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Instruments and TestingInstruments and Testing
ElectaCourse.com
© 2005
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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
.35
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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