Topics to be covered

OSG-BS7671_2015- BS 7671 18th

RS-18.pdf Ammendment 2_compressed.pdf

Installation

Substation Underground
cable
Transformer
CU

Earthing systems
Protective Wiring systems
(Ze) TNS/ TN-CS/TT devices & Circuits
& Conductors
sizes L/N
Diversity
Cpc
Earthing &
Bonding

Page 1 of 54
Page 2 of 54
1. Types of cables and uses- (Wiring system) [BS7671 chapter 52]

Types of
cables-WIRING SYSTEM-17.docx
• PVC/PVC also known as twin & Earth
In domestic and similar environments
• Single core cables

Have no sheath so they usually protected by metal/PVC conduit or trunking

Single core cables are used in where many circuits exist in harsh and arduous
conditions Workshops/cow shed/ milking parlour/ factories etc.

• Steel wire Armoured (SWA)

Has armoured wire fore mechanical protection making it durable
Installed underground/on tray/cable ladder/cable ducts

• FP200
Fire proof cable - Light with a foil covering the cables – flexible. – fire alarm
circuits
• Mineral Insulated Metal sheath(MIMS) or Mineral Insulated copper
conductor/clad (MICC)
Fire resistant cable/ high current carrying capacitor

• XLPE
Underground high voltage distribution cable
conductor Insulation

Wiring system refers to types of cables used at the

PVC/PVC
installation.
cable
Conductor- copper or Aluminium – carries current
Sheath
Insulation – PVC – separates conductors and
metalwork
Sheath – offers mechanical protection to the cable

Cores – refers to conductors that carry current ONLY – LIVE conductors

Examples –
• 2 core cable – means 2 Live conductor = Line & Neutral

Page 3 of 54
 • 3 core cable – means 3 LIVE conductors = 3 Phase

the first letter relates to the general category of external influence: - BS7671 App 5
A Environment – hot/cold – dry or wet/

B Utilization – house/ school/ petrol/ gas station/ garage

C Construction of buildings – brick wall/ concrete/ partition walls/ stud walls

Page 4 of 54
 Singles – in steel/PVC conduit or steel/ PVC trunking
OSG
Conduit/Trunking will provide the mechanical protection

SWA it has steel armour for mechanical protection

– suitable for underground cable or distribution
cable external wiring

Page 5 of 54
 MIMS cable or MICC
With stand very high
temperatures 50000C

Solid aluminium conductors insulated by thermosetting PVC wrapped in

aluminium foil is called FP200

Suitable for High temperature

Cables have different operating temperatures.

• 700 thermoplastic - drews like wax when heated

• 900 thermosetting – become hard and brittle when heated

Page 6 of 54
 Each type of cable has its recommended Installation Methods
(REFERENCE METHODS)
This how the cable can be installed.

PVC/PVC installations methods are 100* /101*/102*/103* /C/ B

Numbers are used where cable are installed in a building fabric –
partition/stud walls

Other cables – A/B/C/D/G/F/E

Letters are used for fabricated /manufactured systems to carry or
contain cables.

There are some installations methods which allow conductors to carry

HIGHER or LOWER currents when used. Impacts on current carrying
capacity.

For each type of cable there are recommended installation methods

Type of cable used

• Thermoplastic – operating temp = 700C

• Thermosetting – 900C or more
Cables are LSF – low smoking fumes
Cable installation and considerations refer to BS7671 Chapter 52 Wiring
systems

Installation
Reference Methods.ppt
2. Installation methods/Reference methods – (Appendix 4)
• 100
• 101
• 102
• 103
• A
• B
• C

Page 7 of 54
 • E/F
• Segregation – is separation of cables - band 1 from Band11

BS7671 App 4
Conductor current carrying capacity
OSG App F

Building fabric – plasterboard/concrete/brick wall

Environment – dry/wet/hot/cold/humid/outside
Utilization – house/factory/bank/fuel station

Page 8 of 54
3. Diversity – (OSG App A) BS 7671 Reg 311
Knowledge for Q6 of Design
project

DIVERSITY CURRENT
-Stud.docx DEMAND.pptx

DIVERSITY Tut.docx

Selecting a cable of reasonable size for the circuits and sub circuits the cable is meant to supply.

Label the diagram below:

Lights 66% x 6A =4A House sockets = 40 %
Kitchen ring 100%
Kitchen ring 100% = 32A

House sockets 40% of 32 =19.2 A Water heater

Lights (Instant)
Water Heater 100% of 5000/230
= 21.7A All circuits or gadgets are NOT
necessarily USED all the time
at FULL capacity or
simultaneously
4A +32A +19.2A +
21.7A + 27A =

103.9A

WITHOUT DIVESITY A 25 mm2 is suitable

6A + 32A + 32A + 21.7A

Maximum is Current = 50A
+ 50A = 141.7A
Give that cooker 10A 10 A + 30 % f.l. of
A 50mm2 is required connected cooking
Also give it (0.3 of the remainder) (0.3 x 40A) =12A appliances in excess of 10
Also give cooker 5A if it has a socket = 5A A+ 5 A if a socket-outlet is
incorporated in the control
If NO socket then NO Amps added unit
27A – this is the Design current (Ib)

Page 9 of 54
A 10KW domestic domestic cooker.
What is the maximum current demand?
I = P/V = 10000 / 230 = 43 A

What is the anticipated current demand?

10A + 30% of remainder 10A +(0.3 x 33) = 20A

10A + 30% of remainder + 5A = 25A

6A CB at 100W per point = 100/230 = 0.43A per light maximum lights = 13

Calculate the anticipated current demand for determining the size of the
supply cable for a 12KW domestic cooker, a) whose cooker unit has NO
socket outlet, b) whose cooker unit has a socket outlet? Also determine
the size of the protective device for this cable.

EQUIPMENT POWER MAXIMUM DIVERSITY ACTUAL

RATING CURRENT CURRENT
DEMAND DEMAND

Domestic cooker 12 KW 12000/230 = 53A 10A = (0.3 x 10A +(0.3x43) =

(cooker unit remainder) 10A + 13A = 23A
without socket
outlet)
Domestic cooker 12KW 12000/230 = 53A 10A = (0.3 x 10 +(0.3 x 43) + 5
(cooker unit with remainder) +5A = 28A
socket outlet)

Page 10 of 54
Calculate the anticipated current demand for determining the size of the
supply cable for the following loads of a 230V supply for a domestic
household. Also determine the size of the protective device for this cable.

EQUIPMENT POWER MAXIMUM DIVERSITY & ACTUAL

RATING CURRENT FACTORS( IF CURRENT
DEMAND ANY) DEMAND

5 x filament 100W 500/230 = 2.2A 66% 0.66 x2.2 = 1.45A

lamps

1x cooker 12KW 12000/230 =53A 10A = (0.3 x 28A

incorporating remainder)+5A
socket outlet

A1 Power circuit 32A 32A

1 x shower 4KW 4000/230 = 17.3A 17.3A

(instantaneous
type)

Total current demand 104.5A 78.8A

25mm2 non- 16mm2 non-
armoured armoured

Page 11 of 54
Calculate the anticipated current demand for determining the size of the
supply cable for the following loads of a 230V supply for a small shop. Also
determine the size of the protective device for this cable.

EQUIPMENT POWER MAXIMUM DIVERSITY & ACTUAL

RATING CURRENT FACTORS (IF CURRENT
DEMAND ANY) DEMAND

6 x filament 100W 600/230 90% 0.9 x 2.6 =

lamps =2.6A

10x discharge 65W 650 x 90% 0.9 x 5.1 =

lamps 1.8/230
=5.1A

A1 Power circuit 7360W 32A 100%

A3 Power circuit 4600W 20A 50%

1x immersion 3KW 3000/230 = 100%

heater 13A

1 x shower 5KW 5000/230 = 100% 21.7A

(instantaneous 21.7A
type)

Total current demand 94.4A 83.6A

Page 12 of 54
Knowledge for Q6 of Design project

Page 13 of 54
Knowledge for Q4 of Design project
4. Conductor sizes selection and volt drop –(Appendix 4) OSG Appendix F
• Ib, Design current – current drawn by a load/appliance
• In, Nominal Current – rating of protective device
• It, - Tabulated current- current in specific tables
• Iz - CCC cable current carrying capacity
• Ca, -ambient temperature
• Ci,- thermal insulation
• Cg,- grouping factor
• Cf,- fusing factor
• 3% & 5% - permissible voltage drops for lighting & power respectively
• Zs- earth loop impedance - for shock protection
• Ze – external earth loop impedance – (DNO)
• Size of earthing conductor – thermal Constrains/adiabatic equation & shock
protection
• Verify selectivity between protective devices.

Conductor Sze CableRatingChallen

Selection Procedure ge Updated-17.ppt
L3-17.docx

Ib ≤ In ≤ Iz ≤ It
8 KW shower
1. Current drawn by this shower is design current ( Ib) = P/ V

Page 14 of 54
 09/11/23
Domestic COOKER
Ib ≤ In ≤ It ≤ Iz

CHOOSE SIZE OF COOKER - 15KW

Maximum current demand for cooker I =P/V =15000/ 230 = 65.2A
Applying diversity for a cooker – OSG 10A + (0.3 x 55.2) + 5 A = 31.6A – This
is the assumed cooker current demand Ib

Ib ≤ In
In is size of protective device = 32A type B to BS EN 60898 – by experience or from
manufacturers/BS7671/OSG
Conditions in which the cable is installed – PVC/PVC Flat – for domestic
Ca,= 300C factor is 1
Ci, = N/A
Cg = 6 circuits = 0.57 – with 5 other circuits
Cf, = for BS 3036 = 0.725 -N/A

In ≤ It
It = In / Factors = 32/ 0.57 = 56.1A – BS7671-Table 4D5/OSG-F6
Assuming the cables are installed – reference method C- site decision/stated

It ≤ Iz
So, 56.1A gives Iz = 64A giving live conductor sizes = 10mm2

This means Line and Neutral are 10 mm2

Page 15 of 54
Check for volt drop assuming the Length = 15m site decision/stated
mV/A/m x Ib x L / 1000
4.4 x 31.6 x 15 / 1000 = 2.1V √
This is acceptable since the volt drop is less than 5% = 11.5V
Can now confirm that the live conductors are 10mm2 - adopted

Check for shock protection

What is the earthing system site decision/stated = TNS - Ze max = 0.8Ω
with Ze = 0.65Ω by enquiry/measurement/state
10mm2 with cpc size 6 mm2
From OSG Table I1
R1 +R2 is calculated as follows
mΩ/m = 4.91
4.91 x 15 /1000

4.91 x 15 /1000 =0.07Ω

Consider heat correction Factor of 1.2
R1 +R2 x 1.2
0.07 x 1.2 = 0.08Ω

Page 16 of 54
Zs = Ze + R1 +R2 = 0.65 + 0.08 = 0.73 Ω
Maximum Zs from OSG is = 1.1 Ω so Zs of 0.73Ω is acceptable.
This means that our circuit will disconnect in the required time hence preventing
SHOCK

TN-0.4s
TT – 0.2s

Knowledge for Q5 of Design project

Check for THERMAL constrains – this means that will the 6mm2 cpc withstand the
HIGH fault current without burning?
I Fault = V/Zs = 230 /0.73 = 315A

Page 17 of 54
So we use the adiabatic equation:
√3152 x 0.4 / 115
√99225 x 0.4/115 = 1.73 mm2
√39690/115 = 199.2/115 = 1.73 mm2 so a 6mm2 will melt under fault conditions of
315A
So a 6mm2 cpc is appropriate

So suitable cable is 10mm2/6mm2 cpc cable

Page 18 of 54
 conductor size – MCO3044FC/B

Ib ≤ In ≤ Iz ≤ It
Calculate the size of conductors used to supply a 14KW domestic cooker?
Maximum current demand of this cooker = I = P/V
14000/230 = 61A

Apply diversity = 10A +(0.3 x remainder) +5A

10A + (0.3 x 51) +5
10 + 15.3 +5 = 30.3A
Design current (Ib) = 30.3A
1
Design current is the current required by an a current using equipment after
applying DIVERSITY if required.

Page 19 of 54
 Now we choose the type and size of protective device to be used to protect the
conductors for cooker.
Fuses -BS 3036 / RCBOs BSEN 61009/ CB – BSEN 60898
Choice is RCBO – Brandon

Ib ≤ In
2
Size is 32A from manufacturers catalogue – most economical
In is known as NOMINAL Current and this is the rating of the PROTECTIVE
DEVICE.

Size is 40A from manufacturers catalogue – cooker in constant use

3

It = In / (FACTORS)
What are FACTORS
Factors are conditions under which the cables/ conductors are
installed which compromise HEAT dissipation/ breathing of cables

Page 20 of 54
Ca – ambient temperature

Ci – thermal insulation which may cover the cable

Cg – grouping – when cables are grouped they heat up#

Page 21 of 54
Cf – ONLY when BS3036 rewireable fuses are used – 0.725

Page 22 of 54
It = In / (FACTORS)

i) It = 32 / (0.88x 0.8) = 45.4A – this Iz

ii) It = 40 / (0.88x 0.8) = 56.8A – this Iz
4

What type of cable is being used to supply

the cooker? – wiring system?

Also, what is the reference/installation method used

to this cable?
Preferred - Method C

Page 23 of 54
 5
It ≥ Iz

These are CCC – L&N

Iz = 45.4A giving It = 47A so conductor size is 6mm2

Iz = 56.8A giving It = 64A so conductor size is 10mm2

6 Check/ confirm voltage drop

H
o
w
lo
n
g is the cable from consumer unit to cooker?

We measured it to be 15m

i) mV/A/m for 6 mm2 cable is 7.3

ii) mV/A/m for 10 mm2 cable is 4.4

Page 24 of 54
so volt drop = 7.3x 30.3 x 15/ 1000 =3.3V √ good
or volt drop is 4.4 x 30.3 x 15 / 1000= 2 V√ good less
than 5% of 230V = 11.5V

7
checking for shock protection – disconnection
time
disconnection times are TN – 0.4s
or 5 sec for distribution
TT – 0.2s or 1 sec for distribution
Zs – Ze + (R1 + R2)
What is Ze value?
TNS so Ze= 0.5Ω by choice
What about (R1 + R2)
Using either 6 mm2 & 4mm2

Page 25 of 54
(R1 + R2) = 7.69 x 15 /1000 = 0.12Ω
Using 10mm2 & 6mm2
(R1 + R2) = 4.91 x 15 /1000 = 0.07Ω
i) Zs = Ze + (R1 + R2) =
i) Zs – 0.5 + (0.12) = 0.62Ω less than 1.1Ω √
ii) Zs – 0.5 + (0.07) = 0.57Ω less than 0.88 √

Checking for thermal constrains – this confirming that

the size of cpc can withstand the fault current within
disconnection time

Page 26 of 54
ADEABATIC equation

Ifault = Uo / Zs
i) 230 / 0.62
371A

ii) 230/0.57
= 404A

S = √(3712 x 0.4) / 115 = 2mm2

S = √(4042 x 0.4) / 115 = 2.5 mm2

Page 27 of 54
14/11/23

Page 28 of 54
 Conductor Sze CableRatingChallen
Selection Procedure ge Updated-17.ppt
L3-17.docx

5. IP codes
• IP 4 X IP54
IP is for protection against ingress of solids and liquids
IP X X
First digit ranges from 0 to 6 where 0 is no protection and 6 is highest protection –
dust tight
Second digit ranges from 0 – no protection to 8 – protection against complete submession

Page 29 of 54
6. Zones in bathrooms and wet rooms – (Part 7)

4-LCL DEI 2018

Special Locations.pptx
• Zone 0
• Zone 1
• Zone 2
• Outside zone

Page 30 of 54
 Overload current
and Fault current- 17.docx
7. Protective devices and types of electrical faults
• BS88
• BS1363
• BS60898- types & Uses
• BS3036
• RCD
• Overload
• Earth Fault
• Overcurrent
• Ia, I2
• Selectivity

Knowledge for Q3 of Design project

7. Protective devices and types of electrical faults - Protective device –
means both fuses on CB, RCD & RCBOs

They operate yet fuses blow and CB, RCDs & RCBOS trip

Overload current
and Fault current- 17.docx

• BS88 – series
• BS1363
• BS3036 – rewireable fuses/ semi enclosed fuses

• RCD
• BS60898 (CB)- & BS EN 61009 (RCBOs)-1 types B, C and D & Uses

Page 31 of 54
Uses

Page 32 of 54
Prospective Fault Current in KA
It is potentially/anticipated fault current which would flow in the event of a fault
between LIVE conductors or Line to Earth Fault

Is determined by
the distance
between
substation And
the Main DB
(Length of cable)

&
The current used
by installation

Ifault = U0/Zs
-4
0.78/1000 = 7.8 x10 = 0.

I = 230/=0.078 =
2948

Ipf is important in that if not verified it may be too high the cause EXPLOSION
and damage to device instead of normal operation

Icn - the rated short-circuit capacity (marked on the device). 6000

Isc - the service short-circuit capacity.

The difference between the two is the condition of the circuit-breaker after manufacturer's
testing.
Icn is the maximum fault current the breaker can interrupt safely, although the breaker
may no longer be usable.

Page 33 of 54
 Ics is the maximum fault current the breaker can interrupt safely without loss of
performance.
Design Q 5

Single phase & Three phase the [Ipf] is in 2 categories, which is Prospective
Fault Current (IPFC) & Prospective Short circuit current (IPSCC)

Prospective Fault Current (IPFC) is between Live conductors to Earth

Prospective Short circuit current (IPSCC) is a fault between LIVE conductors –

L1- L2, L2- L3, L1 – L3, L1 – N, L2 – N, L3 -N

In single phase - Prospective Fault Current (IPFC) is higher Prospective Short

circuit current (IPSCC) – due good earthing causing parallel

In Three Phase - Prospective Fault Current (IPFC) is less than Prospective

Short circuit current (IPSCC) – because IPSCC is x 2 then the higher is recorded.

• Overload
• Earth Fault
• Overcurrent
• Ia, I2
• Selectivity

Page 34 of 54
 Electrical faults
Overload Short circuit- [L-N Earth fault [L- Earth leakage
L-L] E][N-E]
Fuses to BS3036, Fuses to BS3036, Fuses to BS3036, RCD &
BS88 series, BS88 series, BS88 series, BS EN 61009
BS1361 series BS1361 series BS1361 series
CB – BS EN CB – BS EN CB – BS EN
60898, 61009 60898, 61009 60898, 61009
RCD
Insulation
deterioration
Ingress of
moisture/conducting
particles

Unit 203 Outcomes Outcome 5 S1 Protective devices

-17.ppt Protective devices.pptx -Discrimination-16.ppt

Disconnection is directly linked to Zs values

How? Zs determines the amount of fault current by Ifault = U0/ Zs

Page 35 of 54
I= 230/5.8 =39.6A
I = 230 / 0.58 = 396A
I = 230/0.06=3800A
The low the Zs value = the higher the fault current = the higher the fault current
the quicker the disconnection time.
Ia is current causing disconnection in the specified time
BS7671 App 3 graphs

X5 X 10 X 20

Page 36 of 54
Zs for Type B = 230 x 0.95 / 5x10 = 218.5/50 = 4.37Ω
Zs for CB 32 A -Type D -

Selectivity (previously known as discrimination)

Ensuring that the device closest to a fault is the one that operates whether upstream
or downstream.

Page 37 of 54
8. Earthing systems, - Knowledge for Q1 of Design project
• TNC-S-PME
• TNS
• TT

20- earthing
systems.pptx
• Maximum Ze values

4.1 Protective earthing The purpose of protective earthing is

to ensure that, in the event of a fault, such as between a line
conductor and an exposed-conductive-part or circuit
protective conductor, sufficient current flows to operate the
protective device, in the required time i.e. fuse to blow,
circuit-breaker to operate or RCD to operate, in the required
time-

time means 0.4s for TN systems, 5 sec for distribution

circuits, 0.2s for TT system, 1 s for distribution circuit

Zs = Ze +(R1 +R2)
Ze =0.35Ω

Page 38 of 54
 Ze =0.8Ω

- Knowledge for Q9 of Design project

Protective conductor size or cpc size depends on the csa of the LINE conductor –

2
20
Page 39 of 54
Page 40 of 54
9. Earthing and bonding- (Part 5)
• Earthing conductor & cpc sizes
• Bonding conductor sizes
• Table 54.7, Table 54.8 adiabatic eqn
• What is the purpose of earthing?
• What is the purpose of bonding?

MET

Page 41 of 54
10. Maximum earth loop impedance values- (Part 4)
• Zs values determine disconnection times

Onsite Guide
Appendix B.pdf

• Disconnection times 0.4s for TN systems , 5s for Distributions circuits, 0.2s

for TT system & 1s for circuits above 32A in TT system.

In BS 7671 the Zs values are at 200C when conductors are not carrying
current

In OSG the Zs values are at conductor operating temperature

BS7671 Zs value x 0.8 = OSG Zs value

Type C 20A RCBO allows Zs = 1.09Ω = 230 x 0.95/(20x10) = 1.09Ω

Therefore, OSG guide ZS is 1.09 x 0.8 = 0.87Ω

Zs for 10A Type B = 230 x 0.95 / 5x10 = 218.5/50 = 4.37Ω - BS7671

From OSG = 4.37 x 0.8 = 3.5Ω

Page 42 of 54
Zs for CB 32 A -Type D – (230 x 0.95) /(32 x 20) = 218.5/640 =0.34Ω
From OSG = 0.34 x 0.8 = 0.27Ω

The OSG Zs value is the one you compare with any measured values during
testing

A higher than recommended Zs value means high disconnections times –

means risk shock

Page 43 of 54
Any circuit circuit with a high Zs value can be
i) Protected by an RCD or RCBO

ii) Use a bigger csa cpc size to lower (R1+R2) which adds to Ze to
give Zs – (this can only be done at design and construction
stage)

Page 44 of 54
 continued
Standards circuits
• General lighting – 6 A maximum lighting points = P= V x I = 100W/230V
= 0.4A per lighting point so number of lights = 6/0.4 = 13 lighting points
• Power – sockets outlets BS1363
11. Radial circuits
• Lighting, breaker size, switching arrangements, luminaire categories
• Cooker, cooker control unit, current demand, diversity, conductor, size
• Alarm, emergency lighting, band 11 circuits
• Immersion, double pole isolator, current demand
• Shower, isolator, current demand

Onsite Guide Onsite Guide

Appendix H.pdf Appendix A.pdf

Types of circuits
• Lighting – one way, two -way, two way & intermediate
• Power- all other circuits – sockets, cooker etc

Most circuits are radial circuits – lighting, shower, motor, cooker, alarm

Page 45 of 54
ONLY one circuit is wired as ring – socket outlets - even so they are also wired as
radial
•
TN =0.4s

TT = 0.2s

Distribution circuit TN system = 5s

TT system = 1s

Page 46 of 54
12. Sockets – (Appendix 15) Knowledge for Q7 of Design project
OSG - App H
• Ring – A1-100m2 using 2.5 mm2

• Radial- A2- 75m2 using 4mm2 cables

• A3 -50m2 using 4mm2 cables

Page 47 of 54
Page 48 of 54
11. Radial circuits
• Lighting, breaker size, switching arrangements, luminaire categories
• Cooker, cooker control unit, current demand, diversity, conductor, size
• Alarm, emergency lighting, band 11 circuits
• Immersion, double pole isolator, current demand
• Shower, isolator, current demand

Onsite Guide Onsite Guide

Appendix H.pdf Appendix A.pdf

14. Isolation and switching- (Reg 537) Q 10 – design Project

• Isolation
• Isolation for mechanical maintenance
• Functional switching
• Emergency switching

ISOLATION & 20 - Unit 303 ISOLATORS

SWITCHING.ppt Electrical circuits.docx PICs.docx

462.2 Every circuit shall be provided with isolation means for all live conductors, except as
detailed in Regulation 461.2.

Single phase L & N and for 3 phase L1, L2 , L3 & N TT

Page 49 of 54
 Exception is:
TN-C systems and TN-C-S systems, the PEN conductor shall not be isolated or switched. In TN-C-S
and TN-S systems, isolation or switching of the neutral conductor is not required if protective
equipotential bonding is installed and either:

TN systems

Devices for isolation shall be designed and/or installed so as to prevent unintentional or inadvertent
closure.

Examples of precautions are as follows: -

Located within a lockable space or lockable enclosure –

Padlocking –

Located adjacent to the associated equipment.

Isolators must be lockable or in lockable enclosures and if NOT then they must be
positioned near the equipment
Lockable isolator no lockable

If an isolator is for appliances like

water heater, cooker, shower and the
like it MUST be a double pole
isolator – it breaks / cuts both LIVE
conductors – L & N
Isolate – cut off supply

Page 50 of 54
 63 FUNCTIONAL SWITCHING (CONTROL)
463.1

General 463.1.1

Functional switching shall be provided for

each part of a circuit which may require
to be controlled independently of other
parts of the installation.

Turn ON/OFF
START/STOP
1. Most isolators are permissible for functional switching
2. Single pole switches or TP for 3 phase or TPN for TT systems

SWITCHING OFF FOR MECHANICAL MAINTENANCE 464.1

Means for switching off shall be provided where mechanical maintenance may involve a risk of
physical injury. – routine cleaning

EMERGENCY SWITCHING OFF 465.1

Means shall be provided for emergency switching off of any part of an installation where it may be
necessary to control the supply to remove an unexpected danger.

It is rapid disconnection of supply from danger.

Page 51 of 54
. Inspection &Testing
• Inspect-visual/see, touch/feel, smell-C1, C2, C3
• Dead test- continuity, insulation resistance, polarity
• Live test – Ze, Ipf, Zs, RCD
• Record results
• Completion of forms
Initial Verification, Minor Works Certificate, Electrical Condition Report

TESTING TEST & PRAC New Condition

Pics-16.pptx Criterio-17.docx Report- (7).ppt

Calculate the size of conductors for a circuit comprising of 30 luminaires of 65W discharge lighting
circuit, if 700 thermoplastic single core cables in metal conduit is used. Ambient temperature is 350

Total watts = 65 x 30 =1950W

Ib = Pt/V x 1.8 = 65 x 30 x 1.8/230 = 15.2 A

Ib = Pt/V x 1.8 = 25 x ---------

In = 16A

Factors are

Ca - temperature

Cg - grouping

Ci – thermal insulation

Cf – rewirable fuse

Reference/ installation method is B

Factor in this case is Ca – 350 = 0.94

It = In/ (Factors) = 16/0.94 = 17A

Page 52 of 54
 I
Giving z of 17.5 so conductor size is 1.5mm2

If the cable run is 22m calculate the volt drop.

MV/A/m x L x Ib / 1000 - must be less than 3% - (6.9V) for lighting

29 x 22 x 15.2/1000 = 9.7V DANGER !!! NO No no

Volt drop for 1. 5mm2 not compliant so use 2.5mm2

Check volt drop

18 x 22 x 15.2 / 1000 = 6V compliant happy

If Ze is 0.25Ω confirm adequate shock protection

Zs = Ze + (R1+R2)
(R1+R2) = 22 x 14.82/1000 = 0.4Ω from Table I1

Zs = Ze + (R1+R2) x 1.2= 0.64Ω

Maximum Zs for 16A TYPE C is 1.09Ω

So measured Zs ≤ max Zs so circuit is compliant

So disconnection time of less than 0.4s can be met

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So measured 0.64Ω ≤ max 1.09Ω so circuit is compliant

I = V/Zs 230 / 0.64 = 359A

t = 1152 x 2.52 /3592 =0.64 sec

Confirm that the cpc can withstand the thermal constraints.

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