2391 questions sample 3

City and Guilds 2391 Sample Paper C
Page 1 of 6
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.
1 State the document that indicates the
a) statutory requirements for electrical systems (1 mark)
b) detailed inspection and testing requirements of BS 7671 (1 mark)
c) selection and use of electricians’ test equipment (1 mark)
2 The owner of a small industrial unit requests an inspection and test for
insurance purposes, Several circuits will be unavailable for testing. State
a) the main document to be completed (1 mark)
b) which part of this document will be of particular importance (1 mark)
c) who should be consulted regarding b) above (1 mark)
3 List the three documents that must be completed after the installation of a
new cooker circuit.
(3 marks)
4 State the three items of technical information that should be recorded on a
minor works certificate, excluding test results.
(3 marks)
5 Identify the form of contact defined by BS 7671 as
a) accidentally touching a live part (1 mark)
b) touching an extraneous conductive part made live due to a fault (1 mark)
c) touching the casing of a class I appliance made live due to a fault (1 mark)
.
6 State the units measured by each of the following instruments
a) low resistance ohmmeter (1 mark)
b) insulation resistance tester (1 mark)
c) RCD tester (1 mark)
City and Guilds 2391 Sample Paper C
Page 2 of 6
7 A new radial socket outlet circuit has been installed. List, in sequence, the
first three instrument tests to be carried out.
(3 marks)
8 State the terms identifying the protective conductor connecting each of the
following
a) TNC-S (PME) supply terminal and the main earthing terminal (MET) (1 mark)
b) MET and the earth terminal of an immersion heater (1 mark)
c) shaver unit and copper pipes in a bathroom (1 mark)
9 State the IP code for an
a) accessible top surface of an enclosure (1 mark)
b) intermediate barrier in a distribution board. (2 marks)
10 A continuity of c.p.c. test (utilising the phase conductor) is to be carried out
on a lighting circuit. State the
a) instrument to be used (1 mark)
b) action to be taken regarding the test leads (1 mark)
c) significance of the reading at the last point. (1 mark)
11 For a standard ring final circuit continuity test, state
a) two reasons for conducting the test (2 marks)
b) the other dead test that is automatically conducted. (1 mark)
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
a) was doubled in length (2 marks)
b) length was the same but the conductor cross-sectional area was
halved.
(1 mark)
13 For an insulation resistance test on a SELV circuit, state the
a) instrument to be used (1 mark)
b) test voltage (1 mark)
c) minimum value of insulation resistance (1 mark)
City and Guilds 2391 Sample Paper C
Page 3 of 6
14 An insulation resistance test between P N conductors on three individual
single-phase circuits revealed the following values
0.00 MΩ; 0.08 MΩ; >200 MΩ
What circuit conditions are indicated by these values?
(3 marks)
15 For an earth fault loop impedance test on a new c ircu i t, state
a) why the 3/4 rule is applied (2 marks)
b) if a measured value of 0.7 Ω is acceptable for the circuit maximum of
0.9 Ω.
(1 mark)
16 State
a) the purpose of conducting an earth fault loop impedance test (1 mark)
b) one means of overcoming too high a value of Zs (1 mark)
c) which of the s values measured at socket outlets on a ring final circuit
should be recorded.
(1 mark)
17 State three circumstances that would require the installation of a 30 mA
RCD,
(3 marks)
18 State the three tests to be carried out on a 500 mA RCD. (3 marks)
19 State three methods of determining a value for the prospective fault current
at the origin of an installation.
(3 marks)
20 For a TNC-S system, supplied at 230V, 50 Ha, state
a) why PSCC and PEFC are the same (1 mark)
b) the value of PFC if Ze was 0.01 (1 mark)
c) the approximate value of PFC between phases if the single-phase value
was 10 000A.
(1 mark)
City and Guilds 2391 Sample Paper C
Page 4 of 6
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).
21 a) List all the certification/documentation to be completed by the
inspector.
(4 marks)
b) State who should retain the original copies listed in a). (1 mark)
c) State where a copy of the attached installation schedule should
be kept
(1 mark)
d) State which information regarding shock risk has not been recorded on
the schedule.
(2 marks)
e) State which statutory and non-statutory documents would be relevant
to the inspection and testing process.
(4 marks)
f) State the period of time recommended before the next inspection and
test.
(2 marks)
g) Give one reason why an inspection and test may be required before the
next due date.
(1 mark)
22 a) State why the existing installation will need an inspection and test.
(5 marks)
b) List five items from the BS 7671 schedule of inspections relevant to the
new cooker circuit.
(5 marks)
c) Identify a practical electrical problem commonly encountered when
replacing the c.c.u.
(2 marks)
d) Explain how the installer could have overcome the problem in c). (3 marks)
23 a) i) List, in sequence, the tests required on the cooker circuit (4 marks)
ii) State the test instruments used and the measured units. (6 marks)
b) State the details that should be recorded on a schedule of test results
regarding
i) the test instruments (2 marks)
ii) details of the supply (3 marks)
City and Guilds 2391 Sample Paper C
Page 5 of 6
24 a) Describe how an insulation resistance test would be conducted on the
whole installation.
(8 marks)
b) Individual circuit test values are tabulated as shown below.
Circuit 1 2 3 4 5 6 7 8
MΩ 100 4 10 3 5 100 5 100
What would be the approximate overall value?
(4 marks)
c) State if the value in b) is acceptable, giving reasons/comments (show
all calculations).
(3 marks)
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.
(3 marks)
b) State
i) the conditions that need to be taken into account when comparing
measured and maximum values of Zs
(2 marks)
ii) how this comparison is simply achieved. (1 mark)
c) Refer to the measured values, tabulated below.
Circuit 1 2 3 4 5 6 7 8
Measured
Zs
0.8 1.1 1.3 6.2 5.1 2 0.6 1.3
Calculate these values are acceptable.
(3 marks)
d) Should any Zs value given in c) not comply with BS 7671, state how
this situation may be overcome.
(2 marks)
e) State
i) why it may not be possible to conduct an earth fault loop
impedance test on the lighting circuits
(2 marks)
ii) how this problem may be resolved. (2 marks)
26 State
a) i) the reasons why circuits 2, 3 and 8 are protected by 30 mA
RCBOs, and the others are not
(5 marks)
ii) the test currents to be applied and the maximum operating times
for these RCBOs
(3 marks)
b) i) why there is a difference between the PEFC and PSCC
(5 marks)
ii) which of these two values should be recorded on a schedule of
test results.
(2 marks)
City and Guilds 2391 Sample Paper C
Page 6 of 6
T-NS 100A Main Switch
Circuit Description Points Cable
mm2
Cpc
mm2
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

Guidance Note 3: Inspection & Testing