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1 1

Session 3:

LV Electrical Installations of Buildings

Earthing Systems


2 2

Contents

General

Earthing arrangements

Types of earthing conductors

Protective conductors (PE conductors)

Protective bonding conductors

Earth fault loop impedance

Miscellaneous


3 3

Earthing: Functions

Within the scope of MS IEC 60364

Provides electrical potential or voltage reference point

o The Earth is taken as the “0” volt reference point in electrical

engineering application. PE conductor is always connected to

Earth by earth electrodes and thus assumed “0” volt

o Any phase and line voltage is referenced to this reference

Provide protection for safety against electric shock & earth

fault

o PE provides the return path to operate protective devices

o Ensure safe voltage of exposed conductive parts during earth

fault: < 50/120 Vac/dc


4 4

Protective Earthing (PE) Conductor: Functions

Low resistance paths for diverting (shunting) electric shock

current away from the victim

o Universally, human being body resistance from hand–to–leg is

taken as 1,000Ω

o PE conductor’s resistance in mΩ – 100 meters of 2.5 mm2

copper PE cable has resistance of about 750 mΩ

Low resistance paths for diverting electrical surges, noise, etc

Secondary functions

o EMI shielding by equipotentialization of conductive enclosure of

equipment (MS IEC 61000)

o Functional earth (Not within the scope of MS IEC 60364)


5 5

Protective and Bonding Conductors: Colour Code

Malaysia & UK prior to 31 March 2004: Green

o Malaysia: Green still used to – date

o UK comply with IEC 60446

IEC 60446: EU & UK after 2004: Green/yellow

o On any 15 mm length of the conductor insulation jacket, one of

these two colours should cover between 30% and 70% of the

area and the other the remaining area


6 6

Preservation of Electrical Continuity of Conductor

A PE conductor shall be suitable protected against

mechanical, chemical and electro–dynamic deterioration

A PE conductor having CSA up to and including 6 mm2

o Shall be protected throughout by a covering at least

equivalent to that provided by the insulation of a single core

non–sheathed cable of appropriate size having a voltage

rating of at least 450/750V

o Where the sheath of the cable is removed adjacent to joints

and terminations, the PE conductor shall be protected by

insulating sleeving comply with IEC 60684 series


7 7

Preservation of Electrical Continuity of Conductor

A switching device shall not be inserted in a PE conductor

o If a switching device is inserted in a PE conductor, the PE conductor

circuit shall not be interrupted before the live connectors and shall be

re–connected not later than when the live conductors are

reconnected

Joints intended to be disconnected for test and/or inspection

purposes are permitted in a PE conductor circuit

Every joint in metallic conduit shall be mechanically and

electrically satisfactory and continuous

When electrical monitoring of earthing is used, no dedicated

devices shall be connected in series with the PE conductor


8 8

PE and PB Systems & Others Connections

The PE and PB systems shall be connected via MPBT and MET

only

The MET of the installation shall be connected to the earthed

point of the incoming supply system

Connection of other non–electrical installation or safety

earthing systems, such as telecommunication, computer

network, etc., to MET requires consent of the owner

Connection of lightning protection system earthing to the MET

or earth electrode shall be made in accordance with MS IEC

62305

o This connection shall be “outside” the building


9 9

Earthing & Lightning Protection Standards

External earthing and lightning protection

o Not within the scope of MS IEC 60364 series

o Outdoor LV installation is within the scope of MS IEC 60364

External earthing

o BS 7430: Code of practice for earthing

Lightning protection

o MS IEC 62305: Protection against lightning

o Connecting the lightning protection system to MET shall be

made in according to MS IEC 62305

Shall be done “outside” the building


10 10

Earthing Arrangements


11 11

Definition: Earth of LV Electrical Installation

Generally means an electrical connection from the neutral of

the incoming supply transformer or generator, and the main

earth terminal (MET) of the electrical installation to the general

mass of Earth using a suitable conductor

o The conductor is usually copper or steel, Al is not suitable

o This definition is central to MS IEC 60364

o Some parts of an electrical installation may not be connected

to Earth but practically, the whole electrical installation is

considered earthed

Unearthed sub–modules of an electrical installation are

IT system


12 12

Main Functions of an Earthing System To provide voltage reference for an electrical installation

o This voltage reference is usually taken as “0” volt

To ensure step and touch voltages during fault below

hazardous value (< 50Vac or <120Vdc)

To provide low impedance for reliable operation of protective

devices

To provide an equipotential on which electrical and

electronic equipment can function safely and reliably

To discharge electrical noise and static charges

To protect the electrical installations against lightning

o Not the scope of MS IEC 60364


13 13

MS IEC 60364: Types of Earthing Systems

Three (3) types of earthing systems for LV electrical installations

o TT

o TN (Thee variants)

TN–S

TN–C

TN–C–S

o IT (Two variants)

“Unearthed or floating”: Very high impedance

High impedance


14 14


Malaysia practices the following LV earthing systems

o TT

o TN

TN–S

o IT

“Unearthed or floating” IT

Only within the LV electrical installations

Operating theatre to MS IEC 60364–7–710

MS IEC 60364: Earthing Systems (Symbols)

1st Letter (Source of Supply)

T The source of LV electrical installation is connected directly to

Earth at a certain point, normally at the supplying transformer (T = Latin : Terra)

I The source of LV electrical installation is not connected to

Earth or connected to Earth via a large impedance, normally

at the supplying transformer (I = Isolated)

2nd Letter (Load: Installation or Equipment)

T

The exposed conductive parts (Electrical equipment, motors,

cable trays, metal enclosure of switchboard, etc) of the load

are connected directly to Earth at the MET disregarding

whether the power system is earthed or not

N The exposed conductive parts are connected directly to Earth at the source

15


16 16


Additional Letters

C

The protective conductor (PE) and neutral conductor (N)

are one common insulated conductor (PEN)

(C = Common)

S

The protective conductor (PE) and neutral conductor (N)

are two different and separated insulated conductors (S = Separate)

Note: S connection must be downstream of C connection

Earthing System: TT

Installation

Earth Supply

Earth

L1 (R)

Installation

L2 (Y)

L3 (B)

N

Incoming Transformer

Installation: T Supply: T

Earth Return Path Supply: T Installation: T 17


18 18

TT Earthing System: Properties

The supply transformer neutral is earthed

The conductive parts of installation also earthed

The supply transformer earth and the installation earth are

connected via the general mass Earth

Earth fault current is limited by Earth connection impedance

Protection is provided by circuit breakers (CB) and additional

protection by residual current device (RCD)

The Earth resistivity and earth electrodes are critical in ensuring

the reliability operation of protective devices

Earthing System: TN–S

Supply

Earth

L1 (R)

Installation

L2 (Y)

L3 (B)

N


Installation: N – S Supply: T

PE

Supply: T

N – S: N

N – S: S

Earthing System: TN–C

N – C: N

Supply: T


N – C: C

L1 (R)

L2 (Y)

L3 (B)

PEN

Installation

Supply: T Installation: N – C

Earthing System: TN–C–S


N – C – S: N

Supply: T

Supply

Earth

L1 (R)

L2 (Y)

L3 (B)

N

PE

Installation

N – C – S : S N – C – S: C

Supply: T Installation: N – C – S


22 22

TN Earthing Systems: Properties

The supply transformer neutral is earthed

TN–S

o PE and neutral are separate insulated conductors

o PE and neutral conductors are connected at the supply

transformer

o The conductive parts of installation are connected to PE

conductor

o Only TN–S system permitted in Malaysia

TN–C

o PEN insulated conductor has dual functions as PE conductor

and neutral conductor


23 23

TN Earthing Systems: Principle & Properties

TN–C–S

o Combination of TN–S and TN–C

o PE and neutral conductors are separated downstream of the

installation in the TN–C system

o TN–S cannot be placed upstream of the TN–C

An earth fault becomes a short–circuit and the faulty circuit is

disconnected by a short–circuit protective devices

o Fault protective devices: Fuses, MCB, MCCB

High short–circuit current may cause mechanical and/or

thermal damage to the cable insulation, installation and

equipment

Earthing System: IT (Unearthed)

Earth

L1 (R)

Installation

L2 (Y)

L3 (B)


Installation: T Supply: I

Installation

Earth

Supply: I Installation: T

Earthing System: IT (High Impedance)

Earth

L1 (R)

Installation

L2 (Y)

L3 (B)


Installation: T Supply: I

Installation

Earth

Supply: I Installation: T

High

Impedance


26 26

IT Earthing System: Properties

The supply transformer neutral is un–earthed or earthed via a

high impedance > 1.5kΩ

o Practically, it is intrinsically earthed by stray capacitances

The conductive parts of installation are earthed

1st fault: phase voltage raised to line–line voltage

1st fault: An earth fault will develop a low current due a result

of the stray capacitances

o The contact voltage developed in the conductive parts is no

more than a few volts which is not hazardous


27 27

IT Earthing Systems: Properties

2nd fault: If a second earth fault occurs on another phase

before the 1st earth fault is cleared, the conductive parts of

the faulty load in the faulty circuit are brought to the

potential developed by the fault current in the PE

connecting them

o The IT system becomes a TN system

o The short – circuit protective device should provide the

necessary protection

2/4 pole circuit breakers are required to isolated live and

“neutral” conductors because all outgoing conductors are

“live” – Neutral labelled as L2/L4 for 1P/3P system

Earthing System: TT (Single Phase)

L1 (R)

Installation

L2 (Y)

L3 (B)

N


Earth Return Path Supply: T Installation: T

Earthing System: TN–S (Single Phase)

L1 (R)

Installation

L2 (Y)

L3 (B)

N


Supply: T Installation: N

PE

Comparison of Earthing Systems (Installations)

TT IT TN – S TN – C TN–C–S

Malaysia Yes No Yes No No

Earth Loop Impedance Variable Highest Low Low Low

Overcurrent Protection MCB/MCCB/Fuse

Types of OC Protection 1 Pole 2 Pole 1 Pole 1 Pole 1 Pole

RCD protection Yes No Yes No No

Earth Electrode at Site Yes Yes No No No

Risk of Broken Earth Highest High Low No No

Earth Fault Detection RCD IMD MCB MCB MCB

1st Earth Fault Trip No Trip Trip Trip Trip

2nd Earth Fault N/A Trip N/A N/A N/A

EMI Low Least Low High Low

RCD – Residual Current Device

IMD – Insulation Monitor Device – Expensive


33 33

General Properties of Earthing Arrangement The earthing system of an installation may be subdivided. Each

sub–part shall comply with the requirements discussed above

The value of impedance from the MET to the earthed point of

the supply for TN systems, or to Earth for TT or IT systems, comply

with the protective and functional requirements of the

installation and to be continuously effective

Earth fault currents and protective conductor currents which

may occur should be carried without danger, particularly from

thermal, thermo mechanical and electromechanical stresses

Adequately robust or have additional mechanical protection

appropriate to the external influences present


34 34

Earth Electrodes: Basic Types

Types of earth electrode recognized for the purposes of

complying with MS IEC 60364

o Earth rods or pipes – Most common

o tapes or wires

o Earth plates

o Underground structural metalwork embedded in foundations

o Welded metal reinforcement of concrete (except pre –

stressed concrete) embedded in the Earth

o Lead sheaths and other metal coverings of cables

o Other suitable underground metalwork


35 35

Earth Electrodes: General Requirements

The depth of an earth electrode shall be such that seasonal soil

drying will not increase its resistance above the required value

The design and construction of an earth electrode shall

o Reach the permanent water table

o Withstand damage

o Take into account increase in resistance due to corrosion

o Variation in weather conditions

o Precaution shall be taken against its removal, damage, etc.,

which would affect its long term reliability and suitability as

earth electrode


36 36


Protect against the risk of damage through electrolysis or

cathodic corrosion

When a number of installations have separate earth

electrodes, any protective conductor common to any of

these installation shall either

o Be capable of carrying the maximum fault current likely to flow

through them, or

o Be earthed within one installation only and insulated from the

earth arrangement of any other installation

Protect against the risk of works (upgrading, modifications,

etc) that will render the earth electrodes ineffective


37 37


Lead sheaths (Not SWA) or other metal coverings of cables

used as earth electrode shall be subject to all of the following

conditions

o Adequate precautions to prevent excessive deterioration by

corrosion

o The sheath or covering should be in effective contact with Earth

o The written consent of the owner of the cable shall be obtained

o Arrangement shall exist for the owner of the LV electrical

installation to be warned of any proposed change to the cable

which might affect its continual suitability as an earth electrode


38 38


Earth electrodes can be used jointly or separately for

protective earth and functional earth

o Practically, it is recommended to use separate protective and

functional earths

For mixed materials, such as Cu and Al, are used, ensure the

earthing system is protected against galvanic corrosion

o Al: Not permitted for buried applications

Electrical earth electrode system shall be connected to

lightning protection system in accordance with EN 62305:

Protection against lightning


39 39

Earth Electrodes: Not Permitted

Critical services – Fire services hydrant, hose reel pipework,

medical gas pipeline systems

Pipes or storage tanks for gases or flammable or corrosive

liquids

Pipes of a water utility supply / water reticulation pipework

Any structure not in the installation premises and/or not owned

by the owner of the installation

Structures for which the owner declined permission

Non–permanent structures that can be or may be removed

Structures subject to vibrations

CSA of Earth Conductors: Buried

The cross–sectional–area (CSA) of earth conductors when

buried in the ground shall not less than stated in Table A

o For a tape or strip conductor, the thickness shall be such

as to withstand mechanical damage and corrosion

Table A: Minimum CSA of A Buried Earthing/PE Conductor

Protection Against

Corrosion

Protected against

mechanical damage

(mm2)

Not protected against

mechanical damage

(mm2)

By a sheath Copper 2.5 16.0

Steel 10.0 16.0 (Copper Coated Steel)

Not protected Copper 25.0

Steel 50.0

40


41 41

Earth Electrodes: Connection with MET

The connection of an earth conductor to an earth electrode or

other means of earthing shall be soundly made and be

electrically and mechanical satisfactory

The connection shall be labelled properly

Means shall be provide for periodic inspection and verifications


42 42

Main Earthing Terminals or Bars: MET

In every LV electrical installation, a MET shall be provided to

connect the following to the earth conductor

o The circuit protective conductors

o The protective bonding conductor

o Functional earthing conductors, if required

Functional earthing system is not within the scope of MS

IEC 60364

o Lightning protective system bonding conductor

Comply with MS IEC 62305

Connection shall be done external to the building


43 43

Earth Electrodes: Measuring Earth Resistance

To facilitate measurement of the resistance of the earthing

arrangement, means shall be provided in an accessible

position for disconnecting the earthing conductor

o Such means may conveniently be combined with the MET

o Any joint shall be capable of disconnection only by means

of a tools


44 44

Types of Earthing

Conductors


45 45

Earthing Systems of an LV Electrical Installations

MS IEC 60364: Two types of LV electrical installation earthing

conductors for the protection for safety against electric shock

o Protective earthing (PE)

o Equipotential bonding (EB)

Other types of “earthing conductors” for non–MS IEC 60364

electrical installations applications

o Functional earth

o Isolated earth

o Clean and/or dirty earth

o Common mode rejection earth, etc.


46 46

Conductive Parts

Conductive parts: Any material with insulation resistance < 50

kΩ tested with 500Vdc at 25oC

o For LV electrical installation purposes, misnomer to refer to

metallic parts only as conductive parts

“Safe” insulation resistance: Any material for electrical

insulation shall have insulation resistance > 1000 kΩ ( <0.25 mA)

tested with 500Vdc at 25oC

Insulator: An insulator shall have insulation resistance > 100 MΩ

tested with 500Vdc at 25oC


47 47

Exposed & Extraneous Conductive Parts

Exposed conductive parts: conductive parts of an electrical

equipment

o Examples: metallic bodies of electric kettles, microwave

ovens, table drills, etc

Extraneous conductive parts: Conductive parts of a non–

electrical equipment

o Examples: metallic cable management system, mounting

brackets, furniture, mounting platforms, steel tanks, etc

Exposed and Extraneous Conductive Parts

Extraneous-conductive parts

Exposed-conductive-parts Simultaneously accessible parts

< 2500 mm

Dry Floor 48


49 49

Protective Conductors

(PE Conductors)


50 50

PE Conductors: Cross Sectional Area (CSA)

The CSA of every PE conductor shall be

o Calculated

Necessary if the choice of CSA of line conductors has

been determined by considerations of short–circuit

current and if the earth fault current is expected to be

less than the short–circuit current

o Selected

Where a PE conductor is common to two or more circuits, its

CSA shall be

o Calculated for the most onerous of the fault current

o Selected correspond to CSA of the largest line conductor

CSA of PE Conductor: Table B

CSA of PE conductor shall be per Table B if the PE conductor is

not

o An integral part of a cable, or

o Formed by conduit, ducting or trunking, or

o Contained in an enclosure formed by a wiring system

Table B: Minimum CSA of PE Conductor

Protection Against

Corrosion

Protected against

mechanical damage

(mm2)


mechanical damage

(mm2)

By a sheath Copper 2.5 4

Others Equivalent Equivalent

Equivalent = Copper equivalent


52 52

PE Conductors: Min. CSA of 10 mm2 Copper

A PE conductor for the following types of PE conductor of CSA

10 mm2 or less shall be of copper

o A single core cable

o A conductor in a cable

o An insulated or bare conductor in a common enclosure with

insulated live conductors

o A fixed bare or insulated conductor

CSA of PE Conductors: Buried

The CSA of buried conductors when buried in the ground shall

not less than stated in Table A

o For a tape or strip conductor, the thickness shall be such as to

withstand mechanical damage and corrosion

All requirements for buried earth conductors apply

Table A: Minimum CSA of A Buried Earth/PE Conductor

Protection Against

Corrosion

Protected against

mechanical damage

(mm2)


mechanical damage

(mm2)

By a sheath

Copper 2.5 16.0

Steel 10.0 16.0 (Copper Coated

Steel)

Not protected Copper 25.0

Steel 50.0

PE Conductors: CSA By Calculation

CSA, S, shall not be less than the value determined by the

following

Where

S = CSA (mm2) rounded to next size

I = rms value of fault current (A)

t = Disconnection time of the disconnecting device (s)

k = Cable factor (example: Table k)

k

tI S

2

54

Disconnection Time: Final Circuit <32A

U0 is the nominal a.c. rms or d.c. line voltage to earth

Note 1: Disconnection is not required when Uo < 50Vac or 120Vdc

but may be required for other reasons, such as protection

against thermal effects

Note 2: TT system, if the disconnection is achieved by an overcurrent

protective device and protective equipotential bonding are

connected to all extraneous conductive parts, the maximum

disconnection time applicable to TN system may be used

Maximum Disconnection Time (s)For Final Circuits <32A

System

50V<U0 50V<U0<120V 120V<U0<230V 230V< U0<400V U0 > 400V

a.c./d.

c. a.c d.c a.c d.c a.c d.c a.c d.c

TN Note 1 0.8 Note 1 0.4 0.5 0.2 0.4 0.1 0.1

TT(Note2) Note 1 0.3 Note 1 0.2 0.4 0.07 0.2 0.04 0.1

Final Circuits >32A, Distribution Circuits & Circuits

not Covered by MS IEC 60364

For final circuits exceeding 32A, distribution circuits, and for

circuits not covered by MS IEC 60364, the disconnection time

permitted are

Maximum Disconnection Time (s) for Final Circuits > 32A,

Distribution Circuits, and for Circuits Not Covered in MS IEC 60364

System Maximum Disconnection time

TN < 5 seconds

TT < 1 second

56

PE Conductors: Example of Values of k

Value of k for PE Conductor Incorporated in a Cable or Bunched with

Cables, Where the Assumed Initial Temperature is 70oC or Greater

Material of conductor

Insulation Material

70oC

Thermoplastic

90oC

Thermoplastic

90oC

Thermosetting

Copper

Aluminum

115/103*

76/68*

100/86*

66/57*

143

94

Assumed initial

temperature

Final temperature

70oC

160oC/140oC*

90oC

160oC/140oC

90oC

250oC

* = Above 300 mm2

57

PE Conductors: Example of Values of k

Value of k for PE Conductor as a Sheath or Armour of a Cable

Material of conductor

Insulation Material

70oC

Thermoplasti

c

90oC

Thermoplastic

90oC

Thermosettin

g

Alunimium

Steel

Lead

93

51

26

85

46

23

85

46

23

Assumed initial

temperature

Final temperature

60oC 200oC

80oC 200oC

80oC 200oC

Refer to cable manufacturer for insulation material not listed in this

table

PE Conductors: CSA By Selection

Table B – Minimum CSA of PE Conductor in Relation to the CSA

of Associated Line Conductor (By Selection

CSA of line

conductor

S (mm2)

If the PE conductor is of

the same material as the

line conductor

If the PE conductor is not

of the same material as

the line conductor

S < 16

16 < S < 35

S > 35

S

16

S/2

K1/K2 x S

K1/K2 x 16

K1/K2 x S/2

K1 = The value of k for the line conductor, selected from Table 43.1

according to the materials of both conductor and insulation.

K2 = the value of k for the PE conductor, selected from Table 54.2 to 54.6 as

applicable.

Assumption: Harmonics are under control


60 60

PE Conductors: Types

Single sheathed cable or single sheathed PE conductor in a

multi–core cable

An insulated or bare conductor in a common enclosure with

insulated live conductors

A fixed bare or insulated conductor

Metal covering – Sheath, screen or armour of cable

A metal conduit, metallic cable management system or other

enclosure or electrically continuous support system for

conductors, frame of switchboard, etc. with linking copper bar

or jumper PE earth cable

o Long term continuity must be ensured


61 61

PE Conductors: Not Permitted

Critical services, such as fire hydrant, hose reel, etc

Gas pipe, oil pipe, medical gas pipeline, etc.

Flexible or pliable conduits

Support wire or other flexible metallic parts

Constructional parts subject to mechanical stress in normal

operation – tie or hanging rod

Conductive parts not permitted by owners

Non–electrical, especially ELV services

Exposed conductive parts

Conductors subject to excessive vibrations


62 62

PE Conductors: Metal Enclosures, Switchboards

A metal enclosure, switchboard or control board used as a PE

conductor, shall satisfy all following requirements

o Long term electrical continuity shall be assured by

Construction, or

Suitable connection

Protected against mechanical, chemical or

electrochemical deterioration

o Its CSA shall be at least equal to the calculated or selected

value or tested to MS IEC 60439–1

o Permit connection of other PE conductors at every pre–

determined tap–off point


63 63

PE Conductors: Extraneous Conductive Parts

An extraneous conductive part may be used as a PE

conductor if it complies all following requirements

o Electrical continuity shall be assured by construction or by

suitable connection, and protected against mechanical,

chemical or electrochemical deterioration

o The CSA are shall be at least equal to that result from

calculation or selection of equivalent PE conductor

o Unless compensatory measures are provided, precautions

shall be taken against its removal

o Suitably adapted for use as PE conductor


64 64

PE Conductors: Shields, Conduits, Trunking, etc

Where the PE conductor is formed by conduit, trunking,

ducting or the metal sheath or armour of a cable, the earthing

terminal of each accessory shall be connected by a separate

PE conductor to an earth terminal incorporated in the

associated box or other enclosure

An exposed conductive part of an equipment shall not be

used to form a PE conductor for other equipment

The circuit PE conductor of every ring final circuit shall also be

run in the form of a ring having both ends connected to the

earthing terminal at the origin of the circuit (BS 7671)


65 65

PE Conductor: Socket Outlet

Where two or more similar radial circuits in adjacent areas

and are fed from the same distribution board, have identical

means of short–circuit and over–current protection and circuit

protection of the same CSAs, then a second PE conductor

may be provided at the final socket outlet on one circuit by

connection to the PE conductor of the adjacent circuit

PE System: “Star” Configuration

MSB

SSB DB

Final Circuits

DB

Final Circuits

DB – Guard House

Final Circuits

SSB

Earth

MET

MEBT “0” Volt

LET

LET


67 67

Protective Bonding

Conductors

(PB Conductors)


68 68

Main Protective Bonding Conductor: CSA

Where protective multiple earthing (PME) conditions do not

apply, a main protective bonding (MPB) conductor shall CSA

o Not less than half the CSA required for the earthing conductor

of the installation, and

o Not less than 6 mm2

o Need not exceed 25 mm2 if the bonding conductor is of

copper or equivalent conductance in other materials

Where PME conditions applies, the MPB conductor shall be

selected in accordance to Table C

o Exceptions – Highway power supplies & street furniture

Main Protective Bonding Conductor: CSA

Table C: Minimum CSA of the MPB Conductor

in Relation to

the Neutral Conductor of the Supply

Copper CSA of the supply

neutral conductor

Minimum copper

equivalent CSA of the

MPB conductor

35 mm2 or less

Over 35 mm2 up to 50 mm2



Over 150 mm2

10 mm2

16 mm2

25 mm2

35 mm2

50 mm2

69

MPB Conductors: CSA Summary

MPB Conductor Sizes (Copper)

Phase conductor (TN–S) MPB Conductor Size (mm)

PME Supply Non–PME Supply

4 6 10

6 6 10

10 6 10

16 10 10

25 16 10

35 25 10

50 25 16

70 25 25

95 25 35

120 25 35

150 25 35

> 150 mm2 25 50


71 71

MPB Conductor: Requirements

When an installation has more than one source of supply to

which PME conditions apply, a MPB conductor shall be

selected according to the largest neutral conductor of the

supply

Extraneous exposed parts which are required to be bonded to

the MPBT at the main service point

o Pipe–works such as water, LPG, medical gas

o Ducting

o Structures, platforms, furniture, etc

o chemical racks and cabinets

Use multiple PB earthing if there is electrical discontinuity along

the run of the service such as rubber coupling


72 72

MPB Conductor: Connection Point

Gas, water or other services: As near as practicable to the

point of entry of that services into the premises

o Where there is an insulating section or insert at the point of

entry or where there is a meter, the connection shall be made

to the consumer’s hard metal pipe–work and before any

branch pipe–work

o Where practicable, the connection shall be made within 600

mm of the meter outlet union or at the point of entry to the

building if the meter is external to the building


73 73

Supplementary Bonding (SB) Conductor

Supplementary bonding (SB) conductors connect together

the extraneous exposed parts of an installation

o To ensure that no dangerous potential differences can occur

during an earth fault

o To ensure earth fault current flows along desired path so that

protective device will operate to remove potential differences


74 74

Supplementary Bonding (SB) Conductor

SB is not mandatory

SB is required in location of increased electric shock risk or to

provide increased safety

o Exposed conductive parts with an insulated break

o Medical group 2 locations

o Explosive atmospheres

o Confined conductive locations

o Wet area such as swimming pool

There is no specific requirements to carry out SB in domestic

kitchen, wash rooms and laboratory wash areas, etc.

SB Conductors: CSA

Connecting exposed

conductive part to

exposed conductive

part (Not less than CPC of

the smaller PE

conductor)

CPC (mm) of smaller PE

conductor

SB (mm2)

Not

Protected

Mechanically

Protected

1.0 4.0 2.5

1.5 4.0 2.5

2.5 4.0 2.5

4.0 4.0 4.0

6.0 6.0 6.0

10.0 10.0 10.0

75

SB Conductors : CSA

Connecting exposed

conductive part to

extraneous conductive

part

(Not less than half of the

PE conductor connected

to the exposed

conductive part)

CPC (mm) of

smaller PE

conductor

SB (mm2)

Not Protected Mechanically

Protected

1.0 4.0 2.5

1.5 4.0 2.5

2.5 4.0 2.5

4.0 4.0 4.0

6.0 6.0 4.0

10.0 6.0 6.0

76

SB Conductors

Connecting extraneous

conductive part to

extraneous conductive

part

(Not less than 2.5 mm2)

CPC (mm) of

smaller PE

conductor

SB (mm2)

Mechanically

Protected

Not

Protected

N/A 2.5 4.0

Fixed equipment

supplied via a short

length of flexible cord to

an adjacent connection

unit

CPC (mm) of

smaller PE

conductor

SB (mm2)

Not Protected Mechanically

Protected

N/A

SB is provided by PE

conductor within the flexible

cable

77


78 78

SB Conductor: Sheathed

If sheathed or provided with mechanical protection, SB shall

have a conductance not less than that of the smaller PE

conductor

o If sheathed or provided with mechanical protection, SB shall

have a CSA not 2.5 mm2

o If not sheathed or mechanical protection is not provided, SB

CSA shall be not less than 4 mm2


79 79

SB Conductor: Fixed Appliances

Where SB is to be applied to a fixed appliance which is

supplied via a short length of flexible cord from an adjacent

connection unit or other accessory, the circuit PE conductor

within the flexible cord shall be deemed to provide the SB

PB System: “Star” Configuration

Extraneous conductive part

Earth Electrode

System

MET

“0” Volt

Extraneous conductive part Extraneous conductive part

LEBT

MEBT

Extraneous

conductive parts –

Utility Services

Mains

LEBT LEBT

80

PB System : Motor Control Room

Source: EIG, Schneider Electric

< 50Vac

LEBT (Connect to MET (EB))

LEBT

81

PB System: Utilities Services

EB

Terminal

82

PB System: Swimming Pool


84 84

Earth Fault Loop

Impedance, Zs

Earth Fault Loop Impedance: Zs

IEF

ZE

ZL1

ZT

ΣZPE

ZSB ZL2

PEEL2SBL1TS Z Z Z Z Z ZZ

Use earth loop impedance meter to measure Zs

Uo

Zs: Maximum Values

The maximum tripping current of the protective devices, Ia,

and Zs, shall fulfil the following requirement

Where,

a

SM

0EFmin0aSM I

Z

UIor U I x Z

ZSM = Maximum fault loop impedance (Ω)

Ia = Current (A) causing tripping of the disconnecting device

within the maximum disconnection time

IEFmin = Minimum earth fault current (A)

U0 = Nominal a.c. rms or d.c. line voltage to Earth (V)

86

Disconnection Time: Final Circuit <32A

U0 is the nominal a.c. rms or d.c. line voltage to earth

Note 1: Disconnection is not required when Uo < 50Vac or 120Vdc

but may be required for other reasons, such as protection

against thermal effects

Note 2: TT system, if the disconnection is achieved by an overcurrent

protective device and protective equipotential bonding are

connected to all extraneous-conductive-parts, the maximum

disconnection time applicable to TN system may be used

Maximum Disconnection Time (s)For Final Circuits <32A

System

50V<U0 50V<U0<120V 120V<U0<230V 230V< U0<400V U0 > 400V

a.c./d.

c. a.c d.c a.c d.c a.c d.c a.c d.c

TN Note 1 0.8 Note 1 0.4 0.5 0.2 0.4 0.1 0.1

TT(Note2) Note 1 0.3 Note 1 0.2 0.4 0.07 0.2 0.04 0.1

Final Circuits >32A, Distribution Circuits & Circuits

not Covered by MS IEC 60364

For final circuits exceeding 32A, distribution circuits, and for

circuits not covered by MS IEC 60364, the disconnection time

permitted are

Maximum Disconnection Time (s) for Final Circuits > 32A,

Distribution Circuits, and for Circuits Not Covered in MS IEC 60364

System Maximum Disconnection time

TN < 5 seconds

TT < 1 second

88


89 89

Zs: Properties Shall be reliable, effective and adequate under all conditions

of external influences - Influences of moistures in Earth, etc

Shall be sufficiently low to operate the protective device in

the event of earth fault within the maximum disconnection

time of the protective device as well as meeting the

functional requirements of the installation

o Protective devices: Circuit breakers (MCB, MCCB, etc) fuses

and residual current device (RCD)

Shall be able to carry earth fault currents and protective

conductors current without danger, particularly from thermal,

thermo–mechanical and electromechanical stresses


90 90

Zs: Earthing Systems

TT: ZS must be sufficiently low to ensure reliable operation of

over–current protective devices

o RCD is required to interrupt the earth fault under high ZS

conditions

TN–S: ZS is negligible resulting a high earth fault current which

may damage or deteriorate equipment during earth fault

IT: ZS is too high to produce sufficient earth fault current during

1st fault to operate over–current devices and result in

hazardous earth fault current

o Insulation monitor device (IMD) required to monitor the

1st earth fault of IT system


91 91

Miscellaneous


92 92

Earthing System: Failure & Degradation

Non – compliance with design and standards

Theft

Corrosion

Sub – standard materials

Poor design and installation methods

Example: Lightning Down-Conductor

Shunting path

Lightning down conductor

ELV Trunking

Break (Electrical)

Different Sources Sharing Same Trunking

DB - 1 DB - 2

A

A-ΔA

ΔA

ΔA

DB-1-By DB-2-Bx

EMI Coupling

During Short –

Circuit Fault

Trunking

94


95 95

Other “Types” of Earthing: Functional Earth

Earthing of a point or points in an electrical installation or in an

electrical equipment for the proper functioning of electronic

equipment, such as measuring equipment, IT and

telecommunication equipment

Functional earthing may function as protective and/or

equipotential earthing

o If possible, use separate conductors for protective earth and

functional earth

o The requirements for protective measures shall take

precedence

Functional Earth – Input EMI Filter

Source: Industrial Training Center, USA

96

Functional Earth – Variable Speed Drives

Source: SumoBrain Co


98 98

Other “Types” of Earthing: Isolated Earth Not defined in (Not within the scope of) MS IEC 60364

ANSI:T1.313:1997 – A set of conductors connected to only one

equipotential reference point which is isolated electrically from

all earth metal structures and any other electrical earthing

systems in the building

o Practically, isolated is electrically connected to the rest of

earthing systems via high impedances – Stray capacitive

effects and resistive effects of Earth

To ensure electrical noise currents do not flow from electrical

system into equipment via the isolated earth (equipment) –

same concept as IT system

Isolated earth should be properly protected against misuse

“Independent” Earthing Arrangement

An earthing arrangement may be considered electrically

independent of another earthing arrangement if a rise of

potential with respect to Earth in one earthing arrangement

does not cause an unacceptable rise of potential with respect

to Earth in the other earthing arrangement

Protective Earth Isolated Earth

IPI < Icritical

99

Isolated Earth – Telecom Infrastructure

Source: NTT 100

Isolated Earthing

High Resistivity High Resistivity

Distribution Board

Supply Load

Depth Electrode

Low Resistivity Region

Isolated Earth Main Terminal

101


102 102

Thanks for Listening

Any Questions ?

Earthing System

102

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