This examination consists of two sections.
Section A - Twenty short answer questions worth three marks each. Candidates must answer ALL TWENTY questions. It is recommended that candidates allow approximately one hour for this section.
Section B—Six structured questions worth 15 marks each. Candidates must answer ALL SIX questions. It is recommended that candidates allow approximately 11/2 hours for this section.
Section A - Answer ALL
TWENTY questions in this section.
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1 |
State
the document that indicates the |
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a) |
statutory
requirements for electrical systems |
(1 mark) |
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b) |
detailed
inspection and testing requirements of BS 7671 |
(1 mark) |
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c) |
selection
and use of electricians’ test equipment |
(1 mark) |
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2 |
The owner of a small industrial unit requests an inspection and test for insurance purposes, Several circuits will be unavailable for testing. State |
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a) |
the main document to be completed |
(1 mark) |
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b) |
which part of this document will be of particular importance |
(1 mark) |
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c) |
who should be consulted regarding b) above |
(1 mark) |
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3 |
List
the three documents that must be completed after the installation
of a new cooker circuit. |
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4 |
State
the three items of technical information that should be recorded
on a minor works certificate, excluding test results. |
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5 |
Identify
the form of contact defined by BS 7671 as |
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a) |
accidentally
touching a live part |
(1 mark) |
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b) |
touching
an extraneous conductive part made live due to a fault |
(1 mark) |
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c) |
touching
the casing of a class I appliance made live due to a fault |
(1 mark) |
.
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6 |
State
the units measured by each of the following instruments |
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a) |
low
resistance ohmmeter |
(1 mark) |
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b) |
insulation
resistance tester |
(1 mark) |
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c) |
RCD
tester |
(1 mark) |
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7 |
A new radial socket outlet circuit has been installed.
List, in sequence, the first three
instrument tests to be carried out. |
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8 |
State the terms
identifying the protective conductor connecting each of the following |
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a) |
TNC-S (PME) supply
terminal and the main earthing terminal (MET) |
(1 mark) |
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b) |
MET
and the earth terminal of an immersion heater |
(1 mark) |
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c) |
shaver
unit and copper pipes in a
bathroom |
(1 mark) |
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9 |
State the IP code for an |
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a) |
accessible
top surface of an enclosure |
(1 mark) |
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b) |
intermediate barrier in a
distribution board. |
(2 marks) |
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10 |
A continuity of c.p.c.
test (utilising the phase conductor) is to be carried out on a lighting
circuit. State the |
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a) |
instrument
to be used |
(1 mark) |
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b) |
action
to be taken regarding the test leads |
(1 mark) |
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c) |
significance
of the reading at the last point. |
(1 mark) |
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11 |
For a standard ring final
circuit continuity test, state |
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a) |
two reasons for conducting the test |
(2 marks) |
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b) |
the other dead test that is
automatically conducted. |
(1 mark) |
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12 |
A
twin cable has a phase to neutral insulation resistance value of 100 MΩ
and an individual conductor
resistance value of 0.8 Ω. Determine the values, if the cable |
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a) |
was
doubled in length |
(2 marks) |
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b) |
length
was the same but the
conductor cross-sectional area was halved. |
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13 |
For
an insulation resistance test on a SELV circuit, state the |
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a) |
instrument
to be used |
(1 mark) |
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b) |
test
voltage |
(1 mark) |
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c) |
minimum
value of insulation resistance |
(1 mark) |
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14 |
An
insulation resistance test between P N conductors on three individual
single-phase circuits revealed the following values What
circuit conditions are indicated by these values? |
(3 marks) |
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15 |
For
an earth fault loop impedance test
on a new circuit, state |
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a) |
why
the 3/4 rule is applied |
(2 marks) |
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b) |
if
a measured value of 0.7 Ω is acceptable for the circuit maximum of
0.9 Ω. |
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16 |
State |
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a) |
the
purpose of conducting an earth fault loop impedance test |
(1 mark) |
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b) |
one
means of overcoming too high a value of Zs |
(1 mark) |
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c) |
which
of the s values measured at socket outlets on a ring final circuit
should be recorded. |
(1 mark) |
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17 |
State
three circumstances that would require
the installation of a 30 mA RCD, |
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18 |
State
the three tests to be carried out on a 500 mA RCD. |
(3 marks) |
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19 |
State
three methods of determining a value for the prospective fault current
at the origin of an installation. |
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20 |
For
a TNC-S system, supplied at 230V, 50 Ha, state |
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a) |
why
PSCC and PEFC are the same |
(1 mark) |
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b) |
the
value of PFC if Ze was 0.01 |
(1 mark) |
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c) |
the
approximate value of PFC between phases if the single-phase value was
10 000A. |
(1 mark) |
Section
B Questions 21 to
26 refer to the following scenario. Answer ALL SIX questions. All questions carry
equal marks.
The inspection and testing
of a domestic premises is to be carried out after an existing consumers’
control unit (c.c.u.), housing BS 3036 fuses,
has been replaced and a cooker circuit added.
The new c.c.u. has a 100A
main switch and circuits are now protected by a combination of circuit
breakers and RCBOs. The
existing installation is 25 years old and the wiring, together with the new circuit,
comprises flat profile thermoplastic (p.v.c.) cable, clipped direct.
There is an isolator between
the supply intake and the c.c.u. A periodic inspection and test was carried ..
out five years previously, where all defects were rectified.
The supply and installation
form a TN-S system with measured values of
0.3 Q
for Ze, 0.8 kA for prospective earth
fault current (PEFC) and 1.2 kA
for prospective
short circuit current (PSCC).
The schedule for the
installation is attached (See Fig. 1).
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21 |
a) |
List all the
certification/documentation to be completed by the inspector. |
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b) |
State
who should retain the original copies listed in a). |
(1 mark) |
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c) |
State where a copy of the attached installation schedule
should be kept |
(1 mark) |
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d) |
State which information
regarding shock risk has not been recorded on the schedule. |
(2 marks) |
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e) |
State which statutory and
non-statutory documents would be relevant to the inspection and testing
process. |
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f) |
State the period of time
recommended before the next
inspection and test. |
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g) |
Give one reason why an
inspection and test may be required before the next due date. |
(1 mark) |
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22 |
a) |
State why the existing
installation will need an inspection and test. |
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b) |
List
five items from the BS 7671 schedule of inspections relevant to the new
cooker circuit. |
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c) |
Identify
a practical electrical problem commonly encountered when replacing the
c.c.u. |
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d) |
Explain how the installer
could have overcome the problem in c). |
(3 marks) |
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23 |
a) |
i) |
List, in sequence, the
tests required on the cooker circuit |
(4 marks) |
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ii) |
State the test instruments
used and the measured units. |
(6 marks) |
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b) |
State the details that
should be recorded on a schedule of test results regarding |
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i) |
the test instruments |
(2 marks) |
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ii) |
details of the supply |
(3 marks) |
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24 |
a) |
Describe how an insulation
resistance test would be conducted on the whole
installation. |
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b) |
Individual
circuit test values are tabulated as
shown below.
What would be the
approximate overall value? |
(4 marks) |
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c) |
State
if the value in b) is acceptable, giving reasons/comments (show all
calculations). |
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25 |
a) |
Explain the particular
importance of the earth fault loop impedance test on circuits of the
existing installation now that the c.c.u. has been changed. |
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b) |
State |
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i) |
the
conditions that need to be taken into account when comparing measured
and maximum values of Zs |
(2 marks) |
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ii) |
how
this comparison is simply achieved. |
(1 mark) |
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c) |
Refer
to the measured values, tabulated below.
Calculate these values
are acceptable. |
(3 marks) |
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d) |
Should
any Zs value given in c) not comply with BS 7671, state how this situation
may be overcome. |
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e) |
State |
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i) |
why
it may not be possible to conduct an earth fault loop impedance test on
the lighting circuits |
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ii) |
how this problem may be resolved. |
(2 marks) |
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26 |
State |
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a) |
i) |
the
reasons why circuits 2, 3 and 8 are protected by 30 mA RCBOs, and the
others are not |
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ii) |
the test currents to be applied and the maximum operating times
for these RCBOs |
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b) |
i) |
why
there is a difference between the PEFC and PSCC |
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ii) |
which of these two values should be recorded on a schedule of test results. |
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T-NS
100A Main Switch
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Circuit |
Description |
Points |
Cable |
Cpc |
Type |
Protection |
Rating |
Maz
Zs Ω |
|
1 |
Cooker |
1 |
6.0 |
4 |
pvc |
cb
BS EN 60898-B |
40A |
1.2 |
|
2 |
S/O’s
Up |
10 |
2.5 |
1.5 |
pvc |
RCBO
BS EN 61009 |
32A/30mA |
1.5 |
|
3 |
S/O’s
Down |
16 |
2.5 |
1.5 |
pvc |
RCBO
BS EN 61009 |
32A/30mA |
1.5 |
|
4 |
Lights
Up |
6 |
1.0 |
1 |
pvc |
cb
BS EN 60898-B |
6A |
8 |
|
5 |
Lights
Down |
8 |
1.0 |
1 |
pvc |
cb
BS EN 60898-B |
6A |
8 |
|
6 |
Imm.
Htr |
1 |
1.5 |
1 |
pvc |
cb
BS EN 60898-B |
16A |
3 |
|
7 |
Shower |
1 |
10.0 |
4 |
pvc |
cb
BS EN 60898-B |
50A |
0.96 |
|
8 |
Garage |
1 |
4.0 |
2.5 |
SWA |
RCBO
BS EN 61009 |
32A/30mA |
1.5 |
FIG 1