EET402

ELECTRICAL SYSTEM DESIGN AND ESTIMATION

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 Syllabus

Module 1
IS Product Standards and Codes of practice, The Electricity Act 2003 and NEC 2011 (6 hours):
General awareness of IS Codes - IS 732 - IS 3043 –IS 2026- IS 3646-part 1&2 - IS 5216 part 1&2
- Electricity supply code-2014 (Relevance of each code in electrical installation applications only).
The Electricity Act 2003- General introduction- Distribution of Electricity (Part VI)- Central
Electricity Authority (Part IX)- Regulatory Commissions (Part IX).
National Electric Code (NEC 2011) - Scope – Wiring installation (Section 9)- Short circuit
calculations (Section 10).
Graphical symbols and signs as per NEC for electrical installations.
Classification of voltages-standards and specifications, tolerances for voltage and frequency.

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 Module 2
Lighting Schemes and calculations (6 hours):
Lighting design calculations - Definitions of luminous flux, Lumen, Luminous
intensity/illuminance (Lux), Illumination calculations, factors affecting Coefficients of Utilization
(CoU) - and Light Loss Factor (LLF).
Benefits of LED lamps over the yesteryear luminaires – Efficacy of present-day LED lamps.
Design of illumination systems – Average lumen method - Space to mounting height ratio.
Design of lighting systems for a medium area seminar hall using LED luminaires
Exterior lighting design- point to point method - road lighting and public area lighting- Space to
mounting height ratio - selection of luminaires- Metal Halide- High & Low pressure Sodium–
LED lamps.

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 Module 3
Domestic Installation (10 hours)
General aspects as per NEC and IS 732 related to the design of domestic dwellings availing
single phase supply (LV) and three phase supply (MV) for a connected load less than 15kW.
Load Survey- common power ratings of domestic gadgets- connected load-diversity factor
selection of number of sub circuits (lighting and power)-selection of MCB distribution boards to
provide over load, short circuit and earth leakage protection.
Principle of operation of MCB, MCB Isolator, ELCB/RCCB and RCBO. Selection of CBs for
protection and grading between major and minor sections.
Selection of wiring cables, conduits as per NEC and IS 732
Design of electrical schematic and physical layout drawings for low and medium class domestic
installation. Preparation of schedule of works and bill of quantities (cost estimation excluded).
Pre-commissioning tests- Insulation resistance measurement, continuity test, polarity test, and
earth resistance measurement as applicable to domestic installations.

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 Module 4
Industrial Power and Lighting Installations (9 hours):
Industrial installations –classifications- Design of electrical distribution systems with main
switch board, sub switch boards and distribution boards with ACBs, MCCBs and MCBs as the
case may be, for feeding power (mainly motors) and lighting loads of small and medium
industries.
Selection of armoured power cables (AYFY, A2XFY, YWY) – calculation of ampacity, voltage
drop, short circuit withstand capacity etc.
Design of MSB & SSB including Motor Control Centre (MCC) for motor controls - selection of
bus bars and switchgears.
Selection of 11kV indoor and outdoor transformer substations upto 630kVA - selection of
switchgears and protective devices –Preparation of schedule of works and bill of quantities
(cost estimation excluded).
Short circuit calculations and earthing design for the HV and LV sides of an 11 kV substation of
capacity up to 630 kVA.
Pre-commissioning tests of 11kV indoor/outdoor substation of an HT consumer.

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 Module 5
High Rise building, Solar PV system, Standby generators and Energy conservation (8
hours):
Electrical installations of high-rise buildings: Distribution systems – rising main, cable
system - Installation of lifts, standby generators, fire pumps - electric schematic drawing.
Selection of standby Diesel Generator set (DG set) –power rating - Continuous, Prime and
Standby power ratings- installation and essential protections-Introduction to Automatic Mains
failure (AMF) systems.
Energy Conservation Techniques in electrical power distribution - Automatic Power Factor
Correction (APFC) panel – Principle of operation and advantages.
Introduction to Solar PV Systems, off-grid and on-grid systems, Solar panel efficiencies
design of a PV system for domestic application-Selection of battery for off-grid domestic
systems.
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Text/Reference Books
1. National Electrical Code 2011, Bureau of Indian Standards.
2. National Lighting Code 2010, Bureau of Indian Standards.
3. National Building Code of INDIA 2016 - Bureau of Indian Standards.
4. M. K. Giridharan, Electrical Systems Design, I K International Publishers, New Delhi,
2nd edition, 2016.
5. U.A.Bakshi, V.U.Bakshi Electrical Technology, Technical publications, Pune.
6. Narang K.L., A Text Book of Electrical Engineering Drawing, Tech India Publications.
7. J. B. Gupta, A Course in Electrical Installation Estimating and Costing, S.K. Kataria &
Sons; Reprint 2013 edition (2013).
8. K. B. Raina, S. K. Bhattacharya, Electrical Design Estimating Costing, NEW AGE;
Reprint edition (2010).
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Course Outcomes:
After the completion of the course the student will be able to:
CO 1 Explain the rules and regulations in the design of components for medium and
high voltage installations.
CO 2 Design lighting schemes for indoor and outdoor applications.
CO 3 Design low/medium voltage domestic and industrial electrical installations.
CO 4 Design, testing and commissioning of 11 kV transformer substation.
CO 5 Design electrical installations in high rise buildings.

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 Module 1
IS Product Standards and Codes of practice,
The Electricity Act 2003 and NEC 2011

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Electrical system design involves distribution of electrical energy from the
metering point down to the last point or equipment of a building, which is
connected to the supply system.
Two important aspects of electrical system design are:
● To assure proper functioning of the installation for the use intended

by the designer.
● To provide safety to persons, livestock and property against
dangers and damages that may arise in the use of electrical
installations

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Role of regulations in Electrical System Design
Act: A bill which has passed through the various legislative steps required for it and
which has become law.
Statutes: An Act passed by a legislative body.
Rule: In context to an act, rules define the guidelines that must be followed for the
successful implementation of the act.
The electricity supply industry in our country was governed by three major laws
● The Indian Electricity Act,1910
● The Electricity (Supply) Act,1948
● The Electricity Regulatory Commission Act,1998

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The Indian Electricity Act,1910
This act created the basic framework for the development of electric
supply industry in India. It also created the legal framework for
laying down of conductors and other works relating to the supply
of electricity.

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The Electricity (Supply) Act,1948
This act mandated the creation of State Electricity Boards with the
responsibility of making available the electricity in respective states.
The responsibility was handed over to the State Electricity Boards and
they undertook rapid expansion programmes by utilizing plan funds.
However there was gradual deterioration in the performance of state
electricity boards.
They were unable to take decision on tariff in a professional and
independent manner .
To address these issues, The Electricity Regulatory Commission act
was enacted by the parliament in 1998.

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The Electricity Regulatory Commission Act,1998
To help the government to determine the tariff, Regulatory Commission
Act was passed in 1998.
The main objectives were:
● Replacing existing laws while preserving the core features .

● Introducing new concepts like power trading, open access .

● To prevent the requirement of each SEB’s(State Electricity
Boards) to pass their own act .
● Give SEBs to develop their own power sector .
● Include progressive features and endeavors.
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Indian Electricity Act, 2003
The economic liberalisation policies of 1990’s have opened up many opportunities for
massive industrialisation.

With the policy adopted for private participation in generation, transmission and
distribution and with the objective of separating the regulatory responsibilities
from the Government, the need for a more sensible law was necessary.

In consultation with state Governments, other stake holders and other experts a new
act called ‘The Electricity Act,2003’ came into existence.

This act replaces The Indian Electricity Act 1910,The Electricity (Supply) Act
1948 and The Electricity Regulatory Commission Act 1998.

The Electricity Act, 2003 is an act promoted by the parliament to consolidate the
laws relating to generation, transmission ,distribution, trading and use of
electricity.
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 This act aims at
● Promoting measures conductive to the development of electrical industry
● Promoting competition
● Protecting the interest of consumers
● Providing electric supply to all areas
● Providing transparent policies on subsidies
● Promoting efficient and environmental friendly policies
● Constitution of Central Electricity Authority and regularity Commission
● Establishment of Appellate Tribunals

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Various parts of this Act are
PART-I: This part deals with the jurisdiction of the law and important
definitions
PART-II: This part deals about National Policy and Plan to be
prepared by Central Govt. in consultation with state Govt. National
Policy and National Electricity plan needs to be published in Gazette /
News paper once in 5 years.
PART-III: This part deals about generation of electricity
PART-IV: This part deals licensing for transmission of electricity,
distribution and undertaking trading in electricity.

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PART V: This part deals transmission of electricity including inter-state,
regional and interregional transmission system.
PART-VI: This deals with provisions of distribution of electricity with
respect to distribution licensee
PART-VII: This chapter deals about terms and conditions for the
determination of tariff.
PART-VIII: This part deals work of licensees includes provision as to
opening up of streets, railways etc., overhead lines, notice to telegraph
authority.
PART-IX: This part deals about constitution and functions of Central
Electricity Authority
PART-X: This part deals about Regulatory Commissions and its
constitution, power and functions of central commission
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PART-XI: This part deals about appellate tribunal for electricity
PART XII: This part deals about investigation, enforcement of assessment for
electricity consumed by consumer by State Govt. or board or licensee.
PART XIII: This part deals about reorganization of Electricity Board
PART XIV: This part deals mainly about offences and penalties for
misusing/theft of electricity.
PART XV: This part deals constitution of special courts for the purpose of
providing speedy trial of offences referred to in sections 135 to 139 PART XVI:
This part deals mainly resolution of dispute by arbitration under this Act.
PART XVII: This part deals mainly protection of railways, highways, airports
and canals, docks, wharfs and piers, protection of telegraphic, telephonic and
electric signalling lines, amendment of sections 40 and 41 of Act 1 of 1894
PART XVIII: This part mainly deals miscellaneous matter
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 PART VI
DISTRIBUTION OF ELECTRICITY

Provisions with respect to distribution licensee

❖Section 42. (Duties of distribution licensee and open access):
❖Section 43. (Duty to supply on request):
❖Section 44. (Exceptions from duty to supply electricity):
❖Section 45. (Power to recover charges):
❖Section 46. (Power to recover expenditure):
❖Section 47. (Power to require security):
❖Section 48. (Additional terms of supply):
❖Section 49. (Agreement with respect to supply or purchase of electricity):
❖Section 50. (The Electricity Supply Code):
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 PART VI
DISTRIBUTION OF ELECTRICITY

❖Section 51. (Other businesses of distribution licensees):

❖Section 52. (Provisions with respect to electricity traders):
❖Section 53. (Provisions relating to safety and electricity supply):
❖Section 54. (Control of transmission and use of electricity):
❖Section 55. (Use, etc., of meters):
❖Section 56. (Disconnection of supply in default of payment):
❖Section 57. (Consumer Protection: Standards of performance of licensee):
❖Section 58. (Different standards of performance by licensee):
❖Section 59. (Information with respect to levels of performance):
❖Section 60. (Market domination):
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 PART IX
CENTRAL ELECTRICITY AUTHORITY
Constitution and functions of Authority
Section 70. (Constitution, etc., of Central Electricity Authority):
Section 71. (Members not to have certain interest):
Section 72. (Officers and staff of Authority):
Section 73. (Functions and duties of Authority):
Section 74. (Power to require statistics and returns):
Section 75. (Directions by Central Government to Authority):

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 PART X
REGULATORY COMMISSIONS

Constitution, powers and functions of Central Commission

Section 76. (Constitution of Central Commission)
Section 77. (Qualifications for appointment of Members of Central
Commission):
Section 78. (Constitution of Selection Committee to recommend Members): ---
Section 79. (Functions of Central Commission):
Section 80. (Central Advisory Committee):
Section 81. (Objects of Central Advisory Committee):

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 PART X
REGULATORY COMMISSIONS

Constitution, powers, and functions of State Commissions

❖Section 82. (Constitution of State Commission):
❖Section 83. (Joint Commission):
❖Section 84. (Qualifications for appointment of Chairperson and Members of
❖State Commission):
❖Section 85. (Constitution of Selection Committee to select Members of State
Commission):
❖Section 86. (Functions of State Commission
❖Section 87. (State Advisory Committee):
❖Section 88. (Objects of State Advisory Committee):

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 PART X
REGULATORY COMMISSIONS
Appropriate Commission – other provisions
❖Section 89. (Term of office and conditions of service of Members):
❖Section 90. (Removal of Member):
❖Section 91. (Secretary, officers and other employees of Appropriate Commission):
❖Section 92. (Proceedings of Appropriate Commission):
❖Section 93. (Vacancies, etc. not to invalidate proceedings):
❖Section 94. (Powers of Appropriate Commission
❖Section 95. (Proceedings before Commission):
❖Section 96. (Powers of entry and seizure):
❖Section 97. (Delegation):
❖Section 98. (Grants and loans by Central Government)
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 PART X
REGULATORY COMMISSIONS
Appropriate Commission – other provisions
❖Section 99. (Establishment of Fund by Central Government):
❖Section 100. (Accounts and audit of Central Commission):
❖Section 101. (Annual Report of Central Commission):
❖Section 102. (Grants and Loans by State Government):
❖Section 103. (Establishment of Fund by State Government):
❖Section 104. (Accounts and audit of State Commission):
❖Section 105. (Annual Report of State Commission):
❖Section 106. (Budget of Appropriate Commission):
❖Section 107. (Directions by Central Government):
❖Section 108. (Directions by State Government):
❖Section 109. (Directions to Joint Commission):
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IS codes
IS codes are intended for standardization in the field of electrical power
generation, transmission, distribution and utilization equipment &
insulating materials, winding wires, measuring and process control
instruments and primary and secondary batteries. Major IS codes are

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Code Content

IS 3043 Code for practice for earthing

IS 732 Code for practice for electrical installations

IS 2026 Specification of Power Transformers

Code of practice for interior illumination - general requirements and

IS 3646 P1 recommendations for working interiors

Code of practice for interior illumination – schedule for values of illumination

IS 3646 P2 and glare index

Recommendations on safety procedures and practices in electrical work-

IS 5216 P1 General

IS 5216 P2 Recommendations on safety procedures and practices in electrical work- Life

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IS 3043-CODE OF PRACTICE FOR EARTHING
This Indian Standard (First Revision) was adopted by the Bureau of Indian
Standards on 6 August 1987.

This code of practice is intended to serve as a consolidated guide to all those who
are concerned with the design, installation, inspection and maintenance of
electrical systems and apparatus.

Scope

This code of practice gives guidance on the methods that may be adopted for system
earthing and equipment earthing. This Code applies only to land-based
installations and it does not apply to ships, aircrafts or offshore installations.

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 Various sections in this code are
SECTION 1 GENERAL GUIDELINES
This section includes various definitions, exchange of information ,system earthing,
equipment earthing etc.
SECTION 2 CONNECTIONS TO EARTH
Includes details about resistance to earth, earth electrode , earthing arrangement for
various purposes etc.
SECTION 3 EARTH FAULT PROTECTION ON CONSUMER'S PREMISES
Includes earth fault protection in installations and various devices for automatic
disconnection.

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 SECTION 4 POWER STATIONS, SUBSTATIONS AND OVERHEAD LINES

Deals with earthing in power and substations and overhead power lines.

SECTION 5 INDUSTRIAL PREMISES

Guidelines for earthing in industries.

SECTION 6 STANDBY AND OTHER PRIVATE GENERATING PLANTS

SECTION 7 MEDICAL ESTABUSHMENT

SECTION 8 STATIC AND LIGHTNING PROTECTION EARTHING

SECTION 9 MISCELLANEOUS INSTALLATIONS AND CONSIDERATIONS

Guidelines for earthing in hazardous areas, telecommunication ,building sites, mines and quarries, street
lighting etc.

SECTION 10 MEASUREMENTS AND CALCULATIONS

Guidelines about measurement of earth resistivity,earth electrode resistance loop impedsnce etc.

SECTION 11 DATA PROCESSING INSTALLATIONS

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IS 732 -CODE OF PRACTICE FOR ELECTRICAL WIRING INSTALLATIONS
This covers the requirements & precautions regarding wiring installations for
ensuring satisfactory & reliable service & safety from all possible hazards from
the use of electricity.

This code applies to the design, selection, erection and inspection and testing of
wiring installations whether permanent or temporary, in and about buildings.

It relates generally to all wiring installations in non-industrial and industrial

locations, whether the electric supply is derived from an external source or from a
private generating plant.

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This code is not applicable to:
● Systems for distribution of energy to the public, or to power generation and
transmission for such systems.

● Wiring installations in special locations such as mines.

● Lightning conductors, telecommunications & alarm systems.

● Traction installations, motor vehicles, installations on board ships, aircraft or offshore

installations

● Matters concerning specifications of individual items of equipment and does not deal
with requirements for the construction of prefabricated assemblies of electrical
equipment.

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 Various sections of this code are
SECTION 1 TERMINOLOGY
Explains all terminologies used in standards
SECTION 2 ASSESSMENT OF GENERAL CHARACTERISTICS OF
INSTALLATIONS
Assessment of general characteristics like purpose of wiring, supply available, maintainability
etc.
Assesses external influences like environmental factors, construction of building etc that affects
the installation.

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 SECTION 3 PROTECTION FOR SAFETY
Protection Against Direct Contact
Protection Against Indirect Contact
Protection Against Thermal Effects in Normal Service
Protection against Overcurrent, earth leakage and earth fault currents, Overvoltage,
under voltage etc.
Protection against switching and isolation for maintenance

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 SECTION 4 DESIGN OF INSTALLATION, SELECTION AND ERECTION OF
EQUIPMENT
Fundamental Requirements for Design
Fundamental Requirements for Selection of Electrical Equipment
Fundamental Requirements for Erection and Initial Testing of Electrical Installations
SECTION 5 INSPECTION AND TESTING
Guidelines for inspection and testing

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IS 5216 (Part 1)-Guide for safety procedures in electrical work
This code is divided into 9 sections.
S1 Scope

This standard (Part 1) gives recommendations regarding safety procedures and practices which
should be followed to the extent applicable in all major electrical installations, such as generating
stations, substations, industrial establishments, transmission and distribution lines, and cable
networks
S2 Statuary Regulations

This section gives the details of statuary regulations to be followed for electrical installations.

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 S3 Permit to work system

All work on major electrical installations shall be carried out under permit
to work system unless standing instructions are issued by the competent
authority to follow other procedures.
S4 Register of messages

All messages and instructions relating to the operation of switches and

other important communications concerning the work shall be recorded in
the register of messages, preferably by an independent person not directly
connected with the work.
S5 Safety instructions for working on Low & medium mains and
apparatus.
S6 Safety instructions for working on high voltage mains and
apparatus.

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 S7 Workmen’s safety devices and appliances

Rubber gauntlets, gloves, mats, boots and galoshes, insulated platforms and
stools, safety belts etc shall be used as required for working on electrical
equipment and apparatus as precaution against electric shock.
S8 Fires and Fire extinguishers

In the event of fire on electrical mains or apparatus, the effected part shall
immediately be isolated completely from its source of electrical energy.
S9 Training of employees

Foe maximum effectiveness, a sound safety procedure would include in

addition to the instructions on the hazards of electricity, through training of
all employees who work on electrical installations and equipments.

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IS 5216(Part 2)-Recommendation on safety practices in electrical work-Life saving
techniques
This code is divided into 4 sections
S1 Scope

This standard (Part II) covers methods of dealing with electrical accidents and techniques
for saving the life of a person who is affected.
S2 Accidents

Guidelines regarding DO’s and DON’TS, First aid, Fire fighting, reporting of accidents
etc.
S3 Treatment of Electric shock

Guidelines for treatment of electric shock and immediate action to be performed.

S4 Artificial Respiration

Explains various methods of artificial respiration in case of electrocution.

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 IS 3646 Part 1 Code of practice for interior illumination
General requirements and recommendations for working interiors
SCOPE
▪This code ( Part 1 ) covers the principles and practice governing good lighting in
buildings and relates chiefly to the lighting of & working areas in industrial, commercial
and public buildings, hospitals and schools.
▪The primary objective of this code is to indicate the factors which should be taken into
account to achieve good lighting.
▪It confines itself primarily to the lighting of working interiors, such as factories,
workshops, offices, commercial premises, public buildings, hospitals and schools, keeping
two objectives in mind, namely, to make the task easy to see and to create a good visual
environment.
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 This code consist of the following parts:
Part 1 General requirements and recommendations for working interiors
Part 2 Method of calculation of the glare indices for interiors
Part 3 Recommendations for lighting in industries
Part 4 Recommendations for lighting in offices
Part 5 Recommendations for lighting in hospitals
Part 6 Recommendations for lighting in libraries
Part 7 Recommendations for lighting in educational institutions
Part 8 Emergency lighting

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 IS 3646 Part 2 Code Of Practice For Interior Illumination
Schedule for values of illumination and glare index
▪This part covers schedule for illumination values and limiting values of glare index.
▪Part I of this standard covers the principles of good lighting and aspects of design and Part III deals
with the calculation of coefficients of utilization based on BZ classification.

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1. Scope
This standard covers the recommended values of illumination and limiting values of glare index.
2. Terminology
For the purpose of this standard, the definitions given in Part I of this standard shall apply.
3. Schedule Of Recommended Values Of Illumination And Limiting Values Of Glare Index
3.1 This schedule gives values of illumination and limiting values of glare index commensurate with the
general standards of lighting described in this code and related to many occupations and buildings. 3.2
Illumination Values
3.3 Determining Illumination for Acceptable Visual Performance
3.4 Glare Index

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 IS 2026 : Specification of Power Transformer
▪This standard applies to three-phase and single phase power transformers (including autotransformers)
with the exception of certain categories of small and special transformers such as
a) single-phase transformers with rated power less than 1 kVA and three-phase transformers less
than 5 kVA;
b) instrument transformers;
c) transformers for static convertors;
d) traction transformers mounted on rolling stock;
e) starting transformers;
f) testing transformers; and
g) welding transformers.
▪Where Indian Standards do not exist for such categories of transformers, this part of IS 2026 may still be
applicable either as a whole or in part.
▪The requirements for power transformers are covered in eight parts.
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National Electrical Code (NEC)
• As technology advanced with new products and processes, a more
rational and unified code became a necessity.
• NEC unifies the practices, procedures and safety requirements to be
complied within the design, execution, inspection and maintenance
of electrical installations in the country.
• NEC is formulated to elaborate the IE rules which are statutory in
nature and serve as a compilation document on electrical practices in our
country.

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Objective of NEC
To complement IE rules by the way of elaborating as well as
recommending practices to comply with their requirements. It provides
information in a consolidated form to the electrical engineers and
contractors who are concerned with the design and operation of
electrical installations.

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NEC covers the following
∙ Std good practices for the selection of various items of electrical equipment forming
part of power system.
∙ Recommendations concerning safety and related matter in the wiring of electrical
installations of buildings or industrial structures.
∙ General safety procedures and practices.
∙ Additional precautions to be taken in explosive and active atmosphere.
NEC applies to Hotels, sports buildings, industrial premises, temporary and permanent
installations,agricultural areas etc.
NEC does not applies to effects of lightning, Payment of electrical work in installations.
And systems of distribution of energy to public and power generation and transmission for
subsystems.

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Information in NEC is presented in eight parts:-
∙ General and common aspects
∙ Electrical installation in standby generating stations and substations
∙ Electrical installations in non-industrial buildings
∙ Electrical installations in industrial buildings
∙ Outdoor installations
∙ Electrical installations in agricultural premises
∙ Electrical installations in hazardous areas.
∙ Solar photovoltaic supply systems

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 NEC 2011 SECTION 9 – WIRING INSTALLATION

This Section 9 of the Code covers the essential design and constructional requirements
for electrical wiring installations.
It includes general and common aspects for selection of wiring systems such as cables,
equipment, fittings and accessories,conduit etc. It also includes methods of
installation of Cables and Conductors
It also gives information about Current—Carrying Capacity of Conductors , Voltage
Drop in Consumer’s Installations and Cross-sectional Areas of Conductors.

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NEC 2011 SECTION 10 – SHORT CIRCUIT CALCULATIONS
Section 10 covers guidelines and general requirements associated with
circuit calculations namely, short circuit calculations and voltage drop,
calculations for cables and flexible cords.
The objective of the circuit calculation is to ensure that the selection of
equipment under consideration is designed for safe and reliable long
period of operation.

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 Kerala Electricity Supply Code,
2014
This Code shall be applicable to all distribution licensees including
deemed licensees and all consumers and users in the State of Kerala.
It shall come into force with effect from the first day of April, 2014.

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This code explains
system, safety and standards of supply of electricity.
security deposit for electricity charges and meter.
procedures and processes.
billing and mode of payment.
disconnection, dismantling and reconnection.
theft, unauthorised use and other irregularities.
review and amendement to the code.

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Graphical symbols and signs as per NEC for
electrical installations

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Standard values of voltages

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Distribution voltage for direct current system shall be 220/440V.
Classification of voltages
Standard voltages are classified in NEC as follows.
Low voltage (less than 250 V)
Medium voltage (250 V to less than 650 V)
High voltage (650 V to less than 33kV)
Extra high voltage (33 kV)

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Voltage limits for alternating current systems
Supply authorities are required to maintain the voltages on the system under normal
condition within the tolerances specified below.
6% in the case of low and medium voltage installations
6% on the higher side or 9% on the lower side in the case of high voltage systems
12.5% in the case of extra high voltage systems.
Under Indian Electricity Rules, the voltage fluctuation may not vary by more than 5%
above or below the declared nominal voltage .(228V to 252V for nominal voltage of
240V & 394.25V to 435.75V for nominal voltage of 415V )
Frequency must be within ±1% of the declared frequency of 50Hz .

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