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Session 3:
LV Electrical Installations of Buildings
Earthing Systems
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Contents
General
Earthing arrangements
Types of earthing conductors
Protective conductors (PE conductors)
Protective bonding conductors
Earth fault loop impedance
Miscellaneous
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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
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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)
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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
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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
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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
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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
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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
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Earthing Arrangements
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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
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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
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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
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MS IEC 60364: Types of Earthing Systems
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
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MS IEC 60364: Types of Earthing Systems
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
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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
Incoming Transformer
Installation: N – S Supply: T
PE
Supply: T
N – S: N
N – S: S
Earthing System: TN–C
N – C: N
Supply: T
Incoming Transformer
N – C: C
L1 (R)
L2 (Y)
L3 (B)
PEN
Installation
Supply: T Installation: N – C
Earthing System: TN–C–S
Incoming Transformer
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
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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
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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)
Incoming Transformer
Installation: T Supply: I
Installation
Earth
Supply: I Installation: T
Earthing System: IT (High Impedance)
Earth
L1 (R)
Installation
L2 (Y)
L3 (B)
Incoming Transformer
Installation: T Supply: I
Installation
Earth
Supply: I Installation: T
High
Impedance
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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
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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
Incoming Transformer
Earth Return Path Supply: T Installation: T
Earthing System: TT (Single Phase)
L1 (R)
Installation
L2 (Y)
L3 (B)
N
Incoming Transformer
Earth Return Path Supply: T Installation: T
Earthing System: TN–S (Single Phase)
L1 (R)
Installation
L2 (Y)
L3 (B)
N
Incoming Transformer
Supply: T Installation: N
PE
Earthing System: TN–S (Single Phase)
L1 (R)
Installation
L2 (Y)
L3 (B)
N
Incoming Transformer
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
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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
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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
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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
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Earth Electrodes: General Requirements
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
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Earth Electrodes: General Requirements
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
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Earth Electrodes: General Requirements
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
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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
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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
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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
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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
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Types of Earthing
Conductors
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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.
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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
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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
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Protective Conductors
(PE Conductors)
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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)
Not protected against
mechanical damage
(mm2)
By a sheath Copper 2.5 4
Others Equivalent Equivalent
Equivalent = Copper equivalent
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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)
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
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
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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
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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
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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
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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
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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
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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
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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)
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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
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Protective Bonding
Conductors
(PB Conductors)
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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 50 mm2 up to 95 mm2
Over 95 mm2 up to 150 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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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Miscellaneous
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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
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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
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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
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Thanks for Listening
Any Questions ?
Earthing System
102