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Earthing Concepts
By Vinay Rai
Technology Conclave at STC Vadodara
11th & 12th July 2014
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Earthing Fundamentals
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Earthing : Fundamentals Vinay Rai
What is Earthing ?
By earthing we mean making electrical
connection to the general mass ofconductingearth
Slide 3
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Earthing : Fundamentals Vinay Rai
Safety Provided By Earthing
Safety of Life
Safety of Property/Installation
Safety of Power System
Slide 4
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Earthing : Fundamentals Vinay Rai
Types of Earthing
System Earthing
Equipment EarthingLightning Protection Earthing
Static Earthing
Slide 5
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Earthing : Fundamentals Vinay Rai Slide 6
As per IS : 3043
Definition
Earthing of the current
carrying conductor which is
usually the neutral point of
the transformer or thegenerator is known as
System Earthing
L1
L2
L3
N
Rn
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As per IS : 3043
L1
L2
L3
N
Rn RA
PE
Definition
Earthing of the current
carrying conductor which is
usually the neutral point of
the transformer or thegenerator is known as
System Earthing
Earthing of non current
carrying exposedconductive parts of the
installation is known as
Equipment Earthing
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Limitation of abnormal voltage hazards
Reduction in occurrences of multiple faults toground
Easier location of faults
Fewer arcing fault burndowns
Greater service continuity
Greater safety
System Earthing Why ?
Slide 8
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Solid (Effective) Earthing
Resistance Earthing
Inductance Earthing
System Earthing - How?
Slide 10
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Equipment Earthing Why ?
Provides Safety of Life & Property by:By ensuring freedom from dangerous electricshock voltages exposure (Uc) to persons in thearea
By ensuring current carrying capability both inmagnitude & duration adequate to accept theground fault current without creating a fire orexplosive hazard
By ensuring the proper return path for earthfault currents & hence better performance ofthe electrical system
Slide 11
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Earthing : Fundamentals Vinay Rai
As direct as possible
by ensuring equipotential bonding
between all simultaneouslyaccessible exposed & extraneousconductive parts
Equipment Earthing - How?
Slide 12
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Earthing : Fundamentals Vinay Rai
Equipotential Bonding Electrical connection puttingvarious exposed conductive parts and extraneousconductive parts at a substantially equal potential.
Slide 13
As per IS: 3043
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Earthing : Fundamentals Vinay Rai Slide 14
Equipotential Bonding
No bonding - Unsafe Earthed equipotential bonding - safe
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Earthing : Fundamentals Vinay Rai
Earthing of all the exposed conductive parts of electricalequipment and all accessible conductive parts
Simultaneously accessible exposed and extraneousconductive parts must be connected to the same earthelectrode/earth grid.
Slide 15
IS : 3043
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Earthing : Fundamentals Vinay Rai Slide 16
No Equipotential Bonding
L1 L2 L3L1 L2 L3
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Earthing : Fundamentals Vinay Rai Slide 17
Grounding is about connecting parts to theearth, while bonding is about connecting partsto each other. One achieves 'zero-potential' &other 'equi-potential.'
Grounding & Bonding
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Network Classification
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Earthing : Fundamentals Vinay Rai
TN SystemTN-S
TN-CTN-C-S
TT System
IT System
Classification Of Earthing Systems
Slide 19
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Earthing : Fundamentals Vinay Rai Slide 20
TN-S System
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Earthing : Fundamentals Vinay Rai Slide 21
TN-C System
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Earthing : Fundamentals Vinay Rai Slide 22
TN-C-S System
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Earthing : Fundamentals Vinay Rai Slide 23
TT System
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Earthing : Fundamentals Vinay Rai Slide 24
IT System
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Earthing : Fundamentals Vinay Rai Slide 25
Human Safety In TT System
415V / 240V
L1
L2
L3
N
Id = 34.3A
RA
5
Rn
2
U0 = 240 V
Uc = 171 V
Rc
1000
Ud
SCPD
100 AExposed conductive
metallic part
Load
Rn = 2 RA = 5Uc = 171 V
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Earthing : Fundamentals Vinay Rai Slide 26
Human Safety In TN-S System
415V / 240V
L1
L2
L3
N
PE
Id= 3850A
Rn
U0 = 240 V
Uc
Exposed
conductive
metallic part
Load
Fault
SCPD 100 A
Uc = 120 VRn = 2 Uc = 120 V
ZS= 50m
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Rules & Regulations
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Earthing : Fundamentals Vinay Rai
Earth at each voltage level
Earth at source & not at load
Earth only once (at source) & avoidfurther connections to earth
Earth by two separate & distinct
connections with earth i.e. minimum twoearth pits
System Earthing Basic Rules
Slide 28
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Earthing : Fundamentals Vinay Rai
Earth all exposed & extraneousconductive parts
Earth as directly as possible withminimum impedance
Earth by two separate & distinct
connections with earth i.e. minimum twoearth pits
Equipment Earthing Basic Rules
Slide 29
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Earthing : Fundamentals Vinay Rai
IE RULES: 32, 33, 51, 61, 62, 67, 69, 88(2), 90,92, 115, & 116
IS 3043 - 1987; IS 2309 - 1989; IS 7689 1989
NEC 2011 (SP 30)
IEC 60364-5-54; IEC 60364-5-548; IEC 60364-7-707; IEC 62305-3; IEC TR 61000-5-2
IEEE GUIDELINES: Green & Emareld Book
Rules & Regulations
Slide 30
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Earthing : Fundamentals Vinay Rai
System Earthingdepends on method; for solid earthing within 2 Ohmsis ideal (general practice)
Equipment Earthingnot exceeding 5 Ohms (as per NEC)
Lightning Protection Earthing
not exceeding 10 Ohms (as per IS 2309)Static Earthing
even 20 Ohms can achieve objective (as per IS 7689)
Earth Electrode Resistance
Slide 31
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Earthing Of Electronic
Equipments
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 33
Sensitive Electronic Equipment
1) Equipment earthing - metallic enclosures, orframe of electronic equipment.
2) Signal Common Earthing - the zero referencesystem for data lines & the signal portion ingeneral.
3) DC Power Supply Reference Earthing - theelectronic equipment may have different DCvoltage systems, such as +12/0/12V, +5/0/5V.
Systems to be Earthed...
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 34
Basic Issues
1) Susceptible to random voltages far below thelevels that are perceptible to humans & thathave no effect on electrical power equipment
(even the static voltage charges generated bylightning strokes within several thousand feetcan cause damage).
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 35
Basic Issues
2) Problem of noise coupling (capacitive &inductive) between signal circuits & powercircuits.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 36
Basic Issues
3) Impedance considerations related to thepower frequency safety aspects of an earthingsystem may not necessarily provide the desirable
low impedance at the high frequency signals.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 37
Basic Issues
4) Several elements at different locations, butlinked by a data cable that carries its own zeroreference - a conductor linking the earthing
connections at different locations. Under certainconditions substantial differences can existbetween distant elements of the system -leading to component failures.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 38
Earthing Methods
1) Multiple Earthing Connections
# In a commercial/non-industrial building it is
not unusual to find neutral connected toearth/panel enclosures at more than onelocation.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 39
Multiple Earthing Connections
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 40
Earthing Methods
1) Multiple Earthing Connections
Results in noise causing errors or worse. Whether accidental or intentional, this
practice is not recommended.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 41
Earthing Methods
2) Separate/Isolated Earthing Connection
# To earth computers to isolated earthing
electrodes separate from the power systemearthing electrode system.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 42
Isolated Earthing
Building Steel/Power
System EarthingSignal & Ground Wire
(Insulated)
Isolated Computer Earthing
1 Ohm
Building to Computer
Capacitance
10 KV
10 KA Stroke to
building
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 43
Isolated Earthing
Earth Fault
Computer Modules
Isolated Earthing
32A CB
IF
415V/240V
5 Ohm 5 Ohm
IF = 240/10 = 24A
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 44
Isolated Earthing
Large voltages impressed on computercomponents under thunderstorm conditions(direct strike or charge induced because ofclouds overhead).
With isolated earthing, a fault in a computerrequires fault current to pass thru theresistance of both the isolated & power systemground in series. In this case the current wouldbe insufficient to operate the protective device.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 45
As per IS 3043
Vide Cl. 39.4.1 :
Whatevermeasures are taken to provide a low-noise earthing connection, it is required that
exposed conductive parts of data processing shallbe connected to the main earthing terminal.
NOTE The use of separate earth electrodes for
simultaneously accessible exposed conductiveparts is not permitted.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 46
As per IEC TR 61000-5-2:1997
The use of independent, "isolated" earth electrodes for computer or
electronic systems is not recommended/permitted.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 47
2) Separate/Isolated Earthing Connection
While continuous low-level noise are eliminated,other catastrophic incidents are encountered.
Since unsafe, therefore Isolated Earthing forSensitive Electronic Equipment is not
recommended (and in fact not permitted).
Earthing Methods
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 48
3) Single Point Earthing Connection
# To prevent stray/circulating currents from
affecting the computer signals & operations, it isnecessary to keep the computer ground systemseparate from the equipment groundcomponents & connect together at only one
point.
Earthing Methods
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 49
Single Point Earthing Connection
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 50
3) Single Point Earthing Connection
Recommended method, as it eliminates problemsof earlier two methods.
Earthing Methods
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 51
Single Point Earthing Connection
Due to length of the grounding conductor fromthe computer units to the grounding point, thereis possibility of computer conductors beingsubjected to high-frequency resonance with RFsignals.
Only Limitation...
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 52
As per IEC TR 61000-5-2:1997
This approach has been found satisfactory & is suitable for safety (at power
frequencies); it is generally not suitable for high-frequency EMC concerns.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 53
Single Point Earthing Connection
Equipotential earth plane to ensure minimalvoltage variances exist among the connectedsignal circuit & interconnected equipment (Sinceequipment earthing employing long earthingconductors exhibit higher impedances at higher
frequencies)
In addition requires......
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 54
Single Point Earthing Connection
The multiple and parallel paths have differentresonance frequencies. So, if there is for a givenfrequency a path with a high impedance, thispath is certainly shunted by another which hasnot the same resonance frequency.
SRG Resonance Reduction...
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 55
Single Point Earthing Connection
SRG Resonance Reduction...
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 56
4) Single Point Earthing Connection plusConnection with Grid in the Floor
# For each group of computer equipment,provide a grid network in the raised floor, withtie wires from each computer unit to the grid &one from the grid to the room grounding point.
# Recommended method, as it also eliminatesproblems of interference from radio frequencies.
Earthing Methods
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 57
Single Point Earthing Connection
With connection with grid in the floor...
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 58
As per IEC TR 61000-5-2:1997
It is the recommended approach in the general case, for safety as well as for EMC.
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Earthing of Sensitive Electronic Equipment Vinay Rai Slide 59
Earthing In Industrial Installation
A schematic diagram of various apparatus or systems connected to
the earthing network in an industrial installation
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Case Histories
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Earthing of Sensitive Electronic Equipment Vinay Rai
Erratic computer operation within a large office
building experiencing several lightning storms
Case 1 :
Slide 61
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Earthing of Sensitive Electronic Equipment Vinay Rai
The earthing conductors of all the computers inthe building were connected to isolated earthingelectrode system (consisted of 6 rods driven into
the earth away from building).The computer manufacturer was persuaded to
permit earthing of the computer system to the
building earthing system, which had concreteencased earthing electrodes. Immediately theerratic operations ceased.
Case 1 :
Slide 62
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Earthing of Sensitive Electronic Equipment Vinay Rai
Intermittent data memory errors & data
transmission errors between remote terminals &a central computer system.
Case 2 :
Slide 63
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Earthing of Sensitive Electronic Equipment Vinay Rai
In the installation of a multistory office building,several floors of modular workstations werepowered from a common, 3 phase step downtransformer with a shared neutral. Mainframe
terminals in these workstations experiencedintermittent data memory errors & datatransmission errors, & occasionally hardwarefailures.
It was found that considerable (& variable) neutralcurrent existed. RMS values of N to earth didntexceed 3.7V, but the peak voltage ranged up to10V.
Case 2 :
Slide 64
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Earthing of Sensitive Electronic Equipment Vinay Rai
Each floor of the building was isolated into 2sections via shielded isolation transformers.Individual N conductors were installed for allworkstation branch circuits.
Re-establishment of the N-E bond at the newisolation transformers, combined with thereduced neutral current in the dedicatedneutrals, reduced N-E voltage to less than 2V.The problem was solved.
Case 2 :
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Earthing of Sensitive Electronic Equipment Vinay Rai
Case 2 :
Slide 66
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Thank You
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Contact
Vinay RaiSr. Deputy General Manager
Electrical Standard Products
Larsen & Toubro Limited
32 Shivaji MargNear Moti Nagar
New Delhi 110015
Tel: +91-11-41419590
Mob: +91-8860476555
Email: [email protected]
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IS 3043 1987: CODE OF PRACTICE FOR EARTHING
IS 2309 1989: PROTECTION OF BUILDINGS AND ALLIED STRUCTURES AGAINST LIGHTNING
SP 30: NATIONAL ELECTRICAL CODE 2011
INDIAN ELECTRICITY RULES 1956 (AS AMENDED UPTO 25TH NOV., 2000)
IEC 60364 (VARIOUS PARTS)
TECHNICAL REPORT IEC 61000-5-2 - 1997: INSTALLATION & MITIGATION GUIDELINES EARTHING & CABLING
IEEE GREEN BOOK
IEEE STD 80-2000: IEEE GUIDE FOR SAFETY IN AC SUBSTATION GROUNDING
EARTHING SYSTEM BY FREDERIC ROUESN
References