2391- instruments &testing

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Instruments and TestingInstruments and Testing

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Installation Testing



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REMEMBER

Visual inspection must precede all testing



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REMEMBER

Dead testing precedes

Testing



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Dead Testing



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Isolate

before carrying

out dead tests



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Approved voltage indicator

to GS 38



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Maximum of 4mm on exposed prods

Preferably not more than 2mm

Fused leads

Finger guards



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Continuity Testing



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Continuity

Low-resistance

ohmmeter



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Battery operated instrument

Low voltaged.c.d.c.



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200 mA

4-24V



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Verifying Continuity

Method 1



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CautionSupply must be isolated



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Temporary Link

Instrument

measures (R1+R2)



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Along with verification of the cpc, state

the TWO other tests which are

automatically undertaken when carrying

out this test



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The value of (R1 + R2)

Polarity



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Unacceptable practice of connecting c.p.c.

to outgoing side of fuse or circuit breaker



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Why is it unacceptable?



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Unacceptable practice

of connecting c.p.c. to

outgoing fuse or circuit breaker way



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Verifying Continuity

Method 2



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CautionCautionSupply must be isolated



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State TWO disadvantages of using

Method 2, as compared to Method 1



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Use of long wander lead

Value of R2 only obtained



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What consideration should be given to

the long wander lead?

Its resistance must be measured and

deducted from the measured value

of R2



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Continuity of bonding

conductors



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Why is it necessary to remove one end

of a bonding conductor when verifying

its continuity?



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To avoid the possibility of parallel

earth paths



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Break in c.p.c.

Parallel path



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Continuity

of ferrous enclosures



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Continuity of ferrous enclosures

• visual inspection

• low resistance ohmmeter

• high current test



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High current test

25A

50 Volt maximum



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High current-low-resistance

ohmmeter



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Insulation Testing

Instrument must becapable of producing ashort-circuit current of 1mA



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CautionCautionSupply must be isolated



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Prior to insulation resistance testing

close main switch if testing from tails

fuses in circuit breakers closed

local switches closed/operate two-way

switches during test

neon's/capacitors disconnectedremove voltage sensitive equipment



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Insulation resistance

testing between live

conductors



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Insulation resistance

testing between liveconductors and earth



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State the test voltage and minimum value of

insulation permitted for the following circuits

230V domestic lighting circuit

3 phase, 400V motor circuit

12V SELV circuit

750V discharge lighting circuit

50V FELV circuit

25V PELV circuit

500V - 0.5M

500V - 0.5M

250V - 0.25M

250V - 0.25M

1000V - 1.0M

500V - 0.5M

BS 7671 Table 71A - Page 172



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Live Testing



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Measurement of external impedance Ze

impedance

tester

Main switch

open

Earthing conductor

disconnected

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Why MUST the supply be isolated

before disconnecting the earthing

conductor?



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Because if you don’t you could possibly kill

somebody. If there is a defect with the

insulation, and phase touches exposed

metalwork, the whole of the installationearthing could become live



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State THREE other instances where

earth-fault loop impedance testing would

be required.

At the furthest point in every final circuit

At every distribution board

At every socket outlet



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What precautions should be observed

when undertaking impedance tests withina circuit?

Ensure that persons or livestock arenot in contact with exposed metalwork



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- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Measurement of prospective earth fault current

Prospective fault

current tester

Bonding conductors

connected

El t C



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Measurement of prospective short circuit fault current

Prospective fault

current tester

El t C



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Why is it necessary to verify the value

of prospective fault current at the originof an electrical installation?

To ensure the rated breaking capacity

of the main switch and overcurrent devices

are capable of breaking the prospective

fault current level

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