48778976 electronic earthing

8/12/2019 48778976 Electronic Earthing

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Introduction to

Earthing of SensitiveElectronic Equipment

Electrical Standard Products/VR

(Computers/IT Loads/PLCs/OtherSimilar Sensitive Electronic Equipments)


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Sensitive Electronic Equipment

Sstems to !e Earthed"""#) Equipment earthing$ metallic

enclosures% or frame of electronic

equipment"

&) Signal Common Earthing$ the 'ero

reference sstem for data lines the

signal portion in general"

) *C Po+er Suppl ,eference Earthing

$ the electronic equipment ma have

different *C voltage sstems #&-/&.-"


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asic Issues

# Suscepti!le to random voltages far

!elo+ the levels that are percepti!le tohumans that have no effect on

electrical po+er equipment (even the

static voltage charges generated !

lightning stro0es +ithin severalthousand feet can cause damage)"


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& Pro!lem of noise coupling (capacitive

inductive) !et+een signal circuits po+er circuits"


asic Issues


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Impedance considerations related to

the po+er frequenc safet aspects ofa earthing sstem ma not necessaril

provide the desira!le lo+ impedance

at the high frequenc signals"


asic Issues


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. Several elements at different

locations% !ut lin0ed ! a data ca!lethat carries it o+n 'ero reference $ a

conductor lin0ing the earthing

connections at different locations"

1nder certain conditions su!stantialdifferences can e2ist !et+een distant

elements of the sstem $ leading to

component failures"


asic Issues


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Earthing 3ethods

#) 3ultiple Earthing Connections

4 In a commercial/non$industrial

!uilding it is not unusual to find

neutral connected to earth/panelenclosures at more than one location"

4 ,esults in noise causing errors or

+orse"

4 5hether accidental or intentional%

this practice is not recommended"


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3ultiple Earthing

Building Steel (Earthed)

Signal 6round 5ire

7"# Ohm 8

5V Pick-Up if (say)

5! stray current

flo"

#round $oops

%he & current gets

di'ided a part of it

"ill e flo"ing thru

ground/ground "ire*e'en "/o earth fault


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Earthing 3ethods

&) Separate/Isolated Earthing Connection

4 To earth computers to isolated earthing

electrodes separate from the po+er

sstem earthing electrode sstem"

4 5hile continuous lo+$level noise are

eliminated% other catastrophic incidents

are encountered"

4 Since unsafe% therefore not

recommended"


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Isolated Earthing

Building Steel/Po"er

Syste+ EarthingSignal 6round 5ire

(Insulated)

,solated o+puter Earthing

uilding to Computer

Capacitance

# Ohm

#7 9-

#7 9: Stro0e to

uilding


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Isolated Earthing

Earth 2ault

o+puter 3odules

,solated Earthing

4! B

,2

65V/4V

5 7h+ 5 7h+

,2 8 4/6 8 4!


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Earthing 3ethods

) Single Point Earthing Connection

4 To prevent stra/circulating currents

from affecting the computer signals

operations% it is necessar to 0eep thecomputer ground sstem separate from

the equipment ground components

connect together at onl one point"

4 ,ecommended method% as it eliminates

pro!lems of earlier t+o methods"


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Single Point Earthing

,

CO3P1TE, S


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Computer Isolation Transformer


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9ue to length of the grounding conductor

fro+ the co+puter units to the grounding

point* there is possiility of co+puterconductors eing su:ected to high-fre1uency

resonance "ith R2 signals

Onl Limitation"""


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In addition requires"""

. Since equipment earthing emploing

long earthing conductors e2hi!it

higher impedances at higherfrequencies

. Therefore% requirement of

equipotential earth plane to ensure

minimal voltage variances e2ist

among the connected signal circuit

interconnected equipment


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Equipotential Plane

Includes?

. Conductive grid em!edded in or attached

to a concrete floor

. 3etallic screen or sheet metal under floor

tile

. Ceiling grid a!ove sensitive equipment


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Earthing 3ethods

.) Single Point Earthing Connection plusConnection +ith 6rid in the @loor

4 @or each group of computer

equipment% provide a grid net+or0 in theraised floor% +ith tie +ires from each

computer unit to the grid one from the

grid to the room grounding point"

4 ,ecommended method% as it also

eliminates pro!lems of interference from

radio frequencies"


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,

phase step do"ntransfor+er "ith a shared neutral 3ainfra+eter+inals in these "orkstations e


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Pro!lem

. Each floor of the uilding "as isolated into 4sections 'ia shielded isolation transfor+ers

,ndi'idual & conductors "ere installed for all

"orkstation ranch circuits

. Re-estalish+ent of the &-E ond at the ne"

isolation transfor+ers* co+ined "ith the

reduced neutral current in the dedicated

neutrals* reduced &-E 'oltage to less than 4V%he prole+ "as sol'ed

48778976 electronic earthing

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