Answer all of the following questions on the sheet provided.
1. The required instrument tests for an initial test are, a protective conductor continuity
b phase-earth loop impedance c ring circuit continuity
d polarity
e earth electrode resistance f insulation resistance g prospective fault current h RCD effectiveness
The order in which these tests are to be conducted is,
(a) a-c-d-e-f-g-b-h (b) c-a-d-e-h-g-f-c (c) a-c-f-d-e-g-b-h (d) c-a-h-e-d-f-b-g
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2. When conducting a test of protective conductor continuity the resistance measure is symbolised as,
(a) Ra + Rb (b) Zs (c) R1 + R2 (d) Ze
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3. If a protective conductor continuity test were to be conducted where the insulating material is PVC and enclosed, if referenced to tables 41B or 41D, the recorded resistance would have to be corrected for short circuit
temperature by,
(a) multiplying by 1.2 (b) dividing by 0.38 (c) dividing by 1.38 (d) multiplying by 1.38
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Inspection and Testing. A.W.Croucher 2 004 page 128
4.What is represented by the symbol Ze ?
(a) p-e loop impedance (b) external p-e loop impedance (c) protective conductor continuity (d) protective conductor resistance
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5. On conducting test 1 on a ring circuit 0.8 ohms are measured. What will be the resistance recorded for test 2 if the circuit is correctly wired ? Assume test 1 was conducted on individual loops of the ring.
(a) 0.4 ohms (b) 0.2 ohms
(c) 0.08 ohms (d) 1.6 ohms
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6. Insulation resistance measured individually on four circuits was,
1.0 MΩ - 10 MΩ - 100 MΩ and 200 MΩ. Which of the following statements is true ?
(a) the insulation meets the
requirements of BS 7671 (b) the overall insulation resistance is less than 1 MΩ
(c) the overall insulation resistance is
greater than 1 MΩ (d) the insulation resistance overall is 311 MΩ
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(7) What is the minimum required test voltage for insulation resistance for a 400/230V installation ?
(a) 500 V dc (b) 500 V ac
(c) 400 V dc (d) 230 V dc
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(8) What are the requirements of BS 7671 regarding insulation resistance ? (a) minimum overall insulation
resistance is to be no less than 2MΩ (b) 0.5MΩ minimum insulation
resistance overall, 2MΩ for individual circuits
(c) all circuit are to be tested individually and in each case to be not less than 2MΩ
(d) no individual circuit to be less than 1MΩ
Inspection and Testing. A.W.Croucher 2 004 page 129
(9) Which of the following statements is untrue regarding correct polarity?
(a) a p-n reversal will result in earth fault current bypassing the circuit fuse
(b) a test of polarity can only be properly conducted with certainty when the installation is dead (c) a live polarity test could not make
a distinction between n and e (d) a p-e reversal will always cause a short circuit
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(10) The resistance of an earth electrode is found to be 300 Ω. Controlling the installation is a 300 mA RCD. Will the electrode resistance enable the RCD to function correctly? Which of the following statements is correct?
(a) Yes, the maximum permitted
electrode resistance is 166Ω (b) Yes, the maximum permitted resistance is 300Ω
(c) No, the resistance is excessive, under earth fault conditions only 240 mA would flow.
(d) No, the maximum permitted resistance is 16.6Ω
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(11) The purpose of an earth-fault loop impedance test is, (a) to measure the resistance of all
installation protective conductors (b) to determine the earth- fault loop impedance at each point of
termination of wiring.
(c) to ensure that in the event of a phase-earth fault, sufficient current will flow to operate the main
overcurrent device
(d) to ensure that earth fault current is not of a magnitude that will damage any circuit or protective conductor
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(12) A ring circuit is protected against overcurrent by a 32A HBC fuse manufactured to BS 88. When the maximum P-E loop impedance is measured for the circuit how will this measurement be assessed ? (a) by reference to table 41A1 (b) by reference to table 41B1 (c) by reference to table 41B2 (d) by reference to table 41D
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(13) If the above circuit were controlling lighting, which would be the table of reference if overcurrent protection is by mcb ?
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(14) If the measured P-E loop impedance is found to be excessive, which of the following suggestions is most appropriate ?
Inspection and Testing. A.W.Croucher 2 004 page 130
(a) the current rating of the fuse or
circuit breaker should be reduced (b) an RCD should be fitted (c) a differing type of mcb should be
used (d)additional main equipotential bonds
should be connected
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(15) When measuring the characteristics of a BS EN 61008 RCD for
satisfactory operation, the disconnection time is not to exceed --- mS at the rated --- operating current. The missing words are?
(a) 200, residual (b) 30, maximum
(c) 40, residual (d) 30, continuous
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(16) If an RCD is to provide protection against direct contact, the test
parameters are ________ mA and __________ mS. The missing values are
(a) 30,30 (b) 150, <40
(c) 40, <150 (d) 30, 40
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(17) If an installation is to tested for prospective short circuit current using a single phase tester, the correction factor for a symmetrical three phase fault would be,
(a) x 1 (b) x 2
(c) x 3 (d) x 4
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Inspection and Testing. A.W.Croucher 2 004 page 131
(18) A single-phase prospective short circuit current is measure on a TP&N installation and is found to be 25kA. Overcurrent protection is provided by type B m10 mcb's. The situation could be summarised,
(a) Overcurrent protection is
satisfactory (b) Overcurrent protection should be
provided by type 3 mcb's (c) Overcurrent protection should be
provided by BS 1362 fuses (d) Overcurrent protection should be provided by BS 88 fuses
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(19) You are commissioned to provide an overcurrent survey part of which involves a determination of maximum demand for both the installation as a whole and for individual circuits. Maximum demand vales may be obtained by,
(a) Comparing the current rating of the cable with that of the connected fuse
(b) By taking measurements with a clamp meter, after dark but during the working day
(c) By making an assessment of the
connected load (d) By clamping all circuit conductors (P-N-E) together with a clamp
ammeter and taking measurements at a time when the maximum load is expected to be connected
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(20) As part of an earthing survey you have discovered that a current of 10A is flowing in the main equipotential bond. Which of the following comments will be most appropriate on your report? The system is TN-C-S.
(a) A characteristic of a TN-C-S system is the discharge to earth of a proportion of neutral current, which is totally harmless.
(b) An insulation resistance fault clearly exists - only a very small
proportion of load current will flow in a protective conductor attached to TN-C-S system.
(c) A fault exists in the earthing
system. If properly installed no current will flow through the equipotential bonds. A very high fire risk exists and remedial action must be taken
immediately.
(d) The current results from neutral load current and should be eliminated by balancing the single phase loads over three phases
Inspection and Testing. A.W.Croucher 2 004 page 132
Fig. 92
On completion of an inspection documentation must be completed. Shown above is the first page of six of a periodic inspection report, published by the NICEIC
Inspection and Testing. A.W.Croucher 2 004 page 133
List of figures
Fig. Description Page
1 Approved voltage testers 8
2 Typical defects to be found on an old installation 10 3 Line diagrams showing the organisation of an installation 12
4 Measurement of circuit length 15
5 Measurement of earth continuity (R2) 18
6 The phase earth loop path 20
7 Earthing and supply systems 21
8 Measurement of earth continuity (R1+ R2) 23
9 Equipotential bonding – principles and resistance measurement 27
10 Neutral/earth current in a TN-C-S system 28
11 A main earthing terminal 29
12 Tests of ring circuit continuity 32
13 Instrument and preparation for a ring circuit test 33 14 Identification of cables size and circuit breaker rating for a ring
circuit. 34
15 The parallel circuit nature of insulation resistance 35
16 Causes of low insulation resistance 36
17 Conducting an insulation resistance test 37
18 Preparing a 3 phase installation for an IR test 1 38
19 Conducting an IR test 1 38
20 Preparing a 3 phase installation for an IR test 2 38 21 Conducting an IR test - all live conductors with respect to earth 40 22 Conducting an IR test - all phase conductors with respect to
neutral 41
23 Conducting an IR test - phase conductors with respect to each
other 42
24 Problems in identifying the location of circuits having low
insulation resistance 43
25 The construction of a polarity tester 45
26 The application of a polarity tester 45
27 An earth electrode 48
28 An earth electrode resistance test 1 48
29 An earth electrode resistance test 2 49
30 Measurement of earth electrode resistance using a phase-earth
loop impedance tester. 50
31 A Null Balance tester 51
32 Measurement of soil resistivity 52
33 A 400A TN-C-S service 57
34 Measurement of phase-earth loop impedance 1 58
35 Measurement of phase-earth loop impedance 2 60
36 Determination of R1+R2 by loop[ impedance measurement 60 37 Measurement of p-e loop impedance at a floor socket 61 38 Measurement of p-e loop impedance at a luminaire 62
39 Testing an RCD 65
40 Single phase RCD’s 65
41 The construction of an RCD 66
42 HBC and rewirable fuses 69
43 Circuit breakers 70
44 Measuring earth leakage current 1 70
45 Temperature measurement 70
46 Construction of a large installation 71
47 Principles of earth leakage current measurement 79
48 Measuring earth leakage current 2 79
Inspection and Testing. A.W.Croucher 2 004 page 134
56 Flexible cord adapted for measurement of earth leakage current 89
57 IT equipment – earth leakage considerations 90
58 IT equipment - protective conductor requirements 90
59 IT equipment – regulation requirements 91
60 IT equipment – regulation requirements 91
61 A BS 4343 socket 91
62 IT equipment – regulation requirements 92
63 A symmetrical three phase fault 93
64 Workshop illumination 97
65 Principle of overcurrent protection 99
66 Cross sectional view of a rewirable fuse 100
67 Cut off characteristics 101
68 Admitted energy characteristics 103
69 Circuit breaker characteristics 105
70 Cut off characteristics for HBC fuses 106
71 Time-current characteristics for type B circuit breakers 107
72 High voltage ring main schematic 108
73 High voltage distribution system 109
74 Link box
75 Low voltage distribution board 111
76 Urban low voltage distribution system 112
77 The series circuit 113
78 The parallel circuit 114
79 Coil reactance 115
80 Z,X and R phasor relationship 115
81 Resistance and impedance in series 116
82 Phasor diagram for above 116
83 Earthing and bonding terms 121
84 Instrument displays 122
85 A phase earth loop impedance tester 123
86 An RCD tester 123
87 An insulation resistance tester 124
88 A clamp ammeter 124
89 A multimeter 125
90 A PAT tester 125
91 Reading analogue instruments 127
92 A PIR report form 133