Basic concept of earthing

1. E54530
ASIF EQBALASIF EQBAL
Electrical & Electronics EngineerElectrical & Electronics Engineer
BASICS OF EARTHINGBASICS OF EARTHING

2. ContentsContents
1.1. TERMINOLOGIESTERMINOLOGIES
2.2. DISADVANTAGES OF UNEARTHED SYSTEMDISADVANTAGES OF UNEARTHED SYSTEM
3.3. TYPES OF EARTHINGTYPES OF EARTHING
4.4. BASIC PRINCIPLEBASIC PRINCIPLE
& METHODS OF SYSTEM EARTHING& METHODS OF SYSTEM EARTHING
5.5. SCHEME ADOPTED IN PROCESS PLANT FORSCHEME ADOPTED IN PROCESS PLANT FOR
SYSTEM EARTHINGSYSTEM EARTHING
6.6. EARTHING CONDUCTORS SCHEDULE FOREARTHING CONDUCTORS SCHEDULE FOR
SUBSTATIONS OF PROCESS PLANTSUBSTATIONS OF PROCESS PLANT
7.7. RECOMMENDED PRACTICES AS PER IEC 60364RECOMMENDED PRACTICES AS PER IEC 60364
AND IS 3043AND IS 3043

3. 33
TerminologiesTerminologies
1.1. CLASS I EQUIPMENTCLASS I EQUIPMENT
2.2. CLASS II EQUIPMENTCLASS II EQUIPMENT
3.3. EARTH ELECTRODEEARTH ELECTRODE
4.4. EARTH ELECTRODE RESISTANCEEARTH ELECTRODE RESISTANCE
5.5. EARTH FAULT LOOP IMPEDANCEEARTH FAULT LOOP IMPEDANCE
6.6. EARTH LEAKAGE CURRENTEARTH LEAKAGE CURRENT
7.7. PROTECTIVE CONDUCTORPROTECTIVE CONDUCTOR
8.8. NEUTRAL CONDUCTORNEUTRAL CONDUCTOR
9.9. PEN CONDUCTORPEN CONDUCTOR
10.10. RESIDUAL CURRENT DEVICERESIDUAL CURRENT DEVICE
11.11. RESIDUAL OPERATING CURRENTRESIDUAL OPERATING CURRENT
12.12. TOUCH VOLTAGETOUCH VOLTAGE
13.13. STEP VOLTAGESTEP VOLTAGE
14.14. EARTH GRIDEARTH GRID
15.15. EARTH MATEARTH MAT

4. 44
Disadvantages of Unearthed SystemDisadvantages of Unearthed System
1.1. Unearthed system experience repeatedUnearthed system experience repeated
arcing grounds.arcing grounds.
2.2. Insulation failure occurs during single phaseInsulation failure occurs during single phase
to ground faults.to ground faults.
3.3. Earth fault protection for unearthed systemEarth fault protection for unearthed system
is difficult.is difficult.
4.4. Voltage due to lightning surges do not findVoltage due to lightning surges do not find
path to earth.path to earth.

5. 55
Types of EarthingTypes of Earthing
1.1. SYSTEM EARTHINGSYSTEM EARTHING
2.2. EQUIPMENT EARTHINGEQUIPMENT EARTHING
3.3. REFERENCE OR SIGNAL EARTHINGREFERENCE OR SIGNAL EARTHING
4.4. STATIC AND LIGHTNING PROTECTION EARTHINSTATIC AND LIGHTNING PROTECTION EARTHING

6. 66
Equipment EarthingEquipment Earthing
TheThe connection between non current carrying metallic partsconnection between non current carrying metallic parts
in electrical installation to earth is equipment or bodyin electrical installation to earth is equipment or body
earthing.The basic objectives are:-earthing.The basic objectives are:-
1.1. Freedom from Electric shock.Freedom from Electric shock.
2.2. To provide adequate current carrying capability.To provide adequate current carrying capability.
3.3. Avoidance of thermal distress & preservation of systemAvoidance of thermal distress & preservation of system
performance.performance.

7. 77
Reference or Signal EarthingReference or Signal Earthing
The connection of floating point in the circuit to earth is called referenceThe connection of floating point in the circuit to earth is called reference
or signal earthing. It is performed to achieve both a suitable level ofor signal earthing. It is performed to achieve both a suitable level of
protection for personnel and equipment,& to provide suitable electricprotection for personnel and equipment,& to provide suitable electric
noise immunity for signal ground references in generating stations.noise immunity for signal ground references in generating stations.
1.1. Mainly used in electronic, communication & data processing equipmentMainly used in electronic, communication & data processing equipment
in electrical installation building.in electrical installation building.
2.2. Earthing of chassis of instruments, computer room ensures freedomEarthing of chassis of instruments, computer room ensures freedom
from electromagnetic disturbances on operation of isolator,thyristors infrom electromagnetic disturbances on operation of isolator,thyristors in
main power circuits.main power circuits.
3.3. It is of three type Single point earthing, Multiple point earthing & floatingIt is of three type Single point earthing, Multiple point earthing & floating
earth.earth.

8. 88
Basic Principles & Methods ofBasic Principles & Methods of
System EarthingSystem Earthing
1.1. The potential of neutral is held atThe potential of neutral is held at
earth potential due to earthing.earth potential due to earthing.
2.2. The fault current lags behind theThe fault current lags behind the
voltage of unhealthy line by 90 degreevoltage of unhealthy line by 90 degree
due to predominantly inductive naturedue to predominantly inductive nature
of circuit.of circuit.
3.3. The current through neutral in thisThe current through neutral in this
case is in phase opposition tocase is in phase opposition to
capacitive ground current.capacitive ground current.
4.4. By neutralisation of capacitive groundBy neutralisation of capacitive ground
currents arcing grounds is eliminated.currents arcing grounds is eliminated.
R
Y
B
N
PE

9. 99
Basic Principles & Methods ofBasic Principles & Methods of
System Earthing(System Earthing(contcont…….)…….)
1.1. For a ground fault in line B the vectorialFor a ground fault in line B the vectorial
sum of current measured by CBCT nonsum of current measured by CBCT non
zero.zero.
2.2. In case of small unbalance this sum isIn case of small unbalance this sum is
non zero and there will be flow currentnon zero and there will be flow current
through neutral.through neutral.
3.3. So the current flowing through neutralSo the current flowing through neutral
has to be distinguished for being due tohas to be distinguished for being due to
ground fault or due to smallground fault or due to small
unbalances.unbalances.
4.4. To make this differentiation we employTo make this differentiation we employ
a protective earth conductor (PE) .a protective earth conductor (PE) .
5.5. The path of fault current getsThe path of fault current gets
essentially completed through thisessentially completed through this
conductor providing low impedance.conductor providing low impedance.
R
B
N
PE
Y
F

10. 1010
Basic Principles & Methods ofBasic Principles & Methods of
System Earthing(System Earthing(contcont…….)…….)
1.1. So measuring the current through PESo measuring the current through PE
which is equal to fault current is thewhich is equal to fault current is the
principle of System earthing.principle of System earthing.
2.2. Any other normal current especiallyAny other normal current especially
the neutral current under smallthe neutral current under small
unbalances must not flow through PEunbalances must not flow through PE
in order to avoid nuisance tripping.in order to avoid nuisance tripping.
3.3. Two ways to measure the currentTwo ways to measure the current
through PE is by Residual currentthrough PE is by Residual current
sensing & by source ground returnsensing & by source ground return
sensing.sensing.
R
N
PE
Y
B

11. 1111
Methods OF System EarthingMethods OF System Earthing
1.1. Non-effective earthing with resistance or reactance.Non-effective earthing with resistance or reactance.
2.2. Effective earthing or solid earthing.Effective earthing or solid earthing.
3.3. Resonant earthing.Resonant earthing.
There is no rule or theory as regards which earthing should be usedThere is no rule or theory as regards which earthing should be used
resistance or reactance. If resistance is used fault current is limited and system reactanceresistance or reactance. If resistance is used fault current is limited and system reactance
provides the necessary phase opposition between capacitive ground current & faultprovides the necessary phase opposition between capacitive ground current & fault
current. Circuits where high charging currents are involved such as transmission lines,current. Circuits where high charging currents are involved such as transmission lines,
underground cables Reactance earthing is preferred.underground cables Reactance earthing is preferred.
Generally one neutral ground is provided at each voltage level. Between generator voltageGenerally one neutral ground is provided at each voltage level. Between generator voltage
level and distribution voltage levels. One ground is provided at each voltage level. Thelevel and distribution voltage levels. One ground is provided at each voltage level. The
earth is provided at source end & not load end.earth is provided at source end & not load end.
To avoid circulating current only one generator neutral is earthed at a time if severalTo avoid circulating current only one generator neutral is earthed at a time if several
generators are operating in parallel.generators are operating in parallel.

12. 1212
Scheme Adopted in Process plants forScheme Adopted in Process plants for
System EarthingSystem Earthing
SYSTEMSYSTEM VOLTAGEVOLTAGE NEUTRALNEUTRAL
EARTHINGEARTHING
MAIN RECEIVING SUBSTATIONMAIN RECEIVING SUBSTATION 220kV,3 phase,3 wire220kV,3 phase,3 wire Solidly earthedSolidly earthed
MAIN POWER GENERATORSMAIN POWER GENERATORS 11-19kV,3 phase,3 wire11-19kV,3 phase,3 wire High resistance earthedHigh resistance earthed
MAIN POWER DISTRIBUTIONMAIN POWER DISTRIBUTION 33kV,3 phase,3 wire33kV,3 phase,3 wire Solidly earthedSolidly earthed
SECONDARY POWERSECONDARY POWER
DISTRIBUTIONDISTRIBUTION
11kV,3 phase, 3 wire11kV,3 phase, 3 wire
6.6kV,3 phase,3 wire6.6kV,3 phase,3 wire
Low resistance earthedLow resistance earthed
EMERGENCY POWEREMERGENCY POWER
GENERATIONGENERATION
6.6kV,3 phase,3 wire6.6kV,3 phase,3 wire
415V,3 phase,3 wire415V,3 phase,3 wire
Low resistance earthedLow resistance earthed
Solidly earthedSolidly earthed
LV POWER DISTRIBUTIONLV POWER DISTRIBUTION 415V,3 phase,4 wire415V,3 phase,4 wire Solidly earthedSolidly earthed

13. 1313
Earthing ConductorsEarthing Conductors
ScheduleSchedule
EQUIPMENTEQUIPMENT BODY EARTHBODY EARTH
CONNECTIONCONNECTION
INSTRUMENT/CLEAINSTRUMENT/CLEA
N EARTHN EARTH
TransformerTransformer
33/6.6kV33/6.6kV
75X10mm, at 475X10mm, at 4
placesplaces
Not RequiredNot Required
Neutral Point ToNeutral Point To
NERNER
Single Core XLPESingle Core XLPE
cable of relevantcable of relevant
sizesize
Not RequiredNot Required
NER to Earth PitNER to Earth Pit 75X10mm,with 2 pit75X10mm,with 2 pit
connectionsconnections
Not RequiredNot Required
Marshalling BoxMarshalling Box 75X10mm (2 No's)75X10mm (2 No's) Not RequiredNot Required

14. 1414
Earthing Conductors ScheduleEarthing Conductors Schedule
EQIPMENTEQIPMENT BODY EARTHBODY EARTH
CONNECTIONCONNECTION
INSTRUMENT/CLEAINSTRUMENT/CLEA
N EARTHN EARTH
Transformer 6.6/0.433kVTransformer 6.6/0.433kV 75X10mm,at 4 places75X10mm,at 4 places Not requiredNot required
NeutralNeutral 75X10mm,with 2 pit75X10mm,with 2 pit
connectionsconnections
Not requiredNot required
Bus-DuctBus-Duct 1cX70 sq mm1cX70 sq mm Not requiredNot required
Trip Push button, WeldingTrip Push button, Welding
Socket, HVAC Duct,Socket, HVAC Duct,
1cX35 sq mm1cX35 sq mm Not requiredNot required

15. 1515
Earthing Conductors ScheduleEarthing Conductors Schedule
EQUIPMENTEQUIPMENT BODY EARTHBODY EARTH
CONNECTIONCONNECTION
INSTRUMENT/INSTRUMENT/
CLEAN EARTHCLEAN EARTH
6.6kV Switchgear6.6kV Switchgear
PCC,MCC,BatteryPCC,MCC,Battery
charger,VFD,main earthcharger,VFD,main earth
grid & riser conductorgrid & riser conductor
75X10mm75X10mm 1cX16 mm sq only for1cX16 mm sq only for
PCC,MCC VFDPCC,MCC VFD
Fiber optic panel, HVACFiber optic panel, HVAC
control panel DBscontrol panel DBs
Space heater panel.Space heater panel.
50X6mm50X6mm Only for Fiber opticOnly for Fiber optic
panel & HVAC controlpanel & HVAC control
panelpanel

16. 1616
Recommended practices for systemRecommended practices for system
EarthingEarthing
Power system earthing arrangements are distinguished as follows:Power system earthing arrangements are distinguished as follows:
The first letter denotes the connection between earth and powerThe first letter denotes the connection between earth and power
supply equipment (generator or transformer). The second lettersupply equipment (generator or transformer). The second letter
denotes the relationship of the exposed conductive parts of thedenotes the relationship of the exposed conductive parts of the
installation to earth i.e. connection between earth and electricalinstallation to earth i.e. connection between earth and electrical
device being supplied.device being supplied.
1.1. T-direct connection of one or more points to earth. (French:terre).T-direct connection of one or more points to earth. (French:terre).
2.2. N-direct electrical connection of the exposed conductive parts toN-direct electrical connection of the exposed conductive parts to
the earthed points of the source of energy, which for AC,isthe earthed points of the source of energy, which for AC,is
usually the neutral pointusually the neutral point

17. 1717
Recommended practices for systemRecommended practices for system
EarthingEarthing
Further classification of TN system of earthingFurther classification of TN system of earthing
For low voltage systems the designation 'TN' is further subdividedFor low voltage systems the designation 'TN' is further subdivided
depending on the arrangement of neutral and protective conductors, thedepending on the arrangement of neutral and protective conductors, the
arrangement being denoted by a further letter or letters:arrangement being denoted by a further letter or letters:
SS == neutral and protective functions provided by separate conductors (Nneutral and protective functions provided by separate conductors (N
and PE).and PE).
CC == neutral and protective functions combined in a single conductorneutral and protective functions combined in a single conductor
(PEN).(PEN).

18. Earthing system IEC 60364Earthing system IEC 60364
TT systemTT system
1.1. The Neutral point ofThe Neutral point of
LV transformer is directlyLV transformer is directly
connected to an earthconnected to an earth
electrodeelectrode
2.2. The exposed conductiveThe exposed conductive
parts of the installation areparts of the installation are
connected to an electricallyconnected to an electrically
separate earth electrodeseparate earth electrode
3.3. The protective earth connection ofThe protective earth connection of
the consumer is provided by athe consumer is provided by a
local connection to earth,local connection to earth,
independent of any earthindependent of any earth
connection at the generator orconnection at the generator or
supply end.supply end.
Rn Ru
PE
E56888
R
Y
B
N

19. Earthing system IEC 60364Earthing system IEC 60364
TN systemTN system
1.1. The star point of the LVThe star point of the LV
transformer is directlytransformer is directly
connected to an earthconnected to an earth
electrode (source earth)electrode (source earth)
2.2. The exposed conductiveThe exposed conductive
parts of the installation areparts of the installation are
connected by the PE to theconnected by the PE to the
same earth electrode (Thesame earth electrode (The
body of the electrical device isbody of the electrical device is
connected with earth via this earthconnected with earth via this earth
connection at the transformer).connection at the transformer).
E56890
R
Y
B
N
PE

20. Earthing system IEC 60364Earthing system IEC 60364
TN-S systemTN-S system
The PE and NeutralThe PE and Neutral
conductor are separate (Theyconductor are separate (They are connectedare connected
together only near the power source. ).together only near the power source. ).
R
Y
B
N
PE
E56890

21. Earthing system IEC 60364Earthing system IEC 60364
TN-C systemTN-C system
The PE and Neutral conductor are commonThe PE and Neutral conductor are common
= the PEN= the PEN
(A combined PEN conductor fulfils the functions(A combined PEN conductor fulfils the functions
of both a PE and an N conductorof both a PE and an N conductor).).
E56892
R
Y
B
PEN

22. 2222
Earthing system IEC 60364Earthing system IEC 60364
TN-C–S SystemTN-C–S System
Part of the system uses a combined PENPart of the system uses a combined PEN
conductor, which is at some point split up intoconductor, which is at some point split up into
separate PE and N lines.separate PE and N lines.
The combined PEN conductor typically occursThe combined PEN conductor typically occurs
between the substation and the entry point into the building,between the substation and the entry point into the building,
whereas within the building separate PE and N conductorswhereas within the building separate PE and N conductors
are used.are used.
(This system is also known as protective multiple earthing(This system is also known as protective multiple earthing
(PME), because of the practice of connecting the combined(PME), because of the practice of connecting the combined
neutral-and-earth conductor to real earth at many locations,neutral-and-earth conductor to real earth at many locations,
to reduce the risk of broken neutrals .to reduce the risk of broken neutrals .
This system is also designated as multiple earthed neutralThis system is also designated as multiple earthed neutral
(MEN(MEN)) particularly in Australia.particularly in Australia.
E56892
R
Y
B
N
PE

23. 2323
TN system examplesTN system examples
 For HV Systems supplied from an overhead line, the earthing system shallFor HV Systems supplied from an overhead line, the earthing system shall
be of the TN configuration from the point of supply. Refer Figure forbe of the TN configuration from the point of supply. Refer Figure for
explanatory schematic.explanatory schematic.
SOURCE OVERHEAD LINE POINT OF SUPPLY
L1
L2
L3
PE
EXPOSED
CONDUCTIVE
PARTS ARE
CONNECTED TO PE
CONSUMER
EQUIPMENT
SOURCE
EARTH
INSTALLATION
EARTH
 Figure : TN System for installation supplied from Overhead LineFigure : TN System for installation supplied from Overhead Line

24. 2424
TN system examplesTN system examples
TN-S System is adopted for LV System Earthing.TN-S System is adopted for LV System Earthing.
Refer following Fig. for an explanatory schematic of aRefer following Fig. for an explanatory schematic of a
TN-S system.TN-S system.
SOURCE
L1
L2
L3
N
PE
EXPOSED CONDUCTIVE
PARTS ARE CONNECTED TO
PE
CONSUMER EQUIPMENT
CONSUMER EQUIPMENT
SOURCE EARTH

25. 2525
The Protective Conductor (PE) systemThe Protective Conductor (PE) system
1.1. An electrically continuous system which provides aAn electrically continuous system which provides a permanent direct return path forpermanent direct return path for
fault currents between exposed conductive parts (e.g. the metallic enclosure offault currents between exposed conductive parts (e.g. the metallic enclosure of
electrical equipment) and the neutral of the source of supply. In conjunction withelectrical equipment) and the neutral of the source of supply. In conjunction with
protective devices, the PE system controls magnitude and duration of touch voltages toprotective devices, the PE system controls magnitude and duration of touch voltages to
safe levels.safe levels.
2.2. In permanent LV systems PE's and protective devices shall ensure automaticIn permanent LV systems PE's and protective devices shall ensure automatic
disconnection of an earth fault from the source of supply within one second Fordisconnection of an earth fault from the source of supply within one second For
personnel safety and to ensure proper operation of the protection relays the impedancepersonnel safety and to ensure proper operation of the protection relays the impedance
of the return path shall be as low as possible, hence the PE should be integrated in theof the return path shall be as low as possible, hence the PE should be integrated in the
power cable.power cable.
3.3. Common examples of PE's are Cable armouring, cable screens, neutral pointCommon examples of PE's are Cable armouring, cable screens, neutral point
connections, earth bars etc. Where no suitable cable armour or screen is availableconnections, earth bars etc. Where no suitable cable armour or screen is available
either the power cable shall have an additional PE conductor or a separate PEeither the power cable shall have an additional PE conductor or a separate PE
conductor shall be installed parallel to the power cable (yellow/green PVC sheath).conductor shall be installed parallel to the power cable (yellow/green PVC sheath).

26. 2626
The Equi potential bondingThe Equi potential bonding
Conductor(EB) systemConductor(EB) system
1.1. An electricallyAn electrically continuouscontinuous system which directly or indirectly (via the earth grid)system which directly or indirectly (via the earth grid)
interconnects exposed conductive parts (e.g., the metallic enclosure of electricalinterconnects exposed conductive parts (e.g., the metallic enclosure of electrical
equipment) with extraneous conductive parts (of non-electrical equipment, e.g., aequipment) with extraneous conductive parts (of non-electrical equipment, e.g., a
skid) and earth to ensure Equi potential between these parts and earth under normalskid) and earth to ensure Equi potential between these parts and earth under normal
and electrical fault conditions. This system generally consists of a common earthand electrical fault conditions. This system generally consists of a common earth
grid and EB conductors connecting exposed and extraneous parts to the earth grid.grid and EB conductors connecting exposed and extraneous parts to the earth grid.
2.2. Common examples of EBs are Earth grids in oil and gas facilities ,substations andCommon examples of EBs are Earth grids in oil and gas facilities ,substations and
earth mats in switchyards with outdoor equipment.earth mats in switchyards with outdoor equipment.
3.3. The general rule is that, for reasons of reliability, the exposed and extraneousThe general rule is that, for reasons of reliability, the exposed and extraneous
conductive parts of equipment shall be connected to the EB system by twoconductive parts of equipment shall be connected to the EB system by two
separately routed earth conductors, marked green/yellow. These conductors shall beseparately routed earth conductors, marked green/yellow. These conductors shall be
connected to the equipment at physically different points (e.g., diametricallyconnected to the equipment at physically different points (e.g., diametrically
opposite).opposite).
4.4. The cross-section of conductors for the PE and EB systems shall in general beThe cross-section of conductors for the PE and EB systems shall in general be
determined by the prospective fault level, which will vary from location to location,determined by the prospective fault level, which will vary from location to location,
and the type of fault.and the type of fault.

27. 2727
PE and EB systemPE and EB system
Although the PE-system and the EB-system have distinctlyAlthough the PE-system and the EB-system have distinctly
different functions (namely fault clearing and Equipotential), these systemsdifferent functions (namely fault clearing and Equipotential), these systems
are permanently interconnected. Thus, in addition to its function the EB-are permanently interconnected. Thus, in addition to its function the EB-
system will affect earth loop impedance and fault clearing. Similarly, insystem will affect earth loop impedance and fault clearing. Similarly, in
addition to its function, the PE-system will provide supplementaryaddition to its function, the PE-system will provide supplementary
connections between exposed conductive parts and the earth grid, via theconnections between exposed conductive parts and the earth grid, via the
neutral point of the source of supply.neutral point of the source of supply.

28. Earthing system IEC 60364Earthing system IEC 60364
IT systemIT system
1.1. The star point of the LVThe star point of the LV
transformer is not connectedtransformer is not connected
to an earth electrode (or it has only a highto an earth electrode (or it has only a high
impedance connection).impedance connection).
2.2. The exposed conductive partsThe exposed conductive parts
of the loads are connected byof the loads are connected by
the PE conductor to a commonthe PE conductor to a common
earth electrodeearth electrode
3.3. In such systems, an insulationIn such systems, an insulation monitoringmonitoring
device is used to monitor the impedance.device is used to monitor the impedance.
E56894
L1
L2
L3
N
PE

29. Earthing System conclusionsEarthing System conclusions
IEC 60364
Earthing TN-C TN-S TT IT
System
I fault High High Low Very low
Protection SCPD SCPD RCD No problem
of people
Fire Forbidden Not Recommended Recommended
Protection recommended with RCD with RCD
Cost Most economical Expensive
economical than TN
TT and IT Systems naturally manage the Fire Risk by limiting the fault current

30. ELECTROMAGANETICELECTROMAGANETIC
COMPATIBILITYCOMPATIBILITY
IEC 60364
Earthing TN-C TN-S TT IT
System
EM Forbidden Good Very good Very good
disturbances PE and But be careful No problems No problems
Neutral are avoiding PE even if Neutral even if Neutral
together and Neutral to and PE are in and PE are in
(PEN) be in contacts contacts contacts
l
There isn't any fault current in TT and IT System even if the PE
and Neutral are in contact

31. 3131
Thank YouThank You