the methods
NOTE — The external influences categorized in Table 7 which
are of significance to wiring systems are included in this clause. of 5.2.5.6, 5.2.5.7 and 5.2.5.8.

5.2.5.1 Ambient temperature (AA) 5.2.5.4 Presence of solid foreign bodies (AE)

5.2.5.1.1 Wiring systems shall be selected and erected 5.2.5.4.1 Wiring systems shall be selected and erected
so as to be suitable for any temperature between the so as to minimize the danger arising from the ingress
highest and the lowest local ambient temperature and of solid foreign bodies. The completed wiring system
to ensure that the limiting temperature in normal shall comply with the IP degree of protection relevant
operation (see Table 8) and the limiting temperature in to the particular location.
case of a fault will not be exceeded. 5.2.5.4.2 In a location where dust in significant quantity
NOTE — “Limiting temperature” means maximum continuous is present (AE4), additional precautions shall be taken
operating temperature. to prevent the accumulation of dust or other substances
5.2.5.1.2 Wiring system components including cables in quantities which could adversely affect the heat
and wiring accessories shall only be installed or handled dissipation from the wiring system.
at temperatures within the limits stated in the relevant NOTE — A wiring system which facilitates the removal of dust
product standard or as given by the manufacturer. may be necessary (see 5.2.12).

5.2.5.2 External heat sources 5.2.5.5 Presence of corrosive or polluting substances

(AF)
5.2.5.2.1 In order to avoid the harmful effects of heat
from external sources, one or more of the following 5.2.5.5.1 Where the presence of corrosive or polluting
methods or an equally effective method shall be used substances, including water, is likely to give rise to
to protect wiring systems: corrosion or deterioration, parts of the wiring system
likely to be affected shall be suitably protected or
– heat shielding; manufactured from a material resistant to such
– placing sufficiently far from the source of heat; substances.
– selecting of the wiring system components NOTE — Suitable protection for application during erection
with due regard for the additional temperature may include protective tapes, paints or grease. These measures
rise which may occur; should be coordinated with the manufacturer.
– local reinforcement of insulating material, for 5.2.5.5.2 Dissimilar metals, liable to initiate electrolytic
example, by heat-resisting insulated sleeving. action, shall not be placed in contact with each other
NOTE — Heat from external sources may be radiated, unless special arrangements are made to avoid the
convected or conducted, for example, consequences of such contact.
a) from hot water systems, 5.2.5.5.3 Materials liable to cause mutual or individual

96
 IS 732 : 2019

deterioration or hazardous degradation shall not be 5.2.5.8.2 Where buried in the structure, conduit systems
placed in contact with each other. or cable ducting systems, other than pre-wired conduit
assemblies specifically designed for the installation,
5.2.5.6 Impact (AG)
shall be completely erected between access points
5.2.5.6.1 Wiring systems shall be selected and erected before any insulated conductor or cable is drawn in.
so as to minimize the damage arising from mechanical
stress, for example, by impact, penetration or 5.2.5.8.3 The radius of every bend in a wiring system
compression during installation, use or maintenance. shall be such that conductors or cables do not suffer
damage and terminations are not stressed.
5.2.5.6.2 In fixed installations where impacts of
medium severity (AG2) or high severity (AG3) can 5.2.5.8.4 Where the conductors or cables are not
occur, protection shall be afforded by: supported continuously due to the method of
installation, they shall be supported by suitable means

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
a) the mechanical characteristics of the wiring at appropriate intervals in such a manner that the
system, or conductors or cables do not suffer damage by their own
b) the location selected, or weight, or due to electro-dynamic forces resulting from
c) the provision of additional local or general short-circuit current.
mechanical protection, or

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — Precautions due to electro-dynamic forces resulting
d) by any combination of the above. from short-circuit currents need only be taken on single-core
cables with a cross-sectional area greater than 50 mm².
NOTES
1 Examples are areas where the floor is likely to be penetrated 5.2.5.8.5 Where the wiring system is subjected to a
and areas used by forklift trucks. permanent tensile stress (for example, by its own weight
2 Additional mechanical protection may be achieved by using in vertical runs) a suitable type of cable or conductor
suitable cable trunking/ducting or conduit systems.
with appropriate cross-sectional areas and method of
5.2.5.6.3 A cable installed under a floor or above a mounting shall be selected in such a manner that the
ceiling shall be run in such a position that it is not liable conductors or cables do not suffer damage by
to be damaged by contact with the floor or the ceiling unacceptable tensile stress.
or their fixings.
5.2.5.8.6 Wiring systems intended for the drawing in
5.2.5.6.4 The degree protection of electrical equipment or out of conductors or cables shall have adequate
shall be maintained after installation of the cables and means of access to allow this operation.
conductors.
5.2.5.8.7 Wiring systems buried in floors shall be
5.2.5.7 Vibration (AH) sufficiently protected to prevent damage caused by the
intended use of the floor.
5.2.5.7.1 Wiring systems supported by or fixed to
structures of equipment subject to vibration of medium 5.2.5.8.8 Wiring systems which are rigidly fixed and
severity (AH2) or high severity (AH3) shall be suitable buried in the walls shall be run horizontally, vertically
for such conditions, particularly where cables and cable or parallel to the room edges.
connections are concerned.
Wiring systems in ceilings or in floors may follow the
NOTE — Special attention should be paid to connections to shortest practical route.
vibrating equipment. Local measures may be adopted such as
flexible wiring systems. 5.2.5.8.9 Wiring systems shall be installed so that
5.2.5.7.2 The fixed installation of suspended current- mechanical stress to the conductors and connections is
using equipment, for example, luminaires, shall be avoided.
connected by cable with flexible cores. Where no 5.2.5.8.10 Cables, conduits or ducts that are buried in
vibration or movement can be expected, cable with non- the ground shall either be provided with protection
flexible core may be used. against mechanical damage or be buried at a depth that
5.2.5.8 Other mechanical stresses (AJ) minimizes the risk of such damage. Buried cables shall
be marked by cable covers or a suitable marking tape.
5.2.5.8.1 Wiring systems shall be selected and erected Buried conduits and ducts shall be suitably identified.
so as to avoid during installation, use or maintenance,
damage to cables and insulated conductors and their NOTES
terminations. 1 IS 14930 (Parts 1 & 2) is the standard for buried under ground
conduits.
The use of lubricants containing silicone oil for 2 Mechanical protection may be achieved by using conduit
threading in cables and conductors into conduit systems, systems buried underground according to IS 14930 (Parts 1 & 2)
ducting systems, trunking systems and tray and ladder or armoured cables or other appropriate methods such as cover
plates.
systems is not allowed.
97
IS 732 : 2019

5.2.5.8.11 Cable supports and enclosures shall not have 5.2.5.12 Seismic effects (AP)
sharp edges liable to damage the cables or insulated 5.2.5.12.1 The wiring system shall be selected and
conductors. erected with due regard to the seismic hazards of the
5.2.5.8.12 Cables and conductors shall not be damaged location of the installation.
by the fixing means. 5.2.5.12.2 Where the seismic hazards experienced are
5.2.5.8.13 Cables, busbars and other electrical low severity (AP2) or higher, particular attention shall
conductors which pass across expansion joints shall be paid to the following:
be so selected and erected that anticipated movement a) the fixing of wiring systems to the building
does not cause damage to the electrical equipment, for structure; and
example, by use of flexible wiring system. b) the connections between the fixed wiring and
all items of essential equipment, for example,

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5.2.5.8.14 Where wiring passes through fixed partitions,
it shall be protected against mechanical damage, for safety services, shall be selected for their
example, metallic sheathed or armoured cables, or by flexible quality.
use of conduit or grommets. 5.2.5.13 Wind (AR)
NOTE — No wiring system should penetrate an element of 5.2.5.13.1 See 5.2.5.7, Vibration (AH), and 5.2.5.8,

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

building construction which is intended to be load-bearing
Other mechanical stresses (AJ).
unless the integrity of the load-bearing element can be assured
after such penetration. 5.2.5.14 Nature of processed or stored materials (BE)
5.2.5.9 Presence of flora and/or mould growth (AK) See 4.3.2, measures for protection against fire,
5.2.5.9.1 Where the conditions experienced or expected and 5.2.10, Selection and erection of wiring systems
constitute a hazard (AK2), the wiring system shall be to minimize the spread of fire.
selected accordingly or special protective measures 5.2.5.15 Building design (CB)
shall be adopted.
5.2.5.15.1 Where risks due to structural movement exist
NOTES (CB3), the cable support and protection system
1 An installation method which facilitates the removal of such employed shall be capable of permitting relative
growths may be necessary (see 5.2.12).
movement so that conductors and cables are not
2 Possible preventive measures are closed types of installation
subjected to excessive mechanical stress.
(conduit or cable ducting or cable trunking), maintaining
distances to plants and regular cleaning of the relevant wiring 5.2.5.15.2 For flexible structures or structures intended
system.
to move (CB4), flexible wiring systems shall be used.
5.2.5.10 Presence of fauna (AL) 5.2.6 Current-Carrying Capacities
Where conditions experienced or expected constitute 5.2.6.1 The current to be carried by any conductor for
a hazard (AL2), the wiring system shall be selected sustained periods during normal operation shall be such
accordingly or special protective measures shall be that the temperature limit of the insulation is not
adopted, for example, by exceeded. This requirement is fulfilled by application
a) the mechanical characteristics of the wiring of Table 8, for the types of insulation given in this table.
system, or The value of current shall be selected in accordance
b) the location selected, or with 5.2.6.2 or determined in accordance with 5.2.5.3.
c) the provision of additional local or general 5.2.6.2 The requirement of 5.2.6.1 is considered to be
mechanical protection, or satisfied if the current for insulated conductors and cables
d) by any combination of the above. without armour does not exceed the appropriate values
selected from the tables in Annex S with reference to
5.2.5.11 Solar radiation (AN) and ultraviolet radiation Table 19, subject to any necessary correction factors
Where significant solar radiation (AN2) or ultraviolet given in Annex S. The current-carrying capacities given
radiation is experienced or expected, a wiring system in Annex S are provided for guidance.
suitable for the conditions shall be selected and erected NOTE — It is recognized that there will be some tolerance in
or adequate shielding shall be provided. Special the current-carrying capacities depending on the environmental
conditions and the precise construction of the cables.
precautions may need to be taken for equipment subject
to ionizing radiation. 5.2.6.3 The appropriate values of current-carrying
capacity may also be determined as described in the
NOTE — See also 5.2.5.2.1 dealing with temperature rise.
IEC 60287 series, or by test, or by calculation using a

98
 IS 732 : 2019

Table 8 Maximum Operating Temperatures for Types of Insulation

(Clauses 5.2.5.1.1 and 5.2.6.1)

Type of Insulation Temperature Limit1), 4)

°C
Thermoplastic (PVC) 70 at the conductor
Thermosetting (XLPE or EPR rubber) 90 at the conductor2)
Mineral (thermoplastic (PVC) covered or bare exposed to touch) 70 at the sheath
Mineral (bare not exposed to touch and not in contact with combustible material) 105 at the sheath2), 3)
1)
The maximum permissible conductor temperatures given in Table 8 on which the tabulated current-carrying capacities given in
Annex A are based, have been taken from IEC 60502 and IEC 60702and are shown on these tables.
2)
Where a conductor operates at a temperature exceeding 70 °C, it shall be ascertained that the equipment connected to the conductor is
suitable for the resulting temperature at the connection.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3)
For mineral insulated cables, higher operating temperatures may be permissible dependent upon the temperature rating of the cable, its
terminations, the environmental conditions and other external influences.
4)
Where certified, conductors or cable may have maximum operating temperature limits in accordance with the manufacturer’s
specification.

NOTES

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1 The table does not include all types of cables.
2 This does not apply to busbar trunking systems or powertrack systems or lighting track systems for which the current-carrying capacity
should be provided by the manufacturer according to IS 8623 (Part 2) and powertrack systems to IEC 61534-1.
3 For the temperature limit for other types of insulation, please refer to cable specification or manufacturer.

recognized method, provided that the method is stated. current-carrying capacity as a three-core cable having
Where appropriate, account shall be taken of the the same conductor cross-sectional area for each line
characteristics of the load and, for buried cables, the conductor. Four- and five-core cables may have higher
effective thermal resistance of the soil. current-carrying capacities when only three conductors
are loaded. This assumption is not valid in the case of
5.2.6.4 The ambient temperature is the temperature of
the presence of third harmonic or multiples of 3
the surrounding medium when the cable(s) or insulated
presenting a THD (total harmonic distortion) greater
conductor(s) under consideration are not loaded.
than 15 percent.
5.2.6.5 Groups containing more than one circuit
5.2.6.6.2 Where the neutral conductor in a multicore
The group reduction factors (Tables 36 to Table 40), cable carries current as a result of an imbalance in the
are applicable to groups of insulated conductors or line currents, the temperature rise due to the neutral
cables having the same maximum operating current is offset by the reduction in the heat generated
temperature. by one or more of the line conductors. In this case, the
neutral conductor size shall be chosen on the basis of
For groups containing cables or insulated conductors
the highest line current.
having different maximum operating temperatures, the
current-carrying capacity of all the cables or insulated In all cases, the neutral conductor shall have a cross-
conductors in the group shall be based on the lowest sectional area adequate to afford compliance
maximum operating temperature of any cable in the with 5.2.6.1.
group, together with the appropriate group reduction
5.2.6.6.3 Where the neutral conductor carries current
factor.
without a corresponding reduction in load of the line
If, due to known operating conditions, a cable or conductors, the neutral conductor shall be taken into
insulated conductor is expected to carry a current not account in ascertaining the current-carrying capacity
greater than 30 percent of its grouped current-carrying of the circuit. Such currents may be caused by a
capacity, it may be ignored for the purpose of obtaining significant triple harmonic current in three-phase
the reduction factor for the rest of the group. circuits. If the harmonic content is greater than 15
percent of the fundamental line current, the neutral
5.2.6.6 Number of loaded conductors
conductor size shall not be smaller than that of the line
5.2.6.6.1 The number of conductors to be considered conductors. Thermal effects due to the presence of third
in a circuit are those carrying load current. Where it harmonic or multiples of 3 and the corresponding
can be assumed that conductors in polyphase circuits reduction factors for higher harmonic currents are given
carry balanced currents, the associated neutral in Annex V.
conductor need not be taken into consideration. Under
5.2.6.6.4 Conductors which serve the purpose of
these conditions, a four-core cable is given the same
protective conductors only (PE conductors) shall not
99
IS 732 : 2019

be taken into consideration. PEN conductors shall be 5.2.6.9 Single-core cables with a metallic covering
taken into consideration in the same way as neutral
The metallic sheaths and/or non-magnetic armour of
conductors.
single-core cables in the same circuit shall be connected
5.2.6.7 Conductors in parallel together at both ends of their run. Alternatively, to
improve current-carrying capacity, the sheaths or
Where two or more live conductors or PEN conductors
armour of such cables having conductors of cross-
are connected in parallel in a system, either:
sectional area exceeding 50 mm2 and a non-conducting
a) measures shall be taken to achieve equal load outer sheath may be connected together at one point in
current sharing between them; their run with suitable insulation at the unconnected
This requirement is considered to be fulfilled ends, in which case the length of the cables from the
if the conductors are of the same material, have connection point shall be limited so that voltages from

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
the same cross-sectional area, are sheaths and/or armour to earth:
approximately the same length and have no a) do not cause corrosion when the cables are
branch circuits along the length, and either carrying their full load current, for example,
– the conductors in parallel are multi-core by limiting the voltage to 25 V, and
cables or twisted single-core cables or b) do not cause danger or damage to property

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

insulated conductors, or when the cables are carrying short-circuit
– the conductors in parallel are non-twisted current.
single-core cables or insulated conductors
in trefoil or flat formation and have a 5.2.7 Cross-sectional areas of conductors
cross-sectional area less than or equal to 5.2.7.1 For mechanical reasons, the cross-sectional area
50 mm 2 in copper or 70 mm 2 in of line conductors in a.c. circuits and of live conductors
aluminium, or in d.c. circuits shall be not less than the values given in
– if the conductors in parallel are non- Table 9.
twisted single-core cables or insulated
5.2.7.2 Cross-sectional area of the neutral conductor
conductors in trefoil or in flat formation
and have a cross-sectional area greater In the absence of more precise information, the
than 50 mm2 in copper or 70 mm2 in following shall apply.
aluminium, the special configuration
5.2.7.2.1 The cross-sectional area of the neutral
necessary for such formations is adopted.
conductor, if any, shall be at least equal to the cross-
These configurations consist of suitable
sectional area of the line conductors:
groupings and spacings of the different
phases or poles (see Annex Z). a) in single-phase circuits with two conductors,
or whatever be the cross-sectional area of
b) special consideration shall be given to the load conductors;
current sharing to meet the requirements b) in multi-phase circuits where the cross-
of 5.2.6.1. sectional area of the line conductors is less
than or equal to 16 mm2 copper or 25 mm2
This subclause does not preclude the use of ring final aluminium;
circuits either with or without spur connections.
c) in three-phase circuits likely to carry third
Where adequate current sharing cannot be achieved or harmonic currents and odd multiples of third
where four or more conductors have to be connected harmonic currents and the total harmonic
in parallel, consideration shall be given to the use of distortion is between 15 percent and 33 percent.
busbar trunking. NOTE — Such harmonic levels are to be met, for
instance, in circuits feeding luminaires, including
5.2.6.8 Variation of installation conditions along a
discharge lamps, such as fluorescent lighting.
route
5.2.7.2.2 Where the third harmonic and odd multiples
Where the heat dissipation differs in one part of a route
of third harmonic currents is higher than 33 percent,
to another, the current-carrying capacity shall be
total harmonic distortion, it may be necessary to
determined so as to be appropriate for the part of the
increase the cross-sectional area of the neutral
route having the most adverse conditions.
conductor (see 5.2.6.6.3 and Annex V).
NOTE — This requirement can normally be neglected if heat
dissipation only differs where the wiring is going through a NOTES
wall of less than 0.35 m. 1 These levels occur for instance in circuits dedicated to IT
applications.

100
 IS 732 : 2019

Table 9 Minimum Nominal Cross-Sectional Area of Conductors

(Clause 5.2.7.1)

Sl Type of Wiring System Use of the Circuit Conductor

No. Material Minimum Permissible Nominal Cross
Sectional Area mm2
(1) (2) (3) (4) (5)
i) Cables and insulated Lighting circuits Cu 1.5
conductors Power circuits Cu 2.5
Al 10.0 (see Note 1)
Signalling and control circuits Cu 0.5 (see Note 2)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ii) Bare Conductors Power circuits Cu 10
Al 16
Signalling and control circuits Cu 4
iii) Flexible connections with For a specific appliance Cu As specified in the relevant Indian Standard
insulated conductors and For any other application 0.5 (see Note 2)
cables
Extra low voltage circuits for 0.5

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

special applications

NOTES
1 Connectors used to terminate aluminium conductors shall be tested and approved for this specific use.
2 In multi-core flexible cables containing 7 or more cores and in signalling control circuits intended for electronic equipment a minimum
nominal cross sectional area of 0.1 mm is permitted.

a) For multi-core cables, the cross-sectional area of the line drop between the origin of the consumer’s installation
conductors is equal to the cross-sectional area of the neutral
and the equipment should not be greater than that given
conductor, this cross-sectional area being chosen for the neutral
in Table 47.
to carry 1.45 × IB of the line conductor.
b) For single-core cables, the cross-sectional area of the line NOTE — Other considerations include start-up time for motors
conductors may be lower than the neutral cross-sectional and equipment with high inrush current. Temporary conditions
area, the calculation being made : such as voltage transients and voltage variation due to abnormal
operation may be disregarded.
– for the line: at IB
– for the neutral: at a current equal to 1.45 IB of the line. 5.2.9 Electrical Connections
2 See 4.4.4 for an explanation of IB.
5.2.9.1 Connections between conductors and between
5.2.7.2.3 For polyphase circuits where the cross- conductors and other equipment shall provide durable
sectional areaof line conductorsisgreater than 16 mm2 electrical continuity and adequate mechanical strength
copper or 25 mm2 aluminium, the cross-sectional area and protection.
of the neutral conductor may be lower than the cross-
NOTE — See IEC 61200-52.
sectional area of the line conductors if the following
conditions are fulfilled simultaneously: 5.2.9.2 The selection of the means of connection shall
take account of, as appropriate:
a) the load carried by the circuit in normal service
is balanced between the phases and the third a) the material of the conductor and its insulation;
harmonic and odd multiples of third harmonics b) the number and shape of the wires forming
currents do not exceed 15 percent of the line the conductor;
conductor current; c) the cross-sectional area of the conductor; and
NOTE — Usually, the reduced neutral cross-sectional area
is not lower than 50 percent of the line conductor cross- d) the number of conductors to be connected
sectional area. together.
b) the neutral conductor is protected against NOTES
overcurrents according to 4.4.2.2; and 1 The use of soldered connections should be avoided,
c) the cross-sectional area of the neutral except in communication circuits. If used, the
connections should be designed to take account of creep
conductor is not less than 16 mm2 copper or and mechanical stresses and temperature rise under fault
25 mm2 aluminium. conditions (see 5.2.5.6, 5.2.5.7 and 5.2.5.8).
2 Applicable standards include the IEC 60998 series,
5.2.8 Voltage Drop in Consumers’ Installations IEC 60947 (all Parts ) and IEC 61535.
In the absence of any other consideration, the voltage 3 Terminals without the marking “r” (only rigid
conductors), “f” (only flexible conductors), “s” or “sol”

101
IS 732 : 2019

(only solid conductors) are suitable for the connection connection and junction points which are subject in
of all types of conductors.
service to a relative movement between the soldered
5.2.9.3 All connections shall be accessible for and the non-soldered part of the conductor.
inspection, testing and maintenance, except for the NOTE — Fine and very fine wire is in accordance with
following: IEC 60228, Class 5 and Class 6.

a) joints designed to be buried in the ground; 5.2.9.9 Cores of sheathed cables from which the sheath
b) compound-filled or encapsulated joints; has been removed and non-sheathed cables at the
termination of conduit, ducting or trunking shall be
c) connections between a cold tail and the heating
enclosed as required by 5.2.9.5.
element as in ceiling heating, floor
heating and trace heating systems; 5.2.10 Selection and Erection of Wiring Systems to
d) a joint made by welding, soldering, brazing Minimize the Spread of Fire

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
or appropriate compression tool; and 5.2.10.1 Precautions within a fire-segregated
e) joint forming part of the equipment compartment
complying with the appropriate product
5.2.10.1.1 The risk of spread of fire shall be minimized
standard.
by the selection of appropriate materials and erection

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — A compound filled joint is, for example, a in accordance with 5.2.10.
resin filled joint.
5.2.10.1.2 Wiring systems shall be installed so that the
5.2.9.4 Where necessary, precautions shall be taken so general building structural performance and fire safety
that the temperature attained by connections in normal are not reduced.
service shall not impair the effectiveness of the
insulation of conductors connected to them or 5.2.10.1.3 Cables complying with, at least, the
supporting them. requirements of IEC 60332-1-2 and products classified
as non-flame propagating may be installed without
5.2.9.5 Conductor connections (not only final but also special precautions.
intermediate connections) shall only be made in suitable
NOTE — In installations where a particular risk is identified,
enclosures, for example, in connection boxes, outlet cables complying with the more onerous tests for bunched cables
boxes, or in equipment if the manufacturer has provided described in the IEC 60332-3 series may be necessary.
space for this purpose. In this case, equipment shall be
used where fixed connection devices are provided or 5.2.10.1.4 Cables not complying, as a minimum, with
provision has been made for the installation of the resistance to the flame propagation requirements
connection devices. At the termination of final circuits of IEC 60332-1-2 shall, if used, be limited to short
conductors shall be terminated in an enclosure. lengths for connection of appliances to permanent
wiring systems and shall, in any event, not pass from
5.2.9.6 Connections and junction points of cables and one fire-segregated compartment to another.
conductors shall be relieved from mechanical stress.
Strain relief devices shall be designed so as to avoid 5.2.10.1.5 Products classified as non-flame propagating
any mechanical damage to the cables or conductors. as specified in IS 8623 (Part 2), IEC 61537 and in the
following series: IS 14297 (Part 1) and (Part 2/
5.2.9.7 Where a connection is made in an enclosure, Section 1), IS 14930 (Parts 1 & 2) and IEC 61534, may
the enclosure shall provide adequate mechanical be installed without special precautions. Other products
protection and protection against relevant external complying with standards having similar requirements
influences. for resistance to flame propagation may be installed
5.2.9.8 Connection of multi-wire, fine wire and very without special precautions.
fine wire conductors 5.2.10.1.6 Parts of wiring systems other than cables
5.2.9.8.1 In order to protect against the separation or not classified as non-flame propagating, as specified
spreading of individual wires of multi-wire, fine wire in IS 8623 (Part 2), IEC 60570, IEC 61537 and in the
or very fine wire conductors, suitable terminals shall following series: IS 14297 (Part 1) and
be used or the conductor ends shall be suitably treated. (Part 2/Section 1), IS 14930 (Parts 1 & 2) and
IEC 61534, but which comply in all other respects with
5.2.9.8.2 Soldering of the whole conductor end of multi- the requirements of their respective product standards
wire, fine wire and very fine wire conductors is shall, if used, be completely enclosed in suitable
permitted if suitable terminals are used. non-combustible building materials.
5.2.9.8.3 Soldered (tinned) conductor ends on fine wire 5.2.10.2 Sealing of wiring system penetrations
and very fine wire conductors are not permissible at
5.2.10.2.1 Where a wiring system passes through
102
 IS 732 : 2019

elements of building construction such as floors, walls, product standard, if such a standard is prepared.
roofs, ceilings, partitions or cavity barriers, the openings a) They should be compatible with the materials of the
wiring system with which they are in contact.
remaining after passage of the wiring system shall be
b) They should permit thermal movement of the wiring
sealed according to the degree of fire resistance (if any) system without reduction of the sealing quality.
prescribed for the respective element of building c) They should be of adequate mechanical stability to
construction before penetration. withstand the stresses which may arise through damage
to the support of the wiring system due to fire.
NOTES
2 The requirements of 5.2.10.2.5 may be satisfied if:
1 During erection of a wiring system temporary sealing
arrangements may be required. a) either cable cleats, cable ties or cable supports are
installed within 750 mm of the seal and are able to
2 During alteration work, sealing should be reinstated as quickly
withstand the mechanical loads expected following the
as possible.
collapse of the supports on the fire side of the seal to
5.2.10.2.2 Wiring systems which penetrate elements of the extent that no strain is transferred to the seal; or

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
building construction having specified fire resistance b) the design of the sealing system itself provides
adequate support.
shall be internally sealed to the degree of fire resistance
of the respective element before penetration as well as 5.2.11 Proximity of Wiring Systems to other Services
being externally sealed as required by 5.2.10.2.1.
5.2.11.1 Proximity to electrical services

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

5.2.10.2.3 Conduit systems, cable trunking systems and
cable ducting systems classified as non-flame Band I and band II voltage circuits according to
propagating according to the relevant product standard IS 12360 (Part 2) shall not be contained in the same
and having a maximum internal cross-section area of wiring system unless one of the following methods is
710 mm2 need not be internally sealed provided that: adopted:

a) the system satisfies the test of IS/ IEC 60529 a) every cable or conductor is insulated for the
for IP33; and highest voltage present; or
b) any termination of the system in one of the b) each conductor of a multicore cable is
compartments, separated by the building insulated for the highest voltage present in the
construction being penetrated, satisfies the test cable; or
of IS/IEC 60529 for IP33. c) the cables are insulated for their system
voltage and installed in a separate
5.2.10.2.4 No wiring system shall penetrate an element compartment of a cable ducting or cable
of building construction which is intended to be load trunking system; or
bearing unless the integrity of the load bearing element
d) the cables are installed on a cable tray system
can be assured after such penetration.
where physical separation is provided by a
5.2.10.2.5 Sealing arrangements intended to partition; or
satisfy 5.2.10.2.1 or 5.2.10.2.2 shall resist external e) a separate conduit, trunking or ducting system
influences to the same degree as the wiring system with is employed.
which they are used, and in addition, they shall meet
all of the following requirements: For SELV and PELV systems the requirements of 4.2.14
shall apply.
a) they shall be resistant to the products of
NOTES
combustion to the same extent as the elements
1 Special considerations concerning electrical interference, both
of building construction which have been electromagnetic and electrostatic, may apply to telecommuni-
penetrated; cation circuits, data transfer circuits and the like.
b) they shall provide the same degree of 2 In the case of proximity of wiring systems and lightning
protection systems, the IS/IEC 62305 series should be
protection from water penetration as that
considered.
required for the building construction element
in which they have been installed; 5.2.11.2 Proximity of communications cables
c) the seal and the wiring system shall be In the event of crossing or proximity of underground
protected from dripping water which may telecommunication cables and underground power
travel along the wiring system or which cables, a minimum clearance of 100 mm shall be
may otherwise collect around the seal unless maintained, or the requirements according to (a) or (b)
the materials used in the seal are all resistant shall be fulfilled:
to moisture when finally assembled for use.
a) a fire-retardant partition shall be provided
NOTES
between the cables, for example, bricks, cable
1 These requirements may be transferred to an IEC
protecting caps (clay, concrete), shaped blocks

103
IS 732 : 2019

(concrete), or additional protection provided shall be made so that the protective measure can be
by cable conduit or troughs made of fire- reinstated without reduction of the degree of protection
retardant materials, or originally intended.
b) for crossings, mechanical protection between 5.2.12.3 Provision shall be made for safe and adequate
the cables shall be provided, for example, access to all parts of the wiring system which may
cable conduit, concrete cable protecting caps require maintenance.
or shaped blocks.
NOTE — In some situations, it may be necessary to provide
5.2.11.3 Proximity to non-electrical services permanent means of access by ladders, walkways, etc.

5.2.11.3.1 Wiring systems shall not be installed in the 5.3 Selection and Erection of Electrical
vicinity of services which produce heat, smoke or fumes Equipment— Isolation, Switching and Control
likely to be detrimental to the wiring, unless it is suitably

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
protected from harmful effects by shielding arranged 5.3.1 General and Common Requirements
so as not to affect the dissipation of heat from the wiring. This standard shall provide compliance with the
In areas not specifically designed for the installation measures of protection for safety, the requirements for
of cables, for example, service shafts and cavities, the proper functioning for intended use of the installation,
and the requirements appropriate to the external

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

cables shall be laid so that they are not exposed to any
harmful influence by the normal operation of the influences foreseen. Every item of equipment shall be
adjacent installations (for example, gas, water or steam selected and erected so as to allow compliance with
lines). the rules stated in the following clauses of this part and
the relevant rules in other parts of this standard.
5.2.11.3.2 Where a wiring system is routed below
services liable to cause condensation (such as water, The requirements of this part are supplementary to the
steam or gas services), precautions shall be taken to common rules given in 5.1.
protect the wiring system from deleterious effects. 5.3.1.1 The moving contacts of all poles of multi-pole
5.2.11.3.3 Where electrical services are to be installed devices shall be so coupled mechanically that they make
in proximity to non-electrical services they shall be so and break substantially together, except that contacts
arranged that any foreseeable operation carried out on solely intended for the neutral may close before and
the other services will not cause damage to the electrical open after the other contacts.
services or the converse. 5.3.1.2 Except as provided in 5.3.7.3.2.7, in multiphase
NOTE — This may be achieved by: circuits, single-pole devices shall not be inserted in the
a) suitable spacing between the services; or neutral conductor.
b) the use of mechanical or thermal shielding.
In single-phase circuits single-pole devices shall not
5.2.11.3.4 Where an electrical service is located in close be inserted in the neutral conductor, unless a residual
proximity to non-electrical services, both the following current device complying with the rules of 4.2.13 is
conditions shall be met: provided on the supply side.
a) wiring systems shall be suitably protected 5.3.1.3 Devices embodying more than one function
against hazards likely to arise from the shall comply with all the requirements of this part
presence of the other services in normal use; appropriate to each separate function.
and
5.3.2 Devices for Protection against Indirect Contact
b) fault protection shall be afforded in by Automatic Disconnection of Supply
accordance with the requirements of 4.2.13,
non-electrical metallic services being 5.3.2.1 Overcurrent protective devices
considered as extraneous-conductive-parts. 5.3.2.1.1 TN systems
5.2.11.3.5 No wiring system shall be run in a lift (or In TN systems overcurrent protective devices shall be
hoist) shaft unless it forms part of the lift installation. selected and erected according to the conditions
5.2.12 Selection and Erection of Wiring Systems in specified in 4.4.5.2, 4.4.2 and in 5.3.4.3 for devices
Relation to Maintainability, Including Cleaning for protection against short-circuit, and shall satisfy the
requirements of 4.2.11.3.
5.2.12.1 With regard to maintainability, reference shall
be made to 4.1.5.13. 5.3.2.1.2 TT systems

5.2.12.2 Where it is necessary to remove any protective Under consideration.

measure in order to carry out maintenance, provision

104
 IS 732 : 2019

5.3.2.1.3 IT systems a) protection against indirect contact according

to 4.2.13.1 is ensured even in the case of
Where exposed conductive parts are interconnected,
failure of the auxiliary supply; and
overcurrent protective devices for protection in the
event of a second fault shall comply with 5.3.1.1 taking b) the devices are installed in installations
into account the requirements of 4.2.11.6. operated, tested and inspected by instructed
persons (BA4) or skilled persons (BA5).
5.3.2.2 Residual current protective devices
5.3.2.2.3 TN systems
5.3.2.2.1 General conditions of installation
If for certain equipment or for certain parts of the
Residual current protective devices in d.c. systems shall installation, one or more of the conditions stated
be specially designed for detection of d.c. residual in 4.2.13.1.3 cannot be satisfied, those parts may be
currents, and to break circuit currents under normal protected by a residual current protective device. In

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
conditions and fault conditions. this case, exposed conductive parts need not be
5.3.2.2.1.1 A residual current protective device shall connected to the TN earthing system protective
ensure the disconnection of all live conductors in the conductor, provided that they are connected to an earth
circuit protected. In TN-S systems, the neutral need electrode affording a resistance appropriate to the
not be disconnected if the supply conditions are such operating current of the residual current protective

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

that the neutral conductor can be considered to be device. The circuit thus protected is to be treated as a
reliably at earth potential. TT system.
NOTE —The conditions for verification that the neutral If, however, no separate earth electrode exists,
conductor is reliably at earth potential are under consideration. connection of the exposed conductive parts to the
5.3.2.2.1.2 No protective conductor shall pass through protective conductor needs to be made on the source
the magnetic circuit of a residual current protective side of the residual current protective device.
device. 5.3.2.2.4 TT systems
5.3.2.2.1.3 Residual current protective devices shall be If an installation is protected by a single residual current
so selected, and the electrical circuits so subdivided, protective device, this shall be placed at the origin of
that any earth-leakage current which may be expected the installation, unless the part of the installation
to occur during normal operation of the connected between the origin and the device complies with the
load(s) will be unlikely to cause unnecessary tripping
requirement for protection by the use of class II
of the device.
equipment or equivalent insulation (see 4.2.13.2).
NOTE — Residual current protective devices may operate at
NOTE — Where there is more than one origin, this requirement
any value of residual current in excess of 50 percent of the
rated operating current. applies to each origin.

5.3.2.2.1.4 Influence of d.c. components 5.3.2.2.5 IT systems

Under consideration. Where protection is provided by a residual current

protective device, and disconnection following a first
5.3.2.2.1.5 The use of a residual current protective fault is not envisaged, the residual non-operating current
device associated with circuits not having a protective of the device shall be at least equal to the current which
conductor, even if the rated operating residual current circulates on the first fault to earth of negligible
does not exceed 30 mA, shall not be considered as a impedance affecting a phase conductor.
measure sufficient for protection against indirect
contact. 5.3.2.3 Insulation monitoring devices

5.3.2.2.2 Selection of devices according to their NOTE — Insulation monitoring devices may operate with an
appropriate response time.
method of application
An insulation monitoring device provided is, a device
5.3.2.2.2.1 Residual current protective devices may or
continuously monitoring the insulation of an electrical
may not have an auxiliary source, taking into account
installation. It is intended to indicate a significant
the requirements of 5.3.2.2.2.2.
reduction in the insulation level of the installation to
NOTE — The auxiliary source may be the supply system. allow the cause of this reduction to be found before the
5.3.2.2.2.2 The use of residual current protective occurrence of a second fault, and thus avoid
devices with an auxiliary source not operating disconnection of the supply.
automatically in the case of failure of the auxiliary Accordingly, it is set at a value below that specified
source is permitted only if one of the two following in 6.2.3.3 appropriate to the installation concerned.
conditions is fulfilled:

105
IS 732 : 2019

Insulation monitoring devices shall be so designed or 5.3.4.3 Selection of devices for protection of wiring
installed that it shall be possible to modify the setting systems against short circuits
only by the use of a key or a tool.
The application of the rules of 4.4 for short-circuit
5.3.3 Devices for Protection against Thermal Effects duration up to 5 s shall take into account minimum and
maximum short-circuit conditions.
Under consideration.
NOTE — Pending this consideration, reference should be made
Where the standard covering a protective device
to 705.422 of IEC 60364-7-705. specifies both a rated service short-circuit breaking
capacity, and a rated ultimate short-circuit breaking
5.3.4 Devices for Protection against Overcurrent capacity, it is permissible to select the protective device
5.3.4.1 General requirements on the basis of the ultimate short-circuit breaking
capacity for the maximum short-circuit conditions.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5.3.4.1.1 Fuse bases using screw-in fuses shall be Operational circumstances may, however, make it
connected so that the centre contact is on the supply desirable to select the protective device on the service
side of the fuse base. short-circuit breaking capacity, for example, where a
5.3.4.1.2 Fuse bases for plug-in fuse carriers shall be protective device is placed at the origin of the
arranged so as to exclude the possibility of the fuse installation.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

carrier making contact between conductive parts 5.3.5 Devices for Protection against Overvoltage
belonging to two adjacent fuse bases.
5.3.5.1 General
5.3.4.1.3 Fuses having fuse-links likely to be removed
or placed by persons other than instructed (BA4) or This clause contains provisions for the application of
skilled persons (BA5), shall be of a type which complies voltage limitation to obtain an insulation coordination
with the safety requirements of IEC 60269-3. in the cases described in 4.5, IS 15382 (Part 1), IEC
61312-2 and IEC 61643-12.
Fuses or combination units having fuse-links likely to
be removed and replaced only by instructed persons This clause gives the requirements for the selection and
(BA4) or skilled persons (BA5), shall be installed in erection of:
such a manner that it is ensured that the fuse-links can a) surge protective devices (SPDs) for electrical
be removed or placed without unintentional contact installations of buildings to obtain a limitation
with live parts. of transient overvoltages of atmospheric origin
5.3.4.1.4 Where circuit-breakers may be operated by transmitted via the supply distribution system
persons other than instructed persons (BA4) or skilled and against switching overvoltages; and
persons (BA5), they shall be so designed or installed b) SPDs for the protection against transient
that it shall not be possible to modify the setting of the overvoltages caused by direct lightning strokes
calibration of their overcurrent releases without a or lightning strokes in the vicinity of buildings,
deliberate act involving the use of a key or tool, and protected by a lightning protection system.
resulting in a visible indication of their setting or
This clause does not take into account surge protective
calibration.
components which may be incorporated in the
5.3.4.2 Selection of devices for protection of wiring appliances connected to the installation. The presence
systems against overloads of such components may modify the behaviour of the
main surge protective device of the installation and may
The nominal current (or current setting) of the
need an additional coordination.
protective device shall be chosen in accordance
with 4.4.4.1. This clause applies to a.c. power circuits. For d.c. power
NOTE — In certain cases, to avoid unintentional operation, circuits, the requirements in this clause may be applied
the peak current values of the loads have to be taken into as far as is useful. For special applications, other or
consideration. In the case of a cyclic load, the values of In and additional requirements may be necessary in
I2 shall be chosen on the basis of values of IB and Iz for the IEC 60364-7.
thermally equivalent constant load
where 5.3.5.2 Selection and erection of SPDs in building
IB = the current for which the circuit is designed; installations
IZ = the continuous current-carrying capacity of the cable;
In = the nominal current of the protective device; and
5.3.5.2.1 Use of SPDs
I2 = the current ensuring effective operation of the protective The protection against overvoltages of atmospheric
device.
origin (caused by indirect, distant lightning strokes) and
switching overvoltages are included in 4.5.3. This

106
 IS 732 : 2019

protection is normally provided by the installation of conductor and either the main earthing
test class II SPDs and if necessary test class III SPDs. terminal or the protective conductor,
whichever route is shorter – connection
When required in accordance with 4.5 or otherwise
type 2.
specified, SPDs shall be installed near the origin of the
NOTE — If a line conductor is earthed, it is considered
installation or in the main distribution assembly, closest to be equivalent to a neutral conductor for the application
to the origin of the installation inside the building. of this subclause.

The protection against the effects of direct lightning SPDs at or near the origin of the installation are, in
strokes or strokes near to the supply system are included general, installed as shown in Annexes AA, BB and
in IEC 61312-1 which, also describes the correct CC and according to Table 10.
selection and application of SPDs according to the
Lightning Protection Zones (LPZ) concept. The LPZ 5.3.5.2.3 Selection of surge protective devices (SPDs)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
concept describes the installation of test class I, test The SPDs shall comply with IEC 61643-1. Additional
class II and test class III SPDs. information regarding selection and application is given
When required in accordance with IEC 61312-1 or in IEC 61643-12.
otherwise specified, SPDs shall be installed at the origin 5.3.5.2.3.1 Selection with regard to protection level

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

of the installation. (Up)
Additional SPDs may be necessary to protect sensitive The protection level Up of SPDs shall be selected in
equipment. Such SPDs shall be coordinated with the accordance with impulse withstand voltage category II
SPDs installed upstream (see 5.3.5.2.3.6). of Table 6 (see also 4.5).
In the case where SPDs are part of the fixed electrical If IEC 61312-1 requires SPDs for the protection against
installation, but not mounted inside a distribution board overvoltages caused by direct lightning strokes, the
(for example, in a socket outlet), their presence shall protection level of these SPDs shall also be selected in
be indicated by a label on or as near as is reasonably accordance with impulse withstand voltage category II
possible to the origin of the circuit under consideration. of Table 6 (see 4.4).
5.3.5.2.2 Connection of SPDs For example in 230/400 V installations, the protection
Surge protective devices at or near the origin of the level Up shall not exceed 2.5 kV.
installation shall be connected at least between the When connection type 2 according to 5.3.5.2.2 is used,
following points (see Annexure AA, BB and CC): the above requirements also apply to the total protection
a) if there is a direct connection between the level between line conductors and PE.
neutral conductor and the PE at or near the When the required protection level cannot be reached
origin of the installation or if there is no neutral with a single set of SPDs, additional, coordinated SPDs
conductor: shall be applied to ensure the required protection level.
— between each line conductor and either
5.3.5.2.3.2 Selection with regard to continuous
the main earthing terminal or the main
operating voltage (Uc)
protective conductor, whichever is the
shortest route; The maximum continuous operating voltage Uc of SPDs
NOTE — The impedance connecting the neutral to the shall be equal to or higher than shown in the following
PE in IT systems is not considered as a connection. Table 11.
b) if there is no direct connection between the
neutral conductor and the PE at or near the 5.3.5.2.3.3 Selection with regard to temporary
origin of the installation, then either overvoltages (TOVs)
— between each line conductor and either The SPDs selected according to 5.3.5.2.3 shall
the main earthing terminal or the main withstand the temporary overvoltages due to faults
protective conductor, and between the within low-voltage systems (see 4.5.2).
neutral conductor and either the main
This is confirmed by the selection of SPDs which
earthing terminal or the protective
comply with the relevant test requirements of 7.7.6 of
conductor, whichever is the shortest route
IS/IEC 61643-1.
–connection type 1;
or To fail safely in case of TOVs due to earth faults within
the high-voltage system (see 4.5.2), the SPDs connected
— between each line conductor and the to the PE shall pass the test of 7.7.4 of IS/IEC 61643-1.
neutral conductor and between the neutral

107
IS 732 : 2019

Table 10 Connection of Surge Protective Devices Dependent on System Configuration

(Clause 5.3.5.2.2)

System Configuration at the Installation Point of SPD

TT TN-C TN-S IT with distributed neutral
SPDs Connected IT without
Between Installation according to Installation according to Installation according to distributed
Connection Connection Connection Connection Connection Connection neutral
Type 1 Type 2 Type 1 Type 2 Type 1 Type 2
Each line conductor + . NA + . + . NA
and neutral conductor
Each line conductor . NA NA . NA . NA .
and PE conductor
Neutral conductor and . . NA . . . . NA

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
PE conductor
Each line conductor NA NA . NA NA NA NA NA
and PEN conductor
Line conductors + + + + + + + +
.— mandatory
NA — not applicable

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

+ — optional, in addition

Table 11 Minimum Required Uc of the SPD Dependent on Supply System Configuration

(Clause 5.3.5.2.3.2)

SPDs Connected System Configuration of Distribution Network

Between TT TN-C TN-S IT with distributed IT without
neutral distributed neutral
Line conductor and neutral conductor 1.1 Uo NA 1.1Uo 1.1 Uo NA
Each line conductor and PE conductor 1.1 Uo NA 1.1 Uo √3Uo 1)
Line-to-line
voltage1)
Neutral conductor and PE conductor Uo 1) NA Uo 1) Uo 1) NA
Each line conductor and PEN conductor NA 1.1 Uo NA NA NA
NA — not applicable
NOTES
1 Uo is the line-to-neutral voltage of the low-voltage system.
2 This table is based on IEC 61643-1 amendment 1.
1)
These values are related to worst case fault conditions, therefore the tolerance of 10 percent is not taken into account.

In addition, SPDs installed in location 4a according to for three-phase systems and 10 kA 8/20 for single-phase
Fig. 89 shall withstand such TOVs as defined in test systems.
of 7.7.4 of IS/IEC 61643-1.
If IEC 61312-1 requires SPDs, the lightning impulse
NOTES current I imp according to IEC 61643-1 shall be
1 Appropriate pass criteria are under consideration to define calculated according to IEC 61312-1. Further
the meaning of withstand.
information is given in IEC 61643-12. If the current
2 The loss of neutral is not covered by these requirements.
Though there is currently no specific test in IS/IEC 61643-1,
value cannot be established, the value of Iimp shall not
SPDs are expected to fail safely. be less than 12.5 kA for each mode of protection.
5.3.5.2.3.4 Selection with regard to discharge current In case of an installation according to 5.3.5.2.2
(In) and impulse current (Iimp) connection type 2, the lightning impulse current Iimp
for the surge protective device connected between the
If 4.5.3 requires SPDs, the nominal discharge current neutral conductor and the PE shall be calculated
In shall not be less than 5 kA 8/20 for each mode of similarly to the above mentioned standards. If the
protection. current value cannot be established the value of Iimp
In case of installation according to 5.3.5.2.2 connection shall not be less than 50 kA for three-phase systems
type 2, the nominal discharge current In for the surge and 25 kA for single-phase systems.
protective device connected between the neutral When a single SPD is used for protection according to
conductor and the PE shall not be less than 20 kA 8/20 both 7.7.4 and IEC 61312-1, the rating of In and of Iimp

108
 IS 732 : 2019

shall be in agreement with the above values. may be given either to the continuity of supply or to
the continuity of protection.
5.3.5.2.3.5 Selection with regard to the expected short-
circuit current In all cases, the discrimination between protective
devices shall be ensured.
The short-circuit withstand of the SPDs (in case of SPD
failure) together with the specified associated (internal – If protective devices are installed in the surge
or external) overcurrent protective device shall be equal protective device circuit, the continuity of the
to or higher than the maximum short-circuit current supply is ensured, but neither the installation
expected at the point of installation taking into account nor the equipment is protected against possible
the maximum overcurrent protective devices specified further overvoltages (see Fig. 56). These
by the SPD manufacturer. protective devices may be internal
disconnectors.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
In addition, when a follow current interrupting rating
is declared by the manufacturer, it shall be equal to or – If protective devices are inserted in the
higher than the expected short-circuit current at the installation upstream of the circuit where
point of installation. SPDs are installed, the failure of the surge
protective device may cause interruption of
SPDs connected between the neutral conductor and the supply: the circuit interruption will last until

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

PE in TT- or TN-systems, which allow a power the surge protective device is replaced
frequency follow-up current after operation (for (see Fig. 57).
example, spark gaps) shall have a follow current
interrupting rating greater or equal to 100 A.
In IT systems, the follow current interrupting rating
for SPDs connected between the neutral conductor and
the PE shall be the same as for SPDs connected between
phase and neutral.
5.3.5.2.3.6 Co-ordination of SPDs
According to IEC 61312-3 and IEC 61643-12,
considerations shall be taken regarding the necessary
co-ordination of SPDs in the installation. The SPD
manufacturers shall provide sufficient information in
their documentation about the way to achieve
coordination between SPDs.
5.3.5.2.4 Protection against overcurrent and
consequences of an SPD failure
PD — protective device of the SPD
Protection against SPD’s short-circuits is provided by SPD— surge protective device
the overcurrent protective devices F2 (see figures in E/I — equipment or installation to be protected against
Annexure AA, BB, CC and DD) which are to be overvoltages
selected according to the maximum recommended FIG. 56 P RIORITY TO THE CONTINUITY OF SUPPLY
rating for the overcurrent protective device given in
the manufacturer’s SPD instructions.
If the overcurrent protective devices F1 (which are part
of the installation, see figures in Annexure AA, BB,
CC and DD) have a rating smaller than or equal to the
maximum recommended rating for the overcurrent
protective devices F2, then F2 can be omitted.
The cross-sectional area of conductors connecting the
overcurrent protective devices to the line conductors
shall be rated according to the maximum possible short-
circuit current (F1, F2 and F3 are shown in Annexure
AA, BB, CC and DD).
FIG. 57 PRIORITY TO THE CONTINUITY
Depending on the location of protective devices used
OF P ROTECTION
to disconnect the SPD in case of SPD failure, priority

109
IS 732 : 2019

In order to increase the reliability and the probability RCD with or without time delay, but having an
of having at the same time continuity of supply and immunity to surge currents of at least 3 kA 8/20 shall
continuity of protection, it is permitted to use the be used.
scheme described in Fig. 58. NOTES
1 S-type RCDs in accordance with IS 12640 (Part 1) and
IS 12640 (Part 2) satisfy this requirement.
2 In the case of surge current higher than 3 kA 8/20, the RCD
may trip causing interruption of the power supply.

5.3.5.2.7 Measurement of the insulation resistance

During the measurement of the insulation resistance of
the installation according to 6, SPDs installed at or near

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
the origin of the installation or in a distribution board
and not rated for the test voltage of the insulation
measurement may be disconnected.
In the case where SPDs connected to the PE conductor
FIG. 58 COMBINATION OF CONTINUITY OF SUPPLY AND are part of a socket outlet, they shall withstand the test

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

CONTINUITY OF P ROTECTION voltage for measuring the insulation resistance
according to 6.
In this case, two identical SPDs (SPD1 and SPD2) are
connected to two identical protective devices (PD1 and 5.3.5.2.8 SPD status indication
PD 2). The failure mode of one of the SPDs (for
Indication that the SPD no longer provides overvoltage
example, SPD1) will not influence the effectiveness of protection shall be provided,
the second SPD (for example, SPD2) and will lead to
the operation of its own protective device (for example, a) either by an SPD status indicator, and
PD1). Such an arrangement will significantly increase b) or by a separate SPD protective device such
the probability of having continuity of supply and as addressed in 5.3.5.2.4.
continuity of protection.
5.3.5.2.9 Connecting conductors
5.3.5.2.5 Protection against indirect contact Connecting conductors are the conductors from the line
Protection against indirect contact, as defined in 4.2, conductor to the surge protective device and from the
shall remain effective in the protected installation even surge protective device to the main earthing terminal
in case of failures of SPDs. or to the protective conductor.

In case of automatic disconnection of supply: Because increasing the length of the connecting
conductors of SPDs reduces the effectiveness of
a) in TN systems this may, in general, be fulfilled overvoltage protection, optimum overvoltage
by the overcurrent device on the supply side protection is achieved when all connecting conductors
of the surge protective device; of SPDs are as short as possible (preferably not
b) in TT systems this may be fulfilled by either, exceeding 0.5 m for the total lead length) and without
1) the installation of SPDs on the load side any loops (see Fig. 59). If distance a + b (see Fig. 59)
of an RCD (seeFig. 90), or cannot be reduced below 0.5 m, the scheme in Fig. 60
may be adopted.
2) the installation of SPDs on the supply side
of an RCD. Because of the possibility of 5.3.5.2.10 Cross-section of earthing conductors
the failure of an SPD between N and PE
The earthing conductors of SPDs at or near the origin
conductors, of the installation shall have a minimum cross-sectional
 the conditions of 4.2.11.5.1 shall be area of 4 mm2 copper or equivalent.
met, and
When there is a lightning protection system, a minimum
 the SPD shall be installed in
cross-sectional area of 16 mm2 copper or equivalent
accordance with 5.3.5.2.2 connection
is necessary for SPDs tested in accordance with test
type 2. class I of IS/IEC 61643-1.
c) in IT systems, no additional measure is
needed. 5.3.6 Co-ordination of various Protective Devices

5.3.5 2.6 SPD installation in conjunction with RCDs 5.3.6.1 Discrimination between overcurrent protective
devices
If SPDs are installed in accordance with 5.3.5.2.1 and
are on the load side of a residual current device, an Under consideration.

110
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
FIG. 59 E XAMPLE OF I NSTALLATION OF SPDS AT OR N EAR THE ORIGIN OF THE INSTALLATION

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

FIG. 60 EXAMPLE OF INSTALLATION OF SPDS AT OR NEAR THE ORIGIN OF THE I NSTALLATION

5.3.6.2 Association of residual current protective conditions even when, due to unbalanced
devices with overcurrent protective devices current or to current flowing to earth, the
residual current protective device itself tends
5.3.6.2.1 Where a residual current protective device is
to open.
incorporated or combined with a device for overcurrent
protection, the characteristics of the assembly of NOTE — The stresses mentioned depend on the
prospective short-circuit current at the point where the
protective devices (breaking capacity, operating
residual current prospective device is installed, and the
characteristics in relation to rated current) shall satisfy operating characteristics of the device providing short-
the rules of 4.4.4, 4.4.5, 5.3.4.2 and 5.3.4.3. circuit protection.

5.3.6.2.2 Where a residual current protective device is 5.3.6.3 Discrimination between residual current
neither incorporated in, nor combined with, a device protective devices
for overcurrent protection:
Discrimination between residual current protective
a) overcurrent protection shall be ensured by devices installed in series may be required for service
appropriate protective devices according to reasons, particularly when safety is involved, to provide
the rules of 4.4; continuity of supply to the parts of the installation not
b) the residual current protective device shall be involved in the fault, if any.
able to withstand without damage the thermal
This discrimination can be achieved by selecting and
and mechanical stresses to which it is likely
erecting residual current protective devices which,
to be subjected in the event of a short-circuit
while ensuring the required protection to the different
occurring on the load side of the location
parts of the installation, disconnect from the supply only
where it is installed; and
that part of the installation that is located on the load
c) the residual current protective device shall not side of the residual current protective device installed
be damaged under these short-circuit
111
IS 732 : 2019

on the supply side of the fault, and closest to it. any equipment from being unintentionally energized.
To ensure discrimination between two residual current NOTE — Such precautions may include one or more of the
following measures:
protective devices in series, these devices shall satisfy
a) padlocking;
both the following conditions:
b) warning notices; and
a) the non-actuating time-current characteristic c) location within a lockable space or enclosure.
of the residual current protective device
located on the supply side (upstream) shall lie Short-circuiting and earthing may be used as a
above the total operating time-current supplementary measure.
characteristic of the residual current protective 5.3.7.3.1.3 Where an item of equipment or enclosure
device located on the load side (downstream), contains live parts connected to more than one supply,
and a warning notice shall be placed in such a position that

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
b) the rated residual operating current on the any person gaining access to live parts will be warned
device located on the supply side shall be of the need to isolate those parts from the various
higher than that of the residual current supplies unless an interlocking arrangement is provided
protective device located on the load side. to ensure that all the circuits concerned are isolated.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

In the case of residual current protective devices 5.3.7.3.1.4 Where necessary, suitable means shall be
complying with the requirements of IS 12640 (Part 1) provided for the discharge of stored electrical energy
and IS 12640 (Part 2), the rated residual operating (see 5.5).
current of the device located on the supply side shall
5.3.7.3.2 Devices for isolation
be at least three times that of the residual current
protective device located on the load side. 5.3.7.3.2.1 The devices for isolation shall effectively
isolate all live supply conductors from the circuit
5.3.7 Isolation and Switching
concerned, subject to the provisions of 5.3.7.2.2.
5.3.7.1 Introduction
Equipment used for isolation shall comply
This clause deals with non-automatic local and remote with 5.3.7.3.2.2 to 5.3.7.3.2.8.
isolation and switching measures which prevent or
5.3.7.3.2.2 Devices for isolation shall comply with the
remove dangers associated with electrical installations
following two conditions:
or electrically powered equipment and machines.
a) withstand in the new, clean and dry condition,
5.3.7.2 General
when in the open position, across the terminals
5.3.7.2.1 According to the intended function(s), every of each pole, the impulse voltage value given
device provided for isolation or switching shall comply in Table 12 in relation to the nominal voltage
with the relevant requirements of this part. of the installation.
NOTE — Greater distances than those corresponding
5.3.7.2.2 In TN-C systems, the PEN conductor shall to the impulse-withstand voltages may be necessary from
not be isolated or switched. In TN-S systems, the neutral consideration of aspects other than isolation.
conductor need not be isolated or switched. b) have a leakage current across open poles not
NOTE — Protective conductors in all systems are required not exceeding:
to be isolated or switched (see also 5.4.3.3.3). – 0.5 mA per pole in the new, clean and dry
5.3.7.2.3 The measures described in this part are not condition, and
alternatives to the protective measures described in 4.2 – 6 mA per pole at the end of the
to 4.5, inclusive. conventional service life of the device as
determined in the relevant standard,
5.3.7.3 Isolation
when tested, across the terminals of each pole,
5.3.7.3.1 General with a voltage value equal to 110 percent of
5.3.7.3.1.1 Every circuit shall be capable of being the phase to neutral value corresponding to
isolated from each of the live supply conductors, except the nominal voltage of the installation. In the
as detailed in 5.3.7.2.2. case of d.c. testing, the value of the d.c. voltage
shall be the same as the r.m.s. value of the a.c.
Provisions may be made for isolation of a group of test voltage.
circuits by a common means, if the service conditions
allow this. 5.3.7.3.2.3 The isolating distance between open
contacts of the device shall be visible or be clearly and
5.3.7.3.1.2 Suitable means shall be provided to prevent reliably indicated by “off” or “open” marking. Such

112
 IS 732 : 2019

Table 12 Impulse-withstand Voltage as a Function of the Nominal Voltage

(Clause 5.3.7.3.2.2)

Nominal Voltage of the Installation1) Impulse-withstand Voltage

for Isolating Devices
kV
Three-Phase Systems Single-Phase Systems Overvoltage Category III Overvoltage Category IV
V with Middle Point
V
230/400, 277/480, 120 – 240 3 5
00/690, 577/1 000 5 8
8 10

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
1)
According to IS 12360.

NOTES
1 As regards transient atmospheric overvoltages no distinction is made between earthed and unearthed systems.
2 The impulse withstand voltages are referred to an altitude of 2 000 m.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

indication shall only occur when the isolating distance 5.3.7.4 Switching-off for mechanical maintenance
between open contacts on each pole of the device has
5.3.7.4.1 General
been attained.
NOTE — The marking required by this subclause may be
5.3.7.4.1.1 Means of switching-off shall be provided
achieved by the use of the symbols “O” and “I” to indicate the where mechanical maintenance may involve a risk of
open and closed positions respectively. physical injury.
5.3.7.3.2.4 Semiconductor devices shall not be used as NOTES
isolating devices. 1 Electrically powered mechanical equipment may include
rotating machines as well as heating elements and
5.3.7.3.2.5 Devices for isolation shall be designed and/ electromagnetic equipment for electrical installations of
or installed so as to prevent unintentional closure. machines).
2 Examples of installations where means for switching-off for
NOTE — Such closure might be caused, for example, by shocks mechanical maintenance are used:
and vibrations.
a) cranes,
5.3.7.3.2.6 Provision shall be made for securing off- b) lifts,
load isolating devices against inadvertent and c) escalators,
unauthorized opening. d) conveyors,
e) machine-tools, and
NOTE — This may be achieved by locating the device in a
f) pumps.
lockable space or enclosure or by padlocking. Alternatively,
the off-load device may be interlocked with a load-breaking 3 Systems powered by other means, for example, pneumatic,
one. hydraulic or steam, are not covered by these rules. In such cases,
switching-off any associated supply of electricity may not be a
5.3.7.3.2.7 Means of isolation shall preferably be sufficient measure.
provided by a multipole switching device which 5.3.7.4.1.2 Suitable means shall be provided to prevent
disconnects all poles of the relevant supply but single- electrically powered equipment from becoming
pole devices situated adjacent to each other are not unintentionally reactivated during mechanical
excluded. maintenance, unless the means of switching-off is
NOTE — Isolation may be achieved, for example, by the continuously under the control of any person
following means: performing such maintenance.
a) disconnectors (isolators), switch-disconnectors, multipole
or single-pole; NOTE — Such means may include one or more of the following
b) plugs and socket outlets; measures:
c) fuse-links; a) padlocking;
b) warning notices; and
d) fuses; and
e) special terminals which do not require the removal of a wire. c) location within a lockable space or enclosure.

5.3.7.3.2.8 All devices used for isolation shall be clearly 5.3.7.4.2 Devices for switching-off for mechanical
identified, for example by marking, to indicate the maintenance
circuit which they isolate. 5.3.7.4.2.1 Devices for switching-off for mechanical

113
IS 732 : 2019

maintenance shall be inserted preferably in the main a) pumping facilities for flammable liquids;
supply circuit. b) ventilation systems;
c) large computers;
Where for this purpose switches are provided, they shall d) discharge lighting with high-voltage supply, for example,
be capable of cutting off the full-load current of the neon signs;
relevant part of the installation. They need not e) certain large buildings, for example department stores;
necessarily interrupt all live conductors. f) electrical testing and research facilities;
g) teaching laboratories;
Interruption of a control circuit of a drive or the like is
h) boiler-rooms;
permitted only where, j) large kitchens.
– supplementary safeguards, such as mechanical
5.3.7.5.1.2 Where a risk of electric shock is involved,
restrainers, or
the emergency switching device shall cut off all live

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
– requirements of an IS specification for the conductors except as provided in 5.3.7.2.2.
control devices used
5.3.7.5.1.3 Means for emergency switching, including
provide a condition equivalent to the direct emergency stopping, shall act as directly as possible
interruption of the main supply. on the appropriate supply conductors.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — Switching-off for mechanical maintenance may be
achieved, for example, by means of: The arrangement shall be such that one single action
a) multipole switches; only will cut off the appropriate supply.
b) circuit breakers; 5.3.7.5.1.4 The arrangement of the emergency
c) control switches operating contactors; and switching shall be such that its operation does not
d) plugs and sockets. introduce a further danger or interfere with the complete
5.3.7.4.2.2 Devices for switching-off for mechanical operation necessary to remove the danger.
maintenance or control switches for such devices shall NOTES
require manual operation. 1 Where this switching includes the function of emergency, in
the case of machines, the relevant requirements are
The clearance between open contacts of the device shall 5.3.7.5.1.5.Means of emergency stopping shall be provided
be visible or be clearly and reliably indicated by “off” where electrically produced movements may give rise to danger.
or “open” marking. Such indication shall only occur 2 Examples of installations where means for emergency
when the “off” or “open” position on each pole of the stopping are used:
a) escalators;
device has been attained.
b) lifts;
NOTE — The marking required by this subclause may be c) elevators;
achieved by the use of the symbols “O” and “I” to indicate the
d) conveyors;
open and closed positions respectively.
e) electrically driven doors;
5.3.7.4.2.3 Devices for switching-off for mechanical f) machine-tools; and
maintenance shall be designed and/or installed so as to g) car-washing plants.
prevent unintentional switching on.
5.3.7.5.1.5 Means of emergency stopping shall be
NOTE — Such switching on might be caused for example by provided where electrically produced movements may
shocks and vibrations.
give rise to danger.
5.3.7.4.2.4 Devices for switching-off for mechanical
NOTE — Examples of installations where means for emergency
maintenance shall be placed and marked so as to be stopping are used:
readily identifiable and convenient for their intended use. a) escalators;
b) lifts;
5.3.7.5 Emergency switching
c) elevators;
5.3.7.5.1 General d) conveyors;
NOTE — Emergency switching may be emergency switching- e) electrically driven doors;
on or emergency switching-off. f) machine-tools; and
g) car-washing plants.
5.3.7.5.1.1 Means shall be provided for emergency
switching of any part of an installation where it may be 5.3.7.5.4.2 Devices for emergency switching
necessary to control the supply to remove an
5.3.7.5.4.2.1 The devices for emergency switching shall
unexpected danger.
be capable of breaking the full-load current of the
NOTE — Examples of installations where means for emergency relevant parts of the installation taking account of
switching (apart from emergency stopping in accordance
stalled motor currents where appropriate.
with 5.3.7.5.1.5) are used:

114
 IS 732 : 2019

5.3.7.5.4.2.2 Means for emergency switching may the neutral conductor.

consist of
5.3.7.6.1.3 In general, all current-using apparatus
a) one switching device capable of directly requiring control shall be controlled by an appropriate
cutting off the appropriate supply, or functional switching device.
b) a combination of equipment activated by a A single-functional switching device may control
single action for the purpose of cutting off the several items of apparatus intended to operate
appropriate supply. simultaneously.
For emergency stopping, retention of the supply may 5.3.7.6.1.4 Plugs and socket-outlets rated at not more
be necessary, for example, for braking of moving parts. than 16 A may be used for functional switching.
NOTE — Emergency switching may be achieved, for example,
5.3.7.6.1.5 Functional switching devices ensuring the

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
by means of:
a) switches in the main circuit, and change-over of supply from alternative sources shall
b) push-buttons and the like in the control (auxiliary) circuit. affect all live conductors and shall not be capable of
putting the sources in parallel, unless the installation is
5.3.7.5.4.2.3 Hand-operated switching devices for specifically designed for this condition.
direct interruption of the main circuit shall be selected

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

where practicable. In these cases, no provision is to be made for isolation
of the PEN or protective conductors.
Circuit-breakers, contactors, etc, operated by remote
control shall open on de-energization of coils, or other 5.3.7.6.2 Functional switching devices
equivalent failure-to-safety techniques shall be 5.3.7.6.2.1 Functional switching devices shall be
employed. suitable for the most onerous duty they may be called
5.3.7.5.4.2.4 The means of operating (handles, push- upon to perform.
buttons, etc) devices for emergency switching shall be 5.3.7.6.2.2 Functional switching devices may control
clearly identified, preferably coloured red with a the current without necessarily opening the
contrasting background. corresponding poles.
5.3.7.5.4.2.5 The means of operating shall be readily NOTES
accessible at places where a danger might occur and, 1 Semiconductor switching devices are examples of devices
where appropriate, at any additional remote position capable of interrupting the current in the circuit but not opening
the corresponding poles.
from which that danger can be removed.
2 Functional switching may be achieved, for example by means
5.3.7.5.4.2.6 The means of operation of a device for of
emergency switching shall be capable of latching or a) switches;
being restrained in the “off” or “stop” position, unless b) semiconductor devices;
both the means of operation for emergency switching c) circuit-breakers;
and for re-energizing are under the control of the same d) contactors;
e) relays; and
person.
f) plugs and socket-outlets up to 16 A.
The release of an emergency switching device shall not
re-energize the relevant part of the installation. 5.3.7.6.2.3 Disconnectors, fuses and links shall not be
used for functional switching.
5.3.7.5.4.2.7 Devices for emergency switching,
including emergency stopping, shall be so placed and 5.3.7.6.3 Control circuits (auxiliary circuits)
marked as to be readily identifiable and convenient for Control circuits shall be designed, arranged and
their intended use. protected to limit dangers resulting from a fault between
5.3.7.6 Functional switching (control) the control circuit and other conductive parts liable to
cause malfunction (for example, inadvertent operations)
5.3.7.6.1 General of the controlled apparatus.
5.3.7.6.1.1 A functional switching device shall be 5.3.7.6.4 Motor control
provided for each part of a circuit which may require
5.3.7.6.4.1 Motor control circuits shall be designed so
to be controlled independently of other parts of the
as to prevent any motor from restarting automatically
installation.
after a stoppage due to a fall in or loss of voltage, if
5.3.7.6.1.2 Functional switching devices need not such starting is liable to cause danger.
necessarily control all live conductors of a circuit.
5.3.7.6.4.2 Where reverse-current braking of a motor
A single-pole switching device shall not be placed in is provided, provision shall be made for the avoidance

115
IS 732 : 2019

of reversal of the direction of rotation at the end of 5.4.2.2 Earth electrodes

braking if such reversal may cause danger.
5.4.2.2.1 The type, materials and dimensions of earth
5.3.7.6.4.3 Where safety depends on the direction of electrodes shall be selected to withstand corrosion and
rotation of a motor, provision shall be made for the to have adequate mechanical strength for the intended
prevention of reverse operation due to, for example, a lifetime (see IS 3043).
reversal of phases. NOTES
NOTE — Attention is called to danger which may arise from 1 For corrosion, the following parameters may be considered:
the loss of one phase. the soil pH at the site, soil resistivity, soil moisture, stray and
leakage a.c. and d.c. current, chemical contamination, and
5.4 Selection and Erection of Electrical Equipment proximity of dissimilar materials. For materials commonly used
—Earthing Arrangements and Protective for earth electrodes, the minimum sizes, from the point of view
of corrosion and mechanical strength, when embedded in the
Conductors

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
soil or in concrete, shall be as specified in IS 3043.
5.4.1 Void 2 The minimum thickness of protective coating is greater for
vertical earth electrodes than for horizontal earth electrodes
5.4.2 Earthing Arrangements because of their greater exposure to mechanical stresses while
being embedded.
5.4.2.1 General requirements If a lightning protection system is required, 5.4 of

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

IS/IEC 62305-3 applies.
5.4.2.1.1 The earthing arrangements may be used jointly
or separately for protective and functional purposes 5.4.2.2.2 The earthing arrangement shall not rely on a
according to the requirements of the electrical metallic pipe for flammable liquids or gases as the earth
installation. The requirements for protective purposes electrode and their buried length shall not be considered
shall always take precedence. when dimensioning the earth electrode.
5.4.2.1.2 Where provided, earth electrodes within an NOTE —This requirement does not preclude the protective
equipotential bonding via the main earthing terminal
installation shall be connected to the main earthing (see 5.4.2.4) of such pipes for compliance with 4.2.
terminal using an earthing conductor.
Where cathodic protection is applied and the exposed-
NOTE — An installation does not need to have its own earth
electrode.
conductive-part of an item of electrical equipment
supplied by a TT system is directly connected to the
5.4.2.1.3 Where the supply to an installation is at high pipe, a metallic pipe for flammable liquids or gases
voltage, requirements concerning the earthing may act as the sole earth electrode for this specific
arrangements of the high voltage supply and of the low- equipment.
voltage installation shall also comply with 4.5.2.
5.4.2.3 Earthing conductors
5.4.2.1.4 The requirements for earthing arrangements
are intended to provide a connection to earth which: 5.4.2.3.1 Earthing conductors shall comply
with 5.4.3.1.1 or 5.4.3.1.2. Their cross-sectional area
a) is reliable and suitable for the protective shall be not less than 6 mm2 for copper or 50 mm2 for
requirements of the installation; steel. Where a bare earthing conductor is buried in the
b) can carry earth fault currents and protective soil, its dimensions and characteristics shall also be in
conductor currents to earth without danger accordance with Table 13.
from thermal, thermo-mechanical and
Where no noticeable fault current is expected to flow
electromechanical stresses and from electric
through the earth electrode (for example, in TN systems
shock arising from these currents;
or IT systems), the earthing conductor may be
c) if relevant, is also suitable for functional dimensioned according to 5.4.4.1.
requirements;
d) is suitable for the foreseeable external Aluminium conductors shall not be used as earthing
influences (see 5.1), for example, mechanical conductors.
stresses and corrosion. NOTE — Where a lightning protection system is connected to
the earth electrode, the cross-sectional area of the earthing
5.4.2.1.5 Consideration shall be given to the earthing conductor should be at least 16 mm² for copper (Cu) or 50 mm²
arrangements where currents with high frequencies are for iron (Fe) (see IS/IEC 62305 series).
expected to flow (see 4.5.4). 5.4.2.3.2 The connection of an earthing conductor to
5.4.2.1.6 Protection against electric shock, as stated an earth electrode shall be soundly made and
in 4.2, shall not be adversely affected by any foreseeable electrically satisfactory. The connection shall be by
change of the earth electrode resistance (for example, exothermic welding, pressure connectors, clamps or
due to corrosion, drying or freezing). other suitable mechanical connectors. Mechanical

116
 IS 732 : 2019

Table 13 Minimum Size of Commonly Used Earth Electrodes, Embedded in Soil or Concrete Used to
Prevent Corrosion and Provide Mechanical Strength
(Clause 5.4.2.3.1)

Material and Surface Shape Diameter Cross- Thickness Weight of Thickness of

Sectional Coating Coating/
Area Sheathing
mm mm2 mm g/m2 µm
(1) (2) (3) (4) (5) (6) (7)
Steel embedded in concrete Round wire 10
(bare, hot galvanized or
stainless) Solid tape or strip 75 3
2)
Strip or shaped strip/plate –

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
90 3 500 63
Solid plate – Lattice plate
Round rod installed vertically 16 350 45
Round wire installed
10 350 45
horizontally
Steel hot-dip galvanized3)
Pipe 25 2 350 45

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Stranded (embedded in
70
concrete)
Cross profile installed
(290) 3
vertically
Steel copper-sheathed Round rod installed vertically (15) 2 000
Round rod installed vertically 14 2505)
Steel with electro-deposited Round wire installed
copper coating (8) 70
horizontally
Strip installed horizontally 90 3 70
Strip2) or shaped strip/plate 90 3
Round rod installed vertically 16
Stainless steel1) Round wire installed
10
horizontally
Pipe 25 2
Strip 50 2
Round wire installed 4
(25) 50
horizontally
Solid round rod installed
(12) 15
vertically
Copper 1.7 for
individual (25)4)
Stranded wire
strands of 50
wire
Pipe 20 2
Solid plate (1.5) 2
Lattice plate 2
NOTE  Values in brackets are applicable for protection against electric shock only, while values not in brackets are applicable for
lightning protection and for protection against electric shock.
1)
Chromium >16 %, Nickel > 5 %, Molybdenum >2 %, Carbon < 0.08 %.
2)
As rolled strip or slit strip with rounded edges.
3)
The coating shall be smooth, continuous and free from flux stains.
4)
Where experience shows that the risk of corrosion and mechanical damage is extremely low, 16 mm² can be used.
5)
This thickness is provided to withstand mechanical damage of copper coating during the installation process. It may be reduced to not
less than 100 µm where special precautions to avoid mechanical damage of copper during the installation process (for example, drilled
holes or special protective tips) are taken according to the manufacturer’s instructions.

connectors shall be installed in accordance with the solder shall not be used independently, as they do not
manufacturer’s instructions. Where a clamp is used, it reliably provide adequate mechanical strength.
shall not damage the electrode or the earthing NOTE — Where vertical electrodes are installed, means may
conductor. be provided to allow the inspection of the connection and there
placement of the vertical rod.
Connection devices or fittings that depend solely on

117
IS 732 : 2019

5.4.2.4 Main earthing terminal 5.4.3 Protective Conductors

5.4.2.4.1 In every installation where protective NOTE — Consideration should be given to requirements given
in 5.1.6.
equipotential bonding is used, a main earthing terminal
shall be provided and the following shall be connected 5.4.3.1 Minimum cross-sectional areas
to it:
5.4.3.1.1 The cross-sectional area of every protective
a) protective bonding conductors; conductor shall satisfy the conditions for automatic
b) earthing conductors; disconnection of supply required in 4.2.11.3.2 and be
c) protective conductors; capable of withstanding mechanical and thermal
d) functional earthing conductors, if relevant. stresses caused by the prospective fault current during
the disconnection time of the protective device.
NOTES

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
1 It is not intended to connect every individual protective The cross-sectional area of a protective conductor shall
conductor directly to the main earthing terminal where they either be calculated in accordance with 5.4.3.1.2, or
are connected to this terminal by other protective conductors. selected in accordance with Table 14. In either case,
2 The main earthing terminal of the building can generally be the requirements of 5.4.3.1.3 shall be taken into
used for functional earthing purposes. For information
technology purposes, it is then regarded as the connection point
account.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

to the earth. Terminals for protective conductors shall be capable
Where more than one earthing terminal is provided, of accepting conductors of dimensions required by this
they shall be interconnected. sub-clause.

5.4.2.4.2 Each conductor connected to the main In TT systems, where the earth electrodes of the supply
earthing terminal shall be able to be disconnected system and of the exposed conductive parts are
individually. This connection shall be reliable and such electrically independent, the cross-sectional area of
that it can only be disconnected by means of a tool. protective conductors need not exceed:
NOTE — Disconnection means may conveniently be combined – 25 mm2 copper,
with the main earthing terminal, to permit measurement of the – 35 mm2 aluminium.
resistance of the earth electrode.

Table 14 Minimum Cross-Sectional Area of Protective Conductors

(where not calculated in accordance with 5.4.3.1.2)
(Clause 5.4.3.1.1)

Cross-sectional Area Minimum Cross-Sectional Area of the Corresponding

of Line Conductor, S Protective Conductor (mm2 Cu)
(mm2 Cu)
If the protective conductor is of the same If the protective conductor is not of the same
material as the line conductor material as the line conductor

(1) (2) (3)

k1
S < 16 S ×S
k2

k1
16 < S < 35 161) × 16
k2

S 1) k1 S
S > 35 ×
2 k2 2

where
k1 = is the value of k for the line conductor derived from the formula given in Annex A or selected from tables given in
IEC 60364-4-43, according to the materials of the conductor and insulation;
k2 = is the value of k for the protective conductor, selected from Tables 58 to Table 62 as applicable.

1)
For a PEN conductor, the reduction of the cross-sectional area is permitted only in accordance with the rules for sizing of the neutral
conductor (see 5.2).

118
 IS 732 : 2019

5.4.3.1.2 The cross-sectional areas of protective a) calculated in accordance with 5.4.3.1.2 for the
conductors shall be not less than the value determined most onerous prospective fault current and
either: operating time encountered in these circuits; or
a) in accordance with IEC 60949; or b) selected in accordance with Table 14 so as to
correspond to the cross-sectional area of the
b) by the following formula applicable only for
largest line conductor of the circuits.
disconnection times not exceeding 5 s:
5.4.3.2 Types of protective conductors
l 2t
S= 5.4.3.2.1 Protective conductors may consist of one or
k
more of the following:
where
S = the cross-sectional area in mm2; a) conductors in multicore cables;

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
b) insulated or bare conductors in a common
I = the r.m.s value expressed in amperes of
enclosure with live conductors;
prospective fault current, for a fault of
negligible impedance, which can flow c) fixed installed bare or insulated conductors;
through the protective device d) metallic cable sheath, cable screen, cable
(IS/IEC 60909-0); armour, wirebraid, concentric conductor,

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

t = the operating time in seconds of the metallic conduit, subject to the conditions
protective device for automatic stated in 5.4.3.2.2(a) and (b).
disconnection; and NOTE — See 5.4.3.8 for their arrangement.
k = the factor dependent on the material of the 5.4.3.2.2 Where the installation contains equipment
protective conductor, the insulation and other having metal enclosures such as low-voltage switchgear
parts and the initial and final temperatures and controlgear assemblies (see IS/IEC 61439-1 and
(for calculation of k, see Annex EE). IS/IEC 61439-2) or busbar trunking systems (IS/
Where the application of the formula produces a non- IEC 60439-2), their metal enclosures or frames may
standard size, a conductor having at least the nearest be used as protective conductors if they simultaneously
larger standard cross-sectional area shall be used. satisfy the following three requirements:
NOTES a) their electrical continuity shall be assured by
1 Account should be taken of the current-limiting effect of the construction or by suitable connection so as
circuit impedances and the limitation of I²t of the protective to ensure protection against mechanical,
device.
chemical or electrochemical deterioration;
2 For limitations of temperatures for installations in potentially
explosive atmospheres (see IS/ IEC 60079-0). b) they comply with the requirements of 5.4.3.1;
3 As the metallic sheaths of mineral-insulated cables according c) they shall permit the connection of other
to IEC 60702-1 have an earth fault capacity greater than that protective conductors at every predetermined
of the line conductors, it is not necessary to calculate the cross-
sectional area of the metallic sheaths when used as protective
tap-off point.
conductors.
5.4.3.2.3 The following metal parts are not permitted
5.4.3.1.3 The cross-sectional area of every protective for use as protective conductors or as protective
conductor which does not form part of a cable or which bonding conductors:
is not in a common enclosure with the line conductor
a) metallic water pipes;
shall be not less than:
b) metallic pipes containing potentially
a) 2.5 mm2 Cu or 16 mm2 Al, if protection against flammable materials such as gases, liquids,
mechanical damage is provided; and powder;
b) 4 mm2 Cu or 16 mm2 Al, if protection against NOTES
mechanical damage is not provided. 1 For cathodic protection, see 5.4.2.2.2.
NOTE — The use of steel for a protective conductor is not i) constructional parts subject to mechanical stress in
excluded (see 5.4.3.1.2). normal service;
ii) flexible or pliable metal conduits, unless designed
A protective conductor not forming part of a cable is for that purpose;
considered to be mechanically protected if it is installed iii) flexible metal parts; and
in a conduit, trunking or protected in a similar way. iv) support wires; cable trays and cable ladders.
2 Examples of a protective conductor include a
5.4.3.1.4 Where a protective conductor is common to protective bonding conductor, a protective earthing
two or more circuits, its cross-sectional area shall be: conductor and an earthing conductor when used for
protection against electric shock.

119
IS 732 : 2019

5.4.3.3 Electrical continuity of protective conductors 2 IS/IEC 60079-14 does not permit the use of a PEN, PEL or
PEM conductor in explosive atmospheres.
5.4.3.3.1 Protective conductors shall be suitably
protected against mechanical damage, chemical or 5.4.3.4.2 The PEN, PEL or PEM conductor shall be
electrochemical deterioration, electrodynamics forces insulated for the rated voltage of the line conductor.
and thermodynamic forces. Metallic enclosures of wiring systems shall not be used
Every connection (for example, screwed connections, as PEN, PEL or PEM conductors, except for busbar
clamp connectors) between protective conductors or trunking systems complying with IS 8623 (Part 2) and
between a protective conductor and other equipment for powertrack systems complying with IEC 61534-1.
shall provide durable electrical continuity and adequate NOTE — Product committees should consider the potential
mechanical strength and protection. Screws for effect of EMI introduced into the equipment from a PEN, PEL
or PEM conductor.
connecting protective conductors shall not serve any

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
other purpose. 5.4.3.4.3 If, from any point of the installation, the
neutral/mid-point/line and protective functions are
Joints shall not be made by soldering.
provided by separate conductors, it is not permitted to
NOTE — All electrical connections should have satisfactory connect the neutral/mid-point/line conductor to any
thermal capacity and mechanical strength to withstand any
other earthed part of the installation. However, it is

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

combination of current/time which may occur in the conductor
or in the cable/enclosure with the largest cross-sectional area. permitted to form more than one neutral/mid-point/line
conductor and more than one protective conductor from
5.4.3.3.2 Joints in protective conductors shall be the PEN, PEL or PEM conductor respectively.
accessible for inspection and testing except for:
The PEN, PEL or PEM conductor shall be connected
a) compound-filled joints, to the terminal or bar intended for the protective
b) encapsulated joints, conductors (see Fig.61A), unless there is a specific
c) joints in metal conduits, ducting and busbar terminal or bar intended for the connection of the PEN,
trunking systems, PEL or PEM conductor (examples are given in Fig. 61B
d) joints forming part of equipment, complying and 61C).
with equipment standards, NOTE — In systems supplied with SELV direct current, for
e) joints made by welding or brazing, and example, telecommunication systems, there is no PEL or PEM
conductor.
f) joints made by compression tool.
5.4.3.4.4 Extraneous-conductive-parts shall not be used
5.4.3.3.3 No switching device shall be inserted in the as PEN, PEL or PEM conductors.
protective conductor, but joints which can be
disconnected for test purposes by use of a tool may be 5.4.3.5 Combined protective and functional earthing
provided. conductors
5.4.3.3.4 Where electrical monitoring of earthing is Where a combined protective and functional earthing
used, dedicated devices (for example, operating conductor is used, it shall satisfy the requirements for
sensors, coils, current transformers) shall not be a protective conductor. In addition, it shall also comply
connected in series in protective conductors. with the relevant functional requirements (see 4.5.4).
5.4.3.3.5 Exposed-conductive-parts of electrical A d.c. return conductor PEL or PEM for an information
equipment shall not be used to form part of the technology power supply may also serve as a combined
protective conductor for other equipment except as functional earthing and protective conductor.
allowed by 5.4.3.2.2. NOTE — For further information, see IEC 61140.
5.4.3.4 PEN, PEL or PEM conductors 5.4.3.6 Currents in protective earthing conductors
NOTE — As these conductors serve two functions, as PE- and The protective earthing conductor should not be used
either as N-, L- or M-conductors, all applicable requirements
for the relevant functions should be considered. as a conductive path for current under normal operating
conditions (for example, connection of filters for EMC-
5.4.3.4.1 A PEN, PEL or PEM conductor may only be reasons), see also IEC 61140.
used in fixed electrical installations and, for mechanical
reasons, shall have a cross-sectional area not less than Where the current exceeds 10 mA under normal
10 mm2 copper or 16 mm² aluminium. operating conditions, a reinforced protective conductor
shall be used (see 5.4.3.7).
NOTES
1 For EMC reasons, the PEN conductor should not be installed NOTE — Capacitive leakage currents, for example, by cables
downstream of the origin of the installation (see 4.5.4.4.3.2). or motors, should be reduced by the design of the installation
and the equipment.

120
 KEY
MDB—main distribution board

121
61A Example 1

Fig.61C Example 3
Fig. 61B Example 2

FIG. 61 EXAMPLES OF A PEN CONDUCTOR CONNECTION

IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
IS 732 : 2019

5.4.3.7 Reinforced protective earthing conductors for 5.4.4.2 Protective bonding conductors for
protective earthing conductor currents exceeding supplementary bonding
10 mA
5.4.4.2.1 A protective bonding conductor connecting
For current-using equipment intended for permanent two exposed conductive parts shall have a conductance
connection and with a protective earthing conductor not less than that of the smaller protective conductor
current exceeding 10 mA the following applies: connected to the exposed conductive parts.
a) where the current-using equipment has only 5.4.4.2.2 A protective bonding conductor connecting
one protective earthing terminal, the protective exposed conductive parts to extraneous conductive
earthing conductor shall have a cross-sectional parts shall have a conductance not less than half that of
area of at least 10 mm2 Cu or 16 mm2 Al, the cross-sectional area of the corresponding protective
through its total run; conductor.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTE — A PEN, PEL or PEM conductor in accordance
with 5.4.3.4 complies with this requirement. 5.4.4.2.3 The minimum cross-sectional area of
protective bonding conductors for supplementary
b) where the current-using equipment has a
bonding, and of bonding conductors between two
separate terminal for a second protective
extraneous conductive parts, shall be in accordance
earthing conductor a second protective

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

with 5.4.3.1.1.
earthing conductor of at least the same cross-
sectional area as required for fault protection 5.5 Selection and Erection of Electrical
shall be run from a point where the protective Equipment — Other Equipment
earthing conductor has a cross-sectional area
not less than 10 mm2 Cu or 16 mm2 Al. 5.5.1 Void
NOTES 5.5.2 Low-Voltage Generating Sets
1 In TN-C systems where the neutral and protective
conductors are combined in a single conductor (PEN 5.5.2.1 General
conductor) up to the equipment terminals, protective
conductor current may be treated as load current. This clause provides requirements for the selection and
2 Current-using equipment normally having high erection of low-voltage and extra-low voltage
protective conductor current may not be compatible with generating sets intended to supply, either continuously
installations incorporating residual current protective
or occasionally, all or part of the installation.
devices.
Requirements are also included for installations with
5.4.3.8 Arrangement of protective conductors the following supply arrangements:
Where overcurrent protective devices are used for a) supply to an installation which is not
protection against electric shock, the protective connected to a system for distribution of
conductor shall be incorporated in the same wiring electricity to the public;
system as the live conductors or be located in their b) supply to an installation as an alternative to a
immediate proximity. system for distribution of electricity to the
5.4.4 Protective Bonding Conductors public;
c) supply to an installation in parallel with a
5.4.4.1 Protective bonding conductors for connection system for distribution of electricity to the
to the main earthing terminal public supply; and
Protective bonding conductors for connection to the d) appropriate combinations of the above.
main earthing terminal shall have a cross-sectional area
This part does not apply to self-contained items of extra-
not less than half the cross-sectional area of the largest
low voltage electrical equipment which incorporate
protective earthing conductor within the installation and
both the source of energy and the energy-using load
not less than:
and for which a specific product standard exists that
a) 6 mm2 copper; or includes the requirements for electrical safety.
b) 16 mm2 aluminium; or NOTE — Requirements of the electricity distributor should be
c) 50 mm2 steel. ascertained before a generating set is installed in an installation
that is connected to a system for distribution of electricity to
The cross-sectional area of protective bonding the public.
conductors for connection to the main earthing terminal 5.5.2.1.1 Generating sets with the following power
need not exceed 25 mm2 Cu or an equivalent cross- sources are considered:
sectional area for other materials.
a) combustion engines;

122
 IS 732 : 2019

b) turbines; operating range. Means shall be provided to

c) electric motors; automatically disconnect such parts of the installation
d) photovoltaic cells [IEC 60364-7-712 also as may be necessary if the capacity of the generating
applies]; set is exceeded.
e) electrochemical accumulators; and NOTES
1 Attention should be given to the size of individual loads as a
f) other suitable sources.
proportion of the capacity of the generating set and to motor
5.5.2.1.2 Generating sets with the following electrical starting currents.
characteristics are considered: 2 Attention should be given to the power factor specified for
protective devices in the installation.
a) mains-excited and separately excited 3 The installation of a generating set within an existing building
synchronous generators; or installation may change the conditions of external influence
for the installation (see 4), for example by the introduction of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
b) mains-excited and self-excited asynchronous moving parts, parts at high temperature or by the presence of
generators; inflammable fluids and noxious gases, etc.
c) mains-commutated and self-commutated static 5.5.2.2.4 Provision for isolation shall meet the
converters with or without by-pass facilities; requirements of 5.3.7 for each source or combination
and of sources of supply.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

d) generating sets with other suitable electrical
characteristics. 5.5.2.3 Protective measure: extra-low-voltage
provided by SELV and PELV
5.5.2.1.3 The use of generating sets for the following
purposes is considered: 5.5.2.3.1 Additional requirements for SELV and PELV
where the installation is supplied from more than one
a) supply to permanent installations; source
b) supply to temporary installations;
Where a SELV or PELV system may be supplied by
c) supply to portable equipment which is not more than one source, the requirements of 4.2.14.3 shall
connected to a permanent installation; and apply to each source. Where one or more of the sources
d) supply to mobile [IEC 60364-7-712 also is earthed, the requirements for PELV systems in 4.2.14
applies]. shall apply.
5.5.2.2 General requirements If one or more of the sources does not meet the
5.5.2.2.1 The means of excitation and commutation requirements of 4.2.14.3, the system shall be treated as
shall be appropriate for the intended use of the a FELV system and the requirements of 4.2.11.7 shall
generating set and the safety and proper functioning of apply.
other sources of supply shall not be impaired by the 5.5.2.3.2 Additional requirements where it is necessary
generating set. to maintain the supply to an extra-low voltage system
NOTE — See 5.5.2.7 for particular requirements where the Where it is necessary to maintain the supply to an extra-
generating set may operate in parallel with a system for the
distribution of electricity to the public. low voltage system following the loss of one or more
sources of supply, each source of supply or combination
5.5.2.2.2 The prospective short-circuit current and of sources of supply which can operate independently
prospective earth fault current shall be assessed for each of other sources or combinations shall be capable of
source of supply or combination of sources which can supplying the intended load of the extra-low voltage
operate independently of other sources or combinations. system. Provisions shall be made so that the loss of
The short-circuit breaking capacity of protective low-voltage supply to an extra-low voltage source does
devices within the installation and, where appropriate, not lead to danger or damage to other extra-low voltage
connected to a system for distribution of electricity to equipment.
the public, shall not be exceeded for any of the intended
NOTE — Such precautions may be necessary in supplies for
methods of operation of the sources. safety services (see4.1.5.14).
NOTE — Attention should be given to the power factor
specified for protective devices in the installation. 5.5.2.4 Fault protection (protection against indirect
contact)
5.5.2.2.3 The capacity and operating characteristics of 5.5.2.4.1 Fault protection shall be provided for the
the generating set shall be such that danger or damage installation in respect of each source of supply or
to equipment does not arise after the connection or combination of sources of supply that can operate
disconnection of any intended load as a result of the independently of other sources or combinations of
deviation of the voltage or frequency from the intended sources.
123
IS 732 : 2019

The fault protective provisions shall be selected or where

precautions shall be taken to ensure that where fault Ia = the maximum earth fault current which can
protective provisions are achieved in different ways be supplied by the static converter alone for
within the same installation or part of an installation a period of up to 5 s.
according to the active sources of supply, no influence
NOTE — Where such equipment is intended to operate in
shall occur or conditions arise that could impair the parallel with a system for distribution of electricity to the public,
effectiveness of the fault protective provisions. the requirements of 5.5.2.7 also apply.
NOTE — This might, for example, require the use of a
transformer providing electrical separation between parts of the 5.5.2.4.3.3.2 Precautions shall be taken or equipment
installation using different earthing systems. shall be selected so that the correct operation of
5.5.2.4.2 The generating set shall be connected so that protective devices is not impaired by d.c. currents
any provision within the installation for protection by generated by a static converter or by the presence of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
residual current devices in accordance with 4.2 remains filters.
effective for every intended combination of sources of 5.5.2.4.3.3.3 A means of isolation shall be installed on
supply. both sides of a static converter.
NOTE — Connection of live parts of the generator with earth
This requirement does not apply on the power source

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

may affect the protective measures.
side of a static converter which is integrated in the same
5.5.2.4.3 Protection by automatic disconnection of enclosure as the power source.
supply 5.5.2.5 Protection against overcurrent
5.5.2.4.3.1 General 5.5.2.5.1 Where overcurrent protection of the
Where the protective measure automatic disconnection generating set is required, it shall be located as near as
of supply is used for protection against electric shock, practicable to the generator terminals.
the requirements of 4.2.11 apply, except as modified NOTE — The contribution to the prospective short-circuit
for the particular cases given in 5.5.2.4.3.2 current by a generating set may be time-dependent and may be
or 5.5.2.4.3.3. much less than the contribution made by a system where the
source is a mv/lv transformer.
5.5.2.4.3.2 Additional requirements for installations
5.5.2.5.2 Where a generating set is intended to operate
where the generating set provides a supply as a
in parallel with another source of supply, including a
switched alternative to the normal supply to the
installation supply from a system for distribution of electricity to
the public, or where two or more generating sets may
Protection by automatic disconnection of supply shall operate in parallel, harmonic currents shall be limited
not rely upon the connection to the earthed point of the so that the thermal rating of conductors is not exceeded.
distribution system when the generator is operating as
a switched alternative. A suitable means of earthing The effects of harmonic currents may be limited as
shall be provided. follows:

5.5.2.4.3.3 Additional requirements for installations a) the selection of generating sets with
incorporating static converters compensated windings;
b) the provision of a suitable impedance in the
5.5.2.4.3.3.1 Where fault protection for parts of the connection to generator star points;
installation supplied by the static converter relies upon
c) the provision of switches which interrupt the
the automatic closure of the by-pass switch and the
operation of protective devices on the supply side of circuit but which are interlocked so that at all
the by-pass switch is not within the time required times fault protection is not impaired;
by 4.2.11, supplementary equipotential bonding shall d) the provision of filtering equipment; and
be provided between simultaneously accessible e) other suitable means.
exposed-conductive-parts and extraneous-conductive- NOTES
parts on the load side of the static converter in 1 Consideration should be given to the maximum voltage
accordance with 4.2.15.2. which may be produced across an impedance connected
tolimit harmonics.
The resistance of supplementary equipotential bonding
2 Monitoring equipment complying with IEC 61557-
conductors required between simultaneously accessible 12 provides information on level of disturbances
conductive parts shall fulfil the following condition: resulting from the presence of harmonics.

50V 5.5.2.6 Additional requirements for installations

R≤ where the generating set provides a supply as a
la

124
 IS 732 : 2019

switched alternative to the normal supply to the for a final circuit of the installation, but in this
installation case all the following additional requirement
shall be fulfilled:
5.5.2.6.1 Precautions complying with the relevant
requirements of 5.3 for isolation shall be taken, so that 1) the conductors of the final circuit shall
the generator cannot operate in parallel with the public meet the following requirement:
supply system for distribution of electricity to the IZ > In + Ig
public. Suitable precautions may include: where
a) an electrical, mechanical or electro- IZ = the current-carrying capacity of the
mechanical interlock between the operating final circuit conductors;
mechanisms or control circuits of the change- In = the rated current of the protective
over switching devices; device of the final circuit; and

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
b) a system of locks with a single transferable Ig = the rated output current of the
key; generating set.
c) a three-position, break-before-make, change- 2) a generating set shall not be connected to
over switch; a final circuit by means of a plug and

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

d) an automatic change-over switching device socket;
with a suitable interlock; and 3) a residual current device providing
e) other means providing equivalent security of protection of the final circuit in
operation. accordance with 4.2.11 or 4.2.15 shall
NOTE — Isolation should include supplies to the control
disconnect all live conductors including
circuits of the generator. the neutral conductor; and
4) the line and neutral conductors of the final
5.5.2.6.2 For TN-S systems where the neutral is not circuit and of the generating set shall not
switched, any residual current device shall be positioned be connected to earth downstream of the
to avoid incorrect operation due to the existence of any protective device of the final circuit.
parallel neutral-earth path.
NOTE — Where the generating set is installed in a final
NOTE — It may be desirable in TN systems to disconnect the circuit on the load side of all the protective devices for
neutral of the installation from the neutral or PEN of the system that final circuit, except where the protective devices
for distribution of electricity to the public to avoid disturbances for the final circuit disconnect the line and the neutral
such as induced voltage surges caused by lightning conductors, the disconnection time in accordance
(see also 4.5.4.4.7). with 4.2.11.3.2 is the combination of the disconnection
time of the protective device for the final circuit and
5.5.2.7 Additional requirements for installations the time taken for the output voltage of the generating
where the generating set may operate in parallel with set to be reduced to less than 50 V.
other sources including systems for distribution of
5.5.2.7.3 In selecting and using a generating set to run
electricity to the public
in parallel with another source, including the system
5.5.2.7.1 Where a generating set is used as an additional for distribution of electricity to the public, care shall
source of supply in parallel with another source, be taken to avoid adverse effects to that system and to
protection against thermal effects in accordance with 4.3 other installations in respect of power factor, voltage
and protection against overcurrent in accordance with changes, harmonic distortion, d.c. current injection,
4.4 shall remain effective in all situations. unbalance, starting, synchronizing or voltage
fluctuation effects. In the case of a system for
Except where an uninterruptible power supply is
distribution of electricity to the public, the distributor
provided to supply specific items of current using
shall be consulted in respect of particular requirements.
equipment within the final circuit to which it is
Where synchronization is necessary, the use of
connected, such a generating set shall be installed on
automatic synchronizing systems which consider
the supply side of all the protective devices for the final
frequency, phase and voltage is to be preferred.
circuits of the installation.
5.5.2.7.4 Where a generating set is intended to run in
5.5.2.7.2 A generating set used as an additional source
parallel with the system for distribution of electricity
of supply in parallel with another source shall be
to the public, means of automatic switching shall be
installed:
provided to disconnect the generating set from the
a) on the supply side of all the protective devices system for distribution of electricity to the public in
for the final circuits of the installation, or the event of loss of that supply or deviation of the
b) on the load side of all the protective devices voltage or frequency at the supply terminals from values
declared for normal supply.
125
IS 732 : 2019

The type of protection and the sensitivity and operating c) IEC 60364-7-713 for electrical installations
times depend upon the protection of the system for in furniture;
distribution of electricity to the public and the number d) IEC 60364-7-714 for outdoor lighting
of generating sets connected and shall be agreed by the installations; and
distributor. e) IEC 60364-7-715 for extra-low-voltage
In case of presence of static converters, the means of lighting installations.
switching shall be provided on the load side of this The requirements of this clause do not apply to:
static converter.
a) high-voltage signs supplied at low voltage
5.5.2.7.5 Where a generating set is intended to run in (called neon-tube);
parallel with the system for distribution of electricity NOTE — Requirements for high-voltage signs supplied
to the public, means shall be provided to prevent the at low voltage (called neon-tube) are included in

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
connection of a generating set to the system for IEC 60598-214.
distribution of electricity to the public in the event of b) signs and luminous-discharge-tube
loss of that supply or deviation of the voltage or installations operating from a no-load rated
frequency at the supply terminals from values declared output voltage exceeding 1 kV but not
for normal supply. exceeding 10 kV; and

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

5.5.2.7.6 Where a generating set is intended to run in c) temporary festoon lighting.
parallel with the system for distribution of electricity NOTE — Safety requirements for luminaires are covered
by IEC 60598 series.
to the public, means shall be provided to enable the
generating set to be isolated from the system for 5.5.3.2 Terms and definitions
distribution of electricity to the public. The accessibility
of this means of isolation shall comply with national For the purposes of this clause, the general terms and
rules and distribution system operator requirements. definitions of 4.1, IS 10322series, IEC 60050-195,
IEC 60050-826 and IEC 60570, as well as the following
5.5.2.7.7 Where a generating set may also operate as shall apply.
switched alternative to the distribution system, the
installation shall also comply with 5.5.2.6. 5.5.3.2.1 Luminaire

5.5.2.8 Requirements for installations incorporating Apparatus which distributes, filters or transforms the
stationary batteries light transmitted from one or more lamps and which
includes, except the lamps themselves, all the parts
5.5.2.8.1 Stationary batteries shall be installed so that necessary for fixing and protecting the lamps and, where
they are accessible only to skilled or instructed persons. necessary, circuit auxiliaries together with the means
NOTE — This generally requires the battery to be installed in for connecting them to the electric supply.
a secure location, or, for smaller batteries, a secure enclosure.
5.5.3.2.2 Display stands for luminaires
The location or enclosure shall be adequately ventilated.
Permanent stands in sales rooms or part of sales rooms
5.5.2.8.2 Battery connections shall have basic which are used to display luminaires.
protection by insulation or enclosures or shall be
NOTE — The following items are not regarded as display
arranged so that two bare conductive parts having stands:
between them a potential difference exceeding 120 V a) trade fair stands, in which luminaires remain connected for
cannot be inadvertently touched simultaneously. the duration of the fair;
b) temporary exhibition panels with permanently connected
5.5.3 Luminaires and Lighting Installations luminaires; and
5.5.3.1 Scope c) exhibition panels with a range of luminaires which can be
connected with a plug-in device.
The particular requirements of this clause apply to the
5.5.3.3 General requirements for installations
selection and erection of luminaires and lighting
installations intended to be part of the fixed installation. Luminaires shall be selected and erected in accordance
with the manufacturer’s instructions and shall comply
Additional requirements for specific types of lighting
with IS 10322 series. An electrical supply track system
installations are covered in:
for luminaires shall comply with the requirements of
a) IEC 60364-7-702 for installations in IEC 60570.
swimming pools and fountains; NOTES
b) IEC 60364-7-711 for installations in 1 Refer to 5.1.2.1.5 regarding compatibility such as between
exhibitions, shows and stands; lamp and control devices. During the installation process of

126
 IS 732 : 2019

luminaires the following items shall at least be considered: b) a device for connecting a luminaire (DCL)
a) starting current; outlet according to IEC 61995 mounted in a
b) harmonics current; box; or
c) compensation;
c) electrical equipment designed to be connected
d) leakage current;
directly to the wiring system.
e) primer ignition current; and
f) voltage dip withstand.
5.5.3.5.2 Fixing of the luminaire
2 Concerning the right selection of the protection and control
devices, information about the currents relevant to all frequency It shall be ensured that adequate means to fix the
generated by lamps and for all transient currents should be
provided.
luminaire to a stable element of the construction are
3 See Annex GG for an explanation of symbols used in provided.
luminaires, in controlgear for luminaires and in the installation
The fixing means may be mechanical accessories (for

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of the luminaires.
example, hooks or screws), boxes or enclosures which
For the purposes of this clause, luminaires without are able to support luminaires (see IS 14772) or
transformer/converter and used with extra-low-voltage supporting devices for connecting a luminaire.
(ELV) lamps connected in series shall be considered
as low-voltage equipment and not as ELV equipment. The fixing means shall be capable of supporting a mass

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

These luminaires shall be either Class I or Class II of not less than 5 kg. Where the mass of the luminaire
equipment. is greater than 5 kg, the installer shall ensure that the
fixing means is capable of supporting the mass of the
A luminaire installed in a pelmet or other architectural luminaire.
or decorative building element shall be selected and
erected such that it shall not be adversely affected by The installation of the fixing means shall be in
the presence and/or operation of curtains or blinds and accordance with the manufacturer’s instructions.
shall not present a risk of fire or electric shock in normal The weight of luminaires, boxes, their fixing means
use. and the eventual accessories shall be compatible with
5.5.3.4 Protection of the surroundings against the mechanical capability of the supporting structure.
thermal effects NOTE — In these conditions, a ceiling or a suspended ceiling
may be considered as a stable element of the construction and
In the selection and erection of luminaires the thermal consequently luminaires may be fixed onto them.
effect of radiant and convection energy on the
Any cable or cord between the fixing means and the
surroundings shall be taken into account, including:
luminaire shall be installed so that any expected stresses
a) the maximum permissible power dissipated by in the conductors, terminals and terminations will not
the lamps; impair the safety of the installation (see also 5.2.5.8).
NOTE — The maximum permissible power dissipated
5.5.3.5.3 Through wiring
by the lamps is found on the luminaire.
b) the resistance to heat of adjacent material The installation of through wiring in a luminaire is only
– at the point of installation, allowed for luminaire designed for through wiring.
– in the thermally affected areas; Where connecting devices are required but not provided
c) the minimum distance to combustible with the luminaire designed for through wiring, the
materials, including those in the path of a connecting devices shall be:
spotlight beam; and a) terminals used for the connection to the supply
d) the relevant markings on the luminaire. according to IEC 60998, or
NOTE — See Annex GG for thermal effects markings
b) installation couplers used for the connection
and symbols.
of through wiring according to IEC 61535, or
Additional requirements regarding protection against c) other suitable and appropriate connecting
thermal effects for luminaires may be found in 4.3.2.3 devices.
and 4.3.2.4.
Cables for through wiring shall be selected in
5.5.3.5 Wiring systems for lighting installations accordance with the temperature information, if
5.5.3.5.1 Connection to the fixed wiring provided, on the luminaire or on the manufacturer’s
instruction sheet:
Wiring systems shall be terminated in
a) for luminaires complying with IS 10322 but
a) a box, which shall comply with the relevant with temperature marking, cables suitable for
part of IS 14772; or the marked temperature shall be used;
127
IS 732 : 2019

b) for luminaires complying with IS 10322 but transformer(s), marked with the symbol ;
with no temperature marking, heat-resistant or
cables are not required unless specified in the
b) a temperature declared thermally protected
manufacturer’s instructions; and
ballast(s)/transformer(s), marked with the
c) in the absence of information, heat-resistant
cables and/or insulated conductors in symbol .
accordance with IEC 60245-3 or those of an 5.5.3.7 Compensation capacitors
equivalent type shall be used.
NOTE — The temperature marking on the luminaire indicates Compensation capacitors having a total capacitance
the maximum temperature according to Table 12.2 of IS 10322 exceeding 0.5 µF shall only be used in conjunction with
and is marked with the symbol (see Annex GG). discharge resistors in accordance with the requirements
of IS 1569.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5.5.3.5.4 Devices for connection to the supply
5.5.3.8 Protection against electric shock for display
If the luminaire does not provide connecting devices stands for luminaires
for connection to the supply, the connecting devices
Protection against electric shock for circuits supplying
shall be:
display stands for luminaires shall be provided by

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

a) terminals used for the connection to the supply either;
according to IEC 60998; or
a) SELV or PELV supply, or
b) devices for connecting a luminaire (DCL) plug
b) a residual current operated protective device
according to IEC 61995; or
having a rated residual operating current not
c) installation couplers used for the connection exceeding 30 mA which provides both
to the supply according to IEC 61535; or automatic disconnection of supply according
d) other suitable and appropriate connecting to 4.2.11 and additional protection according
devices. to 4.2.15.1.
NOTE — For the installation of the supply cables, see
also 5.2.4. 5.5.3.9 Stroboscopic effect

5.5.3.5.5 Groups of luminaires In the case of lighting for premises where machines
with moving parts are in operation, consideration shall
Groups of luminaires divided between the three line be given to stroboscopic effects which can give a
conductors of a three-phase circuit with only one misleading impression of moving parts being stationary.
common neutral conductor shall be provided with at Such effects may be avoided by selecting luminaires
least one device disconnecting simultaneously all line with suitable lamp controlgear (for example, high
conductors (see also 5.3.6). frequency electronic controlgear).
5.5.3.5.6 Protection against heat and UV radiation 5.5.3.10 Ground recessed luminaires
effects within the luminaire
The requirements as given in IS 10322 series shall be
External cables and cores of cables connected within a fulfilled by the selection and erection of ground
luminaire or passing through shall be so selected and recessed luminaires.
erected that they will not suffer damage or deterioration
due to heat and UV radiation generated by the luminaire 5.6 Selection and Erection of Electrical
or its lamps (for example, shielding). Equipment — Safety Services
5.5.3.6 Independent lamp controlgear, for example, 5.6.1 Void
ballasts
5.6.2 Classification
Only independent lamp controlgear marked as suitable
5.6.2.1 An electrical supply system for safety services
for independent use, according to the relevant standard,
is either:
shall be used external to a luminaire.
a) a non-automatic supply, the starting of which
NOTE — The generally recognised symbol is: independent is initiated by an operator, or
ballast standard IEC 60417-5138 (2011-01). b) an automatic supply, the starting of which is
Only the following are permitted to be mounted on independent of an operator.
flammable surfaces: An automatic supply is classified as follows, according
a) a “class P” thermally protected ballast(s)/ to the maximum changeover time:

128
 IS 732 : 2019

a) no-break: an automatic supply which can a) storage batteries;

ensure a continuous supply within specified b) primary cells;
conditions during the period of transition, for c) generator sets independent of the normal
example as regards variations in voltage and supply; and
frequency; d) a separate feeder of the supply network that is
b) Very short break: an automatic supply effectively independent of the normal feeder.
available within 0.15 s;
5.6.4.2 Safety sources for safety services shall be
c) Short break: an automatic supply available
installed as fixed equipment and in such a manner that
within 0.5 s;
they cannot be adversely affected by failure of the
d) Average break: an automatic supply available normal source.
within 5 s;
5.6.4.3 Safety sources shall be installed in a suitable

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
e) Medium break: an automatic supply available
within 15 s; and location and be accessible only to skilled or instructed
persons (BA5 or BA4).
f) Long break: an automatic supply available in
more than 15 s. 5.6.4.4 The location of the safety source shall be
properly and adequately ventilated so that exhaust
5.6.2.2 The essential equipment for safety services shall

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

gases, smoke or fumes from the safety source cannot
be compatible with the changeover time in order to penetrate areas occupied by persons.
maintain the specified operation.
5.6.4.5 Separate, independent feeders from a supply
5.6.3 General network shall not serve as electrical sources for safety
5.6.3.1 Safety services may be required to operate at services unless assurance can be obtained that the two
all relevant times including during main and local supplies are unlikely to fail concurrently.
supply failure and through fire conditions. To meet these 5.6.4.6 The safety source shall have sufficient capability
requirements, specific sources, equipment, circuits and to supply its related safety service.
wiring are necessary. Some applications also have
particular requirements, as given in 5.6.3.2 and 5.6.3.3. 5.6.4.7 A safety source may, in addition, be used for
purposes other than safety services, provided the
5.6.3.2 For safety services required to operate in fire availability for safety services is not thereby impaired.
conditions, the following additional two conditions shall A fault occurring in a circuit for purposes other than
be fulfilled: safety services shall not cause the interruption of any
a) an electrical source for safety supply shall be circuit for safety services.
selected in order to maintain a supply of 5.6.4.8 Special requirements for safety sources not
adequate duration, and capable of operation in parallel
b) all equipment of safety services shall be
5.6.4.8.1 Adequate precautions shall be taken to avoid
provided, either by construction or by
the paralleling of sources.
erection, with protection ensuring fire
resistance of adequate duration. NOTE — This may be achieved by mechanical interlocking.
NOTE — The electrical safety supply source is generally 5.6.4.8.2 Short-circuit protection and fault protection
additional to the normal supply source, for example the
shall be ensured for each source.
public supply network.
5.6.4.9 Special requirements for safety services having
5.6.3.3 Where automatic disconnection of supply is
sources capable of operation in parallel
used as a protective measure against electric shock, non-
disconnection on the first fault is preferred. In IT NOTE — The parallel operation of independent sources
normally requires the authorization of the supply undertaking.
systems, insulation monitoring devices shall be This may require special devices, for example to prevent reverse
provided which give an audible and visible indication power.
in the event of a first fault.
Short-circuit protection and fault protection shall be
5.6.3.4 Regarding control and bus systems, a failure in ensured when the installation is supplied separately by
the control or bus system of a normal installation shall either of the two sources or by both in parallel.
not adversely affect the function of safety services. NOTE — Precautions may be necessary to limit current
circulation in the connection between the neutral points of the
5.6.4 Electrical sources for safety services
sources, in particular the effect of third harmonics.
5.6.4.1 The following electrical sources for safety 5.6.4.10 Central power supply system
services are recognized:
Batteries shall be of vented or valve-regulated

129
IS 732 : 2019

maintenance-free type and shall be of heavy duty impairing the correct operation of circuits of safety
industrial design, for example cells complying with services.
IEC 60623 or the IEC 60896 series.
5.6.5.5 Switchgear and controlgear shall be clearly
NOTE — The minimum design life of the batteries at 20 °C identified and grouped in locations accessible only to
should be 10 years. skilled or instructed persons (BA5 or BA4).
5.6.4.11 Low-power supply system 5.6.5.6 In equipment supplied by two different circuits
The power output of a low-power supply system is with independent sources, a fault occurring in one
limited to 500 W for a 3 h duration and 1500 W for a 1 circuit shall not impair the protection against electric
h duration. Batteries can be of gas-tight or valve- shock, nor the correct operation of the other circuit.
regulated maintenance-free type and shall be of heavy Such equipment shall be connected to the protective
duty industrial design, for example cells complying with conductors of both circuits, if necessary.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
IEC 60623 or the IEC 60896 series. 5.6.5.7 Safety circuit cables, other than metallic
NOTE — The minimum design life of the batteries at 20 °C screened, fire-resistant cables, shall be adequately and
should be 5 years. reliably separated by distance or by barriers from other
5.6.4.12 Uninterruptible power supply sources circuit cables, including other safety circuit cables.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Where an uninterruptible power supply is used, it shall: NOTE — For battery cables, special requirements may apply.

a) be able to operate distribution circuit 5.6.5.8 Circuits for safety services, with the exception
protective devices, of wiring for fire rescue service lift supply cables, and
wiring for lifts with special requirements, shall not be
b) be able to start the safety devices when it is installed in lift shafts or other flue-like openings.
operating in the emergency condition from the
inverter supplied by the battery, 5.6.5.9 In addition to a general schematic diagram, full
c) comply with the requirements of 5.6.4.10, and details of all electrical safety sources shall be given.
d) comply with IEC 62040-1-1, IEC 62040-1-2 The information shall be maintained adjacent to the
or IEC 62040-3, as applicable. distribution board. A single-line diagram is sufficient.

5.6.4.13 Safety generating sets 5.6.5.10 Drawings of the electrical safety installations
shall be available showing the exact location of:
Where a safety generating set is used as a safety source,
it shall comply with ISO 8528-12. a) all electrical equipment and distribution
boards, with equipment designations;
5.6.4.14 The condition of the source for safety services b) safety equipment with final circuit designation
(ready for operation, under fault conditions, feeding and particulars and purpose of the equipment;
from the source for safety services) shall be monitored. and
5.6.5 Circuits of Safety Services c) special switching and monitoring equipment
for the safety power supply (for example, area
5.6.5.1 Circuits of safety services shall be independent switches, visual or acoustic warning
of other circuits. equipment).
NOTE — This means that an electrical fault or any intervention
or modification in one system must not affect the correct 5.6.5.11 A list of all the current-using equipment
functioning of the other. This may necessitate separation by permanently connected to the safety power supply,
fire-resistant materials or different routes or enclosures. indicating the nominal electrical power, nominal
5.6.5.2 Circuits of safety services shall not pass through currents and starting currents and time for current-using
locations exposed to fire risk (BE2) unless they are equipment, shall be provided.
fire-resistant. The circuits shall not, in any case, pass NOTE — This information may be included in the circuit
through zones exposed to explosion risk (BE3). diagrams.

NOTE — Where practicable, the passage of any circuit through 5.6.5.12 Operating instructions for safety equipment
locations presenting a fire risk should be avoided. and electrical safety services shall be available. They
5.6.5.3 According to 4.4.3, protection against overload shall take into account all the particulars of the
may be omitted where the loss of supply may cause a installation.
greater hazard. Where protection against overload is 5.6.6 Wiring Systems
omitted, the occurrence of an overload shall be
monitored. 5.6.6.1 One or more of the following wiring systems
shall be utilized for safety services required to operate
5.6.5.4 Overcurrent protective devices shall be selected in fire conditions:
and erected so as to avoid an overcurrent in one circuit

130
 IS 732 : 2019

a) mineral insulated cable complying with be used so that a short-circuit in one circuit does not
IEC 60702-1 and IEC 60702-2; interrupt the supply to the adjacent luminaires within
b) fire-resistant cables complying with the the fire compartment or the luminaires in other fire
appropriate part of IEC 60331 and with compartments.
IEC 60332-1-2; and No more than 20 luminaires with a total load not
c) a wiring system maintaining the necessary fire exceeding 60 percent of the nominal current of the
and mechanical protection. overcurrent protective device shall be supplied from
Wiring systems shall be mounted and installed in such any final circuit.
a way that the circuit integrity will not be impaired Any circuit distribution, control or protective devices
during the fire. shall not impair the circuit integrity.
NOTE — Examples of a system maintaining the necessary fire

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5.6.7.3 A safe value of minimum illuminance, response
and mechanical protection could be:
time and rated operation time is required to enable
a) constructional enclosures to maintain fire and mechanical
protection, or evacuation of a building. Where there are no national
b) wiring systems in separate fire compartments. or local rules, illumination systems should comply with
ISO 30061.
5.6.6.2 Wiring for control and bus systems of safety

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — Guidance on appropriate systems is given in Table 63.
services shall be in accordance with the same
requirements as the wiring which is to be used for the 5.6.7.4 Emergency lighting shall be wired in maintained
safety services. This does not apply to circuits that do or non-maintained mode. These modes may also be
not adversely affect the operation of the safety combined.
equipment.
5.6.7.5 In the non-maintained mode, the power supply
5.6.6.3 Precautions shall be taken to prevent excavation for the normal lighting shall be monitored at the final
damage to buried safety circuits. circuit for that area. If a loss of supply to the normal
lighting in an area causes the normal lighting to fail,
5.6.6.4 Circuits for safety services which can be
the emergency lighting shall be activated automatically.
supplied by direct current shall be provided with two-
In all cases, arrangements shall be made to ensure that
pole over current protection mechanisms.
local emergency escape lighting will operate in the
5.6.6.5 Switchgear and control gear used for both a.c. event of failure of normal supply to the corresponding
and d.c. supply sources shall be suitable for both a.c. local area.
and d.c. operation.
5.6.7.6 Where maintained and non-maintained modes
5.6.7 Emergency Escape Lighting Applications are used in combination, the changeover devices shall
each have their own monitoring device and shall be
5.6.7.1 Emergency escape lighting systems may be
able to be switched separately.
powered by a central power supply system or the
emergency lighting luminaires may be self-contained. 5.6.7.7 The maintained mode of emergency lighting
The supply to self-contained luminaires is excluded may be simultaneously switched with normal lighting
from the requirements of 5.6.7.1 to 5.6.7.4 inclusive. in locations which either;
Wiring systems for a centrally powered emergency — cannot be darkened when in use, or
lighting system shall retain the continuity of supply from — are not constantly occupied.
the source to the luminaires for an adequate period in
the event of a fire. This shall be achieved by using cables 5.6.7.8 Control and bus systems for safety illumination
with a high resistance to fire, as detailed in 5.6.6.1 shall be independent of control and bus systems for
and 5.6.6.2, to transfer power through a fire general illumination; coupling of both systems is
compartment. permitted only with interfaces that ensure a decoupling/
isolation of both buses from each other. A failure in the
Within the fire compartment, the supplies to the control and bus system of the general illumination shall
luminaire shall either use cables with a high resistance not influence the proper function of the safety
to attack by fire or, for compartments having more than illumination.
one emergency lighting luminaire, such luminaires shall
be wired alternately from at least two separate circuits 5.6.7.9 Changeover from normal to emergency mode
so that a level of illuminance is maintained along the shall start automatically if the supply voltage drops
escape route in the event of the loss of one circuit. below 0.6 times the rated supply voltage for at least
0.5 s. It shall be restored if the supply voltage is greater
5.6.7.2 Where alternate luminaires are supplied by than 0.85 times the rated supply voltage.
separate circuits overcurrent protective devices shall

131
IS 732 : 2019

NOTES 6.2.1 General

1 The actual time for changeover shall be as per National Electric
Code. 6.2.1.1 Every installation or change (namely addition
2 The level of changeover depends on the equipment used for or changes) to an existing installation shall be verified
safety services. during erection, as far as reasonably practicable, and
5.6.7.10 When the normal supply is restored to the on completion, before being put into service by the user.
distribution board or monitored circuit, the emergency 6.2.1.2 The information required by 5.1.4.5 and other
lighting in non-maintained mode shall automatically information necessary for initial verification shall be
switch off. Account shall be taken of the time necessary made available to the person carrying out the initial
for the lamps in the normal lighting to return to normal verification.
luminance.
6.2.1.3 Initial verification shall include comparison of
Account shall also be taken of rooms which had been the results with relevant criteria to confirm that the

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
intentionally ‘blacked-out’ before the supply was lost; requirements this standard have been met.
in these cases, emergency lighting shall not switch off
automatically. 6.2.1.4 Precautions shall be taken to ensure that the
verification shall not cause danger to persons or
5.6.7.11 In addition to central switching, it is livestock and shall not cause damage to property and

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

permissible to monitor and control the supply to parts equipment even if the circuit is defective.
of a building which are occupied.
6.2.1.5 For an addition or alteration to an existing
5.6.7.12 In emergency lighting systems the type of installation, it shall be verified that the addition or
lamps shall be compatible with the changeover time in alteration complies with this standard and does not
order to maintain the specified lighting level. impair the safety of the existing installation.
5.6.7.13 Control switches for emergency lighting shall NOTE — For re-used equipment, see Annex MM.
be placed at a designated location and be arranged and
6.2.1.6 The initial verification shall be made by a skilled
installed in such a way that they cannot be operated by
person, competent in verification.
unauthorized persons.
NOTE — For Requirements concerning qualifications for
5.6.7.14 The switched-on position of the emergency enterprises and persons, refer the relevant Central Electricity
lighting shall be indicated at a convenient location for Regulations.
each source of supply. 6.2.2 Inspection
5.6.7.15 Emergency lighting luminaires and associated 6.2.2.1 Inspection shall precede testing and shall
circuit equipment shall be identified by a red label of normally be done prior to energizing the installation.
at least 30 mm in diameter.
6.2.2.2 The inspection shall be made to confirm that
5.6.8 Fire Protection Applications electrical equipment which is part of the fixed
5.6.8.1 Wiring systems for fire detection and fire installation is:
fighting power supplies shall be supplied by a separate a) in compliance with the safety requirements of
circuit from the main incoming supply. the relevant equipment standards;
5.6.8.2 Preferential circuits, if any, shall be directly NOTE — This may be ascertained by examination of
connected on the supply side of the isolating switch of the manufacturer’s information, marking or certification.
the main distribution board. b) correctly selected and erected according to this
NOTE — A private distribution network is regarded as standard and to the manufacturer’s
equivalent to the distribution network of a public electricity instructions;
company.
c) not visibly damaged so as to impair safety.
5.6.8.3 Alarm devices shall be clearly identified.
6.2.2.3 Inspection shall include at least the checking
5.6.8.4 Except where there are applicable national rules, of the following, where relevant:
the minimum requirements for fire protection systems a) method of protection against electric shock
should be in accordance with Table 64.
(see 4.2);
6 VERIFICATION b) presence of fire barriers and other precautions
against propagation of fire and protection
6.1 Void against thermal effects (see 4.3 and 5.2.10);
6.2 Initial Verification c) selection of conductors for current-carrying
NOTE — In Annex MM guidance on the application of the
capacity and voltage drop (see 4.4, 5.2.6 and
rules of 6 is given. 5.2.8);

132
 IS 732 : 2019

d) choice and setting of protective and g) polarity test (see 6.2.3.8);

monitoring devices (see 5.3); h) test of the order of the phases (see 6.2.3.9);
e) presence and correct location of suitable j) functional and operational tests (see 6.2.3.10);
isolating and switching devices (see 5.3.6); and
f) selection of equipment and protective k) voltage drop (see 6.2.3.11).
measures appropriate to external influences
(see 4.3.2, 5.1.2.2 and 5.2.5); In the event of any test indicating failure to comply,
that test and any preceding test, the results of which
g) neutral and protective conductors correctly
may have been influenced by the fault indicated, shall
identified (see 5.1.4.3);
be repeated after the fault has been rectified.
h) single-pole switching devices connected in the
line conductors (see 5.3.7); NOTE — When testing is in a potentially explosive atmosphere
appropriate safety precautions in accordance with IS/

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
j) presence of diagrams, warning notices or other IEC 60079-17 and IEC 61241-17 are necessary.
similar information (see 5.1.4.5);
6.2.3.2 Continuity of conductors
k) identification of circuits, overcurrent
protective devices, switches, terminals, etc An electrical continuity test shall be made on:
(see 5.1.4);

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

a) protective conductors, including main and
m) adequacy of connection of conductors (see supplementary equipotential bonding
5.2.9); conductors, and
n) presence and adequacy of protective b) in the case of ring final circuits, live conductors.
conductors, including main and NOTE — A ring final circuit is a final circuit arranged
supplementary equipotential bonding in a form of a ring connected to a single point of supply.
conductors (see 5.4);
6.2.3.3 Insulation resistance of the electrical
p) accessibility of equipment for convenience of
installation
operation, identification and maintenance
(see 5.1.3 and 5.1.4). The insulation resistance shall be measured between
live conductors and the protective conductor connected
Inspection shall include all particular requirements for
to the earthing arrangement. For the purposes of this
special installations or locations.
test, live conductors may be connected together.
6.2.3 Testing
Table 15 Minimum Values of Insulation
6.2.3.1 General
Resistance
The test methods described in this clause are given as (Clauses 6.2.3.3 and 6.2.3.4)
reference methods; other methods are not precluded,
provided they give no less valid results. Nominal Circuit Voltage Test Insulation
V Voltage d.c. Resistance
Measuring instruments and monitoring equipment and V MΩ
methods shall be chosen in accordance with the relevant (1) (2) (3)
parts of IEC 61557. If other measuring equipment is SELV and PELV 250 > 0.5
used, it shall provide no less degree of performance Up to and including 500 V, 500 > 1.0
and safety. including FELV
Above 500 V 1 000 > 1.0
The following tests shall be carried out where relevant
and should preferably be made in the following
sequence: The insulation resistance, measured with the test voltage
a) continuity of conductors (see 6.2.3.2); indicated in Table 15, is satisfactory if each circuit,
b) insulation resistance of the electrical with the appliances disconnected, has an insulation
installation (see 6.2.3.3); resistance not less than the appropriate value given in
Table 15.
c) protection by SELV, PELV or by electrical
separation (see 6.2.3.4); Table 15 shall be applied for a verification of the
d) floor and wall resistance/impedance insulation resistance between non-earthed protective
(see 6.2.3.5); conductors and earth.
e) automatic disconnection of supply Where surge protective devices (SPDs) or other
(see 6.2.3.6); equipment are likely to influence the verification test,
f) additional protection (see 6.2.3.7); or be damaged, such equipment shall be disconnected

133
IS 732 : 2019

before carrying out the insulation resistance test. connected to it, at least one of the faulty circuits shall
be disconnected. The disconnection time shall be in
Where it is not reasonably practicable to disconnect
accordance with that for the protective measure
such equipment (for example, in case of fixed socket-
automatic disconnection of supply in a TN-system.
outlets incorporating an SPD), the test voltage for the
particular circuit may be reduced to 250 V d.c., but the 6.2.3.5 Insulation resistance/impedance of floors and
insulation resistance must have a value of at least 1 MΩ. walls
NOTES When it is necessary to comply with the requirements
1 For measurement purposes, the neutral conductor is of MM-1, at least three measurements shall be made
disconnected from the protective conductor.
in the same location, one of these measurements being
2 In TN-C systems, measurement is made between the live
conductors and the PEN conductor.
approximately 1 m from any accessible extraneous-
conductive-part in the location. The other two

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3 In locations exposed to fire hazard, a measurement of the
insulation resistance between the live conductors should be measurements shall be made at greater distances.
applied. In practice, it may be necessary to carry out this
measurement during erection of the installation before the The measurement of resistance/impedance of insulating
connection of the equipment. floors and walls is carried out with the system voltage
4 Insulation resistance values are usually much higher than those to earth at nominal frequency.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

of Table 65. When such values show evident differences, further
investigation is needed to identify the reasons. The above series of measurements shall be repeated
for each relevant surface of the location.
6.2.3.4 Protection by SELV, PELV or by electrical
NOTE — In Annex KK, methods for measuring the insulating
separation
resistance/impedance of floors and walls are given as examples.
The separation of circuits shall be in accordance 6.2.3.6 Protection by automatic disconnection of the
with 6.2.3.4.1 in the case of protection by SELV, supply
6.2.3.4.2 in the case of protection by PELV and
6.2.3.4.3 in the case of protection by electrical NOTE — Where RCDs are applied also for protection against
fire, the verification of the conditions for protection by
separation. automatic
The resistance value obtained in 6.2.3.4.1, 6.2.3.4.2 disconnection of the supply may be considered as
and 6.2.3.4.3 shall be at least that of the circuit with covering the aspects of 4.3.
the highest voltage present in accordance with Table 15.
6.2.3.6.1 General
6.2.3.4.1 Protection by SELV
The verification of the effectiveness of the measures
The separation of the live parts from those of other for protection against indirect contact by automatic
circuits and from earth, according to 4.2.14, shall be disconnection of supply is effected as follows:
confirmed by a measurement of the insulation
resistance. The resistance values obtained shall be in a) For TN systems
accordance with Table 15. Compliance with the rules of 4.2.11.4.4 and 4.2.11.3.2
6.2.3.4.2 Protection by PELV shall be verified by:

The separation of the live parts from other circuits, 1) measurement of the fault loop impedance
according to 4.2.13, shall be confirmed by a (see 6.2.3.6.3).
measurement of the insulation resistance. The resistance NOTE — When RCDs with I n < 500 mA are used as
values obtained shall be in accordance with Table 15. disconnecting devices, measurement of the fault loop impedance
is normally not necessary.
6.2.3.4.3 Protection by electrical separation
Alternatively, where the calculation of the fault loop
The separation of the live parts from those of other impedance or of the resistance of the protective
circuits and from earth, according to 4.2.13, shall be conductors are available, and where the arrangement
confirmed by a measurement of the insulation of the installation permits the verification of the length
resistance. The resistance values obtained shall be in and cross-sectional area of the conductors, the
accordance with Table 15. verification of the electrical continuity of the protective
In case of electrical separation with more than one item conductors (see 6.2.3.2) is sufficient.
of current-using equipment, either by measurement or NOTE — Compliance may be verified by measurement of the
by calculation, it shall be verified that in case of two resistance of protective conductors.
coincidental faults with negligible impedance between 2) verification of the characteristics and/or the
different line conductors and either the protective effectiveness of the associated protective device. This
bonding conductor or exposed-conductive-parts verification shall be made:
134
 IS 732 : 2019

— for overcurrent protective devices, by visual — additions or alterations to an existing

inspection (that is, short time or instantaneous installation where existing RCDs are also to
tripping setting for circuit-breakers, current be used as disconnecting devices for such
rating and type for fuses); additions or alterations.
— for RCDs, by visual inspection and test. NOTE — Where the effectiveness of the protective
measure has been confirmed at a point located
The effectiveness of automatic disconnection of supply downstream of an RCD, the protection of the installation
by RCDs shall be verified using suitable test equipment downstream from this point may be proved by
according to IEC 61557-6 (see 6.2.3.1) confirming that confirmation of the continuity of the protective
the relevant requirements of 4.2 are met. conductors.

It is recommended that the disconnecting times required c) For IT systems

by 4.2 be verified. However, the requirements for Compliance with the rules of 4.2.11.6.2 shall be verified

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
disconnecting times shall be verified in case of: by calculation or measurement of the current Id in case
— re-used RCDs; of a first fault at the line conductor or at the neutral.
— additions or alterations to an existing NOTE — The measurement is made only if the calculation is
installation where existing RCDs are also to not possible, because all the parameters are not known.
Precautions are to be taken while making the measurement in

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

be used as disconnecting devices for such order to avoid the danger due to a double fault.
additions or alterations.
NOTE — Where the effectiveness of the protective Where conditions that are similar to conditions of TT
measure has been confirmed at a point located systems occur, in the event of a second fault in another
downstream of an RCD, the protection of the installation circuit [see 4.2.11.6.4 (a)], verification is made as for
downstream from this point may be proved by
confirmation of the continuity of the protective
TT systems [see 4.2.11.6.4 (b)].
conductors. Where conditions that are similar to conditions of TN
In addition, it shall be confirmed by mutual agreement systems occur, in the event of a second fault in another
between the contractor and the electricity supplier that circuit [see 4.2.11.6.4(b)], verification is made as for
the requirement of 4.2.11.4.1 is complied with. TN systems [see 4.2.11.6.4(a)].
NOTE — During the measurement of the fault loop impedance,
b) For TT systems it is necessary to establish a connection of negligible impedance
between the neutral point of the system and the protective
Compliance with the rules of 4.2.11.5.3 shall be verified
conductor preferably at the origin of installation.
by:
6.2.3.6.2 Measurement of the resistance of the earth
1) measurement of the resistance RA of the earth electrode
electrode for exposed-conductive-parts of the
installation (see 6.2.3.6.2); Measurement of the resistance of an earth electrode,
where prescribed (see 4.2.11.5.3, for TT systems,
NOTE — Where the measurement of RA is not possible, it may
be possible to replace it by the measure of the fault loop 4.2.11.4.1 for TN systems, and 4.2.11.6.2 for IT
impedance as in 6.2.3.6.1 (a) (1). systems), is made by an appropriate method.
2) verification of the characteristics and/or effectiveness NOTES
of the associated protective device. This verification 1 Annex LL, Method LL1, gives, as an example, a description
of a method of measurement using two auxiliary earth electrodes
shall be made:
and the conditions to be fulfilled.
— for overcurrent protective devices, by visual 2 Where the location of the installation (for example, in towns)
inspection (that is, short time or instantaneous is such that it is not possible in practice to provide the two
auxiliary earth electrodes, measurement of the fault loop
tripping setting for circuit-breakers, current impedance according to 6.1.3.6.3, or Annex LL, Methods LL2
rating and type for fuses); and LL3, will give an excess value.
— for RCDs, by visual inspection and by test. 6.2.3.6.3 Measurement of the fault loop impedance
The effectiveness of automatic disconnection of supply An electrical continuity test shall be made according
by RCDs shall be verified using suitable test equipment to 6.2.3.2 before carrying out the fault loop impedance
according to IEC 61557-6 (see 6.2.3.1) confirming that measurement.
the relevant requirements of 4.2 are met.
The measured fault loop impedance shall comply with
It is recommended that the disconnecting times required 4.2.11.4.4 for TN systems and with 4.2.11.6.4 for IT
by 4.2 be verified. However, the requirements for systems.
disconnecting times shall be verified in case of:
Where the requirements of this subclause are not
— re-used RCDs;
135
IS 732 : 2019

satisfied or in case of doubt and where supplementary of the inspection and the results of testing.
equipotential bonding according to 4.2.15.2 is applied,
Any defects or omissions revealed during verification
the effectiveness of that bonding shall be checked
of the work shall be made good before the contractor
according to 4.2.15.2.2.
declares that the installation complies with this
6.2.3.7 Additional protection standard.
The verification of the effectiveness of the measures 6.2.4.2 In the case of initial verification of alterations
applied for additional protection is fulfilled by visual or additions of existing installations, the report may
inspection and test. contain recommendations for repairs and
improvements, as may be appropriate.
Where RCDs are required for additional protection,
the effectiveness of automatic disconnection of supply 6.2.4.3 The initial report shall include:

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
by RCDs shall be verified using suitable test equipment
a) records of inspections; and
according to IEC 61557-6 (see 6.2.3. 1) confirming that
the relevant requirements of 4.2 are met. b) records of circuits tested and test results.

NOTE — Where an RCD is provided for fault protection and The records of circuit details and test results shall
for additional protection, it should be tested according to the identify every circuit, including its related protective

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

relevant most onerous requirements of 4.2. device(s), and shall record the results of the appropriate
Where the rules forbid the installation of single-pole tests and measurements.
switching devices in the neutral conductor, a test shall 6.2.4.4 The person or persons responsible for the safety,
be made to verify that all such devices are connected construction and verification of the installation, shall
in the line conductor(s) only. give the report, which takes account of their respective
6.2.3.8 Check of phase sequence responsibilities, to the person ordering the work,
together with the records mentioned in 6.2.4.3.
In case of multiphase circuits, it shall be verified that
NOTE — The initial report of the electrical installation should
the phase sequence is maintained.
make a recommendation for a period between initial verification
6.2.3.9 Functional tests and the first periodic verification.

Assemblies, such as switchgear and controlgear 6.2.4.5 Reports shall be compiled and signed or
assemblies, drives, controls and interlocks, shall be otherwise authenticated by a person or persons
subjected to a test of their function to verify that they competent in verification.
are properly mounted, adjusted and installed in NOTE — Annexes QQ, RR and SS give model forms of
accordance with the relevant requirements of this schedules that might be used for the description and for initial,
and also periodic, verification of installations, particularly
standard.
suitable for domestic installations.
Protective devices shall be submitted to a test of their
function, as necessary, to check that they are properly 6.3 Periodic Verification
installed and adjusted. 6.3.1 General
NOTE — This functional test does not replace the functional 6.3.1.1 Where required, periodic verification of every
test indicated by the relevant standards.
electrical installation shall be carried out in accordance
6.2.3.10 Verification of voltage drop with 6.3.1.2 to 6.3.1.6.
Where required to verify compliance with 5.2.8, the Wherever possible, the records and recommendations
following options may be used: of previous periodic verifications shall be taken into
account.
a) the voltage drop may be evaluated by
measuring the circuit impedance; 6.3.1.2 Periodic inspection comprising a detailed
b) the voltage drop may be evaluated by using examination of the installation shall be carried out
diagrams similar to the one shown as an without dismantling, or with partial dismantling, as
example in Annex NN. required, supplemented by appropriate tests from 6.2,
including verification, to show that the requirements
6.2.4 Reporting for Initial Verification for disconnecting times as set out in 4.2 for RCDs are
6.2.4.1 Upon completion of the verification of a new complied with, and by measurements, to provide for:
installation or additions or alterations to an existing a) safety of persons and livestock against the
installation, an initial report shall be provided. Such effects of electric shock and burn,
documentation shall include details of the extent of the
b) protection against damage to property by fire
installation covered by the report, together with a record

136
 IS 732 : 2019

and heat arising from an installation defect, d) construction sites; and

e) safety installations (for example emergency luminaires).
c) confirmation that the installation is not
damaged or deteriorated so as to impair safety, For residential dwellings, occupied by the owner
and himself, longer periods (for example, 10 years) between
d) the identification of installation defects and initial inspections and first periodical inspection may
departures from the requirements of this be appropriate. The periodical interval however, may
standard that may give rise to danger. be shorter (for example, 5 years) after a life period of
20 years from initial erection. It is the primary
6.3.1.3 Precautions shall be taken to ensure that the
responsibility of the owner to carry out verification
periodic verification shall not cause danger to persons
(inspection and testing) of the electrical installation in
or livestock and shall not cause damage to property
residential dwelling at the time of renting to a tenant or
and equipment even if the circuit is defective.
at the time when the tenant is changed and report of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Measuring instruments and monitoring equipment and inspection and testing of the electrical installation in
methods shall be chosen in accordance with relevant the building premises should be attached with the rent
parts of IEC 61557. If other measuring equipment is agreement document. When occupancy of a dwelling
used, it shall provide no less degree of performance has changed (for example, from residential to office
and safety. etc), a verification of the electrical installation is

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

strongly recommended.
6.3.1.4 The extent and results of the periodic
verification of an installation, or any part of an The results and recommendations of the previous
installation, shall be recorded. reports, where available, shall be taken into account.
6.3.1.5 Any damage, deterioration, defects or dangerous NOTE — Where no previous report is available, further
investigation is necessary.
condition shall be recorded. Furthermore, significant
limitations of the periodic verification in accordance 6.3.2.2 In the case of an installation under an effective
with this standard and their reasons shall be recorded. management system for preventive maintenance in
normal use, periodic verification may be replaced by
6.3.1.6 The verification shall be made by a skilled
an adequate regime of continuous monitoring and
person, competent in verification.
maintenance of the installation and all its constituent
NOTE — Requirements concerning qualifications for equipment by skilled persons. Appropriate records shall
enterprises and persons are a matter for national consideration.
be kept.
6.3.2 Frequency of Periodic Verification
6.3.3 Reporting for Periodic Verification
6.3.2.1 The frequency of periodic verification of an
6.3.3.1 Upon completion of the periodic verification
installation shall be determined having regard to the
of an existing installation, a periodic report shall be
type of installation and equipment, its use and operation,
provided. Such documentation shall include details of
the frequency and quality of maintenance and the
those parts of the installation and limitations of the
external influences to which it is subjected.
verification covered by the report, together with a
NOTES record of the inspection, including any deficiencies
1 The maximum interval between periodic verifications may listed under 6.3.1.5, and the results of testing. The
be recommended for guidance in the Regulatory Measures periodic report may contain recommendations for
Relating to Electrical Safety and Supply under the Electricity
Act, 2003. repairs and improvements, such as upgrading the
2 The periodic report should recommend to the person carrying installation to comply with the current standard, as may
out the periodic verification the interval to the next periodic be appropriate.
verification.
3 The interval may be, for instance some years (for example, 4 The periodic report shall be given by the person
years), with the exception of the following cases where a higher responsible for carrying out the verification, or a person
risk may exist and shorter periods may be required: authorized to act on their behalf, to the person ordering
a) working places or locations where risks of electric shock, the verification.
fire or explosion exist due to degradation;
b) working places or locations where both high and low voltage 6.3.3.2 The records of test results shall record the
installations exist; results of the appropriate tests detailed in 6.3. Reports
c) communal facilities; shall be compiled and signed or otherwise authenticated
by a competent person or persons.

137
IS 732 : 2019

ANNEX A
(Clause 4.2.13.2)
(Normative)
PROVISIONS FOR BASIC PROTECTION

NOTE — Provisions for basic protection provide protection A-2.2 Horizontal top surfaces of barriers or enclosures
under normal conditions and are applied where specified as a
which are readily accessible shall provide a degree of
part of the chosen protective measure.
protection of at least IPXXD or IP4X.
A-1 BASIC INSULATION OF LIVE PARTS A-2.3 Barriers and enclosures shall be firmly secured
NOTE — The insulation is intended to prevent contact with in place and have sufficient stability and durability to

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
live parts. maintain the required degrees of protection and
Live parts shall be completely covered with insulation appropriate separation from live parts in the known
which can only be removed by destruction. conditions of normal service, taking account of relevant
external influences.
For equipment, the insulation shall comply with the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

relevant standard for the electrical equipment. A-2.4 Where it is necessary to remove barriers or open
enclosures or to remove parts of enclosures, this shall
A-2 BARRIERS OR ENCLOSURES be possible only;
NOTE — Barriers or enclosures are intended to prevent contact a) by the use of a key or tool, or
with live parts.
b) after disconnection of the supply to live parts
A-2.1 Live parts shall be inside enclosures or behind against which the barriers or enclosures afford
barriers providing at least the degree of protection protection, restoration of the supply being
IPXXB or IP2X except that, where larger openings possible only after replacement or reclosure
occur during the replacement of parts, such as certain of the barriers or enclosures, or
lampholders or fuses, or where larger openings are c) where an intermediate barrier providing a
necessary to allow the proper functioning of equipment degree of protection of at least IPXXB or
according to the relevant requirements for the IP2X prevents contact with live parts, by the
equipment: use of a key or tool to remove the intermediate
a) suitable precautions shall be taken to prevent barrier.
persons or livestock from unintentionally A-2.5 If, behind a barrier or in an enclosure, items of
touching live parts; equipment are installed which may retain dangerous
b) it shall be ensured, as far as practicable, that electrical charges after they have been switched off
persons will be aware that live parts can be (capacitors, etc), a warning label is required. Small
touched through the opening and should not capacitors such as those used for arc extinction, for
be touched intentionally; and delaying the response of relays, etc shall not be
c) the opening shall be as small as is consistent considered dangerous.
with the requirement for proper functioning NOTE — Unintentional contact is not considered dangerous if
and for replacement of a part. the voltage resulting from static charges fall below 120 V d.c.
in less than 5 s after disconnection from the power supply.

138
 IS 732 : 2019

ANNEX B
(Clause 4.5.3.2.2.1)
(Normative)
OBSTACLES AND PLACING OUT OF REACH
B-1 APPLICATION B-3 PLACING OUT OF REACH
The protective measures of obstacles and placing out NOTE — Protection by placing out of reach is intended only
to prevent unintentional contact with live parts.
of reach provide basic protection only.
They are for application in installations with or without B-3.1 Simultaneously accessible parts at different
fault protection that are controlled or supervised by potentials shall not be within arm’s reach.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
skilled or instructed persons. NOTE — Two parts are deemed to be simultaneously accessible
if they are not more than 2.50 m apart (see Fig. 62).
The conditions of supervision under which, the basic
protective provisions of this Annex may be applied, as B-3.2 If a normally occupied position is restricted in
part of the protective measure are given in 4.2.6. the horizontal direction by an obstacle (for example,
handrail, mesh screen etc) affording a degree of

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

B-2 OBSTACLES protection less than IPXXB or IP2X, arm’s reach shall
NOTE — Obstacles are intended to prevent unintentional
extend from that obstacle. In the overhead direction,
contact with live parts but not intentional contact by deliberate arm’s reach is 2.50 m from the surface, S, not taking
circumvention of the obstacle. into account any intermediate obstacle providing a
degree of protection less than IPXXB.
B-2.1 Obstacles shall prevent:
NOTE — The values of arm’s reach apply to contact directly
a) unintentional bodily approach to live parts, with bare hands without assistance (for example, tools or
and ladder).
b) unintentional contact with live parts during the B-3.3 In places where bulky or long conductive objects
operation of live equipment in normal service. are normally handled, the distances required by B-3.1
B-2.2 Obstacles may be removed without using a key and B-3.2 shall be increased, taking account of the
or tool but shall be secured so as to prevent relevant dimensions of those objects.
unintentional removal.

All dimensions in metres.

FIG. 62 ZONE OF ARM’S REACH

139
IS 732 : 2019

ANNEX C
(Clause 4.2.13.1.3)
(Normative)
PROTECTIVE MEASURES FOR APPLICATION ONLY WHEN THE INSTALLATION
IS CONTROLLED OR UNDER THE SUPERVISION OF SKILLED OR INSTRUCTED PERSONS

NOTE — The conditions of supervision under which the fault 2 000 V. Leakage current shall not exceed 1 mA in
protective provisions (protection against indirect contact) of
normal conditions of use.
Annex C may be applied as part of the protective measure are
given in 4.2.7. C-1.5 The resistance of insulating floors and walls at
every point of measurement under the conditions

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
C-1 NON-CONDUCTING LOCATION
specified in 6 shall be not less than:
NOTE — This protective measure is intended to prevent
simultaneous contact with parts which may be at different a) 50 kΩ, where the nominal voltage of the
potential through failure of the basic insulation of live parts. installation does not exceed 500 V, or
C-1.1 All electrical equipment shall comply with one b) 100 kΩ, where the nominal voltage of the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

of the provisions for basic protection described in installation exceeds 500 V.
Annex A. NOTE — If at any point the resistance is less than the
specified value, the floors and walls are deemed to be
C-1.2 Exposed-conductive-parts shall be arranged so extraneous-conductive-parts for the purposes of
that under ordinary circumstances persons will not protection against shock.
come into simultaneous contact with;
C-1.6 The arrangements made shall be permanent and
a) two exposed-conductive-parts, or it shall not be possible to make them ineffective. They
b) an exposed-conductive-part and any shall also ensure protection where the use of mobile or
extraneous-conductive-part, portable equipment is envisaged.
if these parts are liable to be at different potential NOTES
through failure of the basic insulation of live parts. 1 Attention is drawn to the risk that, where electrical installations
are not under effective supervision, further conductive parts
C-1.3 In a non-conducting location there shall be no may be introduced at a later date (for example, mobile or
protective conductor. portable Class I equipment or extraneous-conductive-parts such
as metallic water pipes), which may invalidate compliance with
C-1.4 The requirement of C-1.2 is fulfilled if the C-1.6.
location has an insulating floor and walls and one or 2 It is essential to ensure that the insulation of floor and walls
cannot be affected by humidity.
more of the following arrangements applies:
C-1.7 Precautions shall be taken to ensure that
a) Relative spacing of exposed-conductive-parts
extraneous-conductive-parts cannot cause a potential
and of extraneous-conductive-parts as well as
to appear externally to the location concerned.
spacing of exposed-conductive-parts.
This spacing is sufficient if the distance C-2 PROTECTION BY EARTH-FREE LOCAL
between two parts is not less than 2.50 m; this EQUIPOTENTIAL BONDING
distance may be reduced to 1.25 m outside
NOTE — Earth-free local equipotential bonding is intended
the zone of arm’s reach. to prevent the appearance of a dangerous touch voltage.
b) Interposition of effective obstacles between
C-2.1 All electrical equipment shall comply with one
exposed-conductive-parts and extraneous-
of the provisions for basic protection (protection against
conductive-parts.
direct contact) described in Annex A.
Such obstacles are sufficiently effective if they
extend the distances to be surmounted to the C-2.2 Equipotential bonding conductors shall
values stated in point C-1.4 (a). They shall interconnect all simultaneously accessible exposed-
not be connected to earth or to exposed- conductive-parts and extraneous-conductive-parts.
conductive-parts; as far as possible they shall C-2.3 The local equipotential bonding system shall not
be of insulating material. be in electrical contact with earth directly, nor through
c) Insulation or insulating arrangements of exposed-conductive-parts, nor through extraneous-
extraneous-conductive-parts. conductive-parts.
The insulation shall be of sufficient mechanical strength NOTE — Where this requirement cannot be fulfilled, protection
and be able to withstand a test voltage of at least by automatic disconnection of supply is applicable (see 4.2.11).

140
 IS 732 : 2019

C-2.4 Precautions shall be taken to ensure that persons earthed equipotential bonding conductors. Such
entering the equipotential location cannot be exposed conductors shall not be connected to the protective
to a dangerous potential difference, in particular, where conductors or exposed-conductive-parts of other
a conductive floor insulated from earth is connected to circuits or to any extraneous-conductive-parts (see Note
the earth-free equipotential bonding system. under 4.2.13.3.6).

C-3 ELECTRICAL SEPARATION FOR THE C-3.5 All socket-outlets shall be provided with
SUPPLY OF MORE THAN ONE ITEM OF protective contacts which shall be connected to the
CURRENT-USING EQUIPMENT equipotential bonding system provided in accordance
with C-3.4.
NOTE — Electrical separation of an individual circuit is
intended to prevent shock currents through contact with C-3.6 Except where supplying equipment with double
exposed-conductive-parts that may be energized by a fault in or reinforced insulation, all flexible cables shall embody

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
the basic insulation of the circuit.
a protective conductor for use as an equipotential
C-3.1 All electrical equipment shall comply with one bonding conductor in accordance with C-3.4.
of the provisions for basic protection described in
C-3.7 It shall be ensured that if two faults affecting
Annex A.
two exposed-conductive-parts occur and these are fed

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

C-3.2 Protection by electrical separation for the supply by conductors of different polarity, a protective device
of more than one item of apparatus shall be ensured by shall disconnect the supply in a disconnecting time
compliance with all the requirements of 4.2.13 conforming with Table 1.
except 4.2.13.1.2, and with the following requirements.
C-3.8 It is recommended that the product of the nominal
C-3.3 Precautions shall be taken to protect the separated voltage of the circuit in volts and length, in metres, of
circuit from damage and insulation failure. the wiring system should not exceed 100 000 V/m, and
that the length of the wiring system should not exceed
C-3.4 The exposed-conductive-parts of the separated
500 m.
circuit shall be connected together by insulated, non-

ANNEX D
(Clause 4.4)
(Normative)
PROTECTION OF CONDUCTORS IN PARALLEL AGAINST OVERCURRENT

D-1 INTRODUCTION D-2 OVERLOAD PROTECTION OF

CONDUCTORS IN PARALLEL
Overcurrent protection for conductors connected in
parallel should provide adequate protection for all of When an overload occurs in a circuit containing parallel
the parallel conductors. For two conductors of the same conductors of multicore cables, the current in each
cross-sectional area, conductor material length and conductor will increase by the same proportion.
method of installation arranged to carry substantially Provided that the current is shared equally between the
equal currents, the requirements for parallel conductors, a single protective device can be
overcurrent protection are straightforward. For more used to protect all the conductors. The current-carrying
complex conductor arrangements, detailed capacity (Iz) of the parallel conductors is the sum of
consideration should be given to unequal current the current-carrying capacity of each conductor, with
sharing between conductors and multiple fault current the appropriate grouping and other factors applied.
paths. This annex gives guidance on the necessary
The current sharing between parallel cables is a function
considerations.
of the impedance of the cables. For large, single-core
NOTE — A more detailed method for calculating the current cables the reactive component of the impedance is
between parallel conductors is given in IEC 60287-1-3.
greater than the resistive component and will have a

141
IS 732 : 2019

significant effect on the current sharing. The reactive The value used for Iz in 4.4.4.1, Equations (1) and (2),
component is influenced by the relative physical is either the continuous current-carrying capacity of
position of each cable. If, for example, a circuit consists each conductor, Izk, if an overload protective device is
of two large cables per phase, having the same length, provided for each conductor (see Fig. 63) hence:
construction and cross-sectional area and arranged in
IBk < Ink < Izk ....(6)
parallel but with adverse relative positioning (that is,
cables of the same phase bunched together) the current or
sharing may be 70 percent/30 percent rather than the sum of the current-carrying capacities of all the
50 percent/50 percent). conductors, ∑Izk, if a single overload protective device
Where the difference in impedance between parallel is provided for the conductors in parallel (see Fig. 64)
conductors causes unequal current sharing, for example hence:

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
greater than 10 percent difference, the design current IB < In < Izk ....(7)
and requirements for overload protection for each
conductor should be considered individually. where
Ink = the nominal current of the protective device
The design current for each conductor can be calculated
for conductor k;
from the total load and the impedance of each

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

conductor. Izk = the continuous current-carrying capacity of
conductor k;
For a total of m conductors in parallel, the design current
In = the rated current of the protective device; and
IBk for conductor k is given by:
Izk = the sum of the continuous current-carrying
IB capacities of the m conductors in parallel.
I Bk = NOTE — For busbar systems, information should be obtained
 Zk Zk Zk Zk Zk Z k  ... (3)
 Z + Z + ⋅⋅⋅ + Z + Z + Z + ⋅⋅⋅ + Z  either from the manufacturer or from IEC 60439-2.
1 2 k −1 k k +1 m

where
IB = the current for which the circuit is designed;
IBk = the design current for conductor k;
Zk = the impedance of conductor k; and
Z1 and Zm = the impedances of conductors 1 and m,
respectively.

In case of parallel conductors up to and including 120

mm2 the design current IBk for conductor k is given by:
Sk
I Bk = I B ... (4)
( S1 + S2 + ...... + Sm )
where
Sk = the cross-sectional area of conductor k; and
S1 … Sm= the cross-sectional area of the conductors.
FIG. 63 CIRCUIT IN WHICH AN O VERLOAD PROTECTIVE
In the case of single-core cables, the impedance is a
DEVICE IS P ROVIDED FOR EACH OF THEM CONDUCTORS
function of the relative positions of the cables as well
IN P ARALLEL
as the design of the cable, for example armoured or
unarmoured. Methods for calculating the impedance
are given in IEC 60287-1-3. It is recommended that D-3 SHORT-CIRCUIT PROTECTION OF
current sharing between parallel cables is verified by CONDUCTORS IN PARALLEL
measurement. Where conductors are connected in parallel, the effect
The design current IBk is used in place of IB for Equation of a short-circuit within the parallel section should be
(1) of 4.4.4.1 as follows: considered with respect to the protective device
arrangement.
IBk < In < Izk .... (5)

142
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 65 CURRENT FLOW AT THE B EGINNING OF THE
FAULT
FIG. 64 CIRCUIT IN WHICH A SINGLE OVERLOAD
P ROTECTIVE DEVICE IS P ROVIDED FOR THE m
CONDUCTORS IN P ARALLEL

Individual conductors in a parallel arrangement may

not be effectively protected when using single
protective devices, thus consideration should be given
to providing other protective arrangements. These could
include individual protective devices for each
conductor, protective devices at the supply and load
ends of the parallel conductors, and linked protective
devices at the supply end. Determination of the
particular protection arrangement will be dependent on
the likelihood of fault conditions.
Where conductors are connected in parallel, then
multiple fault current paths can occur resulting in
continued energizing of one side of the fault location. FIG. 66 CURRENT FLOW AFTER OPERATION OF THE
This could be addressed by providing short-circuit P ROTECTIVE DEVICES
protection at both the supply (s) and load (l) end of
each parallel conductor. This situation is illustrated in the protective device cl is necessary. It should be noted
Fig. 65 and Fig. 66. that the current flowing through cl will be less than the
current which caused cs to operate. If the fault was close
Figure 65 shows that, if a fault occurs in parallel enough to cl then cl would operate first. The same
conductor 3 at point x, the fault current will flow in situation would exist if a fault occurred in conductors
conductors 1, 2 and 3. The magnitude of the fault 1 or 2, hence the protective devices al and bl will be
current and the proportion of the fault current which required.
flows through protective devices cs and cl will depend
on the location of the fault. In this example it has been The method of providing protective devices at both ends
assumed that the highest proportion of the fault current has two disadvantages compared to the method of
will flow through protective devices. Figure 66 shows providing protective devices at the supply ends only.
that, once cs has operated, current will still flow to the Firstly, if a fault of x is cleared by the operation of cs
fault at x via conductors 1 and 2. Because conductors and cl, then the circuit will continue to operate with
1 and 2 are in parallel, the divided current through the load being carried by conductors 1 and 2. Hence,
protective devices as and bs may not be sufficient for the fault and subsequent overloading of conductors 1
them to operate in the required time. If this is the case, and 2 may not be detected, depending on the fault

143
IS 732 : 2019

impedance. Secondly, the fault at x may burn open-

circuit at the cl side, leaving one side of the fault live
and undetected.
An alternative to the six protective devices would be
to provide linked protective device(s) at the supply end
(see Fig. 67). This would prevent the continued
operation of the circuit under fault conditions.

FIG. 67 ILLUSTRATION OF LINKED PROTECTIVE DEVICE

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ANNEX E

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(Clause 4.4)
(Normative)
CONDITIONS 1 AND 2 OF 4.4.4.1

IB < In < IZ ....(8)

I2 < 1.45 × IZ ....(9)

FIG. 68 ILLUSTRATION OF CONDITIONS 1 AND 2 OF 4.4.4.1

144
 IS 732 : 2019

ANNEX F
(Clause 4.4)
(Normative)
POSITION OR OMISSION OF DEVICES FOR OVERLOAD PROTECTION

F-1 GENERAL requirements of 4.4.4.2.2 (b) its length does

not exceed 3 m, and the risk of short-circuit,
Devices for overload protection and devices for short-
fire and danger to person is reduced to a
circuit protection have to be installed for each circuit.
minimum for this length.
These protective devices generally need to be placed
at the origin of each circuit. For some applications, one

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of the devices for overload protection or for short-
circuit protection may not follow this general
requirement, provided the other protection remains
operative.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

F-2 CASES WHERE OVERLOAD PROTECTION
NEED NOT BE PLACED AT THE ORIGIN OF
THE BRANCH CIRCUIT
a) With reference to 4.4.4.2.2(a) and Fig. 69, an FIG. 70 OVERLOAD P ROTECTIVE DEVICE (P2)
overload protective device P2 may be moved INSTALLED WITHIN 3 m OF THE ORIGIN OF THE BRANCH
from the origin (O) of the branch circuit (B) CIRCUIT (B) [see 4.4.4.2.2(b)]
provided that there is no other connection or
socket-outlet on the supply side of P2, the It is accepted that for a length of 3 m, the branch circuit
protective device of this branch circuit, and is not protected against short-circuit, but precautions
in accordance with the requirements of have to be taken to ensure safety [see 4.4.4.2.2(b)]. In
4.4.4.2.2(a), short-circuit protection for this addition it may be possible that the short-circuit
part of the branch circuit is provided. protection of the supply circuit also provides short-
circuit protection to the branch circuit up to the point
where P2 is installed (see Annex G).

F-3 CASES WHERE OVERLOAD PROTECTION

MAY BE OMITTED
a) With reference to 4.4.4.3.1 and Fig.71,
omission of overload protection is permitted
provided that there is no other connection or
socket-outlet on the supply side of the
protective device of this branch circuit, and
FIG. 69 OVERLOAD PROTECTIVE DEVICE (P2) NOT AT that one of the following applies:
THE O RIGIN OF B RANCH CIRCUIT (B) – branch circuit S2 is protected against
[see 4.4.4.2.2(a)] overload by P1 [see 4.4.4.3.1(a)]; or
The overload protective device is to protect – branch circuit S3 is not likely to carry
the wiring system. Only current-using overload [see 4.4.4.3.1(b)]; or
equipment may generate overload; therefore – BRANCH circuit S 4 is for
the overload protective device may be moved telecommunication, control, signalling
along the run of the branch circuit to any place and the like [see 4.4.4.3.1(d)].
provided short-circuit protection of the branch
With reference to 4.4.4.3.2.1 and Fig. 72, additional
circuit remains operational.
requirements of F-2 and F-3 (a), only applicable to IT
b) With reference to 4.4.4.2.2(b) and Fig. 70, an systems, are required by 4.4.4.3.2.1. Overload
overload protective device P2 may be moved protection may be omitted provided that there is no
up to 3 m from the origin (O) of the branch other connection or socket-outlet on the supply side of
circuit (B) provided that there is no other P2, the protective device of this branch circuit, and that
connection or socket-outlet on this length of one of the following applies:
the branch circuit, and in accordance with the

145
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTE — P2, P3 and P4 are the short-circuit protective devices for branch circuits S2, S3 and S4 respectively.

FIG. 71 I LLUSTRATION OF CASES WHERE OVERLOAD PROTECTION MAY BE OMITTED

[see 4.4.4.3.1(a), (b) and (d)]

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

— branch circuit S 2 employs the protective In an IT system, consideration needs to be given to the
measures described in 4.2.12 and consists of possible occurrence of two separate insulation faults
class II equipment; or affecting different circuits. In most cases, the occurrence
— branch circuit S3 is protected by an RCD that of two separate faults results in a short-circuit situation.
will operate immediately on the occurrence However, the fault impedance, lengths and cross-
of a second fault; or sectional areas of both circuits involved may be
— branch circuit S4 is equipped with an insulation unknown. As a consequence, the possible occurrence
monitoring device that causes the of two separate insulation faults may result in an
disconnection of the circuit when the first fault overload situation for at least one of the protective
occurs or provides an alarm signal indicating devices.
the presence of a fault.

NOTE — P2, P3 and P4 are the short-circuit protective devices for branch circuits S2, S3 and S4, respectively.

FIG. 72 ILLUSTRATION OF CASES WHERE OVERLOAD P ROTECTION MAY BE OMITTED IN AN IT SYSTEM

146
 IS 732 : 2019

ANNEX G
(Clauses 4.4.4.4.2 and 4.4.5.2.2)
(Normative)
POSITION OR OMISSION OF DEVICES FOR SHORT-CIRCUIT PROTECTION

G-1 GENERAL installed at a point on the supply side of the

origin (O) of the branch circuit (B) provided
Devices for overload protection and devices for short-
that, in conformity with 4.4.5.2.2, the
circuit protection have to be installed for each circuit.
maximum length between the origin of the
These protective devices generally need to be placed
branch circuit and the short-circuit-protective
at the origin of each circuit.
device of this branch circuit respect the

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
For some applications, one of the devices for overload specification proposed by the “triangular
protection or for short-circuit protection may not follow rule”.
this general requirement, provided the other protection
The maximum length of the conductor branched off at
remains operative.
O, with the cross-sectional area S2, that is protected

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

G-2 CASES WHERE SHORT-CIRCUIT against a short-circuit by the protective device P1 placed
PROTECTION DOES NOT NEED TO BE at A, is given as length ON in the triangle BON.
PLACED AT THE ORIGIN OF BRANCH This clause may be used in the case where only
CIRCUIT protection against short-circuit is provided. Protection
a) With reference to 4.4.5.2.1 and Fig. 73, short- against overload is not considered in this example
circuit protective device may be moved up to (see F-3).
3 m from the origin (O) of the branch circuit These maximum lengths correspond to the minimum
(S2) provided that there is no other connection short-circuit capable of activating the protective device
or socket-outlet on this length of the branch P1. This protective device protecting branch circuit S1
circuit, and in the case of 4.4.5.2.1 the risk of up to the length AB also protects the branch circuit S2.
short-circuit, fire and danger to persons is The maximum length of branch circuit S2 protected by
reduced to a minimum for this length. P1 depends on the location where the branch circuit S2
The 3 m length of conductor in the branch is connected to S1.
circuit is not protected against short-circuit,
The length of branch circuit S2 cannot exceed the value
but the short-circuit protection provided for
determined by the triangular diagram. In this case, the
the supply circuit may still provide short-
protective device P2 may be moved along branch circuit
circuit protection for the branch circuit up to
S2 up to the point N.
the point where P2 is installed.
b) With reference to 4.4.5.2.2 and Fig. 74, the NOTES
short-circuit protective device P2 may be 1 This method may also be applied in the case of three
successive conductor runs of different cross-sectional area.

NOTE — S = cross-sectional area of conductor.

FIG. 73 LIMITED CHANGE OF POSITION OF SHORT-CIRCUIT P ROTECTIVE D EVICE (P2) ON A BRANCH CIRCUIT
(see 4.4.5.2.1)

147
IS 732 : 2019

A O B
P1
S1
S2 P
N P 22
S2

P2
M

S2
P2

L1
A 0 B

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
S1
S2
L2

N
M

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

AB = is the maximum length L1 of the conductor of the cross-sectional area S1 protected against short-circuit by the protective device
P1 placed at A.
AM = is the maximum length L2 of the conductor of the cross-sectional area S2 protected against short-circuit by the protective device
P1placed at A.

FIG. 74 SHORT-CIRCUIT P ROTECTIVE D EVICE P2 I NSTALLED AT A P OINT ON THE SUPPLY SIDE OF

THE ORIGIN OF A B RANCH C IRCUIT (see 4.4.5.2.2)

2 If, for section S2, the lengths of wiring differ according to the protective device may be omitted for some applications
nature of insulation, the method is applicable by taking the
such as transformers or measuring circuits provided
length:
that, in accordance with the requirements of 4.4.5.3,
AB = L2S1/S2
If, for section S2, the lengths of wiring are the same whatever to
the risk of short-circuit, fire and danger to persons is
the nature of insulation, the method is applicable by taking the reduced to a minimum.
length:
Note that a measuring circuit employing a current
AB= L1
transformer must not be open-circuited otherwise an
G-3 CASE WHERE SHORT-CIRCUIT overvoltage will result.
PROTECTION MAY BE OMITTED For some applications, such as a magnetic crane, short-
With reference to 4.4.5.3 and Fig. 75, the short-circuit circuit protection may be omitted (see 4.4.5.3).

FIG. 75 SITUATION WHERE THE SHORT-CIRCUIT PROTECTIVE DEVICE MAY BE OMITTED

FOR SOME APPLICATIONS (see 4.4.5.3)

148
 IS 732 : 2019

ANNEX H
(Clause 4.5)
(Normative)
EXPLANATORY NOTES CONCERNING 4.4.5.1 AND 4.4.5.2

H-1 GENERAL The following fault conditions in the high-voltage

The rules in these two clauses are intended to provide system are taken into consideration:
for the safety of persons and equipment in an LV system Effectively earthed high-voltage systems
in the event of an earth-fault in the HV system.
These systems include those systems where the neutral
Faults between systems at different voltages refer to is connected to earth either directly or via a low

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
those that may occur on the high-voltage side of the impedance and where earth faults are cleared in a
substation supplying a low-voltage system through a reasonably short time given by the protective
distribution system operating at a higher voltage. Such equipment.
faults cause a current to flow in the earth electrode to
which the exposed-conductive-parts of the substation No connection of the neutral to earth in the relevant
transformer substation is considered.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

are connected.
The magnitude of the fault-current depends on the fault- In general, capacitive currents are neglected.
loop impedance, that is, on how the high-voltage neutral
is earthed. Isolated high-voltage systems

The fault-current flowing in the earth electrode of the Only single-fault conditions due to a first earth fault
exposed-conductive-parts of the substation causes a rise between a high-voltage live-part and exposed-
of the potential with respect to earth of the exposed- conductive-parts of the transformer substation are taken
conductive-parts of the substation whose magnitude is into account. This (capacitive) current may or may not
governed by: be interrupted, depending on its magnitude and the
protective system.
a) the fault-current magnitude, and
b) the resistance of the earth electrode of the High-voltage systems with arc-suppression coils
exposed-conductive-parts of the substation. No arc-suppression coils in the relevant transformer
The fault-voltage may be as high as several thousand substation are considered.
volts and, depending on the earthing systems of the
Where an earth fault in the high-voltage system occurs
installation, may cause
between a high-voltage conductor and the exposed-
a) a general rise of the potential of the exposed- conductive-parts of the transformer substation, only
conductive-parts of the low-voltage system small fault currents occur (residual currents mostly in
with respect to earth, which may give rise to the order of some tens of amperes). These currents may
fault and touch-voltages; persist for longer times.
b) a general rise of the potential of the low-
voltage system with respect to earth, which H-2 OVERVOLTAGES IN LV-SYSTEMS DURING
may cause a breakdown in the low-voltage A HIGH-VOLTAGE EARTH FAULT
equipment. Figure 28 has been derived from curve c2 of Fig. 20 of
It usually takes longer to clear a fault in a high-voltage IS/IEC 60479-1 and was also taken as a practical
system than in a low-voltage system, because the relays proofed decision in IEC 61936-1.
have time delays for discrimination against unwanted When considering the values for the fault-voltage, the
tripping on transients. The operating times of the high- following should be taken into account:
voltage switchgear are also longer than for low-voltage
switchgear. This means that the resulting duration of a) the low risk of an earth-fault in the HV system;
the fault-voltage and the corresponding touch-voltage and
on the exposed-conductive-parts of the low-voltage b) the fact that the touch voltage is always lower
system may be longer than required by the LV than the fault-voltage due to the main
installation rules. equipotential bonding required in 4.2.11.3.1.2
There may also be a risk of breakdown in the low- and the presence of additional earth electrodes
voltage system of the substation or consumer’s at the consumer’s installation or elsewhere.
installation. The operation of protective devices under Values given by ITU-T 650 V for 0.2 s and 430 V for
abnormal conditions of transient recovery voltages may automatic disconnection in longer than 0.2 s are slightly
give rise to difficulties in opening the circuit or even in excess of the values given in Fig. 28.
failure to do so.
149
IS 732 : 2019

ANNEX J
(Clause 4.5)
(Normative)
GUIDANCE FOR OVERVOLTAGE CONTROL BY SPDs APPLIED TO OVERHEAD LINES

J-1 In the conditions of 4.5.3.3.2.1 and according to accordance with (a) at each transition point
Note 1, the protective control of the overvoltage level from and overhead line to an underground
may be obtained either by installing surge protective cable;
devices directly in the installation, or with the consent c) in a TN distribution network supplying
of the network operator, in the overhead lines of the electrical installations, where protection
supply distribution network.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
against indirect contact is provided by
As an example, the following measures may be applied: automatic disconnection of supply, the
earthing conductors of the overvoltage
a) in the case of overhead supply distribution protective devices connected to the line
networks, overvoltage protection is erected at conductors are connected to the PEN
network junction points and especially at the

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

conductor or to the PE conductor; and
end of each feeder longer than 500 m. d) in a TT distribution network supplying
Overvoltage protective devices should be electrical installations, where protection
erected at every 500 m distance along the against indirect contact is provided by
supply distribution lines. The distance automatic disconnection of supply,
between overvoltage protective devices overvoltage protective devices are provided
should be less than 1 000 m; for the phase conductors and for the neutral
b) if a supply distribution network is erected conductor. At the place where the neutral
partly as overhead network and partly as conductor of the supply network is effectively
underground network, overvoltage protection earthed, an overvoltage protective device for
in the overhead lines should be applied in the neutral conductor is not necessary.

Table 16 Different Possibilities for IT Systems

(taking into account a first fault in the LV installation)

System Exposed- Neutral Exposed-conductive U1 U2 Uf

Conductive-parts of Impedance, parts of Equipment
LV Equipment of if any of the LV
the Substation Installation
a R × Im
U0 3 U0 3

b 0 01)
U0 3 R × Im + U0 3

C2) 0 0 0 01)
R × Im + U0 3 U0 3

d 0 01)
R × Im + U0 3 U0 3

e2) 0 R × Im
R × Im + U0 3 R × Im + U0 3
1)
In fact, Uf is equal to the product of first fault current by the resistance of the earth electrode of the exposed-conductive-parts
(RA × Id) which shall be less or equal to UL.
Further, in systems a, b and d, the capacitive currents which flow through the first fault may increase in certain cases the value of Uf,
but this is disregarded.
2)
In systems c1 and e1, an impedance is installed between the neutral and earth (impedance neutral).
In systems c2 and e2, no impedance is installed between the neutral and earth (isolated neutral).

150
 IS 732 : 2019

ANNEX K
(Clause 4.5.3.3.2.2)
(Normative)
DETERMINATION OF THE CONVENTIONAL LENGTH, d

K-1 The configuration of the low-voltage distribution unscreened line of the structure, limited to
line, its earthing, insulation level and the phenomena 1 km;
considered: (induced coupling, resistive coupling) lead
d3 = the length of the high-voltage overhead
to different choices for d. The determination proposed
supply line of the structure, limited to 1 km;
below represents, by convention, the worst case.
The length of a high-voltage underground

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTE — This simplified method is based on IEC 61662.
supply line is neglected.
d 2 d3 The length of a screened low-voltage
d =d1 + + underground line is neglected.
Kg K t
Kg = 4 is the reduction factor based on the ratio

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

By convention d is limited to 1 km, on the influence of strikes between the
overhead lines and underground unscreened
where cables, calculated for a resistivity of soil of
d1 = the length of the low-voltage overhead 250 Ωm;
supply line to the structure, limited to 1 km; Kt = 4 is the typical reduction factor for a
d2 = the length of the low-voltage underground transformer.

HV and LV overhead lines

HV overhead line and buried LV lines

151
IS 732 : 2019

HV and LV buried lines

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
HV line overhead

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

NOTE — When the HV/LV transformer is inside the building, d1 = d2 = 0.

FIG. 76 EXAMPLES OF HOW TO APPLY d 1, d 2 AND d 3 FOR THE DETERMINATION OF d

152
 IS 732 : 2019

ANNEX L
(Clause 5.1)
(Normative)
CONCISE LIST OF EXTERNAL INFLUENCES

A Environmental conditions AK Flora AM22 Conducted

AK1 No hazard unidirectional transients
AA Temperature (°C) AK2 Hazard of the nanosecond time
AA1 –60 +5 AM22-1 scale
AA2 –40 +5 AL Fauna AM22-2 Negligible level
AA3 –25 +5 AL1 No hazard AM22-3 Medium level
AA4 –5 +40 AL2 Hazard AM22-4 High level
AA5 +5 +40 Very high level

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
AA6 +5 +60 AM Electromagnetic, electrostatic, or AM23 Conducted
AA7 –25 +55 ionizing influences unidirectional transients
AA8 –50 +40 Low-frequency electromagnetic of the microsecond to
phenomena (conducted or the millisecond time
AB Temperature and humidity radiated) scale
AB1 –60°C +5°C 3% 100% Harmonics, interharmonics Controlled level
AB2 –40°C +5°C 10% 100% Controlled level Medium level

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

AB3 –25°C +5°C 10% 100% AM1 Normal level AM23-1 High level
AB4 –5°C +40°C 5% 95% AM1-1 High level AM23-2
AB5 +5°C +40°C 5% 85% AM1-2 AM23-3 Conducted oscillatory
AB6 +5°C +60°C 10% 100% AM1-3 Signalling voltages transients
AB7 –25°C +55°C10% 100% Controlled level Medium level
AB8 –50°C +40°C15% 100% AM2 Normal level AM24 High level
AM2-1 High level
AC Altitude (m) AM2-2 AM24-1 Radiated high frequency
AC1 < 2 000 AM2-3 Voltage amplitude variations AM24-2 phenomena
AC2 2 000 Controlled level Negligible level
AM3 Normal level AM25 Medium level
AD Water AM3-1 High level
AD1 Negligible AM3-2 Voltage unbalance AM25-1
AD2 Drops AM25-2 Electrostatic discharges
AD3 Spray AM4 Power frequency variations AM25-3 Small level
AD4 Splashes Medium level
AD5 Jets AM5 Induced low-frequency voltages AM31 High level
AD6 Waves AM31-1 Very high level
AD7 Immersion AM6 Direct current in a.c. voltages AM31-2
AD8 Submersion AM31-3 Ionization
Radiated magnetic field AM31-4
AE Foreign bodies AM7 Medium level Solar radiation
AE1 Negligible High level AM41 Low
AE2 Small Medium
AE3 Very small AM8 Electric fields AN High
AE4 Light dust AM8-1 Negligible level AN1
AE5 Moderate dust AM8-2 Medium level AN2 Seismic effects
AE6 Heavy dust High level AN3 Negligible
Very high level Low severity
AF Corrosion AM9 Medium severity
AF1 Negligible AM9-1 High frequency electromagnetic AP High severity
AF2 Atmospheric AM9-2 phenomena conducted, induced or AP1
AF3 Intermittent AM9-3 radiated (continuous or transient) AP2 Lightning
AF4 Continuous AM9-4 Induced oscillatory voltages or AP3 Negligible
currents AP4 Indirect exposure
Mechanical stress Direct exposure
AG Impact AQ
AG1 Low severity AQ1 Movement of air
AG2 Medium severity AQ2 Low
AG3 High severity AQ3 Medium
AM21 High
AH Vibration AR
AH1 Low severity AR1 Wind
AH2 Medium severity AR2 Low
AH3 High severity AR3 medium
High
AS
AS1
AS2
AS3

153
IS 732 : 2019

B Utilization BC Contact of persons with earth BE Nature of processed or

None stored materials
BA Capability of persons BC1 Low BE1 No significant risk
BA1 Ordinary BC2 Frequent BE2 Fire risk
BA2 Children BC3 Continuous BE3 Explosion risk
BA3 Handicapped BC4 BE4 Contamination risk
Utilisation

BA4 Instructed Condition of evacuation in an

BA5 Skilled BD emergency
Low density/easy exit
BB Electrical resistance of the human BD1 Low density/difficult exit
body BD2 High density/easy exit
BD3 High density/difficult exit
BD4
C Construction and buildings CB Building design

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
CB1 Negligible risks
CA Construction materials CB2 Propagation of fire
Building

CA1 Non-combustible CB3 Movement

CA2 Combustible CB4 Flexible or unstable

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

ANNEX M
(Clause 5.1)
(Normative)
INTERDEPENDENCE OF AIR TEMPERATURE, RELATIVE AIR HUMIDITY
AND ABSOLUTE AIR HUMIDITY
M-1 This Annex contains climatograms for each class considered in connection with the rather low value of
of ambient climatic conditions, showing the high absolute humidity for the limit value of high air
interdependence of air temperature, relative air humidity temperature in these classes.
and absolute air humidity by curves for constant
M-1.5 To give a review of this situation, Table 17 for
absolute humidity and lines for temperature and relative
each class the highest value of air temperature which
humidity.
may occur is given together with the highest value of
M-1.1 As far as air temperature is concerned, the relative air humidity of the class. At air temperatures
climatogram shows the possible maximum temperature higher than the value given in the table the relative air
difference for any location covered by the class. humidity will be lower, that is, below the limit value of
the class.
M-1.2 As far as air humidity is concerned, the
climatogram comprises the complete scatter of values of
Table 17 Highest Value of Air Temperature
relative air humidity in accordance with any air
Corresponding to Class Code
temperature occurring within the range covered by the
(Clauses 5.2.4.1 and M-1.5)
class. The interdependence of both temperature and
humidity is fixed by the values of absolute air humidity Class Limit Value of Highest Value of Air
occurring within the range of the class. Code Relative Air Temperature
Humidity to Occur with Limit Value of
M-1.3 As already stated in the notes of Table 7, the limit Relative Air Humidity
values of, for example, high air temperature and high AB1 100 % +5 °C
relative air humidity given in the classes will normally AB2 100 % +5 °C
not occur in combination. Normally higher values of air AB3 100 % +5 °C
temperature will occur combined with lower values of AB4 95 % +31 °C
relative air humidity. AB5 85 % +28 °C
M-1.4 Exceptions from this rule will be found for AB6 100 % +33 °C
classes AB1, AB2 and AB3, where any value of relative AB7 100 % +27 °C
humidity specified for the range may be combined with AB8 100 % +33 °C
the highest value of air temperature. This fact should be

154
 IS 732 : 2019

M-1.6 In practice, the climatograms may be used as climatogram for class AB6 up to the point where it
follows: meets the curve for 35 g/m3 absolute air humidity
which is the limit value for high absolute air humidity
The relevant value of relative air humidity at
for this class. From this point one draws a horizontal
a certain value of air temperature within the
line to the scale of relative air humidity, and one will
temperature range of a class may be found at
find a value of 67 percent relative air humidity.
the point where the curve for constant
absolute air humidity cuts the straight lines Using this method, any other possible combination of
for air temperature and relative air humidity air temperature and relative air humidity within the
respectively. range of the class may be found, for example, in class
AB6 a value of 27 percent relative air humidity will
Example:
be found at the limit value of high air temperature
A product may be selected for installation conditions which is 60 °C.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
covered by class AB6. To find out which relative air
Climatogram
humidity the product will have to withstand in the
utmost at, for example, 40 °C, one follows the Interdependence of air temperature, relative air
vertical line for air temperature 40 °C in the humidity and absolute air humidity.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Class AB 1

155
 Class AB 2
Climatogram
IS 732 : 2019

156
Interdependence of air temperature, relative air humidity and absolute air humidity.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 3
Climatogram

157
Interdependence of air temperature, relative air humidity and absolute air humidity.
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 4
Climatogram
IS 732 : 2019

158
Interdependence of air temperature, relative air humidity and absolute air humidity.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 5
Climatogram

159
Interdependence of air temperature, relative air humidity and absolute air humidity.
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 6
Climatogram
IS 732 : 2019

160
Interdependence of air temperature, relative air humidity and absolute air humidity.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 7
Climatogram

161
Interdependence of air temperature, relative air humidity and absolute air humidity.
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 Class AB 8
Climatogram
IS 732 : 2019

162
Interdependence of air temperature, relative air humidity and absolute air humidity.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 IS 732 : 2019

ANNEX N
(Clause 5.1)
(Normative)
CLASSIFICATION OF MECHANICAL CONDITIONS
Environmental Unit Class
Parameter
AG1/AH1 AG2/AH2 AG3/AH3

3M1 3M2 3M3 3M4 3M5 3M6 3M7 3M8

4M1 4M2 4M3 4M4 4M5 4M6 4M7 4M8

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Stationary
vibration,
sinusoidal
Displacement mm 0.3 1.5 1.5 3.0 3.0 7.0 10 15
amplitude

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Acceleration m/s2 1 5 5 10 10 20 30 50
amplitude
Frequency Hz 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200 2-9 9-200
range
Non-stationary
vibration, in-
cluding shock
Shock response
spectrum m/s2 40 40 70 – – – – –
type L (â)
Shock response
spectrum m/s2 – – – 100 – – – –
type I (â)
Shock response
spectrum m/s2 – – – – 250 250 250 250
type II (â)
NOTE — â = maximum acceleration.

Spectrum type L Duration = 22 ms

Spectrum type I Duration = 11 ms
Spectrum type II Duration = 6 ms

FIG. 77 MODEL SHOCK RESPONSE SPECTRA

(FIRST ORDER “MAXIMAS” SHOCK RESPONSE SPECTRA)

163
IS 732 : 2019

ANNEX P
(Clause 5.1)
(Normative)
CLASSIFICATION OF MACRO-ENVIRONMENTS

Category Climatic Chemically and

of Environment Conditions Mechanically Active
Substances1)
I AB 5 AF 2/AE 1

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3K 3 3C 2/3S 1
II AB 4 AF 1/AE 4
3K 5, but the high air temperature 3C 1/3S 2
is restricted to +40 °C
III AB 7 AF 2/AE 5

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

3K 6 3C 2/3S 3
IV AB 8 AF 3/AE 6
4K 3 3C 3/3S 4
1)
The first line in each box shows the class designation according to Table 7.
The second line shows the class designation according to IEC 60721-3-0.

NOTE  The macro-environment is the environment of the room or other location in which the equipment is installed or used.

ANNEX Q
(Clause 5.1.6)
(Normative)
PERMISSIBLE PROTECTIVE CONDUCTOR CURRENTS FOR EQUIPMENT
As additional information to 5.1.6, IEC 61140 The requirements of 7.5.2 of IEC 61140 take into
specifies protective conductor currents and their account equipment intended to be supplied by plug
limits as follows. and socket-outlet systems, or by a permanent
NOTE  Subclauses are reproduced directly from IEC 61140.
connection, or the case of stationary equipment.

Q-1 PROTECTIVE CONDUCTOR CURRENTS Q-1.2 Maximum a.c. Limits of Protective

Conductor Currents of Current-using Equipment
Measures shall be taken in the installation and in
NOTE  A protective conductor current measurement
equipment to prevent excessive protective conductor method, which takes into account high-frequency components
currents impairing safety or normal use of the weighted according to IS/ IEC 60479-2, is under consideration.
electrical installation. Compatibility shall be ensured
for currents of all frequencies supplied to and Measurements shall be carried out on equipment as
produced by the equipment. delivered.
The following limits are applicable to equipment
Q-1.1 Requirements for the Prevention of supplied at rated frequency of 50 Hz or 60 Hz.
Excessive Protective Conductor Currents of
Current-using Equipment a) Plug-in current using equipment fitted with a
single or multi-phase plug and socket-outlet-
The requirements for electrical equipment which system rated up to and including 32 A. Limit
causes, under normal operating conditions, a current values are given in Annex B from IEC
to flow in its protective conductor, shall allow normal 61140.
use and be compatible with protective provisions.

164
 IS 732 : 2019

b) Current-using equipment for permanent Q-1.5 Information

connection and current using stationary
For equipment intended for permanent connection
equipment, both without special measures
with reinforced protective conductor, the value of the
for the protective conductor, or plug-in
protective conductor current shall be provided by the
current using equipment fitted with a single
manufacturer in his documentation and indication
phase or multiphase plug and socket-outlet
shall be given in the instructions for installation, that
system, rated more than 32 A. Limit values
the equipment shall be installed as described in 7.5.3
are given in Annex B from IEC 61140.
of IEC 61140.
c) Current-using equipment for permanent
connection intended to be connected to a Q-2 VALUES OF MAXIMUM ac LIMITS OF
reinforced protective conductor according to PROTECTIVE CONDUCTORS CURRENT FOR
7.5.2.4 of IEC 61140. Product committees CASES Q-1.2 (A) AND Q-1.2 (B)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
should state the maximum values for the
protective conductor current, which in no These values are for consideration by product
case shall exceed 5 percent of the rated committees in order to prevent excessive protective
input current per phase. conductor currents and to provide co-ordination of
electrical equipment and of protective measures
However, product committees shall consider that, for within an electrical installation.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

protective reasons, residual current devices may be
provided in the installation, in which case, the Product committees are encouraged to use the lowest
protective conductor current shall be compatible with practical values of protective conductor current
the protective measures provided. Alternatively a limits.
transformer with a separate winding and with at least Product committees should be aware that adoption of
simple separation, shall be used. limits not exceeding the values below may avoid
unwanted tripping of residual current devices in most
Q-1.3 d.c. Protective Conductor Current cases.
In normal use, a.c. equipment shall not generate Values for 7.5.2.2(a)
current with a d.c. component in the protective
conductor which could affect the proper functioning Values for plug-in current-using equipment fitted
of residual current devices or other equipment. with a single phase or multiphase plug and socket-
outlet system, rated up to and including 32 A:
NOTE  Requirements related to fault currents with d.c.
component are under consideration. Maximum Protective
Equipment Rated Current
Conductor Current
Q-1.4 Provisions in Equipment in Case of
<4A 2 mA
Connection to Reinforced Protective Conductor
> 4 A but < 10 A 0.5 mA/A
Circuits for Protective Conductor Currents
exceeding 10 mA > 10 A 5 mA

The following shall be provided in the current-using Values for 7.5.2.2(b)

equipment: Values for current-using equipment for permanent
a) a connecting terminal designed for the connection and current using stationary equipment,
connection of a protective conductor, both without special measures for the protective
measuring at least of 10 mm2 Cu or 16 mm2 conductor, or plug-in current-using equipment, fitted
Al, or with a single phase or multiphase plug and socket-
outlet system, rated more than 32 A:
b) a second terminal designed for the
connection of a protective conductor of the Maximum Protective
same cross-section as that of the normal Equipment Rated Current
Conductor Current
protective conductor so as to connect a <7A 3.5 mA
second protective conductor to the current- > 7 A but < 20 A 0.5 mA/A
using equipment. > 20 A 10 mA

165
IS 732 : 2019

ANNEX R
(Clause 5.2.4.1)
(Normative)
METHODS OF INSTALLATIONS

Table 17 Methods of Installation in Relation to Conductors and Cables

(Clause 5.2.4.1)
Method of Installation
Cable Trunking Cable
Conductors Systems (Including Cable Ladder,
Without Clipped Conduit On Support

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
and Cables Skirting Trunking, Ducting Cable Tray,
Fixings Direct Systems Insulators Wire
Flush Floor Systems Cable
Trunking) Brackets
1. Bare conductors – – – – – – + –
2. Insulated conductors2) – – + +1) + – + –
Sheathed Multi- + + + + + + 0 +

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

cables core
3. (including Single- 0 + + + + + 0 +
armoured core
and
mineral
insulated)
+ Permitted.
– Not permitted.
0 Not applicable, or not normally used in practice.
1)
Insulated conductors are admitted if the cable trunking systems provide at least the degree of protection IP4X or IPXXD and if the cover
can only be removed by means of a tool or a deliberate action.
2)
Insulated conductors which are used as protective conductors or protective bonding conductors may use any appropriate method of
installation and need not be laid in conduits, trunking or ducting systems.

Table 18 Erection of Wiring Systems

(Clause 5.2.4.2)
Method of Installation
Cable
Trunking
Situations (Including Cable Cable Ladder,
Without Clipped Conduit Support
Skirting Ducting Cable Tray, On Insulators
Fixings Direct Systems Wire
Trunking, Systems Cable Brackets
Flush Floor
Trunking)
Building Accessible 40 33 41, 42 6, 7, 8, 9, 12 43, 44 30, 31, 32, 33, 34 – 0
voids Not 40 0 41,42 0 43 0 0 0
accessible
Cable channel 56 56 54, 55 0 30, 31, 32, 34 – –
Buried in ground 72, 73 0 70, 71 – 70, 71 0 – –
Embedded in structure 57, 58 3 1, 2, 59, 50, 51, 52, 53 46, 45 0 – –
60
Surface mounted – 20, 21, 4, 5 6, 7, 8, 9, 12 6, 7, 8, 9 30, 31, 32, 34 36 –
22, 23, 33
Overhead/free in air – 33 0 10, 11 10,11 30, 31, 32,34 36 35
Window frames 16 0 16 0 0 0 - -
Architrave 15 0 15 0 0 0 – –
Immersed 1 + + + – + 0 – –
– Not permitted.
0 Not applicable or not normally used in practice.
+ Follow manufacturer’s instructions.
NOTE  The number in each box, for example, 40, 46, refers to the number of the method of installation given in Table 19.

166
 IS 732 : 2019

Table 19 Examples of Methods of Installation Providing Instructions

for Obtaining Current-Carrying Capacity
(Clause 5.2.4.3)

Reference Method of
Installation to be Used to
Item No. Methods of Installation Description Obtain Current-Carrying
Capacity
(see Annex S)

Room Insulated conductors or single-core cables in

1 A1

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
conduit in a thermally insulated wall11.3)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Room Multi-core cables in conduit in a thermally
2 A2
insulated wall1.3)

Room Multi-core cable direct in a thermally

3 A1
insulated wall1.3)

Insulated conductors or single-core cables in

conduit on a wooden or masonry wall or
4 B1
spaced less than
0.3  conduit diameter from it3)

Multi-core cable in conduit on a wooden or

masonry wall or spaced less than 0.3 
5 B2
conduit diameter
from it3)

Insulated conductors or single-core cables in

6 cable trunking (includes multi-compartment
trunking) on a wooden or masonry wall B1
7 – run horizontally2)
– run vertically2,3
6 7

Multi-core cable in cable trunking (includes

8 multi-compartment trunking) on a wooden
Under considerationd
or masonry wall
Method B2 may be used
9 – run horizontally2)
– run vertically2,3)
8 9
Insulated conductors or single-core cable in
B1
10 suspended cable trunking2)

Multi-core cable in suspended cable

11 B2
trunking2)
10 11

167
IS 732 : 2019

Table 19 — (Continued)

Reference Method of
Installation to be Used to
Item
Methods of Installation Description Obtain Current-Carrying
No.
Capacity
(see Annex S)

Insulated conductors or single-core cable run in

12 A1
mouldings3,5)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Insulated conductors in conduit or single-core or
15 A1
multi-core cable in architrave3,6)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Insulated conductors in conduit or single-core or
16 multi-core cable in window frames3,6) A1

Single-core or multi-core cables:

20 – fixed on, or spaced less than 0.3  cable C
diameter from a wooden or masonry wall3)

Single-core or multi-core cables:

C, with item 3 of
21 – fixed directly under a wooden or masonry
Table 36
ceiling

Single-core or multi-core cables: Under consideration

22
– spaced from a ceiling Method E may be used

Fixed installation of suspended current- using C, with item 3 of

23
equipment Table 36

30 > <
 0,3 De C with item 2
of Table 36

Single-core or multi-core cables:

On unperforated tray run horizontally or
vertically3,8)

> <
 0,3 De

168
 IS 732 : 2019

Table 19 — (Continued)

Reference Method of
Installation to be Used to
Item
Methods of Installation Description Obtain Current-Carrying
No.
Capacity
(see Annex S)

31 > <
 0,3 De

Single-core or multi-core cables:

On perforated tray run horizontally or
vertically3,8)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
E or F
NOTE  Refer to S-6.2 of Annex S for
description

> <  0,3 De

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

32
> <
 0,3 De

Single-core or multi-core cables:

On brackets or on a wire mesh tray run
horizontally or vertically3,8) E or F

> <
 0,3 De

Single-core or multi-core cables:

33 E or F
Spaced more than 0.3 times
or method G7)
cable diameter from a wall

34

Single-core or multi-core cables:

On ladder3) E or F

35 Single-core or multi-core cable suspended

from or incorporating E or F
a support wire or harness

36
Bare or insulated conductors on insulators G

40 1.5 De < V < 5 De

B2
V
V Single-core or multi-core cable in a building
5 De < V < 20 De
D
De void3,8,9)
e B1

41 1.5 De < V < 20 De

B2
V
V Insulated conductor in conduit in a building
D
De
e void3,9,10)
V> 20 De
B1

169
IS 732 : 2019

Table 19 — (Continued)

Reference Method of
Installation to be Used to
Item
Methods ofInstallation Description Obtain Current-Carrying
No.
Capacity
(see Annex S)
Under consideration
42 The following may be used:
Single-core or multi-core cable in conduit in a 1.5 De < V < 20 De
building void3) B2
V > 20 De
B1

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
1.5 De < V < 20 De
43 B2
D V Insulated conductors in cable ducting
Dee V > 20 De
in a building void3,9,10)
B1

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Under consideration
The following may be used:
44 Single-core or multi-core cable in cable 1.5 De < V < 20 De
D V
V
Dee ducting in a building void3) B2
V > 20 De
B1

1.5 De < V < 5 De

45 Insulated conductors in cable ducting in B2
V masonry having a thermal resistivity not 5 De < V < 50 De
greater than 2 K·m/W3,8,9) B1

Under consideration
The following may be used
Single-core or multi-core cable in cable 1.5 De < V < 20 De
46 De V ducting in masonry having a thermal resistivity B2
not greater than 2 K·m/W3) V > 20 De
B1

1.5 De < V < 5 De

47 Single-core or multi-core cable: B2
V – in a ceiling void 5 De < V < 50 De
D
Dee
– in a raised floor8,9) B1

Insulated conductors or single-core

50 cable in flush cable trunking in the floor B1

Multi-core cable in flush cable trunking in the

51 B2
floor

Insulated conductors or single-core cables in

52 B1
TV
TV TV
TV flush cable trunking3)

ICT
ISDN ICT
ISDN

Multi-core cable in flush trunking3) B2

53
52 53

170
 IS 732 : 2019

Table 19 — (Continued)

Reference Method of
Installation to be Used to
Item No. Methods of Installation Description Obtain Current-Carrying
Capacity
(see Annex S)

1.5 De < V < 20 De

D V Insulated conductors or single-core cables in B2
Dee
54 conduit in an unventilated cable channel run
horizontally or vertically3,9,11,13) V > 20 De
B1

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Insulated conductors in conduit in
55 an open or ventilated cable channel B1
in the floor12,13)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Sheathed single-core or multi-core cable in an
56 open or ventilated cable channel run B1
horizontally or vertically13)

Single-core or multi-core cable direct in

masonry having a thermal resistivity not
57 greater than 2 K·m/W C
Without added mechanical
protection14,15)

Single-core or multi-core cable direct in

masonry having a thermal resistivity not
58 greater than 2 K·m/W C
14,15)
With added mechanical protection

Insulated conductors or single-core cables in

59 B1
conduit in masonry15)

60 Multi-core cables in conduit in masonry15) B2

Multi-core cable in conduit or in cable

70 D1
ducting in the ground

Single-core cable in conduit or in cable

71 D1
ducting in the ground

171
IS 732 : 2019

Table 19 — (Concluded)

Reference Method of
Installation to be Used to
Item No. Methods of Installation Description Obtain Current-Carrying
Capacity
(see Annex S)

Sheathed single-core or multi-core cables

73 direct in the ground D2
16)
– With added mechanical protection

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
1)
The inner skin of the wall has a thermal conductance of not less than 10 W/m2·K.
2)
Values given for installation methods B1 and B2 in Annex S are for a single circuit. Where there is more than one circuit in the
trunking the group reduction factor given in Table 36 is applicable, irrespective of the presence of an internal barrier or partition.
3)
Care shall be taken where the cable runs vertically and ventilation is restricted. The ambient temperature at the top of the vertical
section can be increased considerably. The matter is under consideration.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4)
Values for reference method B2 may be used.
5)
The thermal resistivity of the enclosure is assumed to be poor because of the material of construction and possible air spaces. Where
the construction is thermally equivalent to methods of installation 6 or 7, reference method B1 may be used.
6)
The thermal resistivity of the enclosure is assumed to be poor because of the material of construction and possible air spaces. Where
the construction is thermally equivalent to methods of installation 6, 7, 8, or 9, reference methods B1 or B2 may be used.
7)
The factors in Table 36 may also be used.
8)
De is the external diameter of a multi-core cable:
— 2.2  the cable diameter when three single core cables are bound in trefoil, or
—3  the cable diameter when three single core cables are laid in flat formation.
9)
V is the smaller dimension or diameter of a masonry duct or void, or the vertical depth of a rectangular duct, floor or ceiling void or
channel. The depth of the channel is more important than the width.
10)
De is the external diameter of conduit or vertical depth of cable ducting.
11)
De is the external diameter of the conduit.
12)
For multi-core cable installed in method 55, use current-carrying capacity for reference method B2.
13)
It is recommended that these methods of installation are used only in areas where access is restricted to authorized persons so that
the reduction in current-carrying capacity and the fire hazard due to the accumulation of debris can be prevented.
14)
For cables having conductors not greater than 16 mm2, the current-carrying capacity may be higher.
15)
Thermal resistivity of masonry is not greater than 2 K·m/W, the term “masonry” is taken to include brickwork, concrete, plaster
and the like (other than thermally insulating materials).
16)
The inclusion of directly buried cables in this item is satisfactory when the soil thermal resistivity is of the order of 2.5 K·m/W. For
lower soil resistivity, the current-carrying capacity for directly buried cables is appreciably higher than for cables in ducts.

172
 IS 732 : 2019

ANNEX S
(Clause 5.2.6.2)
(Normative)
CURRENT-CARRYING CAPACITIES

S-1 INTRODUCTION S-2 AMBIENT TEMPERATURE

The recommendations of this Annex are intended to S-2.1 The current-carrying capacities tabulated in this
provide for a satisfactory life of conductor and Annex assume the following reference ambient
insulation subjected to the thermal effects of carrying temperatures:
current for prolonged periods of time in normal
a) for insulated conductors and cables in air,
service. Other considerations affect the choice of the

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
irrespective of the method of installation:
cross-sectional area of conductors, such as the
30 °C; and
requirements for protection against electric shock
(see 4.2), protection against thermal effects (see 4.3), b) for buried cables, either directly in the soil
overcurrent protection (see 4.4), voltage drop or in ducts in the ground: 20 °C.
(see 5.2.8), and limiting temperatures for terminals S-2.2 Where the ambient temperature in the intended

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

of equipment to which the conductors are location of the insulated conductors or cables differs
connected (see 5.2.9). from the reference ambient temperature, the
For the time being, this Annex relates to non- appropriate correction factor given in Tables 33 and
34 shall be applied to the values of current-carrying
armoured cables and insulated conductors
capacity set out in Tables 21 to 32. For buried cables,
having a nominal voltage not exceeding 1 kV further correction is not needed if the soil temperature
a.c. or 1.5 kV d.c. This Annex may be applied exceeds the chosen ambient temperature by an
for armoured multi-core cables but does not amount up to 5 K for only a few weeks a year.
apply to armoured single-core cables.
NOTE  For cables and insulated conductors in air, where the
NOTES ambient temperature occasionally exceeds the reference
1 If armoured single-core cables are used, an appreciable ambient temperature, the possible use of the tabulated current-
reduction of the current-carrying capacities given in the annex carrying capacities without correction is under consideration.
may be required. The cable supplier should be consulted. This
is also applicable to non-armoured single-core cables in single S-2.3 The correction factors in Tables 33 and 34 do
way metallic ducts (see 5.2.4.5). not take account of the increase, if any, due to solar
2 If armoured multi-core cables are used, the values given in or other infra-red radiation. Where the cables or
this Annex will be on the safe side. insulated conductors are subject to such radiation, the
3 Current-carrying capacities of insulated conductors are the current-carrying capacity may be derived by the
same as for single core cables.
methods specified in IEC 60287 series.
The values given in Table 21 to Table 32 apply to
cables without armour and have been derived in S-3 SOIL THERMAL RESISTIVITY
accordance with the methods given in IEC 60287 The current-carrying capacities tabulated in this
series using such dimensions as specified in Annex for cables in the ground relate to a soil thermal
IEC 60502 and conductor resistances given in IS resistivity of 2.5 K·m/W. This value is considered
8130. Known practical variations in cable necessary as a precaution for worldwide use when the
construction (for example, form of conductor) and soil type and geographical location are not specified
manufacturing tolerances result in a spread of (see IEC 60287-3-1).
possible dimensions and hence current-carrying
capacities for each conductor size. Tabulated current- In locations where the effective soil thermal
carrying capacities have been selected so as to take resistivity is higher than 2.5 K·m/W, an appropriate
account of this spread of values with safety and to lie reduction in current-carrying capacity should be
on a smooth curve when plotted against conductor made or the soil immediately around the cables shall
cross-sectional area. be replaced by a more suitable material. Such cases
can usually be recognized by very dry ground
For multi-core cables having conductors with a cross- conditions. Correction factors for soil thermal
sectional area of 25 mm2 or larger, either circular or resistivities other than 2.5 K·m/W are given in Table
shaped conductors are permissible. Tabulated values 35.
have been derived from dimensions appropriate to
NOTE  The current-carrying capacities tabulated in this
shaped conductors.
Annex for cables in the ground are intended to relate only to
runs in and around buildings. For other installations, where
investigations establish more accurate values of soil thermal

173
IS 732 : 2019

resistivity appropriate for the load to be carried, the values of containing different sizes of equally loaded insulated
current-carrying capacity may be derived by the methods of
calculation given in IEC 60287 series or obtained from the
conductors or cables is dependent on the total number
cable manufacturer. in the group and the mix of sizes. Such factors cannot
be tabulated but shall be calculated for each group.
S-4 GROUPS CONTAINING MORE THAN ONE The method of calculation of such factors is outside
CIRCUIT the scope of this standard. Some specific examples of
where such calculations may be advisable are given
S-4.1 Installation Types A to D in Table 20
below.
The current-carrying capacities given in Tables 21 to
Table 26 relate to single circuits consisting of the NOTE  A group containing sizes of conductor spanning a
following numbers of conductors: range of more than three adjacent standard sizes may be
considered as a group containing different sizes. A group of
a) two insulated conductors or two single-core similar cables is taken to be a group where the current-carrying

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
capacity of all the cables is based on the same maximum
cables, or one twin-core cable; and permissible conductor temperature and where the range of
b) three insulated conductors or three single- conductor sizes in the group spans not more than three adjacent
core cables, or one three-core cable. standard sizes.

Where more insulated conductors or cables, other S-5.1 Groups in Conduit Systems, Cable
than bare mineral insulated cables not exposed to Trunking Systems or Cable Ducting Systems

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

touch, are installed in the same group, the group
reduction factors specified in Tables 36 to Table 38 The group reduction factor which is on the safe side,
shall be applied. for a group containing different sizes of insulated
conductors or cables in conduit systems, cable
NOTE  The group reduction factors have been calculated on trunking systems or cable ducting systems is:
the basis of prolonged steady-state operation at a 100 percent
load factor for all live conductors. Where the loading is less 1
than 100 percent as a result of the conditions of operation of F
the installation, the group reduction factors may be higher. n

S-4.2 Installation Types E and F in Table 20 where

F = the group reduction factor; and
The current-carrying capacities of Tables 27 to Table
32 relate to the reference methods of installation. n = the number of multi-core cables or the
number of circuits in the group.
For installations on perforated cable trays, cleats and
The group reduction factor obtained by this equation
the like, current-carrying capacities for both single
will reduce the danger of overloading the smaller
circuits and groups are obtained by multiplying the
sizes but may lead to under-utilization of the larger
capacities given for the relevant arrangements of
sizes. Such under-utilization can be avoided if large
insulated conductors or cables in free air, as indicated
and small sizes of cable or insulated conductor are
in Tables 27 to Table 32, by the installation and
not mixed in the same group.
group reduction factors given in Tables 39 and 40.
No group reduction factors are required for bare The use of a method of calculation specifically
mineral insulated cables not exposed to touch (see intended for groups containing different sizes of
Tables 26 and 28). insulated conductors or cables in conduit will
produce a more precise group reduction factor. This
The following notes concern S-4.1 and S-4.2:
subject is under consideration.
NOTES
1 Group reduction factors have been calculated as averages for S-5.2 Groups on Trays
the range of conductor sizes, cable types and installation
conditions considered. Attention is drawn to the notes under When a group contains different sizes of cable,
each table. In some instances, a more precise calculation may caution shall be exercised over the current loading of
be desirable. smaller sizes. It is preferable to use a method of
2 Group reduction factors have been calculated on the basis calculation specifically intended for groups
that the group consists of similar equally loaded insulated
conductors or cables. When a group contains various sizes of containing different sizes of cables.
cable or insulated conductor, caution should be exercised over
the current loading of the smaller ones (see S-5).
The group reduction factor obtained in accordance
with S-5.1 will provide a value which is on the safe
S-5 GROUPS CONTAINING DIFFERENT side. This subject is under consideration.
SIZES
S-6 METHODS OF INSTALLATION
Tabulated group reduction factors are applicable to
groups consisting of similar equally loaded cables. S-6.1 Reference Methods
The calculation of reduction factors for groups The reference methods are those methods of

174
 IS 732 : 2019

installation for which the current-carrying capacity increase and the cable becomes overloaded. One way of
avoiding this heating is to use the tables for 70 °C
has been determined by test or calculation. conductor temperature even for cables designed for
a) Reference methods A1, item 1 of Table 19 90 °C.
(insulated conductors in conduit in a e) Reference methods E, F and G, items 32
thermally insulated wall) and A2, item 2 of and 33 of Table 19 (single-core or multi-
Table 19 (multi-core cable in conduit in a core cable in free air):
thermally insulated wall): A cable so supported that the total heat
The wall consists of an outer weatherproof dissipation is not impeded. Heating due to
skin, thermal insulation and an inner skin of solar radiation and other sources shall be
wood or wood-like material having a taken into account. Care shall be taken that
thermal conductance of at least 10 W/m2·K. natural air convection is not impeded. In
The conduit is fixed so as to be close to, but practice, a clearance between a cable and

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
not necessarily touching the inner skin. Heat any adjacent surface of at least 0.3 times the
from the cables is assumed to escape cable external diameter for multi-core cables
through the inner skin only. The conduit can or 1 time the cable diameter for single-core
be metal or plastic. cables is sufficient to permit the use of
b) Reference methods B1, item 4 of Table 19 current-carrying capacities appropriate to

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(insulated conductors in conduit on a free air conditions.
wooden wall) and B2, item 5 of Table 19, S-6.2 Other Methods
(multi-core cable in conduit on a wooden
wall): a) Cable on a floor or under a ceiling: this is
similar to reference method C except that
Conduit mounted on a wooden wall so that
the current-carrying capacity for a cable on a
the gap between the conduit and the surface
ceiling is slightly reduced (see Table 36)
is less than 0.3 times the conduit diameter.
from the value for a wall or a floor because
The conduit can be metal or plastic. Where
of the reduction in natural convection.
the conduit is fixed to a masonry wall the
current-carrying capacity of the cable or b) Cable tray system: a perforated cable
insulated conductors may be higher. This tray has a regular pattern of holes so as
subject is under consideration. to facilitate the use of cable fixings. The
c) Reference method C, item 20 of Table 19 current-carrying capacity for cables on
(single-core or multi-core cable on a wooden perforated cable trays have been derived
wall): from test work utilizing trays where the
Cable mounted on a wooden wall so that the holes occupied 30 percent of the area of
gap between the cable and the surface is less the base. If the holes occupy less than
than 0.3 times the cable diameter. Where the 30 percent of the area of the base, the
cable is fixed to or embedded in a masonry cable tray is regarded as unperforated.
wall the current-carrying capacity may be This is similar to reference method C.
higher. This subject is under consideration.
NOTE  The term "masonry" is taken to include
c) Cable ladder system: this construction
brickwork, concrete, plaster and the like (other than offers a minimum of impedance to the
thermally insulating materials). air flow around the cables, that is,
d) Reference method D1, item 70 of Table 19 supporting metal work under the cables
(multi-core cable in ducts in the ground) and occupies less than 10 percent of the plan
D2 (multi-core cables designed to be buried area.
directly in the ground – refer to
manufacturer’s instructions):
d) Cable cleats, cable ties: devices for
fixing cables to cable tray or bundling
Cables drawn into 100 mm diameter plastic,
earthenware or metallic ducts laid in direct cables together.
contact with soil having a thermal resistivity e) Cable hangers: cable supports which hold
of 2.5 K·m/W and a depth of 0.7 m (see also the cable at intervals along its length and
S-3). permit substantially complete free air flow
Cables laid in direct contact with soil having around the cable.
thermal resistivity of 2.5 K·m/W and a depth General notes to Table 20 to Table 40.
of 0.7 m (see also S-3).
NOTES
NOTE  With cables laid in the ground it is important
1 Current-carrying capacities are tabulated for those
to limit the temperature of the sheath. If the heat of the types of insulated conductor and cable and methods of
sheath dries out the soil, thermal resistivity may

175
IS 732 : 2019

installation which are commonly used for fixed reference method A. It may be necessary to
electrical installations. The tabulated capacities relate to
continuous steady-state operation (100 % load factor)
apply the correction factors due to higher
for d.c. or a.c. of nominal frequency 50 Hz or 60 Hz. ambient temperatures that may arise in the
2 Table 20 itemizes the reference methods of junction boxes and similar mounted in the
installation to which the tabulated current-carrying ceiling.
capacities refer. It is not implied that all these items are NOTE  Where a junction box in the ceiling is used
necessarily recognized in national rules of all countries. for supply to a luminaire, the heat dissipation from the
3 For convenience where computer-aided installation luminaire may provide higher ambient temperatures
design methods are employed, the current-carrying than prescribed in Tables 21 to Table 24 (see
capacities in Tables 21 to Table 32 can be related to also 5.2.5.1). The temperature may be between 40 °C
conductor size by simple formulae. These formulae and 50 °C, and a correction factor according to “Table
with appropriate coefficients are given in Annex U. 33” has to be applied.
f) Cables in a ceiling: this is similar to

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Table 20 Installation Reference Methods Forming Basis of Tabulated Current-Carrying Capacities
(Clauses S-1, S-2.2 and S-4.1)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Table and Column
Reference Method of Installation
Current-Carrying for Single Circuits Ambient Group
Temperature Reduction
Thermoplastic Thermosetting Mineral Factor Factor
Insulated Insulated Insulated
Number of Cores
2 3 2 3 2 and 3

(1) (2) (3) (4) (5) (6) (7) (8) (9)

Insulated
conductors
(single- core
Room 21 23 22 24 33
cables) in A1 – 36
col 2 col 2 col 2 col 2
conduit in a
thermally
insulated wall

Multi-core cable 36
Room in conduit in a 21 23 22 24 33 except D
A2 –
thermally col 3 col 3 col 3 col 3 (Table 38
insulated wall applies)

Insulated
conductors
(single- core 21 23 22 24 33
B1 – 36
cables) in col 4 col 4 col 4 col 4
conduit on a
wooden wall
Multi-core
cable in conduit B2 21 23 22 24 – 33 36
on a wooden col 5 col 5 col 5 col 5
wall

C 21 23 22 24 70 °C 33 36
Single-core or col 6 col 6 col 6 col 6 Sheath
multi-core cable 25
on a wooden 105 °C
wall Sheath
26

Multi-core D1 21 23 22 24 – 34 38
cable in ducts col 7 col 7 col 7 col 7
in the ground

176
 IS 732 : 2019

Table 20 — (Concluded)

Table and Column

Reference Method of Installation
Current-Carrying Capacities
for Single Circuits
Ambient Group Reduction
Thermoplastic Thermosetting Mineral Temperature Factor
Insulated Insulated Insulated Factor

Number of cores

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
2 3 2 3 2 and 3

(1) (2) (3) (4) (5) (6) (7) (8) (9)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Sheathed single-
core or multi-core
D2 col 8 col 8 col 8 col 8 col 8
cables direct in the
ground.

70 °C
Copper Copper Sheath
29 31 27
Multi-core cable 33
E Aluminium Aluminium 39
in free air 105 °C
30 32
Clearance to wall not less Sheath
than 0,3 times 28
cable diameter

Copper Copper 70 °C
29 31 Sheath
Single-core 27 33
cables, touching 40
in free air F Aluminium Aluminium 105 °C
30 32 Sheath
Clearance to wall not less 28
than one cable diameter

70 °C
Copper Copper
Sheath
Single-core 29 31
27 33
cables, spaced in G —
At least one free air 105 °C
Aluminium Aluminium
cable diameter Sheath
30 32
28

177
IS 732 : 2019

Table 21 Current-Carrying Capacities in Amperes for Methods of Installation in Table 20

PVC Insulation/Two Loaded Conductors, Copper or Aluminium—Conductor Temperature: 70 °C,
Ambient Temperature: 30 °C in Air, 20 °C in Ground
(Clauses S-1, S-2.2 and S-4.1)

Installation Methods of Table 20

A1 A2 B1 B2 C D1 D2
Nominal
Cross-sectional
Area of
Conductor
Mm2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(1) (2) (3) (4) (5) (6) (7) (8)
Copper
1.5 14.5 14 17.5 16.5 19,5 22 22

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

2.5 19.5 18.5 24 23 27 29 28
4 26 25 32 30 36 37 38
6 34 32 41 38 46 46 48
10 46 43 57 52 63 60 64
16 61 57 76 69 85 78 83
25 80 75 101 90 112 99 110
35 99 92 125 111 138 119 132
50 119 110 151 133 168 140 156
70 151 139 192 168 213 173 192
95 182 167 232 201 258 204 230
120 210 192 269 232 299 231 261
150 240 219 300 258 344 261 293
185 273 248 341 294 392 292 331
240 321 291 400 344 461 336 382
300 367 334 458 394 530 379 427
Aluminium
2.5 15 14.5 18.5 17.5 21 22
4 20 19,5 25 24 28 29
6 26 25 32 30 36 36
10 36 33 44 41 49 47
16 48 44 60 54 66 61 63
25 63 58 79 71 83 77 82
35 77 71 97 86 103 93 98
50 93 86 118 104 125 109 117
70 118 108 150 131 160 135 145
95 142 130 181 157 195 159 173
120 164 150 210 181 226 180 200
150 189 172 234 201 261 204 224
185 215 195 266 230 298 228 255
240 252 229 312 269 352 262 298
300 289 263 358 308 406 296 336
NOTE  In columns 3, 5, 6, 7 and 8, circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes
relate to shaped conductors and may safely be applied to circular conductors.

178
 IS 732 : 2019

Table 22 Current-carrying Capacities in Amperes for Methods of Installation in Table 20

XLPE or EPR Insulation, Two Loaded Conductors/Copper or Aluminium –
Conductor Temperature: 90 °C, Ambient Temperature: 30 °C in Air, 20 °C in Ground
(Clauses S-1, S-2.2 and S-4.1)

Installation Methods of Table 20

A1 A2 B1 B2 C D1 D2
Nominal
Cross-Sectional
Area of
Conductor
mm2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(1) (2) (3) (4) (5) (6) (7) (8)
Copper
1.5 19 18.5 23 22 24 25 27

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

2.5 26 25 31 30 33 33 35
4 35 33 42 40 45 43 46
6 45 42 54 51 58 53 58
10 61 57 75 69 80 71 77
16 81 76 100 91 107 91 100
25 106 99 133 119 138 116 129
35 131 121 164 146 171 139 155
50 158 145 198 175 209 164 183
70 200 183 253 221 269 203 225
95 241 220 306 265 328 239 270
120 278 253 354 305 382 271 306
150 318 290 393 334 441 306 343
185 362 329 449 384 506 343 387
240 424 386 528 459 599 395 448
300 486 442 603 532 693 446 502
Aluminium
2.5 20 19.5 25 23 26 26
4 27 26 33 31 35 33
6 35 33 43 40 45 42
10 48 45 59 54 62 55
16 64 60 79 72 84 71 76
25 84 78 105 94 101 90 98
35 103 96 130 115 126 108 117
50 125 115 157 138 154 128 139
70 158 145 200 175 198 158 170
95 191 175 242 210 241 186 204
120 220 201 281 242 280 211 233
150 253 230 307 261 324 238 261
185 288 262 351 300 371 267 296
240 338 307 412 358 439 307 343
300 387 352 471 415 508 346 386
NOTE  In columns 3, 5, 6, 7 and 8, circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes
relate to shaped conductors and may safely be applied to circular conductors.

179
IS 732 : 2019

Table 23 Current-carrying Capacities in Amperes for Methods of Installation in Table 20

PVC Insulation, Three Loaded Conductors/Copper or Aluminium—Conductor Temperature: 70 °C,
Ambient Temperature: 30 °C in Air, 20 °C in Ground
(Clauses S-1, S-2.2 and S-4.1)

Installation Methods of Table 20

A1 A2 B1 B2 C D1 D2

Nominal
Cross-sectional
Area of Conductor
mm2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(1) (2) (3) (4) (5) (6) (7) (8)
Copper
1.5 13.5 13 15.5 15 17.5 18 19

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

2.5 18 17.5 21 20 24 24 24
4 24 23 28 27 32 30 33
6 31 29 36 34 41 38 41
10 42 39 50 46 57 50 54
16 56 52 68 62 76 64 70
25 73 68 89 80 96 82 92
35 89 83 110 99 119 98 110
50 108 99 134 118 144 116 130
70 136 125 171 149 184 143 162
95 164 150 207 179 223 169 193
120 188 172 239 206 259 192 220
150 216 196 262 225 299 217 246
185 245 223 296 255 341 243 278
240 286 261 346 297 403 280 320
300 328 298 394 339 464 316 359
Aluminium
2.5 14 13.5 16,5 15.5 18.5 18.5
4 18.5 17.5 22 21 25 24
6 24 23 28 27 32 30
10 32 31 39 36 44 39
16 43 41 53 48 59 50 53
25 57 53 70 62 73 64 69
35 70 65 86 77 90 77 83
50 84 78 104 92 110 91 99
70 107 98 133 116 140 112 122
95 129 118 161 139 170 132 148
120 149 135 186 160 197 150 169
150 170 155 204 176 227 169 189
185 194 176 230 199 259 190 214
240 227 207 269 232 305 218 250
300 261 237 306 265 351 247 282
NOTE  In columns 3, 5, 6, 7 and 8, circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes
relate to shaped conductors and may safely be applied to circular conductors.

180
 IS 732 : 2019

Table 24 Current-Carrying Capacities in Amperes for Methods of Installation in Table 20

XLPE or EPR Insulation, Three Loaded Conductors/Copper or Aluminium —
Conductor Temperature: 90 °C, Ambient Temperature: 30 °C in Air, 20 °C in Ground
(Clauses S-1, S-2.2 and S-4.1)

Installation Methods of Table 20

Nominal A1 A2 B1 B2 C D1 D2
Cross-sectional
Area of
Conductor
mm2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(1) (2) (3) (4) (5) (6) (7) (8)
Copper
1.5 17 16.5 20 19.5 22 21 23
2.5 23 22 28 26 30 28 30

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

4 31 30 37 35 40 36 39
6 40 38 48 44 52 44 49
10 54 51 66 60 71 58 65
16 73 68 88 80 96 75 84
25 95 89 117 105 119 96 107
35 117 109 144 128 147 115 129
50 141 130 175 154 179 135 153
70 179 164 222 194 229 167 188
95 216 197 269 233 278 197 226
120 249 227 312 268 322 223 257
150 285 259 342 300 371 251 287
185 324 295 384 340 424 281 324
240 380 346 450 398 500 324 375
300 435 396 514 455 576 365 419
Aluminium
2.5 19 18 22 21 24 22
4 25 24 29 28 32 28
6 32 31 38 35 41 35
10 44 41 52 48 57 46
16 58 55 71 64 76 59 64
25 76 71 93 84 90 75 82
35 94 87 116 103 112 90 98
50 113 104 140 124 136 106 117
70 142 131 179 156 174 130 144
95 171 157 217 188 211 154 172
120 197 180 251 216 245 174 197
150 226 206 267 240 283 197 220
185 256 233 300 272 323 220 250
240 300 273 351 318 382 253 290
300 344 313 402 364 440 286 326
NOTE In columns 3, 5, 6, 7 and 8, circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes relate
to shaped conductors and may safely be applied to circular conductors.

181
IS 732 : 2019

Table 25 Current-Carrying Capacities in Amperes for Installation Method C of Table 20

Mineral Insulation, Copper Conductors and Sheath — PVC Covered or Bare Exposed to Touch
(see Note 2) — Metallic Sheath Temperature: 70 °C, Reference Ambient Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.1)

Number and Arrangement of Conductors for Method C of Table 20

Three Loaded Conductors

Two Loaded Conductors
Twin or Single-Core Multi-Core or Single-Core Single-Core in Flat Formation
in Trefoil Formation
Nominal Cross-Sectional
Area of Conductor

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
mm2

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(1) (2) (3) (4)

500 V
1.5 23 19 21
2.5 31 26 29
4 40 35 38

750V
1.5 25 21 23
2.5 34 28 31
4 45 37 41
6 57 48 52

10 77 65 70
16 102 86 92
25 133 112 120
35 163 137 147

50 202 169 181

70 247 207 221
95 296 249 264
120 340 286 303

150 388 327 346

185 440 371 392
240 514 434 457

NOTES
1 For single-core cables the sheaths of the cables of the circuit are connected together at both ends.
2 For bare cables exposed to touch, values should be multiplied by 0.9.
3 The values of 500 V and 750 V are the rated voltage of the cable.

182
 IS 732 : 2019

Table 26 Current-Carrying Capacities in Amperes for Installation Method C of Table 20

Mineral Insulation, Copper Conductors and Sheath —
Bare Cable not Exposed to Touch and not in Contact with Combustible Material
Metallic Sheath Temperature: 105 °C, Reference Ambient Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.1)

Number and Arrangement of Conductors for Method C of Table 20

Three Loaded Conductors
Two Loaded Conductors Twin or
Single-Core Multi-Core or Single-Core Single-Core in Flat Formation
in Trefoil Formation
Nominal
Cross-Sectional Area

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of Conductor
mm2

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(1) (2) (3) (4)
500 V
1.5 28 24 27
2.5 38 33 36
4 51 44 47
750 V
1.5 31 26 30
2.5 42 35 41
4 55 47 53
6 70 59 67
10 96 81 91
16 127 107 119
25 166 140 154
35 203 171 187
50 251 212 230
70 307 260 280
95 369 312 334
120 424 359 383
150 485 410 435
185 550 465 492
240 643 544 572

NOTES
1 For single-core cables, the sheaths of the cables of the circuit are connected together at both ends.
2 No correction for grouping need be applied.
3 For this table reference method C refers to a masonry wall because the high sheath temperature is not normally acceptable for a
wooden wall.
4 The values of 500 V and 750 V are the rated voltage of the cable.

183
IS 732 : 2019

Table 27 Current-Carrying Capacities in Amperes for Installation Methods E, F and G of Table 20

Mineral Insulation, Copper Conductors and Sheath/PVC Covered
or Bare Exposed to Touch (see Note 2) –
Metallic Sheath Temperature: 70 °C, Reference Ambient Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.2)

Number and Arrangement of Cables for Methods E, F and G of Table 20

Two Loaded Three loaded conductors

Conductors Twin Or
Single-Core Multi-Core or Single- Single-Core Flat
Nominal Single-Core Touching Single-Core
Core in Trefoil Vertical Spaced
Cross-Sectional Horizontal Spaced

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Formation
Area of Conductor Method E or F Method F Method G
Method E or F Method G
mm2

or or or
or

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Dee
Dee
D

(1) (2) (3) (4) (5) (6)

500 V
1.5 25 21 23 26 29
2.5 33 28 31 34 39
4 44 37 41 45 51

750 V
1.5 26 22 26 28 32
2.5 36 30 34 37 43
4 47 40 45 49 56
6 60 51 57 62 71

10 82 69 77 84 95
16 109 92 102 110 125
25 142 120 132 142 162
35 174 147 161 173 197

50 215 182 198 213 242

70 264 223 241 259 294
95 317 267 289 309 351
120 364 308 331 353 402

150 416 352 377 400 454

185 472 399 426 446 507
240 552 466 496 497 565

NOTES
1 For single-core cables the sheaths of the cables of the circuit are connected together at both ends.
2 For bare cables exposed to touch, values should be multiplied by 0,9.
3 De is the external diameter of the cable.
4 The values of 500 V and 750 V are the rated voltage of the cable.

184
 IS 732 : 2019

Table 28 Current-Carrying capacities in Amperes for Installation Methods E, F and G of Table 20

Mineral Insulation, Copper Conductors and Sheath — Bare Cable not Exposed to Touch (see Note 2) —
Metallic Sheath Temperature: 105 °C, Reference Ambient Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.2)

Number and Arrangement of Cables for Methods E, F and G of Table 20

Two Loaded Three loaded conductors

Conductors, Twin or
Single-Core Multi-Core or Single-Core Single-Core Flat Single-Core
Single-Core in Touching Vertical Spaced Horizontal Spaced
Nominal Trefoil Formation
Cross-Sectional Method G

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Area of Conductor Method E or F Method E or F Method F Method G
mm2

or
or or
or or
or
Dee
D
Dee
D

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(1) (2) (3) (4) (5) (6)

500 V
1.5 31 26 29 33 37
2.5 41 35 39 43 49
4 54 46 51 56 64

750 V
1.5 33 28 32 35 40
2.5 45 38 43 47 54
4 60 50 56 61 70
6 76 64 71 78 89

10 104 87 96 105 120

16 137 115 127 137 157
25 179 150 164 178 204
35 220 184 200 216 248

50 272 228 247 266 304

70 333 279 300 323 370
95 400 335 359 385 441
120 460 385 411 441 505

150 526 441 469 498 565

185 596 500 530 557 629
240 697 584 617 624 704

NOTES
1 For single-core cables the sheaths of the cables of the circuit are connected together at both ends.
2 No correction for grouping need be applied.
3 De is the external diameter of the cable.
4 The values of 500 V and 750 V are the rated voltage of the cable.

185
IS 732 : 2019

Table 29 Current-Carrying Capacities in Amperes for Installation Methods E, F and G of Table 20

PVC Insulation, Copper Conductors – Conductor Temperature: 70 °C, Reference Ambient Temperature:
30 °C
(Clauses S-1, S-2.2 and S-4.2)

Installation Methods of Table 20

Multi-core Cables Single-core Cables
Three Loaded Conductors, Flat
Two Loaded Three Loaded
Two Loaded Three Loaded
Conductors Conductors Touching Spaced
Conductors Conductors
Nominal Cross- Touching Trefoil
Sectional Area Horizontal Vertical

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of Conductor
mm2

or
or or
or De
e
Dee
D

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Method E Method E Method F Method F Method F Method G Method G
(1) (2) (3) (4) (5) (6) (7) (7)
1.5 22 18.5 – – – – –
2.5 30 25 – – – – –
4 40 34 – – – – –
6 51 43 – – – – –
10 70 60 – – – – –
16 94 80 – – – – –
25 119 101 131 110 114 146 130
35 148 126 162 137 143 181 162
50 180 153 196 167 174 219 197
70 232 196 251 216 225 281 254
95 282 238 304 264 275 341 311
120 328 276 352 308 321 396 362
150 379 319 406 356 372 456 419
185 434 364 463 409 427 521 480
240 514 430 546 485 507 615 569
300 593 497 629 561 587 709 659
400 – – 754 656 689 852 795
500 – – 868 749 789 982 920
630 – – 1 005 855 905 1 138 1 070

NOTES
1 Circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes relate to shaped conductors and may
safely be applied to circular conductors.
2 De is the external diameter of the cable.

186
 IS 732 : 2019

Table 30 Current-Carrying Capacities in Amperes for Installation Methods E, F and G of Table 20

PVC Insulation, Aluminium Conductors – Conductor Temperature: 70 °C, Reference Ambient
Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.2)

Installation Methods of Table 20

Multi-core Cables Single-core Cables
Three Loaded Conductors, Flat
Two Loaded Three Loaded
Two Loaded Three Loaded
Conductors Conductors Spaced
Conductors Conductors Touching
Touching Trefoil
Nominal Cross- Horizontal Vertical

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Sectional Area
of Conductor
mm2
or
or or
or
Dee
Dee

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Method E Method E Method F Method F Method F Method G Method G
(1) (2) (3) (4) (5) (6) (7) (8)
2.5 23 19.5 – – – – –
4 31 26 – – – – –
6 39 33 – – – – –

10 54 46 – – – – –
16 73 61 – – – – –
25 89 78 98 84 87 112 99
35 111 96 122 105 109 139 124
50 135 117 149 128 133 169 152
70 173 150 192 166 173 217 196
95 210 183 235 203 212 265 241
120 244 212 273 237 247 308 282
150 282 245 316 274 287 356 327
185 322 280 363 315 330 407 376
240 380 330 430 375 392 482 447
300 439 381 497 434 455 557 519
400 – – 600 526 552 671 629
500 – – 694 610 640 775 730
630 – – 808 711 746 900 852

NOTES
1 Circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes relate to shaped conductors and may
safely be applied to circular conductors.
2 De is the external diameter of the cable.

187
IS 732 : 2019

Table 31 Current-Carrying Capacities in Amperes for Installation Methods E, F and G of Table 20

XLPE or EPR Insulation, Copper Conductors — Conductor Temperature: 90 °C, Reference Ambient
Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.2)

Installation Methods of Table 20

Multi-core Cables Single-core cables
Three Loaded Conductors, Flat
Two Loaded Three Loaded
Two Loaded Three Loaded
Conductors Conductors Spaced
Conductors Conductors Touching
Nominal Touching Trefoil
Horizontal Vertical
Cross-

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Sectional Area
of Conductor
mm2
or
or or
or Dee
D
D
Dee

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Method E Method E Method F Method F Method F Method G Method G
(1) (2) (3) (4) (5) (6) (7) (8)
1.5 26 23 – – – – –
2.5 36 32 – – – – –
4 49 42 – – – – –
6 63 54 – – – – –

10 86 75 – – – – –
16 115 100 – – – – –
25 149 127 161 135 141 182 161
35 185 158 200 169 176 226 201

50 225 192 242 207 216 275 246

70 289 246 310 268 279 353 318
95 352 298 377 328 342 430 389
120 410 346 437 383 400 500 454

150 473 399 504 444 464 577 527

185 542 456 575 510 533 661 605
240 641 538 679 607 634 781 719
300 741 621 783 703 736 902 833

400 – – 940 823 868 1085 1008

500 – – 1083 946 998 1253 1169
630 – – 1 254 1 088 1 151 1 454 1 362

NOTES
1 Circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes relate to shaped conductors and may
safely be applied to circular conductors.
2 De is the external diameter of the cable.

188
 IS 732 : 2019

Table 32 Current-Carrying Capacities in Amperes for Installation Methods E, F and G of Table 20

XLPE or EPR insulation. Aluminium Conductors — Conductor Temperature: 90 °C,
Reference Ambient Temperature: 30 °C
(Clauses S-1, S-2.2 and S-4.2)

Installation Methods of Table 20

Multi-core Cables Single-core Cables
Three Loaded Conductors, Flat
Two Loaded Three Loaded
Two Loaded Three Loaded
Conductors Conductors Spaced
Conductors Conductors Touching
Nominal Touching Trefoil
Horizontal Vertical
Cross-

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Sectional Area
of Conductor
mm2
or
or or
or Dee
Dee

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Method E Method E Method F Method F Method F Method G Method G
(1) (2) (3) (4) (5) (6) (7) (8)
2.5 28 24 – – – – –
4 38 32 – – – – –
6 49 42 – – – – –
10 67 58 – – – – –
16 91 77 – – – – –
25 108 97 121 103 107 138 122
35 135 120 150 129 135 172 153

50 164 146 184 159 165 210 188

70 211 187 237 206 215 271 244
95 257 227 289 253 264 332 300
120 300 263 337 296 308 387 351

150 346 304 389 343 358 448 408

185 397 347 447 395 413 515 470
240 470 409 530 471 492 611 561
300 543 471 613 547 571 708 652

400 – – 740 663 694 856 792

500 – – 856 770 806 991 921
630 – – 996 899 942 1 154 1 077

NOTES
1 Circular conductors are assumed for sizes up to and including 16 mm2. Values for larger sizes relate to shaped conductors and may
safely be applied to circular conductors.
2 De is the external diameter of the cable.

189
IS 732 : 2019

Table 33 Correction Factor for Ambient Air Temperatures Other Than 30 °C

to be Applied to the Current-Carrying Capacities for Cables in the Air
(Clause S-2.3)

Insulation
Ambient
Temperature Mineral1)
°C PVC XLPE and EPR
PVC Covered or Bare and Bare not Exposed to Touch
Exposed to Touch 70 °C 105 °C

(1) (2) (3) (4) (5)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
10 1.22 1.15 1.26 1.14

15 1.17 1.12 1.20 1.11

20 1.12 1.08 1.14 1.07

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

25 1.06 1.04 1.07 1.04

30 1.00 1.00 1.00 1.00

35 0.94 0.96 0.93 0.96

40 0.87 0.91 0.85 0.92

45 0.79 0.87 0.78 0.88

50 0.71 0.82 0.67 0.84

55 0.61 0.76 0.57 0.80

60 0.50 0.71 0.45 0.75

65 – 0.65 – 0.70

70 – 0.58 – 0.65

75 – 0.50 – 0.60

80 – 0.41 – 0.54

85 – – – 0.47

90 – – – 0.40

95 – – – 0.32

1)
For higher ambient temperatures, consult the manufacturer.

190
 IS 732 : 2019

Table 34 Correction Factors for Ambient Ground Temperatures Other Than 20 °C

to be Applied to the Current-Carrying Capacities for Cables in Ducts in the Ground
(Clauses S-2.2 and S-3)

Ground Temperature Insulation

°C
PVC XLPE and EPR
(1) (2) (3)
10 1.10 1.07
15 1.05 1.04
20 1.00 1.00

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
25 0.95 0.96
30 0.89 0.93
35 0.84 0.89
40 0.77 0.85

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

45 0.71 0.80
50 0.63 0.76
55 0.55 0.71
60 0.45 0.65
65 – 0.60
70 – 0.53
75 – 0.46
80 – 0.38

Table 35 Correction Factors for Cables Buried Direct in the Ground

or in Buried Ducts for Soil Thermal Resistivities Other Than 2.5 K·m/W
to be Applied to the Current-Carrying Capacities for Reference Method D
(Clause S-3)
Thermal Resistivity, K·m/W 0.5 0.7 1 1.5 2 2.5 3

Correction Factor for Cables in Buried Ducts 1.28 1.20 1.18 1.1 1.05 1 0.96

Correction Factor for Direct Buried Cables 1.88 1.62 1.5 1.28 1.12 1 0.90

NOTES
1 The correction factors given have been averaged over the range of conductor sizes and types of installation included in Tables 21 to
Table 24. The overall accuracy of correction factors is within 5 percent.
2 The correction factors are applicable to cables drawn into buried ducts; for cables laid direct in the ground the correction factors for
thermal resistivities less than 2.5 K.m/W will be higher. Where more precise values are required they may be calculated by methods
given in IEC 60287 series.
3 The correction factors are applicable to ducts buried at depths of up to 0.8 m.
4 It is assumed that the soil properties are uniform. No allowance had been made for the possibility of moisture migration which can
lead to a region of high thermal resistivity around the cable. If partial drying out of the soil is foreseen, the permissible current rating
should be derived by the methods specified in IEC 60287 series.

191
IS 732 : 2019

Table 36 Reduction Factors for one Circuit or One Multi-core Cable

or for a Group of More Than One Circuit, or More Than One Multi-core Cable,
to be Used with Current-Carrying Capacities of Table 21 to Table 32
(Clauses S-2.6, S-4 and S-6.2)

To be Used with
Arrangement Number of Circuits or Multi-core Cables Current-
Item Carrying
(Cables Touching)
Capacities,
1 2 3 4 5 6 7 8 9 12 16 20 Reference

1 Bunched in air, on a 1.00 0.80 0.70 0.65 0.60 0.57 0.54 0.52 0.50 0.45 0.41 0.38 Tables 21
surface, embedded or to 32

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
enclosed Methods A to F

2 Single layer on wall, 1.00 0.85 0.79 0.75 0.73 0.72 0.72 0.71 0.70
floor or unperforated
cable tray systems Tables 21
to 26
3 Single layer fixed 0.95 0.81 0.72 0.68 0.66 0.64 0.63 0.62 0.61 Method C

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

No further
directly under a reduction factor for
wooden ceiling more than nine
circuits or
4 Single layer on a 1.00 0.88 0.82 0.77 0.75 0.73 0.73 0.72 0.72 multicore cables
perforated horizontal
or vertical cable tray Tables 27
systems to 32
Methods E and F
5 Single layer on cable 1.00 0.87 0.82 0.80 0.80 0.79 0.79 0.78 0.78
ladder systems or
cleats etc.,

NOTES
1 These factors are applicable to uniform groups of cables, equally loaded.
2 Where horizontal clearances between adjacent cables exceeds twice their overall diameter, no reduction factor need be applied.
3 The same factors are applied to:
– groups of two or three single-core cables;
– multi-core cables.
4 If a system consists of both two- and three-core cables, the total number of cables is taken as the number of circuits, and the
corresponding factor is applied to the tables for two loaded conductors for the two-core cables, and to the tables for three loaded
conductors for the three-core cables.
5 If a group consists of n single-core cables it may either be considered as n/2 circuits of two loaded conductors or n/3 circuits of
three loaded conductors.
6 The values given have been averaged over the range of conductor sizes and types of installation included in Tables 21 to Table 32
the overall accuracy of tabulated values is within 5 percent.
7 For some installations and for other methods not provided for in the above table, it may be appropriate to use factors calculated for
specific cases, see for example, Table 39 and Table 40.

192
 IS 732 : 2019

Table 37 Reduction Factors for More Than One Circuit, Cables Laid Directly in the Ground –
Installation Method D2 in Table 21 to Table 24 Single-Core or Multi-Core Cables
(Clauses 5.2.6.5, and S-4.1)

Cable to Cable Clearance

Number
of Circuits Nil One Cable
0.125 m 0.25 m 0.5 m
(Cables Touching) Diameter

2 0.75 0.80 0.85 0.90 0.90

3 0.65 0.70 0.75 0.80 0.85

4 0.60 0.60 0.70 0.75 0.80

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5 0.55 0.55 0.65 0.70 0.80

6 0.50 0.55 0.60 0.70 0.80

7 0.45 0.51 0.59 0.67 0.76

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

8 0.43 0.48 0.57 0.65 0.75

9 0.41 0.46 0.55 0.63 0.74

12 0.36 0.42 0.51 0.59 0.71

16 0.32 0.38 0.47 0.56 0.38

20 0.29 0.35 0.44 0.53 0.66

a Multi-core cables

a Single-core cables

a a

NOTES
1 Values given apply to an installation depth of 0.7 m and a soil thermal resistivity of 2.5 K·m/W. They are average values for the
range of cable sizes and types quoted for Tables 21 to Table 24. The process of averaging, together with rounding off, can result in
some cases in errors up to 10 %. (Where more precise values are required they may be calculated by methods given in
IEC 60287-2-1).
2 In case of a thermal resistivity lower than 2.5 K·m/W the corrections factors can, in general, be increased and can be calculated by
the methods given in IEC 60287-2-1.
3 If a circuit consists of m parallel conductors per phase, then for determining the reduction factor, this circuit should be considered as
m circuits.

193
IS 732 : 2019

Table 38 Reduction Factors for More Than One Circuit, Cables Laid in Ducts in the Ground —
Installation Method D1 in Table 20 to Table 24
(Clauses 5.2.6.5 and S-4.1)

A) Multi-Core Cables in Single-Way Ducts

Number of Cables Duct to Duct Clearancea

Nil
0.25 m 0.5 m 1.0 m
(Ducts Touching)

2 0.85 0.90 0.95 0.95

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3 0.75 0.85 0.90 0.95

4 0.70 0.80 0.85 0.90

5 0.65 0.80 0.85 0.90

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

6 0.60 0.80 0.80 0.90

7 0.57 0.76 0.80 0.88

8 0.54 0.74 0.78 0.88

9 0.52 0.73 0.77 0.87

10 0.49 0.72 0.76 0.86

11 0.47 0.70 0.75 0.86

12 0.45 0.69 0.74 0.85

13 0.44 0.68 0.73 0.85

14 0.42 0.68 0.72 0.84

15 0.41 0.67 0.72 0.84

16 0.39 0.66 0.71 0.83

17 0.38 0.65 0.70 0.83

18 0.37 0.65 0.70 0.83

19 0.35 0.64 0.69 0.82

20 0.34 0.63 0.68 0.82

194
 IS 732 : 2019

Table 38 — (Concluded)

B) Single-core Cables in Non-Magnetic Single-Way Ducts

Number of Single-Core Duct to Duct Clearance

Circuits of Two or Three
Nil
Cables 0.25 m 0.5 m 1.0 m
(Ducts Touching)

2 0.80 0.90 0.90 0.95

3 0.70 0.80 0.85 0.90

4 0.65 0.75 0.80 0.90

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5 0.60 0.70 0.80 0.90

6 0.60 0.70 0.80 0.90

7 0.53 0.66 0.76 0.87

8 0.50 0.63 0.74 0.87

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

9 0.47 0.61 0.73 0.86

10 0.45 0.59 0.72 0.85

11 0.43 0.57 0.70 0.85

12 0.41 0.56 0.69 0.84

13 0.39 0.54 0.68 0.84

14 0.37 0.53 0.68 0.83

15 0.35 0.52 0.67 0.83

16 0.34 0.51 0.66 0.83

17 0.33 0.50 0.65 0.82

18 0.31 0.49 0.65 0.82

19 0.30 0.48 0.64 0.82

20 0.29 0.47 0.63 0.81

a Multi-core cables

b Single-core cables

NOTES
1 Values given apply to an installation depth of 0.7 m and a soil thermal resistivity of 2.5 K·m/W. They are average values for the
range of cable sizes and types quoted for Table 20 to Table 24. The process of averaging, together with rounding off, can result in
some cases in errors up to 10 percent. Where more precise values are required they may be calculated by methods given in the
IEC 60287series.
2 In case of a thermal resistivity lower than 2.5 K·m/W the corrections factors can, in general, be increased and can be calculated
by the methods given in IEC 60287-2-1.
3 If a circuit consists of n parallel conductors per phase, then for determining the reduction factor this circuit shall be considered as
n circuits.

195
IS 732 : 2019

Table 39 Reduction Factors for Group of More Than One Multi-core Cable
to be Applied to Reference Current-Carrying Capacities for Multi-core Cables in Free Air —
Method of Installation E in Table 27 to Table 32
(Clause 5.2.6.5)

Number of Number of Cables Per Tray or Ladder

Method of Installation in Table 19 Trays or
Ladders 1 2 3 4 6 9

Touching
31
1 1.00 0.88 0.82 0.79 0.76 0.73

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
2 1.00 0.87 0.80 0.77 0.73 0.68
3 1.00 0.86 0.79 0.76 0.71 0.66

Perforated cable 6 1.00 0.84 0.77 0.73 0.68 0.64

tray systems  20 mm
mm  300
300 mm

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(Note 3)
Spaced
Dee 1 1.00 1.00 0.98 0.95 0.91 –
2 1.00 0.99 0.96 0.92 0.87 –
3 1.00 0.98 0.95 0.91 0.85 –
 20
20 mm
mm

Touching

1 1.00 0.88 0.82 0.78 0.73 0.72

31 
225 mm 2 1.00 0.88 0.81 0.76 0.71 0.70
225
mm
Vertical
perforated
cable tray systems
Spaced
(Note 4)

1 1.00 0.91 0.89 0.88 0.87 –

 2 1.00 0.91 0.88 0.87 0.85 –

225 mm
Dee
225
mm

Touching

1 0.97 0.84 0.78 0.75 0.71 0.68

Unperforated 31 2 0.97 0.83 0.76 0.72 0.68 0.63
cable tray systems 3 0.97 0.82 0.75 0.71 0.66 0.61
6 0.97 0.81 0.73 0.69 0.63 0.58

 20
20 mm
mm  300
300 mm

Touching

1 1.00 0.87 0.82 0.80 0.79 0.78

Cable ladder 32
systems, cleats, 2 1.00 0.86 0.80 0.78 0.76 0.73
etc 33
3 1.00 0.85 0.79 0.76 0.73 0.70
(Note 3) 34
6 1.00 0.84 0.77 0.73 0.68 0.64
 20
20 mm
300
300 mm
mm

196
 IS 732 : 2019

Table 39 — (Concluded)

Number of Number of Cables Per Tray or Ladder

Method of Installation in Table 19 Trays or
Ladders 1 2 3 4 6 9

Spaced
Dee
D 1 1.00 1.00 1.00 1.00 1.00 –
2 1.00 0.99 0.98 0.97 0.96 –
3 1.00 0.98 0.97 0.96 0.93 –
 20
20mm
mm

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTES
1 Values given are averages for the cable types and range of conductor sizes considered in Tables 27 to Table 32. The spread of
values is generally less than 5 percent.
2 Factors apply to single layer groups of cables as shown above and do not apply when cables are installed in more than one layer
touching each other. Values for such installations may be significantly lower and has to be determined by an appropriate method.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

3 Values are given for vertical spacing between cable trays of 300 mm and at least 20 mm between cable trays and wall. For closer
spacing the factors should be reduced.
4 Values are given for horizontal spacing between cable trays of 225 mm with cable trays mounted back to back. For closer
spacing the factors should be reduced.

Table 40 Reduction Factors for Groups of One or More Circuits of Single-core Cables to
be Applied to Reference Current-Carrying Capacity for One Circuit of Single-Core Cables in
Free Air — Method of Installation F in Table 27 to Table 32
(Clause 5.2.6.5)

Number of Three-Phase Circuits Use as a

Number of Per Tray or Ladder Multiplier to
Method of Installation in Table 19 Trays or Current-Carrying
Ladders 1 2 3 Capacity
for

Touching

Perforated cable 1 0.98 0.91 0.87 Three cables in

tray systems 31 300
300 mm 2 0.96 0.87 0.81 horizontal
(Note 3) 3 0.95 0.85 0.78 formation

20 mm
 20 mm

Touching

Vertical
perforated cable  1 0.96 0.86 – Three cables in
31 225 mm
tray systems 225 2 0.95 0.84 – vertical formation
(Note 4) mm

Touching

Cable ladder
32 1 1.00 0.97 0.96 Three cables in
systems,
33 300
300 mm
mm 2 0.98 0.93 0.89 horizontal
cleats, etc
34 3 0.97 0.90 0.86 formation
(Note 3)

20mm
 20 mm

197
IS 732 : 2019

Table 40 — (Concluded)

Number of Three-Phase Circuits Use as a

Number of Per Tray or Ladder Multiplier to
Method of Installation in Table 19 Trays or Current-Carrying
Ladders 1 2 3 Capacity
for

2Dee
 2D
D
Dee
Perforated cable 1 1.00 0.98 0.96
tray systems 31 2 0.97 0.93 0.89
300
300 mm
mm

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(Note 3) 3 0.96 0.92 0.86

20mm
 20 mm

Spaced

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Vertical
 2D
2Dee Three cables in
perforated cable  1 1.00 0.91 0.89
31 225 mm trefoil formation
tray systems 225 2 1.00 0.90 0.86
(Note 4) mm
Dee

 2D
2De
e D
Dee
Cable ladder
32 1 1.00 1.00 1.00
systems, cleats,
33 2 0.97 0.95 0.93
etc 300
300 mm
mm
34 3 0.96 0.94 0.90
(Note 3)

20mm
 20 mm

NOTES
1 Values given are averages for the cable types and range of conductor sizes considered in Table 27 to Table 32. The spread of
values is generally less than 5 percent.
2 Factors are given for single layers of cables (or trefoil groups) as shown in the table and do not apply when cables are installed in
more than one layer touching each other. Values for such installations may be significantly lower and should be determined by an
appropriate method.
3 Values are given for vertical spacing between cable trays of 300 mm and at least 20 mm between cable trays and wall. For closer
spacing the factors should be reduced.
4 Values are given for horizontal spacing between cable trays of 225 mm with cable trays mounted back to back. For closer spacing
the factors should be reduced.
5 For circuits having more than one cable in parallel per phase, each three phase set of conductors should be considered as a circuit
for the purpose of this table.
6 If a circuit consists of m parallel conductors per phase, then for determining the reduction factor this circuit should be considered
as m circuits.

198
 IS 732 : 2019

ANNEX T
(Normative)
EXAMPLE OF A METHOD OF SIMPLIFICATION OF THE TABLES OF 5.2.6
This Annex is intended to illustrate one possible method by which the Table 21 to Table 24, Table 29 to
Table 32 and Table 36 to Table 40 can be simplified for adoption.
The use of other suitable methods is not excluded (see Note of 5.2.6.2).

Table 41 Current-Carrying Capacity in Amperes

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Reference
Methods in Number of Loaded Conductors and type of Insulation
Table 20
A1 3 PVC 2 PVC 3 XLPE 2 XLPE
A2 3 PVC 2 PVC 3 XLPE 2 XLPE
B1 3 PVC 2 PVC 3 XLPE 2 XLPE

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

B2 3 PVC 2 PVC 3 XLPE 2 XLPE
C 3 PVC 2 PVC 3 XLPE 2 XLPE
E 3 PVC 2 PVC 3 XLPE 2 XLPE
F 3 PVC 2 PVC 3 XLPE 2 XLPE
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
Size (mm2)
Copper
1.5 13 13.5 14.5 15.5 17 18.5 19.5 22 23 24 26 –
2.5 17.5 18 19.5 21 23 25 27 30 31 33 36 –
4 23 24 26 28 31 34 36 40 42 45 49 –
6 29 31 34 36 40 43 46 51 54 58 63 –
10 39 42 46 50 54 60 63 70 75 80 86 –
16 52 56 61 68 73 80 85 94 100 107 115 –
25 68 73 80 89 95 101 110 119 127 135 149 161
35 – – – 110 117 126 137 147 158 169 185 200
50 – – – 134 141 153 167 179 192 207 225 242
70 – – – 171 179 196 213 229 246 268 289 310
95 – – – 207 216 238 258 278 298 328 352 377
120 – – – 239 249 276 299 322 346 382 410 437
150 – – – – 285 318 344 371 395 441 473 504
185 – – – – 324 362 392 424 450 506 542 575
240 – – – – 380 424 461 500 538 599 641 679
Aluminium
2.5 13.5 14 15 16.5 18.5 19.5 21 23 24 26 28 –
4 17.5 18.5 20 22 25 26 28 31 32 35 38 –
6 23 24 26 28 32 33 36 39 42 45 49 –
10 31 32 36 39 44 46 49 54 58 62 67 –
16 41 43 48 53 58 61 66 73 77 84 91 –
25 53 57 63 70 73 78 83 90 97 101 108 121
35 – – – 86 90 96 103 112 120 126 135 150
50 – – – 104 110 117 125 136 146 154 164 184
70 – – – 133 140 150 160 174 187 198 211 237
95 – – – 161 170 183 195 211 227 241 257 289
120 – – – 186 197 212 226 245 263 280 300 337
150 – – – – 226 245 261 283 304 324 346 389
185 – – – – 256 280 298 323 347 371 397 447
240 – – – – 300 330 352 382 409 439 470 530
NOTE  The appropriate table of current-carrying capacity given in Annex S should be consulted to determine the range of conductor
sizes for which the above current-carrying capacities are applicable, for each installation method.

199
IS 732 : 2019

Table 42 Current-Carrying Capacities in Amperes

Installation Method Size Number of Loaded Conductors and Type of Insulation

2
mm 2 PVC 3 PVC 2 XLPE 3 XLPE
Copper
1.5 22 18 26 22
2.5 29 24 34 29
4 38 31 44 37
6 47 39 56 46

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
10 63 52 73 61
16 81 67 95 79
25 104 86 121 101
D1/D2 35 125 103 146 122

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

50 148 122 173 144
70 183 151 213 178
95 216 179 252 211
120 246 203 287 240
150 278 230 324 271
185 312 258 363 304
240 361 297 419 351
300 408 336 474 396
Aluminium
2.5 22 18.5 26 22
4 29 24 34 29
6 36 30 42 36
10 48 40 56 47
16 62 52 73 61
25 80 66 93 78
35 96 80 112 94
D1/D2
50 113 94 132 112
70 140 117 163 138
95 166 138 193 164
120 189 157 220 186
150 213 178 249 210
185 240 200 279 236
240 277 230 322 272
300 313 260 364 308

200
 IS 732 : 2019

Table 43 Reduction Factors for Groups of Several Circuits or of Several Multi-core Cables
(to be Used with Current-Carrying Capacities of Table 41)

Number of Circuits or Multi-core Cables

Item Arrangement
1 2 3 4 6 9 12 16 20

Bunched in air, on a surface,

1 1.00 0.80 0.70 0.65 0.55 0.50 0.45 0.40 0.40
embedded or enclosed

Single layer on walls, floors or

2 1.00 0.85 0.80 0.75 0.70 0.70 – – –
on unperforated trays

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Single layer fixed directly
3 0.95 0.80 0.70 0.70 0.65 0.60 – – –
under a ceiling

Single layer on perforated

4 horizontal trays or on vertical 1.00 0.90 0.80 0.75 0.75 0.70 – – –
trays

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Single layer on cable ladder
5 1.00 0.85 0.80 0.80 0.80 0.80 – – –
supports or cleats, etc.

ANNEX U
(Clause 5.2)
(Normative)
FORMULAE TO EXPRESS CURRENT-CARRYING CAPACITIES
The values given in Table 21 to Table 32 lie on Values of the coefficients and exponents are given in
smooth curves relating current-carrying capacity to the accompanying table. Current-carrying capacities
cross-sectional area of conductor. should be rounded off to the nearest 0.5 A for values
not exceeding 20 A and to the nearest ampere for
These curves can be derived using the following
values greater than 20 A.
formulae:
The number of significant figures obtained is not to
I = a × sm – b × s n
be taken as an indication of the accuracy of the
where current-carrying capacity.
I = the current-carrying capacity, in amperes; For practically all cases, only the first term is needed.
S = the nominal cross-sectional area of The second term is needed in only eight cases where
conductor, in square millimetres [(mm)2]1) large single-core cables are used.
a and b are coefficients and m and n are exponents It is not advisable to use these coefficients and
according to cable and method of exponents for conductor sizes outside the appropriate
installation. range used in Table 21 to Table 32.

1)
Where the nominal size is 50 mm2, for cables with extruded
insulation, the value of 47.5 mm2 should be used. For all other
sizes and for all sizes of mineral insulated cables the nominal
value is sufficiently precise.

201
IS 732 : 2019

Table 44 Table of Coefficients and Exponents

Current-Carrying Column Copper Conductor Aluminium Conductor
Capacity Table a m a m
2 11.2 0.611 8 8.61 0.616
3 (s < 120 mm2) 10.8 0.601 5 8.361 0.602 5
3 (s  120 mm2) 10.19 0.611 8 7.84 0.616
21 4 13.5 0.625 10.51 0.625 4
5 13.1 0.600 10.24 0.599 4
6 < 16 mm2 15.0 0.625 11.6 0.625
6  16 mm2 15.0 0.625 10.55 0.640
7 17.42 0.540 13.6 0.540
2 14.9 0.611 11.6 0.615

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
3(s) < 120 mm2 14.46 0.598 11.26 0.602
3(s)  120 mm2 13.56 0.611 10.56 0.615
22 4 17.76 0.625 0 13.95 0.627
5 17.25 0.600 13.5 0.603
6 < 16 mm2 18.77 0.628 14.8 0.625
6  16 mm2 17.0 0.650 12.6 0.648

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

7 20.25 0.542 15.82 0.541
2 10.4 0.605 7.94 0.612
3(s) < 120 mm2 10.1 0.592 7.712 0.598 4
3(s)  120 mm2 9.462 0.605 7.225 0.612
23 4 11.84 0.628 9.265 0.627
5 11.65 0.600 5 9.03 0.601
6 < 16 mm2 13.5 0.625 10.5 0.625
6 16 mm2 12.4 0.635 9.536 0.632 4
7 14.34 0.542 11.2 0.542
2 13.34 0.611 10.9 0.605
3(s) < 120 mm2 12.95 0.598 10.58 0.592
3(s)  120 mm2 12.14 0.611 9.92 0.605
24 4 15.62 0.625 2 12.3 0.630
5 15.17 0.60 11.95 0.605
6 < 16 mm2 17.0 0.623 13.5 0.625
6  16 mm2 15.4 0.635 11.5 0.639
7 16.88 0.539 13.2 0.539
Coefficients and exponents
a m b n
500 V 2 18.5 0.56 – –
3 14.9 0.612 – –
4 16.8 0.59 – –
25 750 V 2 19.6 0.596 – –
3 16.24 0.599 5 – –
4 18.0 0.59 – –
500 V 2 22.0 0.60 – –
3 19.0 0.60 – –
4 21.2 0.58 – –
26 750 V 2 24.0 0.60 – –
3 20.3 0.60 – –
4 23.88 0.579 4 – –
500 V 2 19.5 0.58 – –
3 16.5 0.58 – –
27 4 18.0 0.59 – –
5 20.2 0.58 – –
6 23.0 0.58 – –
NOTE  a, b are coefficients and m, n are exponents.

202
 IS 732 : 2019

Table 44 — (Concluded)

Current-Carrying Copper Conductor Aluminium Conductor

Capacity Table Column a m a m
27 750 V 2 20.6 0.60 – –
3 17.4 0.60 – –
4 20.15 0.584 5 – –
5 < 120 mm2 22.0 0.58 – –
5  120 mm2 22.0 0.58 1  10–11 5.25
6 < 120 mm2 25.17 0.578 5 – –
6  120 mm2 25.17 0.578 5 1.9  10–11 5.15
500 V 2 24.2 0.58 – –
3 20.5 0.58 – –
4 23.0 0.57 – –

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
5 26.1 0.549 – –
6 29.0 0.57 – –
28 750 V 2 26.04 0.599 7 – –
3 21.8 0.60 – –
4 25.0 0.585 – –
5 < 120 mm2 27.55 0.579 2 – –

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

5  120 mm2 27.55 0.579 2 1.3  10–10 4.8
6 < 120 mm2 31.58 0.579 1 – –
6  120 mm2 31.58 0.579 1 1.8  10–7 3.55
2 < 16 mm2 16.8 0.62 – –
2  16 mm2 14.9 0.646 – –
3 < 16 mm2 14.30 0.62 – –
3  16 mm2 12.9 0.64 – –
4 17.1 0.632 – –
29 5 < 300 mm2 13.28 0.656 4 – –
5  300 mm2 13.28 0.656 4 6  10–5 2.14
6 < 300 mm2 13.75 0.658 1 – –
6  300 mm2 13.75 0.658 1 1.2  10–4 2.01
7 18.75 0.637 – –
8 15.8 0.654 – –
2 < 16 mm2 12.8 0.627 – –
2  16 mm2 11.4 0.64 – –
3 < 16 mm2 11.0 0.62 – –
3  16 mm2 9.9 0.64 – –
30 4 12.0 0.653 – –
(aluminium conductors) 5 9.9 0.663 – –
6 10.2 0.666 – –
7 13.9 0.647 – –
8 11.5 0.668 – –
2 < 16 mm2 20.5 0.623 – –
2  16 mm2 18.6 0.646 – –
3 < 16 mm2 17.8 0.623 – –
3  16 mm2 16.4 0.637 – –
4 20.8 0.636 – –
31 5 < 300 mm2 16.0 0.6633 – –
5  300 mm2 16.0 0.6633 6  10–4 1.793
6 < 300 mm2 16.57 0.665 – –
6  300 mm2 16.57 0.665 3  10–4 1.876
7 22.9 0.644 – –
8 19.1 0.662 – –
2 < 16 mm2 16.0 0.625 – –
2  16 mm2 13.4 0.649 – –
3 < 16 mm2 13.7 0.623 – –
3  16 mm2 12.6 0.635 – –
32 4 14.7 0.654 – –
(aluminium conductors) 5 11.9 0.671 – –
6 12.3 0.673 – –
7 16.5 0.659 – –
8 13.8 0.676 – –
– –

203
IS 732 : 2019

ANNEX V
(Clause 5.2.6.6.3)
(Normative)
EFFECT OF HARMONIC CURRENTS ON BALANCED THREE-PHASE SYSTEMS

V-1 REDUCTION FACTORS FOR HARMONIC current-carrying capacity of a cable with three loaded
CURRENTS IN FOUR-CORE AND FIVE-CORE conductors, will give the current-carrying capacity of
CABLES WITH FOUR CORES CARRYING a cable with four loaded conductors where the current
CURRENT in the fourth conductor is due to harmonics. The
reduction factors also take the heating effect of the

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
The subclause 5.2.6.6.3 states that where the neutral harmonic current in the line conductors into account.
conductor carries current without a corresponding
reduction in load of the line conductors, the current Where the neutral current is expected to be higher
flowing in the neutral conductor shall be taken into than the line current then the cable size should be
account in ascertaining the current-carrying capacity selected on the basis of the neutral current.
of the circuit.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Where the cable size selection is based on a neutral
This Annex is intended to cover the situation where current which is not significantly higher than the line
there is current flowing in the neutral of a balanced current it is necessary to reduce the tabulated current-
three-phase system. Such neutral currents are due to carrying capacity for three loaded conductors.
the line currents having a harmonic content which If the neutral current is more than 135 percent of the
does not cancel in the neutral. The most significant line current and the cable size is selected on the basis
harmonic which does not cancel in the neutral is of the neutral current, then the three line conductors
usually the third harmonic. The magnitude of the will not be fully loaded. The reduction in heat
neutral current due to the third harmonic may exceed generated by the line conductors offsets the heat
the magnitude of the power frequency line current. In generated by the neutral conductor to the extent that
such a case, the neutral current will have a significant it is not necessary to apply any reduction factor to the
effect on the current-carrying capacity of the cables current-carrying capacity for three loaded conductors.
in the circuit.
NOTE  The third harmonic content of the line current is the
The reduction factors given in this Annex apply to ratio of the third harmonic and the fundamental (first
balanced three-phase circuits; it is recognized that the harmonic), expressed in percent.
situation is more onerous if only two of the three
phases are loaded. In this situation, the neutral Table 45 Reduction Factors for Harmonic
conductor will carry the harmonic currents in Currents in Four-Core and Five-Core Cables
addition to the unbalanced current. Such a situation Reduction Factor
Third Harmonic
can lead to overloading of the neutral conductor. Content
Size Selection is Size Selection is
Equipment likely to cause significant harmonic of Line Current
Based Line on Based on
%
currents are, for example, fluorescent lighting banks Current Neutral Current
and d.c. power supplies such as those found in 0–15 1.0 –
computers. Further information on harmonic 15–33 0.86 –
disturbances can be found in the IEC 61000 series. 33–45 – 0.86
45 – 1.0
The reduction factors given in Table 45 only apply to
cables where the neutral conductor is within a four- V-2 EXAMPLES OF THE APPLICATION OF
core or five-core cable and is of the same material REDUCTION FACTORS FOR HARMONIC
and cross-sectional area as the line conductors. These CURRENTS
reduction factors have been calculated based on third
harmonic currents. Consider a three-phase circuit with a design load of
39 A to be installed using four-core PVC insulated
If significant, that is, more than 15 percent, higher cable clipped to a wall, installation method C.
harmonics, for example, 9th, 12th, etc are expected
then lower reduction factors are applicable. Where From Table 23, a 6 mm2 cable with copper
there is an unbalance between phases of more than conductors has a current-carrying capacity of 41 A
50 percent then lower reduction factors may be and hence is suitable if harmonics are not present in
applicable. the circuit.
The tabulated reduction factors, when applied to the If 20 percent third harmonic is present, then a

204
 IS 732 : 2019

reduction factor of 0.86 is applied and the design load For this load a 10 mm2 cable is suitable.
becomes:
If 50 per cent third harmonic is present, the cable size
39 is again selected on the basis of the neutral current,
 45A which is:
0.86
For this load, a 10 mm2 cable is necessary. 39 × 0.5 × 3 = 58.5 A

If 40 percent third harmonic is present, the cable size In this case, the reduction factor is 1 and a 16 mm2
selection is based on the neutral current which is: cable is required.

39 × 0.4 × 3 = 46.8 A All the above cable selections are based on the
current-carrying capacity of the cable; voltage drop
and a reduction factor of 0.86 is applied, leading to a and other aspects of design have not been considered.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
design load of:
46.8
 54.4A
0.86

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

ANNEX W
(Clause 5.2.4.6)
(Normative)
SELECTION OF CONDUIT SYSTEMS
Guidance on the selection of conduit systems is given in Table 46.

Table 46 Suggested Characteristics for Conduit

(classification according to IS 14930 Part 1 & Part 2)

Resistance Resistance Minimum Maximum

Situation to to Operating Operating
Compression Impact Temperature Temperature
Outdoor Exposed installation
3 3 2 1
installation
Indoors use Exposed installation 2 2 2 1
Under floor installations (floor screed) 2 3 2 1
Embedded Concrete 3 3 2 1
Hollow wall/on wood
(inflammable material)
In masonry 2 2 2 1
Building voids
Ceiling voids
Overhead mounting 4 3 3 1

NOTES
1 These values are only a sample of the characteristics for conduit given in IS 14930 (Parts 1 & 2).
2 According to resistance to flame propagation, conduit systems of orange colour are only permitted when embedded in concrete. For
other methods for installation all colours are permitted with the exception of yellow, orange or red.

205
IS 732 : 2019

ANNEX Y
(Clause 5.2)
(Normative)
VOLTAGE DROP IN CONSUMERS’ INSTALLATIONS

Y-1 MAXIMUM VALUE OF VOLTAGE DROP  L 

u  b  1 cos   L sin   lB
The voltage drop between the origin of an installation  S 
and any load point should not be greater than the where
values in Table 47 expressed with respect to the value u = the voltage drop in V;

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of the nominal voltage of the installation b = the coefficient equal to 1 for three-
phases circuits, and equal to 2 for
NOTES
single-phase circuits;
1 A greater voltage drop may be accepted
NOTE  Three-phase circuits with the neutral
– for motor during starting periods,
completely unbalanced (a single phase loaded)
– for other equipment with high inrush current,

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

are considered a single-phase circuits.
provided that in both cases it is ensured that the voltage
variations remains within the limits specified in the 1 = the resistivity of conductors in normal
relevant equipment standard. service, taken equal to the resistivity at
2 The following temporary conditions are excluded: the temperature in normal service, that
– voltage transients; is, 1.25 times the resistivity at 20 °C, or
–voltage variation due to abnormal operation. 0.0225 mm2/m for copper and 0.036
mm2/m for aluminium;
Table 47 Voltage Drop
L = the straight length of the wiring
systems, in m
Type of Installation Lighting Other S = the cross-sectional area of conductors,
% Uses in mm2;
%
cos  = the power factor; in the absence of
A – Low voltage installations supplied 3 5
directly from a public low voltage precise details, the power factor is
distribution system taken as equal to 0.8 (sin  = 0.6);
B – Low voltage installation supplied 6 8 λ = the reactance per unit length of
from private LV supply1) conductors, which is taken to be 0.08
1)
As far as possible, it is recommended that voltage drop within m/m in the absence of other details;
the final circuits do not exceed those indicated in installation IB = the design current (in amps)
type A.
When the main wiring systems of the installations are longer
The relevant voltage drop in per cent is equal to:
than 100 m, these voltage drops may be increased by
u
0.005 percent per metre of wiring system beyond 100 m, without u  100
this supplement being greater than 0.5 percent. U0
Voltage drop is determined from the demand by the current-
using equipment, applying diversity factors where applicable, or U0 = the voltage between line and neutral, in
from the values of the design current of the circuits. volts.
NOTE  In extra-low voltage circuits, it is not
Voltage drops may be determined using the following necessary to fulfil the voltage drop limits of Table 47
for uses other than lighting (for example, bell, control,
formula: door opening, etc.), provided that a check is made that
the equipment is operating correctly.

206
 IS 732 : 2019

ANNEX Z
(Clause 5.2.6.7)
(Informative)
EXAMPLES OF CONFIGURATIONS OF PARALLEL CABLES
The special configurations referred in 5.2.6.7 can be: 2) above each other, see Fig. 82,
a) for 4 three-core cables the connection 3) in trefoil, see Fig. 83;
scheme: L1L2L3, L1L2L3, L1L2L3, L1L2L3; d) for 12 single-core cables
the cables may be touching; 1) in a flat plane, see Fig. 84,
b) for 6 single-core cables 2) above each other, see Fig. 85,

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
1) in a flat plane, see Fig. 78, 3) in trefoil, see Fig. 86.
2) above each other, see Fig. 79, The distances in these figures shall be
3) in trefoil, see Fig. 80; maintained.
c) for 9 single-core cables NOTE  Where possible, the impedance differences between
the phases are also limited in the special configurations.
1) in a flat plane, see Fig. 81,

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

FIG. 78 SPECIAL CONFIGURATION FOR 6 PARALLEL SINGLE-CORE CABLES IN A FLAT PLANE (see 5.2.6.7)

FIG. 79 SPECIAL CONFIGURATION FOR 6 PARALLEL SINGLE-CORE CABLES ABOVE EACH OTHER
(see 5.2.6.7)

FIG. 80 SPECIAL CONFIGURATION FOR 6 PARALLEL SINGLE-CORE CABLES

IN TREFOIL (see 5.2.6.7)

NOTE  D e is the outer diameter of the cable.

FIG. 81 SPECIAL CONFIGURATION FOR 9 PARALLEL SINGLE-CORE CABLES IN A FLAT PLANE (see 5.2.6.7)

207
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
FIG. 82 SPECIAL CONFIGURATION FOR 9 PARALLEL SINGLE-CORE CABLES ABOVE EACH OTHER
(see 5.2.6.7)

NOTE  D e is the outer diameter of the cable.

FIG. 83 SPECIAL CONFIGURATION FOR 9 PARALLEL SINGLE-CORE CABLES IN TREFOIL (see 5.2.6.7)

FIG. 84 SPECIAL CONFIGURATION FOR 12 PARALLEL SINGLE-CORE CABLES IN A FLAT PLANE (see 5.2.6.7)

FIG. 85 SPECIAL CONFIGURATION FOR 12 PARALLEL SINGLE-CORE CABLES ABOVE EACH OTHER
(see 5.2.6.7)

208
 IS 732 : 2019

FIG. 86 SPECIAL CONFIGURATION FOR 12 PARALLEL SINGLE-CORE CABLES

IN TREFOIL (see 5.2.6.7)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ANNEX AA

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(Clause 5.3)
(Normative)
INSTALLATION OF SURGE PROTECTIVE DEVICES IN TN SYSTEMS

3 — Main earthing terminal or bar F1 — Protective device at the origin of the installation
4 — Surge protective devices providing protection against F2 — Protective device required by the manufacturer of
overvoltages of category II the SPD
5 — Earthing connection of surge protective devices, either RA — Earthing electrode (earthing resistance) of the installation
5a or 5b
RB — Earthing electrode (earthing resistance) of the
6 — Equipment to be protected supply system

FIG. 87 SPDS IN TN SYSTEMS

209
IS 732 : 2019

ANNEX BB
(Clause 5.3)
(Normative)
INSTALLATION OF SURGE PROTECTIVE DEVICES IN TT SYSTEMS

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
3 — Main earthing terminal or bar F1 — Protective device at the origin of the installation
4 — Surge protective devices providing protection against F2 — Protective device required by the manufacturer of
overvoltages of category II the SPD
5 — Earthing connection of surge protective devices, either RA — Earthing electrode (earthing resistance) of the installation
5a and/or 5b
RB — Earthing electrode (earthing resistance) of the supply system
6 — Equipment to be protected
7 — Residual current protective device (RCD)

FIG. 88 SPDS ON THE LOAD SIDE OF A RCD [according to 5.3.4.2.5 (a)]

210
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
3 — Main earthing terminal or bar F1 — Protective device at the origin of the installation
4 — Surge protective devices F2 — Protective device required by the manufacturer
4a Surge protective device of the SPD
(a combination 4-4a, providing protection against
RA — Earthing electrode (earthing resistance)
overvoltages of category II)
of the installation
5 — Earthing connection of surge protective devices,
RB — Earthing electrode (earthing resistance)
either 5a and/or 5b
of the supply system
6 — Equipment to be protected
7 — Residual current protective device (RCD), placed
either upstream or downstream of the busbars

FIG. 89 SPDS ON THE SUPPLY SIDE OF RCD [according to 5.3.4.2.5 (b)]

211
IS 732 : 2019

ANNEX CC
(Clause 5.3)
(Normative)
INSTALLATION OF SURGE PROTECTIVE DEVICES IN IT SYSTEMS

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
3 — Main earthing terminal or bar F1 — Protective device at the origin of the installation
4 — Surge protective devices providing protection against F2 — Protective device required by the manufacturer of the SPD
overvoltages of category II
RA — Earthing electrode (earthing resistance) of the installation
5 — Earthing connection of surge protective devices, either 5a
RB — Earthing electrode (earthing resistance) of the supply system
and/or 5b
6 — Equipment to be protected
7 — Residual current protective device (RCD)

FIG. 90 SPDS ON THE LOAD SIDE OF A RCD

212
 IS 732 : 2019

ANNEX DD
(Clause 5.3)
(Normative)
INSTALLATION OF CLASS I, II AND III TESTED SPDS, FOR EXAMPLE IN TN-C-S SYSTEMS

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
1 — Origin of the installation 7 — Fixed equipment to be protected
2 — Distribution board 8 — Surge protective device, test class II
3 — Distribution outlet 9 — Surge protective device, test class II or III
4 — Main earthing terminal or bar 10 — Decoupling element or line length
5 — Surge protective device, test class I F1, F2, F3 — Overcurrent protective devices
6 — Earthing connection (earthing conductor) of surge
protective device
NOTES
1 Reference should be made to IS/ IEC 61643-12 for further information.
2 SPD 5 and 8 can be combined in a single SPD.

FIG. 91 INSTALLATION OF CLASS I, II AND III TESTED SPDS

213
IS 732 : 2019

ANNEX EE
(Clause 5.4)
(Normative)
METHOD FOR DERIVING THE FACTOR k IN 5.4.3.1.2
(see also IEC 60724 and IEC 60949)

The factor k is determined from the following formula:

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
where
Qc = the volumetric heat capacity of conductor material (J/K mm3) at 20 °C;
 = the reciprocal of temperature coefficient of resistivity at 0 °C for the conductor (°C);
20 = the electrical resistivity of conductor material at 20 °C (.mm);

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

I = initial temperature of conductor (°C); and
f = final temperature of conductor (°C).
Table 57 Value of Parameters for Different Materials

°C1 Qc1) 201)

3
Material J/°C mm mm

Copper 234.5 3.45×10–3 17.241×10–6 226

–3 –6
Aluminium 228 2.5×10 28.264×10 148
–3 –6
Steel 202 3.8×10 138×10 78
1)
Values taken from IEC 60949.

Table 58 Values of k for Insulated Protective Conductors not Incorporated in Cables

and not Bunched with Other Cables

Temperature Material of Conductor

Conductor °C2) Copper Aluminium Steel
insulation
Initial Final Values for k 3)
70 °C 30 160/140 1) 143/133 1) 95/881) 52/49 1)
thermoplastic (PVC)
90 °C 30 160/1401) 143/133 1) 95/881) 52/49 1)
thermoplastic
(PVC)
176 116 64
90 °C 30 250
thermosetting
159 105 58
(e.g. XLPE and EPR)
200
60 °C thermosetting 30
166 110 60
(EPR rubber)
220
85 °C thermosetting 30
201 133 73
(EPR rubber)
350
185 °C thermosetting 30
(silicone rubber)
1)
The lower value applies to thermoplastic (for example, PVC) insulated conductors of cross-sectional area greater than 300 mm2.
2)
Temperature limits for various types of insulation are given in IEC 60724.
3)
For the method of calculating k, see the formula at the beginning of this Annex.

214
 IS 732 : 2019

Table 59 Values of k for Bare Protective Conductors in Contact with Cable Covering
but not Bunched with Other Cables

Temperature Material of conductor

°C1)
Cable covering Copper Aluminium Steel
Initial Final Values for k2)
Thermoplastic(PVC) 30 200 159 105 58
polyethylene 30 150 138 91 50
CSP3) 30 220 166 110 60
1)
Temperature limits for various types of insulation are given in IEC 60724.
2)
For the method of calculating k, see the formula at the beginning of this Annex.
3)
CSP = Chloro-Sulphonated Polyethylene.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Table 60 Values of k for Protective Conductors as a Core Incorporated
in a Cable or Bunched with Other Cables or Insulated Conductors
Temperature Material of Conductor
Conductor
°C 2) Copper Aluminium Steel

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Insulation
Initial Final Values for k3
70 °C 70 160/1401) 115/103 1) 76/681) 42/371)
thermoplastic
(PVC)
90 °C 90 160/1401) 100/86 1) 66/571) 36/311)
thermoplastic
(PVC)
90 °C 90 250 143 94 52
thermosetting
(for example, XLPE
and EPR)
60 °C thermosetting 60 200 141 93 51
(rubber)
85 °C thermosetting 85 220 134 89 48
(rubber)
185 °C thermosetting 180 350 132 87 47
(silicone rubber)
1)
The lower value applies to thermoplastic (for example, PVC) insulated conductors of cross-sectional area greater than 300 mm2.
2)
Temperature limits for various types of insulation are given in IEC 60724.
3)
For the method of calculating k, see the formula at the beginning of this Annex.

Table 61 Values of k for Protective Conductors as a Metallic Layer of a Cable,

for example, Armour, Metallic Sheath, Concentric Conductor, etc
Temperature Material of Conductor
1)
Conductor Insulation °C Copper Aluminium Steel
3)
Initial Final Values for k
70 °C thermoplastic 60 200 141 93 51
(PVC)
90 °C thermoplastic 80 200 128 85 46
(PVC)
90 °C thermosetting (for 80 200 128 85 46
example, XLPE and EPR)
60 °C thermosetting (rubber) 55 200 144 95 52
85 °C thermosetting (rubber) 75 220 140 93 51
Mineral thermoplastic 70 200 135 – –
(PVC) covered2)
Mineral bare sheath 105 250 135 – –

1)
Temperature limits for various types of insulation are given in IEC 60724.
2)
This value shall also be used for bare conductors exposed to touch or in contact with combustible material.
3)
For the method of calculating k, see the formula at the beginning of this Annex.

215
IS 732 : 2019

Table 62 Values of k for Bare Conductors where There is no Risk

of Damage to Any Neighbouring Material by the Temperature Indicated

Conditions Initial Material of Conductor

Temperature Copper Aluminium Steel
Maximum Maximum Maximum
Temperature Temperature Temperature
(Final k value (Final k value (Final k value
Temperature) Temperature) Temperature)
°C °C °C °C
Visible and in
30 500 228 300 125 500 82
restricted area

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Normal
30 200 159 200 105 200 58
conditions
Fire risk 30 150 138 150 91 150 50

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

216
217
(Normative)
(Clause 5.4)
ANNEX FF

EXAMPLE OF EARTHING ARRANGEMENTS AND PROTECTIVE CONDUCTORS

IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
IS 732 : 2019

Key
Symbol Name Remark
C Extraneous-conductive-part
C1 Water pipe, metal from outside Or district heating pipe
C2 Waste water pipe, metal from outside
C3 Gas pipe with insulating insert, metal from outside
C4 Air-conditioning
C5 Heating system
C6 Water pipe, metal e.g. in a bathroom See IEC 60364-7-701 701.4.2.15.2

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
C7 Waste water pipe, metal e.g. in a bathroom See IEC 60364-7-701 701.4.215.2
D Insulating insert
MDB Main distribution board
DB Distribution board Supplied from the main distribution board
MET Main earthing terminal See 5.4.2.4

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

SEBT Supplementary equipotential bonding terminal
T1 Concrete-embedded foundation earth electrode or soil-embedded See 5.4.2.2
foundation earth electrode
T2 Earth electrode for LPS if necessary See 5.4.2.2
LPS Lightning protection system (if any)
PE PE terminal(s) in the distribution board
PE/PEN PE/PEN terminal(s) in the main distribution board
M Exposed-conductive-part
1 Protective earthing conductor (PE) See 5.4.3
Cross-sectional area, see 5.4.3.1
Type of protective conductor, see 5.4.3.2
Electrical continuity, see 5.4.3.3
1a Protective conductor, or PEN conductor, if any, from supplying
network
2 Protective bonding conductor for connection to the main earthing See 5.4.4.1
terminal
3 Protective bonding conductor for supplementary bonding See 5.4.4.2
4 Down conductor of a lightning protection system (LPS) if any
5 Earthing conductor See 5.4.2.3

Where a lightning protection system is installed, the additional requirements are given in 6 of IS/IEC 62305-3 :
2006, in particular those given in 6.1 and 6.2.
NOTE  Functional earthing conductors are not shown in this Figure.

FIG. 92 EXAMPLE OF EARTHING ARRANGEMENTS FOR FOUNDATION EARTH ELECTRODE, PROTECTIVE

CONDUCTORS AND PROTECTIVE BONDING CONDUCTORS

218
 IS 732 : 2019

ANNEX GG
(Clause 5.5)
(Normative)
EXPLANATION OF SYMBOLS USED IN LUMINAIRES, IN CONTROLGEAR
FOR LUMINAIRES AND IN THE INSTALLATION OF THE LUMINAIRES

Short-circuit proof (inherently or non-inherently) safety isolating transformer

(IS/IEC 61558-2-6 : 2009)

Luminaire with limited surface temperature (IS 10322 series)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Luminaire not suitable for covering with thermally insulating material (IS 10322
series)
Recessed luminaire not suitable for direct mounting on normally flammable
surfaces (IS 10322 series)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Surface mounted luminaire not suitable for direct mounting on normally flammable
surfaces (IS 10322 series)
Luminaire suitable for direct mounting on normally flammable surfaces (IS 10322
series)
NOTE  Luminaires suitable for direct mounting on normally flammable surfaces were earlier

marked with the symbol according to IS 10322 series). With the publication of IEC 60598-
1 : 2008 (7th edition), luminaires suitable for direct mounting have no special marking and only
luminaires not suitable for mounting on normally flammable surfaces are marked with symbols

and/or (see N-=4 of IS 10322 series for further explanations).

Independent ballast IEC 60417-5138 (2011-01)

Converter with a temperature limitation of 110 °C

Independent ballast for mounting on normally flammable surfaces (IEC 61347-

1 : 2007)

Luminaires not suitable to direct mounting on flammable surfaces (only suitable to

non-flammable surfaces) (IS 10322 series)

Luminaires suitable for direct mounting in/on normally flammable surfaces when
thermally insulating material may cover the luminaire (IS 10322 series)

Thermally protected ballast/transformer (class P) (IS 10322 series)

Use of heat-resistant cables for supply, interconnection, or external wiring (number

of conductors of cable is optional) (IS 10322 series)

Luminaires designed for use with bowl mirror lamps (IS 10322 series)

ta . . . °C Rated maximum ambient temperature (IS 10322 series)

219
IS 732 : 2019

Warning against the use of cool-beam lamps (IS 10322 series )

Minimum distance to the lighted objects (m) (IS 10322 series)

Luminaires suitable for severe conditions of use (IS 10322 series)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Luminaires for use with high pressure sodium lamp requiring external ignition
system (IS 10322 series)

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Luminaires for use with high pressure sodium lamp requiring internal ignition
system (IS 10322 series)

Replace any cracked protective screen (rectangular) or (circular) (IS 10322 series)

Luminaires designed for use with self-shielded tungsten halogen lamps only
(IS 10322 series), and lamps which can be used in open luminaires

Lamps which can be used only in protected luminaires

220
 IS 732 : 2019

ANNEX HH
(Clause 5.6)
(Normative)
GUIDANCE FOR EMERGENCY LIGHTING
The values in ISO 30061 should be considered but additional details of suitable systems are given in Table 63.
Annex HH serves as an informative guide for countries that do not have specific rules or their own guidelines.

Table 63 Guidance for Emergency Lighting

(Clause 5.6.7.3)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Requirements
1 2 3 4 5 6 7 8 9

Motor-
Extended Motor-
Examples of Motor- Generator
Duration Escape Sign Low Self- Generator

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Applications Central Power Generator Unit Dual
or Luminaires Power Contained Unit
Supply Unit with Supply
Remote in Maintained Supply Battery with Short
System with no Medium System
Controlled Mode System Unit Break
Break (0 s) Break
Circuit (< 0.5 s)
(< 15 s)

Assembly halls,
** † † † † † † † †
assembly rooms
Exhibition halls ** † † † † † † † †

Theatres, cinemas ** † † † † † † † †

Sports arenas ** † † † † † † † †

Sales areas ** † † † † † † † †

Restaurants ** † † † † † † † †
Hospitals,
** † † † † † † † †
treatment centres
Hotels, guest
** † † † † † † † †
houses *
Residential care
** † † † † † † † †
homes *
High-rise buildings
** † † † † † † † †
*
Schools ** † † † † † † † †

Enclosed car parks † † † † † † † †

Escape routes in
† † † † † † † †
workplaces
High risk task areas † † † † † † † †

Stages ** † † † † † † † †

† denotes suitable systems.

* In premises (guest houses, hotels, residential care homes and high-rise buildings) used the whole day, the rated operating time for the
emergency lighting should be 8 h or shall be switchable with illuminated push buttons for a fixed time by the occupants. In this case, the
push buttons and their timing equipment should also run in the emergency mode.
** Denotes applications which require either extended duration or a circuit like the remote controlled circuit to ensure protection for
longer than 60 min.

221
 1)
equipment
instructions
IS 732 : 2019

Fire rescue service lifts

CO warning equipment
Smoke and heat extraction
Installations for fire pumps

† Denotes suitable systems.

Devices of alarm and issue of
Lifts with special requirements
Examples for safety equipment

1
3
3
3
8
1

12
Rated operating time of the source, h
2

15
15
15
15
15
15
Response time of the source, s, Max.

Only in case of no separate safety supply equipment.

†
†
†
3

Central power supply system

†
†
†
4

Low power supply system

222
ANNEX JJ

(Normative)
(Clause 5.6)

(Clause 5.6.8.4)

†
†
5

Self-contained battery unit

†
†
†
†
†
†
6

Motor-generator unit with no break (0 s)

Requirements
Table 64 Guidance for Safety Equipment

†
†
†
†
†
†
7

Motor-generator unit with short break (< 0.5 s)

GUIDANCE FOR FIRE PROTECTION EQUIPMENT

†
†
†
†
†
†
8

Motor-generator unit with medium break (< 15 s)

†
†
†
†
†
†
9

Dual supply system

†
†
†
10

†1)
†1)
†1)
Monitoring and changeover in the case of failure of the source

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
 IS 732 : 2019

ANNEX KK
(Clause 6.2.3.5)
(Normative)
METHODS FOR MEASURING THE INSULATION RESISTANCE/ IMPEDANCE OF
FLOORS AND WALLS TO EARTH OR TO THE PROTECTIVE CONDUCTOR

KK-1 GENERAL KK-2 TEST METHOD FOR MEASURING THE

IMPEDANCE OF FLOORS AND WALLS WITH
Measurement of impedance or resistance of
a.c. VOLTAGE
insulating floors and walls shall be carried out with
the system voltage to earth and nominal frequency, or Current I is fed through an ammeter to the test-

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
with a lower voltage of the same nominal frequency electrode from the output of the voltage source or
combined with a measurement of insulation from the phase conductor L. The voltage UX at the
resistance. This may be done, for example, in electrode is measured by means of a voltmeter with
accordance with the following methods of internal resistance of at least 1 M towards PE.
measurement:
The impedance of the floor insulation will then be:

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1) a.c. systems ZX = UX / I.
– by measurement with the nominal a.c. The measurement for ascertaining the impedance
voltage, or shall be carried out at as many points as deemed
necessary, selected at random, with a minimum of
– by measurement with lower a.c.
three.
voltages (minimum 25 V) and
additionally by an insulation test using a The test electrodes may be either of the following
minimum test voltage 500 V (d.c.) for types. In case of dispute, the use of test electrode 1 is
nominal system voltages not exceeding the reference method.
500 V and a minimum test voltage
1 000 V (d.c.) for nominal system KK-3 TEST ELECTRODE 1
voltages above 500 V. The electrode comprises a metallic tripod of which
The following voltage sources may be used the parts resting on the floor form the points of an
optionally: equilateral triangle. Each supporting point is provided
with a flexible base ensuring, when loaded, close
a) the earthed system voltage (voltage to earth) contact with the surface being tested over an area of
that exists at the measuring point; approximately 900 mm2 and presenting a resistance
b) the secondary voltage of a double wound of less than 5 000 .
transformer; and
c) an independent voltage source at the Before measurements are made, the surface being
nominal frequency of the system. tested is cleaned with a cleaning fluid. While
measurements are being made, a force of
In cases as specified under (b) and (c), the measuring approximately 750 N for floors or 250 N for walls is
voltage shall be earthed for the measurement. applied to the tripod.
For safety reasons, when measuring voltages
KK-4 TEST ELECTRODE 2
above 50 V, the maximum output current shall
be limited to 3.5 mA. The electrode comprises a square metallic plate with
2) d.c. systems sides that measure 250 mm, and a square of damped,
water-absorbent paper, or cloth, from which surplus
– insulation test by using a minimum test water has been removed, with sides that measure
voltage of 500 V (d.c.) for nominal approximately 270 mm. The paper is placed between
system voltages not exceeding 500 V; the metal plate and the surface being tested.
– insulation test by using a minimum test
During measurement a force of approximately
voltage of 1000 V (d.c.) for nominal
system voltages above 500 V.
750 N for floors or 250 N for walls is applied on
the plate.
The insulation test should be made using measuring
equipment in accordance with IS/IEC 61557-2.

223
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
All dimensions in millimetres.

FIG. 93 TEST ELECTRODE 1

(*) Protection against unintentional contact by a resistance limiting the current to 3.5 mA.

FIG. 94 TEST ELECTRODE 2

224
 IS 732 : 2019

ANNEX LL
(Clause 6.2.3.6.2)
(Normative)
METHOD LL1, LL2 AND LL3

LL-1 METHOD LL1 — MEASUREMENT OF variable load resistance, and the fault loop impedance
EARTH ELECTRODE RESISTANCE is calculated from the following formula:
As an example, the following procedure may be U1  U 2
Z
adopted when the measurement of the earth IR
resistance is to be made (see Fig. 95).

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
An alternating current of a steady value is passed where
between the earth electrode, T, and an auxiliary earth Z = the fault loop impedance;
electrode, T1, placed at a distance from T such that U1 = the voltage measured without connection
the resistance areas of the two electrodes do not of the load resistance;

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

overlap. U2 = the voltage measured with connection of
A second auxiliary earth electrode, T2, which may be the load resistance; and
a metal spike driven into the ground, is then inserted IR = the current through the load resistance.
half-way between T and T1, and the voltage drop
NOTE  The difference between U1 and U2 should be
between T and T2 is measured. significant.
The resistance of the earth electrode is then the
voltage between T and T2, divided by the current LL-3 METHOD LL3 — MEASUREMENT OF
flowing between T and T1, provided that there is no EARTH LOOP RESISTANCE WITH CURRENT
overlap of the resistance areas. CLAMPS
To check that the resistance of the earth electrode is a This measuring method works with existing earth-
true value, two further readings are taken with the loops within a meshed grounding system, as shown in
second auxiliary electrode T2 moved 6 m from and 6 Fig. 97.
m nearer to T, respectively. If the three results are The first clamp inducts a measuring voltage U to the
substantially in agreement, the mean of the three loop, the second clamp measures the current I within
readings is taken as the resistance of the earth the loop. The loop resistance can be calculated by
electrode T. If there is no such agreement, the tests dividing the voltage U by the current I.
are repeated with the distance between T and T1
increased.
As the resulting value of parallel resistances R1
LL-2 METHOD LL2 — MEASUREMENT OF ... Rn is normally negligible, the unknown
THE FAULT LOOP IMPEDANCE resistance is equal to the measured loop
Measurement of the fault loop impedance shall resistance or a little lower.
be made in accordance with the requirements
of 6.2.3.6.3. Each clamp can be single connected to an
As an example, the following method by means of instrument or can be combined into one special
voltage drop may be used. clamp.
NOTES
This method is directly applicable to TN systems and
1 The method proposed in this Annex gives only approximate
values of the fault loop impedance as it does not take into within meshed earthing system of TT systems.
account the vectorial nature of the voltage, that is, of the
conditions existing at the time of an actual earth fault. The
In TT systems, where only the unknown earth
degree of approximation is, however, acceptable provided that connection is available, the loop can be closed by a
the reactance of the circuit concerned is negligible. short-time connection between earth electrode and
2 It is recommended that a continuity test be made between the neutral conductor (quasi TN system) during
main earthing terminal and the exposed- conductive-parts measurement.
before carrying out the fault loop impedance test.
3 Attention is drawn to the fact that the present method To avoid possible risks due to currents caused by
presents difficulties in the application. potential differences between neutral and earth, the
The voltage of the circuit to be verified is measured system should be switched off during connection and
(see Fig. 96) with and without connection of a disconnection.

225
IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
Resistance areas
(not overlapping)
Key
T — earth electrode under test, disconnected from all other sources of supply;
T1— auxiliary earth electrode;
T2— second auxiliary earth electrode;
X — alternative position of T2 for check measurement; and
Y — further alternative position of T2 for the other check measurement.

FIG. 95 MEASUREMENT OF EARTH ELECTRODE RESISTANCE

FIG. 96 MEASUREMENT OF FAULT LOOP IMPEDANCE BY VOLTAGE DROP

226
 IS 732 : 2019

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00
RT — earth-connection of transformer
Rx — unknown earth-resistance to be measured
R1 ...Rn — parallel earth-connections connected by an equipotential bonding or a PEN conductor

FIG. 97 MEASUREMENT OF EARTH LOOP RESISTANCE WITH CURRENT CLAMPS

ANNEX MM
(Clause 6.2)
(Normative)
GUIDANCE ON THE APPLICATION OF THE RULES OF CLAUSE 6.2 INITIAL VERIFICATION

The numbering of the clauses and subclauses of this The installation of the seals is verified to
Annex follows the numbering of 6.2. confirm compliance with the erection
instructions associated with IEC type test for
The absence of reference of clauses or subclauses
the relevant product (under consideration by
means that no additional explanation is given to
ISO).
them.
No other test is required after this
MM-6.2.2 Inspection
verification.
MM-6.2.2.2 This inspection is also intended to check
– protection against thermal effects (4.3)
that the installation of the equipment is in accordance
with the manufacturer’s instructions in order that its The rules of 4.3 concerning the protection
performance is not adversely affected. against thermal effects apply for normal
service, that is, in the absence of a fault.
MM-6.2.2.3
The overcurrent protection of wiring
b) presence of fire barriers and other precautions systems is the object of 4.4 and of 5.3.4.
against propagation of fire and protection against
thermal effects (4.3 and 5.2.10) The operation of a protective device
resulting from a fault, including short
– presence of fire barriers (5.2.10.2) circuits, or from overloads, is considered as
normal service.

227
IS 732 : 2019

– protection against fire (4.3.2) NOTE  The current used for testing should be sufficiently
low as not to cause a risk of fire or explosion.
The requirements of 4.3.2 for locations with
fire hazards assume that protection against MM-6.2.3.3 Insulation resistance of the electrical
overcurrent is in compliance with the rules installation
of 4.4. The measurements shall be carried out with the
c) and d) Selection of conductors for current-carrying installation isolated from the supply. Generally, the
capacity and voltage drop and choice and setting of insulation measurement is carried out at the origin of
protective and monitoring devices. the installation.

The selection of the conductors including If the value measured is less than that specified in
their materials, installation and cross- Table 15, the installation may be divided into several
sectional area, their erection and the setting circuit groups and the insulation resistance of each

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
of the protective devices is verified group shall be measured. If, for one group of circuits,
according to the calculation of the designer the measured value is less than that specified in
of the installation in compliance with the Table 15, the insulation resistance of each circuit of
rules of this standard, particularly 4.2, 4.4, this group shall be measured.
5.2, 5.3 and 5.4. When some circuits or parts of circuits are

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

i) Presence of diagrams, warning notices or other disconnected by undervoltage devices (for instance
similar information contactors) interrupting all live conductors, the
insulation resistance of these circuits or parts of
A diagram, as specified by 5.1.4.5, is circuits is measured separately.
particularly necessary when the installation
comprises several distribution boards. MM-6.2.3.4 Protection by SELV, PELV or by
electrical separation
m) Adequacy of connections of conductors
The purpose of this verification is to check MM-6.2.3.4.3 Protection by separation of circuits
whether the clamping means are adequate Where equipment includes both a separated circuit
for the conductors to be connected and and other circuits, the required insulation is obtained
whether the connection is properly made. by constructing the equipment in accordance with the
In case of doubt, it is recommended to safety requirements of the relevant standards.
measure the resistance of the connections.
MM-6.2.3.6 Protection by automatic disconnection
This resistance should not exceed the
of the supply
resistance of a conductor having a length of
1 m and a cross-sectional area equal to the MM-6.2.3.6.1 General
smallest cross-sectional area of the
conductors connected. According to 4.2, when verifying the compliance
with the maximum disconnecting times, the test
p) Accessibility of equipment for convenience of should be applied at a residual current equal to 5 In.
operation, identification and maintenance
It shall be verified that the operating devices MM-6.2.3.6.2 Measurement of fault loop impedance:
are so arranged that they are easily consideration of the increase of the resistance of the
accessible to the operator. conductors with the increase of temperature
For devices for emergency switching, see As the measurements are made at room temperature,
5.3.7.4.2. with low currents, the procedure hereinafter
described may be followed to take into account the
For devices for switching off for mechanical increase of resistance of the conductors with the
maintenance, see 5.3.7.5.4.2. increase of temperature due to faults, to verify, for
TN systems, the compliance of the measured value of
MM-6.2.3 Testing
the fault loop impedance with the requirements of
MM-6.2.3.2 Continuity of protective conductors 4.2.11.4.
This testing is required for the verification of the The requirements of 4.2.11.4 are considered to be
protection conditions by means of automatic met when the measured value of the fault loop
disconnection of supply (see 6.2.3.6) and is impedance satisfies the following equation:
considered as satisfactory if the device used for the
2 U
test gives an appropriate indication. Zs  m    0
3 Ia

228
 IS 732 : 2019

where b) the resistance of the line conductor and

Zs(m) = the measured impedance of the fault protective conductor of the distribution
circuit(s) are then measured;
current loop starting and ending at the
point of fault (); c) the resistance of the line conductor and
protective conductor of the final circuit are
Uo = the line conductor to earthed neutral then measured;
voltage (V); and
d) the values of the resistance measured in
Ia = the current causing the automatic accordance with (a), (b) and (c) are
operation of the protective device increased on the basis of the increase of the
within the time stated in Table 1 or temperature, taking into consideration, in the
within 5 s according to the conditions case of fault currents, the energy let-through
stated in 4.2.11.4. of the protective device;

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Where the measured value of the fault loop e) the values of the resistance increased in
impedance exceeds 2Uo/3Ia, a more precise accordance with (d) are finally added to the
assessment of compliance with 4.2.11.4 may be value of the supply line conductor-earthed
made, evaluating the value of the fault loop neutral loop impedance, Ze, so obtaining a
impedance according to the following procedure: realistic value of Zs under fault conditions.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

a) the supply line conductor-earthed neutral
loop impedance, Ze, is first measured at the
origin of the installation;

229
IS 732 : 2019

ANNEX NN
(Clause 6.2.3.10)
(Normative)
EXAMPLE OF A DIAGRAM SUITABLE FOR THE EVALUATION OF THE VOLTAGE DROP
Maximum cable length for 4 percent voltage drop at 400 V a.c. nominal voltage and 55 °C wiring temperature.
Three-phase wiring system, PVC insulated cables, copper wiring
For single-phase wiring system (230 V a.c.): divide maximum cable length by 2
For aluminium wiring: divide maximum cable length by 1.6

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
NOTE  The diagram above is not intended to give guidance on the current-carrying capacity of the conductors. ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

FIG. 98 EXAMPLE OF A DIAGRAM SUITABLE FOR THE EVALUATION OF THE VOLTAGE DROP

230
 IS 732 : 2019

ANNEX PP
(Clause 6)
(Normative)
RECOMMENDATION FOR ELECTRICAL EQUIPMENT, WHICH IS BEING RE-USED IN
ELECTRICAL INSTALLATIONS
Re-used equipment is equipment that has been b) manufacturer;
previously installed. c) relevant installation details;
For re-used equipment, documents should be d) test instruments;
available, at the time of the verification, containing at e) results of inspection; and
least the following information: f) tests performed, including verification of

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
a) type of re-used equipment; disconnecting times for RCDs, and test
results.

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

ANNEX QQ
(Clause 6)
(Normative)

DESCRIPTION OF THE INSTALLATION FOR VERIFICATION

NOTE  Particularly suitable for domestic installations.

Type of verification:
 Initial verification
 Periodic verification
Client name and address:
Installation address:
Installer name and address:
Installation:
 New  Modification
 Extension  Existing
Name of inspector:
Description of installation work:
Date of inspection: Signature: ………………………………………..
Identification of instruments used:

Type Model Serial number

231
IS 732 : 2019

Supply characteristics and earthing arrangements Tick boxes and enter details, as appropriate

Earthing arrangements Number and type of live conductors Nature of supply parameters
Incoming supply
Supply authority  protective device
Consumer's characteristics
earth electrode 
System types
TN-C  a.c  d.c.  Nominal voltage, U/Uo(1)...........................V Type:...................
TN-C-S  1-phase, 2-wire (LN)  2-pole  Nominal frequency, f
(1)
Nominal current
......................Hz rating:...............A
TN-S  1-phase, 3-wire (LLM)  3-pole 

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Prospective highest short-circuit RCD sensitivity,
TT  2-phase, 3-wire (LLN)  other  current, Icc(2)…………… where applicable
IT  ……..............kA ......................mA
3-phase, 3-wire (LLL)  other 
External earth fault loop
3-phase, 4-wire (LLLN)  other  impedance, Ze (2)................................

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

Alternative source 
of supply (to be detailed NOTES
on attached schedules) 1) By enquiry
2) By enquiry, or by measurement or by
calculation

Details of consumers earth electrode(where applicable)

Type Material
Cu Fe Other
Foundation earth electrode   
Ground earth electrode   
Rod   
Tape   
Other: ..............................................................   
Location: ..........................................................
Resistance to earth:.........................................
NOTE  In existing installations where the above information cannot be ascertained, this fact should be noted.

Earthing and main bonding conductors

Earthing conductor: material...................... csa1).................... mm2 connection verified 
Main equipotential material...................... csa...................... mm2 connection verified 
bonding conductors:
To incoming water and/or gas service  To other elements:........................................................
Supplementary equipotential bonding
Bathrooms/showers: material...................... csa................... mm2 connection verified 
Swimming pools: material...................... csa................... mm2 connection verified 
2
Other: material...................... csa.................. mm connection verified 
(please state)
1) csa: conductor cross-sectional area.

232
 IS 732 : 2019

Isolation and protective devices at the origin of installation

Type No. of poles Ratings
V
Main switch
A
In A
Fuse or circuit breaker
Icn, Icu, Ics kA
In A
RCD
In mA

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
ANNEX RR

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(Clause 6)
(Normative)

FORM FOR INSPECTION OF ELECTRICAL INSTALLATIONS

(see EXAMPLES IN CLAUSE RR -2)

RR-1 FORM FOR INSPECTION OF ELECTRICAL INSTALLATIONS

NOTE  Particularly suitable for domestic installations.

A Protection Against Direct Contact

Item Compliance (NOTE 1) Comments

i) Insulation of live parts

ii) Barriers

iii) Enclosures

B Equipment

Equipment Selection (NOTE 2) Erection (NOTE 1) Comments

i) Cables
ii) Wiring accessories
iii) Conduits
iv) Trunking
v) Distribution equipment
vi) Luminaires
vii) Heating
viii) Protective devices RCD, CBs, etc.
ix) Other

233
IS 732 : 2019

C Identification

Item Presence Correct Correct Comments

location wording
i) Labelling of protective devices, switches
and terminals
ii) Warning notices
iii) Danger notices
iv) Identification of conductors

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
v) Isolation devices
vi) Switching devices
vii) Diagrams and schedules
NOTES

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

1 Enter C if it complies with (national) installation standard, NC if it does not comply.
2 Visible indication of compliance with the appropriate product standard. In case of doubt, a declaration of conformity with the
standard needs to be obtained from the manufacturer (for example, from the catalogues).

RR-2 EXAMPLES OF ITEMS TO BE ❑ Barriers (check for adequacy and security)

CHECKED WHEN CARRYING OUT AN ❑ Enclosures have suitable degree of protection
INSTALLATION INSPECTION appropriate to external influences
❑ Enclosures have cable entries correctly sealed
General ❑ Enclosures have unused entries blanked off
where necessary
❑ Good workmanship and proper materials have
been used B Equipment
❑ Circuits to be separate (no interconnection of
neutrals between circuits) 1. Cables and Cords
❑ Circuits to be identified (neutral and protective Non-flexible cables and cords
conductors in same sequence as line conductors) ❑ Correct type
❑ Disconnection times likely to be met by installed ❑ Correct current rating
protective devices ❑ Non-sheathed cables protected by enclosure in
❑ Adequate number of circuits conduit, duct or trunking
❑ Adequate number of socket-outlets provided ❑ Sheathed cables routed in allowed zones or
❑ All circuits suitably identified additional mechanical protection provided
❑ Suitable main switch provided ❑ Where exposed to direct sunlight, of a suitable
❑ Main isolators to break all live conductors, type
where applicable ❑ Correctly selected and installed for use. for
❑ Main earthing terminal provided, readily example. buried
accessible and identified ❑ Correctly selected and installed for use on
❑ Conductors correctly identified exterior walls
❑ Correct fuses or circuit breakers installed ❑ Internal radii of bends in accordance with
❑ All connections secure relevant standard
❑ The whole installation has been earthed in ❑ Correctly supported
accordance with national standards ❑ Joints and connections electrically and
❑ Main equipotential bonding connects services mechanically sound and adequately insulated
and other extraneous-conductive-parts ❑ All wires securely contained in terminals etc,
to the main earth facility without strain
❑ Supplementary bonding has been provided in all ❑ Enclosure of terminals
bath and shower rooms ❑ Installation to permit easy replacement in case of
❑ All live parts are either insulated or contained damaged conductors
within enclosures ❑ Installation of cables to avoid excessive strain on
A Protection Against Direct Contact conductors and terminations
❑ Protection against thermal effects
❑ Insulation of live parts

234
 IS 732 : 2019

❑ One conduit allowed for conductors of the same Socket-outlets

circuit (derogation see 5.2) ❑ Mounting height above the floor or working
❑ Connection of conductors (size of terminals surface suitable
adapted to cross-sectional area of conductors); ❑ Correct polarity
sufficient pressure contact shall be guaranteed ❑ Circuit protective conductor connected directly
❑ Selection of conductors for current-carrying to the earthing terminal of the socket
capacity and voltage drop considering the outlet
method of laying
❑ Identification of N, PEN and PE conductors Joint boxes
❑ Joints accessible for inspection
Flexible cables and cords
❑ Joints protected against mechanical damage
❑ Selected for resistance to damage by heat
Connection unit

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
❑ Prohibited core colours not used
❑ Joints to be made using cable couplers ❑ Out of reach of a person using a bath or shower
❑ Final connections to other current-using ❑ Correct rating of fuse fitted
equipment properly secured or arranged to
Cooker control unit
prevent strain on connections
❑ Mass supported by pendants not exceeding ❑ Sited to the side and low enough for accessibility

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

correct values and to prevent flexes trailing across radiant
plates
Protective conductors ❑ Cable to cooker fixed to prevent strain on
❑ Protective conductors provided to every point connections
and accessory
Lighting controls
❑ Flexible conduit to be supplemented by a
protective conductor ❑ Single pole switches connected in line
❑ Minimum cross-sectional area of copper conductors only
conductors ❑ Correct colour coding or marking of conductors
❑ Insulation, sleeving and terminations identified ❑ Earthing of exposed metalwork, for example,
by colour combination green-and- metal switch plate
yellow ❑ Switch out of reach of a person using a bath or
❑ Joints sound shower
❑ Main and supplementary bonding conductors of Fixed connection of current-using equipment
correct size (including luminaires)
2. Wiring Accessories (Luminaires – see below) ❑ Installation according to manufacturer
General (applicable to each type of accessory) recommendations
❑ Visible indication of compliance with the ❑ Protection against direct contact
appropriate product standard, where required in 3. Conduits
the relevant product standard General
❑ Box or other enclosure securely fixed
❑ Edge of flush boxes not projecting beyond wall ❑ Visible indication of compliance with the
surface appropriate product standard, where required in
❑ No sharp edges on cable entries, screw heads, the relevant product standard
etc. which could cause damage to cables ❑ Securely fixed, covers in place and adequately
❑ Non-sheathed cables, and cores of cable from protected against mechanical damage
which the sheath has been removed, ❑ Number of cables for easy draw-in not exceeded
not exposed outside the enclosure ❑ Adequate boxes for drawing in cables
❑ Correct connection ❑ Radius of bends such that cables are not
❑ Conductors correctly identified damaged
❑ Bare protective conductors sleeved green/yellow ❑ Suitable degree of protection appropriate to
❑ Terminals tight and containing all strands of the external influences
conductors Rigid metal conduit
❑ Cord grip correctly used or clips fitted to cables
❑ Connected to the main earthing terminal
to prevent strain on the terminals
❑ Line and neutral cables enclosed in the same
❑ Adequate current rating
conduit
❑ Suitable for the conditions likely to be
❑ Conduit suitable for damp and corrosive
encountered
situations

235
IS 732 : 2019

Flexible metal conduit ❑ No sharp edges on cable entries, screw heads etc.
❑ Separate protective conductor provided which could cause damage to cables
❑ Adequately supported and terminated ❑ All covers and equipment in place and secure
❑ Adequate access and working space
Rigid non-metallic conduit ❑ Enclosure suitable for mechanical protection
❑ Provision for expansion and contraction and, where applicable, for fire protection
❑ Boxes and fixings suitable for mass of luminaire ❑ Protection against direct contact
suspended at expected temperature ❑ Correct connection of equipment
❑ Protective conductor provided ❑ Choice and setting of protective devices
(protection against overcurrent)
4. Trunking
❑ Protective device attributed individually for each
General circuit

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
❑ Visible indication of compliance with the ❑ Wiring correctly fixed in distribution board
appropriate product standard, where required in
the relevant product standard 6. Luminaires
❑ Securely fixed and adequately protected against Lighting points
mechanical damage ❑ Correctly terminated in a suitable accessory or
fitting

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

❑ Selected, erected and routed so that no damage is
caused by the ingress of water ❑ Not more than one flex unless designed for
❑ Cables supported for vertical runs multiple pendants
❑ Suitable degree of protection appropriate to ❑ Flexible support devices used
external influences and locations ❑ Switch wires identified
❑ Holes in ceiling above rose made good to
Metal trunking — Additional requirements prevent the spread of fire
❑ Phase and neutral cables enclosed in the same ❑ Suitable for the mass suspended
metal trunking ❑ Suitably located
❑ Protected against damp or corrosion ❑ Emergency lighting
❑ Correctly earthed
❑ Joints mechanically sound, and of adequate 7. Heating
continuity with links fitted ❑ Visible indication of compliance with the
appropriate product standard
5. Distribution Equipment ❑ Class 2 insulation or protective conductor
❑ Visible indication of compliance with the connected
appropriate product standard, where required in
the relevant product standard 8. Protective Devices
❑ Suitable for the purpose intended ❑ Visible indication of compliance with the
❑ Securely fixed and suitably labelled appropriate product standard, where required in
❑ Non-conductive finishes on switchgear removed the relevant product standard
at protective conductor connections and if ❑ RCDs provided where required
necessary made good after connecting ❑ Discrimination between RCDs considered
❑ Correctly earthed 9. Other
❑ Conditions likely to be encountered taken
account of, that is suitable for the foreseen C. Identification
environment
❑ Correct IP rating applied Labelling
❑ Suitable as means of isolation, where applicable ❑ Warning notices
❑ Not accessible to person normally using a bath or ❑ Danger notices
shower ❑ Identification of conductors
❑ Need for isolation, mechanical maintenance, ❑ Isolation devices
emergency and functional switching met ❑ Switching devices
❑ All connections secure ❑ Diagrams and schedules
❑ Cables correctly terminated and identified ❑ Protective devices

236
 ANNEX SS
(Clause 6)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(Normative)
REPORT OF VERIFICATION
Table 65 Model Form for Circuit Details and Test Results Schedule

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

INFORMATION REGARDING DISTRIBUTION BOARD (1)
Description: Ref.: Manufacturer
Rated voltage, Un: V Nominal current, In: A Frequency: Hz Protection IP degree: Short-circuit withstand capability of distribution board, Icc
kA
MAIN SUPPLY TO DISTRIBUTION BOARD (6)
Short circuit capacity RCD: CSA supply condition
Protective device: Type: Rating, In: A Icp: kA (2) Zs:
rating kA mA Section: L= mm2; PE= mm2
CIRCUIT DETAILS TEST RESULTS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Circuit Descrip- Number Func- Connec- Insulation resistance RCD Touch Polar- PE Remarks+
Circuit
No. tion of tion tion Cables/Cond. Circuit protection voltage ity conti- national
characteristics
237

room points load test nuity requirements

served
Type Section In (A) Type Zs Ip (A) M In Id Td
L/PE
(5) kW Mm2 Fuse Circuit  L- L-PE N- L1- L2- L3- A m (3) (7) (8) (3)
(9) breaker N PE PE PE PE A (4)

IS 732 : 2019
237
 IS 732 : 2019
NOTES
1 By enquiry (manufacturer, name plate or technical doc.)

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
2 By measurement or calculation
3 Enter C if complies or NC if does not comply
4 Complete test where appropriate shall be performed including touch voltage and tripping time at rated current
5 Enter appropriate function code (see opposite)
6 Only to be completed if the distribution board is not connected directly to the origin of the installation

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

7 Only required where supplementary equipotential bonding has been installed in accordance with 413.1.3.6
8 Record connected load where readily identifiable

Abbreviations Function code (for column 4)

L Line C Cooking W/H Water heating
Td Test trip time S/O Socket outlet S/H Storage heaters

Zs Fault loop impedance UFH Under floor heating Li Lighting

CSA Cross-sectional area H Heating HP Heat pump

I cp Prospective short-circuit current at main busbars of distribution board r.m.s. value
Ip Measured short-circuit current at end of consumer supply line. For socket outlets circuits,
measurement shall be made at each S/O and to record only the worst case
238

I cw Short-circuit withstand of equipment

 IS 732 : 2019

ANNEX TT
(Clause 6)
EXTRACTS FROM CENTRAL ELECTRICTTY AUTHORITY NOTIFICATION
New Delhi, the 20th September, 2010
No. CEVl/59/CEA/EL - In exercise of the powers name of such persons from the register.
conferred by section 177 of the Electricity Act, 2003
5. Electrical Safety Officer—(1) All suppliers of
(36 of 2003); the Central Electricity Authority hereby
electricity including generating companies,
makes the following regulations for Measures
transmission companies and distribution companies
relating to Safety and Electric Supply, namely:-
shall designate an Electrical Safety Officer for
Chapter I ensuring observance of safety measures specified

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
under these regulations in their organisation for
1. Short title and Commencement—(1) These construction, operation and maintenance of power
regulations may be called the Central Electricity stations, sub-stations, transmission and distribution
Authority (Measures relating to Safety and Electric lines.
Supply) Regulations, 2010

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

(2) The Electrical Safety Officer shall be an
(2) They shall come into force on the date of their E1ectrical Engineering degree holder with at least ten
final publication in the Official Gazette. years of experience in operation and maintenance of
electricity plants or an Electrical Engineering
Chapter II Diploma holder with at least fifteen years of
3. Designating person(s) to operate and carry out experience in operation and maintenance of electric
the work on electrical lines and apparatus — (1) A plant.
supplier or a consumer, or the owner, agent or (3) The Electrical Safety Officer designated under
manager of mine, or the agent of any company
sub-regulation (1) shall ensure periodic inspection of
operating in an oil field or the owner of a drilled well such installations, get them tested and keep a record
in an oil field or a contractor who has entered into a thereof and such records shall be made available to
contract with a supplier or a. consumer to carry out
the Electrical Inspector if and when required.
duties incidental to the generation, transformation,
transmission, conversion, distribution or use of Chapter III
electricity shall designate persons for the purpose to General safety requirements
operate and carry out the work on electrical lines and
apparatus. 12. General safety requirements, pertaining to
construction, installation, protection, operation
(2) The supplier or consumer, or the owner, agent or and maintenance of electric supply lines
manager of a mine, or the agent of any company apparatus—(1) All electric supply lines and
operating in an oil-field or the owner of a drilled well apparatus shall be of sufficient rating for power,
in an oil field or a contractor referred to on sub- insulation and estimated fault current and of
regulation (1) shall maintain a register wherein the sufficient mechanical strength, for the duty cycle
names of the designated persons and the purpose for which they may be required to perform under the
which they are engaged, shall be entered. environmental conditions of installation, and shall be
(3) No person shall be designated under sub- constructed, installed, protected, worked and
regulation (l) unless,— maintained in such a manner as to ensure safety of
human beings, animals and property.
(i) he possesses a certificate of competency or
electrical work permit, issued by the (2) Save as otherwise provided in these regulations,
Appropriate Government the relevant code of practice of the Bureau of Indian
Standards or National Electrical Code, if any, may be
(ii) his name is entered in the register referred to followed to carry out the purposes of this regulation
in sub regulation (2) and in the event of any inconsistency, the provisions
4. Inspection of designated officers and other of these regulations shall prevail.
safety measures—(1) The register maintained under (3) The material and apparatus used shall conform to
sub-regulation (2) of regulation 3 shall be produced the relevant specifications of the Bureau of Indian
before the Electrical Inspector when required by him. Standards or International Electro-Technical
(2) If on inspection, the Electrical Inspector finds that Commission where such specifications have already
the designated person does not fulfill the required been laid down.
qualification, he shall recommend the removal of the (4) All electrical equipment shall be installed above

239
IS 732 : 2019

the Mean Sea level (MSL) as declared by local earthed neutral conductor, or the conductor
Municipal Authorities and where such equipment is which is to be connected thereto, to enable
to be installed in the basement, consumer shall ensure such conductor to be distinguished from any
that the design of the basement should be such that live conductor and such indication shall be
there is no seepage or leakage or logging of water in provided-
the basement. (a) where the earthed or earthed neutral
13. Service lines and apparatus on consumer’s conductor is the property of the
premises—(1) The supplier shall ensure that all supplier, at or near the point of
electric supply lines, wires, Fittings and apparatus commencement of supply;
belonging to him or under his control, which are on a (b) where a conductor forming part of a
consumer’s premises, are in a safe-condition and in consumer’s system is to be connected to
all respects fit for supplying electricity and the the supplier’s earthed or earthed neutral

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
supplier shall take precautions to avoid danger arising conductor, at the point where such
on such premises from such supply lines, wires, connection is to be made;
fittings and apparatus. (c) in all other cases, at a point
corresponding to the point of
(2) Service lines placed by the supplier on the
commencement of supply or at such

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

premises of a consumer which are underground or
other points as may be approved by an
which are accessible shall be so insulated and
Electrical Inspector.
protected by the supplier as to be secured under all
ordinary conditions against electrical, mechanical, (ii) no cut-out, link or switch other than a
chemical or other injury to the insulation. linked-switch arranged to operate
simultaneously on the earthed or earthed
(3) The consumer shall, as far as circumstances neutral conductor and live conductors shall
permit, take precautions for the safe custody of the be inserted or remain inserted in any earthed
equipment on his premises belonging to the supplier. or earthed neutral conductor of a two wire-
(4) The consumer shall also ensure that the system or in any earthed or earthed neutral
installation under his control is, maintained in a safe conductor of a multi-wire system or in any
condition. conductor connected thereto.
Provided that the above requirement shall
14. Switchgear on consumer’s premises—(1) The not apply in case of-
supplier shall provide a suitable switchgear in each (a) a link for testing purposes, or
conductor of every service line other than an earthed
or earthed neutral conductor or the earthed external (b) a switch for use in controlling a
conductor of a concentric cable within a consumer’s generator or transformer
premises, in an accessible position and such 16. Earthed terminal on consumer’s premises—(1)
switchgear shall be contained within an adequately The supplier shall provide and maintain on the
enclosed fireproof receptacle: consumer’s premises for the consumer’s use, a
suitable earthed terminal in an accessible position at
Provided that where more than one consumer is or near the point of commencement of supply.
supplied through a common service line, each such
consumer shall be provided with an independent Provided that in the case of installation of voltage
switchgear at the point of rigid junction to the exceeding 250V the consumer shall, in addition to the
common service. aforementioned earthing arrangement, provide his
own earthing system with an independent electrode.
(2) Every electric supply line other than the earthed
or earthed neutral conductor of any system or the Provided further that the supplier may not provide
earthed external conductor of a concentric cable shall any earthed terminal in the case of installations
be protected by suitable switchgear by its owner. already connected to his system on or before the date
to be specified by the State Government in this behalf
15. Identification of earthed and earthed neutral if he is satisfied that the consumer’s earthing
conductors and position of switches and arrangement is efficient.
switchgear therein—Where the conductors include
an earthed conductor of a two-wire system or an (2) The-consumer shall take all reasonable
earthed neutral conductor of a multi-wire system or a precautions to prevent mechanical damage to the
conductor which is to be connected thereto, the earthed terminal and its lead belonging to the
following conditions shall be complied with: supplier.
(i) an indication of a permanent nature shall be (3) The supplier may, recover from the consumer the
provided by the owner of the earthed or cost of installation on the basis of schedule of charges

240
 IS 732 : 2019

published by him in advance and where such supply lines having concentric cables, the
schedule of charges is not published, the procedure external conductor of such cables, shall be
laid down, in regulation 63 shall apply. earthed by two separate and distinct
connections with earth.
Explanation—For the purposes of sub-regulation (1),
the expression "point of commencement of supply of (v) the connection with earth may include a link
electricity" shall mean the point at the incoming by means of which the connection may be
terminal of the switchgear installed by the consumer. temporarily interrupted for the purpose of
testing or for locating fault.
17. Accessibility of bare conductors—Where bare (vi) in a direct current three wire system, the
conductors are used in a building, the owner of such middle conductor shall be earthed at the
conductors shall,— generating station only and the current from
(a) ensure that they are inaccessible; the middle conductor to earth shall be

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
(b) provide in readily accessible position continuously recorded by means of a
switches for rendering them dead whenever recording ammeter, and if at any time the
necessary; and current exceeds one-thousandth part of the
maximum supply current, immediate steps
(c) take such other safety measures as are shall be taken to improve the insulation of

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

specified in the relevant Indian Standards.
the system.
Chapter V (vii) where the middle conductor is earthed by
Safety Provisions for Electrical Installations and means of a circuit breaker with a resistance
Apparatus of Voltage not Exceeding 650 Volts connected in parallel, the resistance shall not
40. Test for resistance of insulation—(1) Where exceed ten ohms and on the opening of the
any electric supply line for use at voltages not circuit breaker, immediate steps shall be
exceeding 650 V has been disconnected from a taken to improve the insulation of the
system for the purpose of addition, alteration or system, and the circuit breaker shall be re-
repair, such electric supply line shall not be closed as soon as possible.
reconnected to the system until the supplier or the (viii) the resistance shall be used only as a
owner has applied the test prescribed under protection for the ammeter in case of earths
regulation 33. on the system and until such earths are
removed and immediate steps shall be taken
(2) The provision under sub-regulation (1) shall not to locate and remove the earth.
apply to overhead lines except overhead insulated
(ix) in the case of an alternating current system,
cables, unless the Electrical Inspector otherwise
there shall not be inserted in the, connection
directs in any particular case.
with earth any impedance, other than that
41. Connection with earth—The following required solely for the operation of
conditions shall apply to the connection with earth of switchgear or instruments, cut-out or circuit
systems at voltage normally exceeding 125 V but not breaker, and the result of any test made to
exceeding 650 V, namely: ascertain whether the current, if any, passing
through the connection with earth is normal,
(i) neutral conductor of a 3-phase, 4-wire shall be duly recorded by the supplier.
system and the middle conductor of a 2-
phase, 3-wire system shall be earthed by not (x) no person shall make connection with earth
less than two separate and distinct by the aid of, nor shall he keep it in contact
connections with a minimum of two with, any water mains not belonging to him
different earth electrodes or such large except with the consent of the owner thereof
number as may be necessary to bring the and ofthe Electrical Inspector.
earth resistance to a satisfactory value both (xi) alternating current systems which are
at the generating station and at the sub- connected with earth as aforesaid shall be
station. electrically interconnected:
(ii) the earth electrodes so provided, shall be Provided that each connection with earth is
inter-connected to reduce earth resistance. bonded to the metal sheathing and metallic
(iii) neutral conductor shall also be earthed at armouring, if any, of the electric supply
one or more points along the distribution lines concerned.
system or service line in addition to any (xii) the frame of every generator, stationary
connection with earth which may be at the motor, portable motor, and the metallic
consumer's premises. parts, not intended as conductors, of all
(iv) in the case of a system comprising electric transformers and any other apparatus used

241
IS 732 : 2019

for regulating or controlling electricity, and works reasonably at earth potential and
all electricity consuming apparatus, of to avoid dangerous contact potentials
voltage exceeding 250 V but not exceeding being developed on such metal works;
650 V shall be earthed by the owner by two b) limit earth resistance sufficiently low to
separate and distinct connections with earth. permit adequate fault current for the
(xiii) neutral point of every generator and operation of protective devices in time
transformer shall be earthed by connecting it and to reduce neutral shifting;
to the earthing system by not less than two c) be mechanically strong, withstand
separate and distinct connections. corrosion and retain electrical
(xiv) all metal casing or metallic coverings continuity during the life of the
containing or protecting any electric supply installation and all earthing systems
line or apparatus shall be connected with shall be tested to ensure efficient

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
earth and shall be so joined and connected earthing, before the electric supply lines
across all junction boxes and other openings or apparatus are energised.
as to make good mechanical and electrical (xvi) all earthing systems belonging to the
connection throughout their whole length: supplier shall in addition, be tested for
Provided that conditions mentioned in this resistance on dry day during the dry season

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

regulation shall not apply, where the supply not less than once every two years.
voltage does not exceed 250 V and the (xvii) a record of every earth test made and the
apparatus consists of wall tubes or brackets, result thereof shall be kept by the supplier
electroliers, switches, ceiling fans or other for a period of not less than two years after
fittings,, other than portable hand lamps and the day of testing and shall be available to
portable and transportable apparatus, unless the Electrical Inspector when required.
provided with earth terminal and to class-II Explanation—The expression “Class-II apparatus and
apparatus and appliances: appliance” shall have the same meaning as is
Provided further that where the supply assigned to it in the relevant Indian Standards.
voltage is not exceeding 250 V and where
the installations are either new or renovated, 42. Earth leakage protective device—The supply of
all plug sockets shall be of the three pin electricity to every electrical installation other than
type, and the third pin shall be permanently voltage not exceeding 250 V below 5 kW and those
and efficiently earthed. installations of voltage not exceeding 250V which do
not attract provisions of section 54 of the Act, shall
(xv) All earthing systems shall, -
be controlled by an earth leakage protective device so
a) consist of equipotential bonding as to disconnect the supply instantly on the
conductors capable of carrying the occurrence of earth fault or leakage of current:
prospective earth fault current and a
group of pipes, rods and plate electrodes Provided that such earth leakage protective device
for dissipating the current to the general shall not be required for overhead supply lines having
mass of earth without exceeding the protective devices which are effectively bonded to
allowable temperature limits as per the neutral of supply transformers and conforming to
relevant Indian Standards in order to regulation 73.
maintain all non-current carrying metal

242
Bureau of Indian Standards

BIS is a statutory institution established under the Bureau of Indian Standards Act, 2016 to promote
harmonious development of the activities of standardization, marking and quality certification of goods
and attending to connected matters in the country.

Copyright

BIS has the copyright of all its publications. No part of these publications may be reproduced in any form
without the prior permission in writing of BIS. This does not preclude the free use, in the course of
implementing the standard, of necessary details, such as symbols and sizes, type or grade designations.
Enquiries relating to copyright be addressed to the Director (Publications), BIS.

SUPPLIED BY BOOK SUPPLY BUREAU UNDER THE LICENSE FROM BIS FOR LNTECC, MAHSR C4, SURAT
Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewed
periodically; a standard along with amendments is reaffirmed when such review indicates that no changes are

ON 19/11/2022 17:07:39 (165.225.120.113) VALID UPTO 18/11/2023 00:00:00

needed; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards
should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of
‘BIS Catalogue’ and ‘Standards : Monthly Additions’.

This Indian Standard has been developed from Doc No.: ETD 20 (10375).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

BUREAU OF INDIAN STANDARDS

Headquarters:
Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002
Telephones : 2323 0131, 2323 3375, 2323 9402 Website: www.bis.org.in

Regional Offices: Telephones

Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg
NEW DELHI 110002 { 2323 7617
2323 3841
Eastern : 1/14 C.I.T. Scheme VII M, V. I. P. Road, Kankurgachi
KOLKATA 700054 { 2337 8499, 2337 8561
2337 8626, 2337 9120
Northern : Plot No. 4-A, Sector 27-B, Madhya Marg, CHANDIGARH 160019
{ 26 50206
265 0290
Southern : C.I.T. Campus, IV Cross Road, CHENNAI 600113
{ 2254 1216, 2254 1442
2254 2519, 2254 2315
Western : Manakalaya, E9 MIDC, Marol, Andheri (East)
MUMBAI 400093 { 2832 9295, 2832 7858
2832 7891, 2832 7892
Branches: A H M E D A B A D . B E N G A L U R U . B H O PA L . B H U B A N E S H WA R . C O I M B ATO R E .
D E H R A D U N . D U R G A P U R . FA R I D A B A D . G H A Z I A B A D . G U WA H AT I .
HYDERABAD. JAIPUR. JAMMU. JAMSHEDPUR. KOCHI. LUCKNOW. NAGPUR.
PA RWA N O O . PAT N A . P U N E . R A I P U R . R A J K O T. V I S A K H A PAT N A M .
Published by BIS, New Delhi