Earthing Electronic Equipments

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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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Safety Provided By Earthing

Safety of Life

Safety of Property/Installation

Safety of Power System

Slide 4


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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


8/68 Earthing : Fundamentals Vinay Rai

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



Solid (Effective) Earthing

Resistance Earthing

Inductance Earthing

System Earthing - How?

Slide 10



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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As direct as possible

by ensuring equipotential bonding

between all simultaneouslyaccessible exposed & extraneousconductive parts

Equipment Earthing - How?

Slide 12


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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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Equipotential Bonding

No bonding - Unsafe Earthed equipotential bonding - safe


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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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No Equipotential Bonding

L1 L2 L3L1 L2 L3


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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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TN SystemTN-S

TN-CTN-C-S

TT System

IT System

Classification Of Earthing Systems

Slide 19


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TN-S System


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TN-C System


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TN-C-S System


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TT System


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IT System


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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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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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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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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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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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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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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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Basic Issues

2) Problem of noise coupling (capacitive &inductive) between signal circuits & powercircuits.


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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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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 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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Multiple Earthing Connections


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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 Methods

2) Separate/Isolated Earthing Connection

# To earth computers to isolated earthing

electrodes separate from the power systemearthing electrode system.


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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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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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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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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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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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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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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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Single Point Earthing Connection


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3) Single Point Earthing Connection

Recommended method, as it eliminates problemsof earlier two methods.

Earthing Methods


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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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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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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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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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SRG Resonance Reduction...


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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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With connection with grid in the floor...


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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 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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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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Intermittent data memory errors & data

transmission errors between remote terminals &a central computer system.

Case 2 :

Slide 63


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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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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 :

Slide 65


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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

Earthing Electronic Equipments

Documents

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