2391 sample questions

Wednesday, 13 July 2011

2391 exam preperation

This Section is highlight the areas covered by the 2391 syllabus. Student are expected to
have knowledge of all that is in the syllabus.
Requirements for the Level 3 Level 3 Certificate in the Certification of Electrical
Installations (inspection, testing and certification of electrical installations) (2391-10)
For this qualification, candidates will be required to complete the following assessments:
A written assessment covering outcomes 1-3
A practical assessment
It will be graded pass or fail.
Duration: 2.5 hours
No of questions: 26
This written paper is in two sections. Section A consists of 20 short answer questions
worth 60 marks (1 hour approximately). Section B will consists of 6 structured questions
worth 90 marks (1.5 hours approximately).
Here is the Break down of the examination content.
Section Outcome Unit Title Number of
items
Approximate
percentage %
1 Preparation for
inspection
and testing
3 6
Section A 2 Inspection 2 4
3 Testing 15 30
1 Preparation for
inspection
and testing
Section B 2 Inspection 6 60
3 Testing
Total 26 100

Technical knowledge of the inspection, testing and certification of electrical
installations
The aim of this unit is to enable the candidate to develop the necessary technical
knowledge and understanding about the inspection, testing and certification of electrical
installations.
It is recommended that 15 hours should be allocated for this unit. This may be on a full
time or part time basis.
This unit will be assessed by written examination.
Learning Areas
There are three areas to this unit. These include a knowledge and understanding of:-
Preparation for inspection and testing
Inspection
Testing
Preparation for inspection and testing
The candidate will be able to:
State the need for and the purpose of initial verification and periodic inspection and testing
State the information required to correctly conduct the inspection and testing of an
installation
State the statutory and non-statutory requirements and relevant guidance material that
apply to the activity of inspecting and testing of electrical installations
State the need to comply with statutory and non-statutory requirements, and guidance
material for particular locations and environments in which electrical installations are
installed
State the information to be contained on Certificates and Inspection Reports and how the
information is recorded on all certificates as indicated in BS 7671 (current edition).

Inspection
The candidate will be able to:
State the human senses that may need to be employed during the inspection of an
installation
Refer to and identify the items to be checked during the inspection process for given
systems and locations as detailed in BS 7671 (current edition)
State the particular requirements for a periodic inspection of an electrical installation as
defined in BS 7671 (current edition)
State the need to establish the extent and limitation of a Periodic Inspection Report, with
the client and any relevant third parties, prior to commencing the inspection, and the need
to record these details on the Periodic Inspection Report.
State the requirements of the Electricity at Work Regulations for safe inspection and
testing in terms of those
carrying out the work
using the installation and the building during the inspection and testing.
Testing
For each topic the candidate will be able to:
Instruments
State the need for instruments to be regularly checked and the need for their compliance
with the requirements of BS 7671 (current edition) and HSE Guidance Note GS 38
List the correct instruments, their characteristics and the appropriate scale to carry out
each test and explain the reasons for each choice
State the recommended sequence of tests and the reasons for that sequence
Protective Conductors
State the requirements which need to be considered for protective conductors in terms of
a) earthing conductors
b) main protective bonding conductors
c) supplementary protective bonding conductors
d) circuit protective conductors

Describe the need for, and methods of verifying, the continuity of protective conductors
and the interpretation of results
State the relationship between conductor length, CSA and resistance
State the effect of temperature on a conductor
Ring Circuits
State the effect on measured resistance when cables are connected in parallel
Describe the need for, and methods of, verifying the continuity of ring final circuit
conductors and the interpretation of results
Insulation Resistance
Explain, by example, the effect on insulation resistance and test results of
a) cables connected in parallel
b) variation in cable length
Compare the differences between measurements taken for insulation resistance and
conductor resistance, stating the order of magnitude that would be expected in each case
State the preconditions required for the performance of insulation testing
State the precautions to be taken before testing insulation resistance
Describe methods of testing insulation resistance
State the required test voltages and minimum values of insulation resistance for
installations operating at various voltages
State the particular requirements for insulation resistance testing of circuits incorporating
surge protection devices (SPDs) or sensitive electronic devices, to include disconnection
and the test voltage to be applied where disconnection cannot be achieved.
Electrical separation/SELV
Describe the tests to verify the separation of SELV circuits
State the particular requirements for protection by electrical separation (NOT SELV)

Special Installations and Locations
Describe the requirements for circuits in prescribed special installations and locations, by:
a) identifying the installations and locations to which special requirements apply
b) demonstrating the ability to make reference to the appropriate requirements in each
case
c) identifying the requirements in relation to specific areas and installations from given
information.
IP Code
State the appropriate minimum degree of protection required for given applications as
identified within the IP classification BS EN 60529
Polarity
Describe the need for and methods of testing used to identify correct polarity
Earth Electrodes
Differentiate between the requirements for testing of earth electrodes for RCD protected
TT systems and electrodes for transformers and generators
Earth Fault Loop Impedance
Describe the earth fault loop impedance paths for the following systems
a) TN-S
b) TN-C-S
c) TT
Describe methods of determining earth fault loop impedance in terms of
a) the tests used for measuring actual earth fault loop impedance
b) methods of calculation of earth fault loop impedance from given data and
measurement of conductor impedance
Given maximum tabulated values of earth fault loop impedance, verify that measured
values are acceptable, taking into account conductor operating and ambient temperatures.

Residual Current Devices (RCCBs/RCBOs)
Describe methods of testing the correct operation of RCDs, independent of in-built test
facilities.
State the applications for various RCD ratings
Prospective Fault Current
Describe methods of determining prospective fault current in terms of
a) prospective short circuit current
b) prospective earth fault current
Explain the importance of selecting protective devices appropriate to the prospective fault
current.
Phase Sequence
Describes the requirements for checking phase sequence in terms of
a) the purpose of checking correct phase sequence
b) test methods used to check phase rotation
Voltage Drop
Describe the methods of verifying voltage drop compliance with BS 7671 in terms of
measuring circuit impedance and calculation.

Practical application of the inspection, testing and certification of electrical
installations
The aim of this unit is to enable the candidate to develop the necessary technical practical
skills about the inspection, testing and certification of electrical installations. Demonstrate a
practical application of the testing inspection, testing and certification of electrical
installations
It is recommended that 15 hours should be allocated for this unit.
Practical Activities
The candidate will be able to:
Select the correct instruments or settings and appropriate scales or ranges to carry out
tests
Check and prove instruments and leads for safety and function
Given the information required carry out the inspection and testing of an installation to the
requirements of BS 7671
Complete a Periodic Inspection report, as given in BS7671, including two Schedules of
Test Results
Carry out an inspection of installation components and record deviations and complete a
Schedule of Inspections
The test rig and inspection and testing equipment
To carry out these inspection and testing practical assessments, simulated installations
should be constructed in accordance with the diagrams given in the Assessment Guide for
Centres.
The test rigs should be located in an area of adequate space and light. All connections
must be directly to the accessories, rather than simulated, and allowance should be made
for the replacement of connections as they become worn.
The test equipment provided by the centre must meet the requirements of BS 7671 and
HSE document GS 38.
To ensure that the candidate has to make a selection from the equipment provided, there
should be a greater range of test instruments available than is actually required to carry
out the tests.
The test instruments for Assessment 4 must include a voltage indicator, with the
necessary proving equipment, to test for correct isolation.

To simulate ‘real’ conditions the test rig must be connected to a 400V three-phase and
neutral supply.
Test procedure
The candidate should be given
a. the appropriate results sheet for the assessment
b. a selection of hand tools where required, to carry out the test of the installation
c. a range of test instruments including those required to complete the tests.
Candidate identification and other relevant information should be completed on the
appropriate result sheet prior to the commencement of each test.
The candidate will be expected to record all relevant information and test results for all
circuits on the appropriate results sheet.
The tests and performance assessment
Consideration should be given to the Electricity at Work Regulations throughout the
assessment process, and it should be made clear to the candidate that failure to observe
appropriate safe working practices will result in the assessment being stopped.

2391 questions sample 2

City and Guilds 2391 Sample Paper A
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 Three single sockets have been added to a ring final circuit. State the.
a) inspection and test certificate that will need to be completed (1 mark)
b) title in law given to the inspector (1 mark)
c) legal status of the inspector (1 mark)
2 An engineering works is 18 years old and is due for inspection and test.
State the
a) type of inspection and test required (1 mark)
b) documents that must accompany the completed certificate (1 mark)
c) circumstances under which the type of inspection and test in a) above
may not be required.
(1 mark)
3 State the legal status of the following
a) BS 7671 2001 (1 mark)
b) Guidance Note 3 (1 mark)
c) HSE GS38 (1 mark)
4 Give ONE example of EACH of the following
a) an exposed conductive part (1 mark)
b) an extraneous conductive part (1 mark)
c) direct contact (1 mark)
5 State THREE methods of protection against indirect contact (3 marks)
6 State the earthing systems that use the following as return earth paths
a) PEN conductor (1 mark)
City and Guilds 2391 Sample Paper A
Page 2 of 6
b) cable sheath (1 mark)
c) general mass of earth (1 mark)
7 State the test instruments to be used for the following tests
a) continuity of supplementary bonding in a bathroom (1 mark)
b) external earth fault loop impedance of a TN-C-S system (1 mark)
c) live polarity (1 mark)
8 Give THREE examples of notices/warning labels that should be present in
an electrical installation
(3 marks)
9 State the IP code that applies to the following enclosures
a) accessible horizontal top surfaces (1 mark)
b) internal intermediate barriers (2 marks)
10 The continuity of a lighting circuit c.p.c. is verified using the phase
conductor as part of the test. 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 furthest point (1 mark)
11 State THREE outcomes of the ring final circuit continuity test. (3 marks)
12 State the test voltage and minimum value of insulation resistance for EACH
of the following
a) 12V fan circuit in a bathroom (1 mark)
b) three-phase commercial installation (1 mark)
c) 800V discharge lighting circuit (1 mark)
13 Give THREE reasons for carrying out a polarity test on an installation, as
required by BS7671 2001
(3 marks)
14 The resistance of an earth electrode is to measured. If a mains supply is
unavailable, state the
a) instrument to be used (1 mark)
b) terms used to describe the TWO other test electrodes. (2 marks)
City and Guilds 2391 Sample Paper A
Page 3 of 6
15 State the maximum disconnection times appropriate to the following
a) a domestic socket outlet circuit (1 mark)
b) site hut lighting on a construction site (1 mark)
c) 110V reduced low-voltage system. (1 mark)
16 State
a) why it may not be possible to obtain a measured value of loop
impedance for a circuit protected by an RCD
(1 mark)
b) how this value may be determined without the use of a special
instrument
(2 marks)
17 A loop impedance test is to be conducted on a radial socket outlet circuit.
State
a) where in the circuit the test should be made (1 mark)
b) TWO conditions that may affect the validity of the measured value as a
comparison to the maximum value
(2 marks)
18 State THREE reasons for the use of a 20mA RCD. (3 marks)
19 In the formula IΔ n = 50/Zs state
a) what is represented by ‘50’ (1 mark)
b) the maximum residual current rating of the RCD required, when the
value of Zs is 500Ω
(2 marks)
20 The PFC at the origin of an installation is to be measured. State the
a) instrument to be used (1 mark)
b) measurement units (1 mark)
c) importance of the breaking capacity of the protective devices at the
origin
(1 mark)
City and Guilds 2391 Sample Paper A
Page 4 of 6
Section B – Answer ALL SIX questions
Questions 21 to 26 all refer to the following scenario and Fig. 1 (attached).
Fig.1 shows the main intake and circuit arrangements for the new electrical installation in a
refurbished dentist’s surgery. The heating, ventilating and air-conditioning unit (HVAC), located
outside the building is supplied using p.c.v./p.c.v./s.w.a. multicore cable. All other circuits are
wired using p.v.c. single-core cables enclosed in concealed p.v.c. conduit and surface trunking
(c.p.c’s are the same size as the phase conductors). The lighting is a mixture of tungsten
filament, fluorescent and PIR-controlled exterior security lights. The installation has been
completed and is ready for inspection and testing.
21 State the
a) type of inspection and test to be completed (1 mark)
b) certificate that will need to be completed (2 marks)
c) signatures that are required on the certificate in b) (3 marks)
d) status of the signatories (2 marks)
e) documents that must accompany the certificate in b) (2 marks)
f) information regarding the incoming supply that should be recorded on
ONE of the documents in e)
(3 marks)
g) person who should keep the original completed documents (2 marks)
22 State
a) the terms used to describe EACH of the following items labelled
i) 1
ii) 2
iii) 3
iv) 4
(4 marks)
b) the earthing system (1 mark)
c) where, on the gas and water supplies, item 2 should be connected (2 marks)
d) the label that should appear at the connection in c) (1 mark)
e) why a type D circuit breaker is used on B9 (3 marks)
f) FOUR relevant items to be considered from the BS7671 2001
installation schedule
(4 marks)
23 List, in the correct sequence, the relevant tests to be carried out on the
installation circuits, indication the instruments to be used for EACH test.
(15 marks)
City and Guilds 2391 Sample Paper A
Page 5 of 6
24 Describe how
a) an insulation resistance test would be carried out on circuit R1 (8 marks)
b) a c.p.c. continuity test would be carried out on circuit Y5 (7 marks)
25 a) The insulation resistance values for circuits R2, B6 and B9 were
3.8MΩ, 4.9Ω and 5.0MΩ respectively. All other circuits were in excess
of 999MΩ. Calculate the approximate value of the overall insulation at
the origin
(7 marks)
b) When the system is energised and before the sequence of live tests is
conducted, it is important to carry out a live polarity test. State
i) the reason for this test
ii) where this test should be conducted
iii) the instrument to be used
iv) why the test will not reveal neutral-earth reversals
(8 marks)
26 The measured values of earth loop impedance for each circuit are as follows:
CIRCUIT 1 2 3 4 5 6 7 8 9 10
MEASURED
VALUES
3.8Ω 2 Ω 2.6 Ω 1.3 Ω 1 Ω 2.5 Ω 2 Ω 1.8 Ω 0.4 Ω 1.2 Ω
a) State the environment and circuit conditions which may have an effect
on these measured values
(4 marks)
b) State how these conditions are compensated for. (1 mark)
c) Show, by calculation, if the measured values are acceptable (5 marks)
d) State a solution for any circuit that fails to comply. (5 marks)
City and Guilds 2391 Sample Paper A
Page 6 of 6
Fig 1

2391 questions sample 5 answers

Sample questions
1) Indicate three main items for which you would require relevant information about
in order to undertake an initial inspection on a new installation.
Possible Answers
Maximum demand
Earthing system
Diagrams, charts or tables
Nature of supply
2) State relevant documentation that relate to the inspection and test of a system
Name one statutory and two non statutory
Possible Answers
Statutory
Electricity at Work Regulations 1989
Health and Safety at Work act 1974
Non Statutory
IEE Wiring Regulations 17th edition BS7671,
Guidance Note 3,
On Site Guide
Documentation GS38
3) An Electrical Installation Certificate and a Periodic Inspection Report should be
accompanied by two other documents what are they?
Possible Answers
Schedule of inspection
Schedule of test results
4) State three areas of inspection you would check when carrying out a Periodic
Inspection Report
Answers
Priority given to
Safety of person's
livestock
property.
Other possible area's are damage caused through overloading, signs of mechanical
damage, compliance to regulations, damage caused by external influences
Basic and fault protection, isolating devices, conductors, enclosures and mechanical
protection

5).State three human senses used when carrying out a Periodic Inspection Report
Answers
Sight
Smell
Touch
6). List the instruments which provided the measurements 20 Megohms, 8KA and
22mS
Answers
Insulation Resistance Meter
Prospective Short Circuit Current Tester
RCD tester
7) Insulation resistance testing requires different test voltages for certain circuits,
identify what circuits require the following voltages 250v, 500v and 1000v.
Answers
SELV or PELV circuit test at 250 volts and results should be ≥ 0.5 MΩ
Circuits 500v or under test at 500v and results should be ≥ 1 MΩ
Circuits above 500v but below 1000v test at 1000 volts test results should be ≥ 1 MΩ
8) State the first three tests that should be taken during the initial verification of a
new installation.
answers
Continuity of protective conductors and bonding
Continuity of ring circuits
Insulation resistance test
9) The test for continuity of the CPC in a radial circuit with one socket requires a
link and a Milli-ohmmeter state: were link is connected, where the meter is
connected, what the meter reading represents.
Answers
Link connected between Line conductor and CPC at the consumer unit
Meter connected at socket between CPC and Line conductor
R1+R2 value

10) State three different protective conductors that need to be connected to the
main earth terminal
Answers
Circuit Protective Conductor (CPC)
Earthing conductor
Main protective bonding conductor
11) The following results were obtained during the initial test on a healthy ring
circuit
P1 > P2 = 0.8 ohms
N1 > N2 = 0.8 ohms
CPC1 > CPC2 = 0.8 ohms
What readings would you expect after cross connection
Between Line and neutral at each socket?
Between Line and CPC at each socket?
What does the Line and CPC represent? The following results
Answers
0.4 Ohms
0.4 Ohms
R1+R2 for the circuit
12) State the effect on
Conductor resistance when cable length increases
Conductor resistance when CSA increases
Conductor resistance when cable length increases
Answers
Resistance increases
Resistance decreases
Resistance decreases
13) State three precautions to be taken before an insulation resistance test on a
circuit
Answers
No danger to person livestock or property while taking test
Lamps or capacitors are removed from circuit
Voltage sensitive equipment is removed/isolated from circuit
There are no shorts in circuit
All switches are in the closed position

14) An enclosure has been fabricated on site state the minimum IP rating, it is not
affected by liquids
IP4X, IP2X, IPXXB
15) State the protection offered by the following IP ratings IP4X, IPX8, IPXXB
Protection against foreign solid bodies up to 1mm diameter
Protection against total submersion
Protection against finger contact only
16) State three reasons for conducting polarity checks on a circuit
Polarity check on circuit wiring
Polarity check on switch wiring to ensure line conductor switching.
Check on switching in Line conductor
Correct polarity of supply,
Centre contact on Edison lamp live
17) ID earthing system that is connected with overhead cables, a multi core supply
cable with separate earth and neutral, supply in which earth and neutral are
performed in one conductor.
TT
TN-S
TN-C or TN-C-S
18) State three location where additional requirements for an electrical installation
are needed.
Locations which contain bath or shower, caravan site, construction site, agricultural or
horticultural location, swimming pool or any other section in part 7 of BS7671:2008.
Additional requirements are also required in some other locations such as petrol stations
these have other British Standards that apply.
19) From the formula Zs = Ze+(R 1 + R 2 ) x 1.2 x L state what is Ze, R2 and 1.2
1000
Ze, external loop impedance
R2 resistance of the circuit CPC
1.2 is conductor temperature multiplier

20) State three functional test to be carried out on an installation
Switching in Line Conductor
RCD test button
Functional switching
Isolation
21) For carrying out initial verification of the installation. What information or
documentation is required? Where should it be found? What particular uncommon
details should be recorded on this installation? What consideration should be given
to the existing installation from which the new one is fed.?
Charts, diagrams or tables relating to the installation and the results of the general
characteristics.
Should be located in or adjacent to the distribution board
Reference to the electronic door equipment and the PIR which may be sensitive to certain
tests
Maximum demand, earthing systems, overload protection, capacity of consumer unit,
capacity of main protective device, diversity

22) List five areas of inspection that should be undertook before testing
To ensure Safety of person's, livestock and property while testing also
method of fault protection, basic protection, number of circuits, identification of circuits,
methods of isolation, suitability of enclosures, cable selection, fire protection,
23) The electronic door/sensor/motor is wired on its own radial circuit.
List ALL the component parts of the earth fault current loop path associated with
this circuit in the event of a fault to earth
If the maximum value of Earth Loop Impedance for this circuit is 2.4Ω and an earth
fault causes a current of 120A show by calculation if this value will disconnect the
circuit in the required time.

You can then list the path looking at both diagrams
Point of fault
The Circuit Protective Conductor (CPC)
Steel wire armour of the garage supply
Main earthing terminal
Earthing conductor
The metallic return path of the supply cable
The transformer Star point
The transformer winding
Line conductor
Point of fault
We need to use ohms law for the second part, given that the supply is a standard 230 volt
and the current is 120A. Resistance = Volts / Current . 230V / 120A = 1.92 Ω
The maximum allowable is 2.4Ω as we have calculated ours as 1.92 Ω the circuit will
disconnect within the time limitations.
24) The test results shown below were obtained from a ring final circuit continuity
test. State whether the readings for each socket are satisfactory or not satisfactory
giving reasons for those readings deemed to be unsatisfactory. The line, neutral
and the circuit protective conductors have loop test results of 0.5Ω
Socket Line to Neutral Line to CPC
A 0.25 0.26
B NO READING 0.25
C 0.35 0.24
D 0.24 NO READING
E 0.26 0.26
Socket A is ok readings are half of the loop test result of 0.5Ω
Socket B Cross polarity between Line and CP conductor or twisted neutrals not in terminal
Socket C Loose Neutral connection.
Socket D Cross polarity between Line and N conductor or twisted CPC not in terminal
Socket E is ok readings are half of the loop test result of 0.5Ω
25) Describe in detail how you would carry out an insulation resistance test on this
installation.

Inform people or warn that a test is about to take place which may introduce dangerous
voltages and that in the case of a periodic inspection the circuit will be isolated.
Ensure during visual inspection that no damage will occur to People, Livestock or
Property.
Check meters and leads confirm to GS38.
Check meter operation against a known source.
Isolate supply and lockout and place isolation notice on isolator
Confirm isolation using voltage meter.
Remove sensitive equipment from the circuit to be tested, e.g dimmer switches, electronic
devices etc.
Ensure switched are in the on position to ensure all circuits are tested.
The meter to be used is an insulation resistance meter set to 500 volts.
With the main isolator off but all fuses and MCB's switched on, test between the Neutral
and Line conductors at the distribution board
Now connect the line and neutral conductor together and test between them and the
Circuit protective conductor.
26) The test result indicates an overall value of 1.75 MΩ. State with reasons, what
actions if any should be taken.
Because the value is below the 2MΩ limit any circuits tested together must be separated
and re tested to eliminate any latent defects that may exist
27) A loop impedance test on the lighting circuit cannot be carried out because the
6A MCB is tripping under the test voltage, why?
The Earth loop impedance tester uses high current for a short length of time which in
some circumstances can trip low rated MCB out on overload.
28) How can this be overcome?
The value must be calculated by measuring the R1+R2 value and adding this value to the
measured value of Ze
Zs = Ze + (R1+R2)
29) State THREE circumstances that would require a periodic inspection and test to
be carried out on an installation.
Change of use of premises, change of occupation, reason to believe damage has
occurred, loading on installation increased or alterations or additions have occurred to
system, frequency of inspection has based the maximum required time

30) There are various documents that are relevant to the Inspection and Testing of
an installation. State a) one statutory item of documentation b) two non-statutory
items of documentation.
Statutory
Electricity at Work regulations1989,
Non statutory
IEE Wiring regulations BS 7671,
Guidance Note 3
GS38 or The IEE Onsite Guide
31) A Electrical Installation Certificate should be accompanied by signed
documentation regarding thee stages of an installation. Identify
TW0 of these stages
The status of the person signing.
Design, construction or inspection and test ,
Competent person
32) List THREE areas other than wear and tear and ageing that should be
considered when carrying out a periodic inspection and test of an insulation.
Conductor correctly connected and no signs of damage, methods of protection against
basic and fault protection are intact, ID of circuits and isolators no damage by heat
33) BS 7671 gives a list of 18 items to be checked, where relevant, during an initial
inspection. List THREE of these.
Ensure no damage will occur to People, Livestock or Property during visual inspection,
methods of basic and fault protection, correct cable sizing, correct protection against
spread of fire, cable selection correct, routing of cable correct.
34) State the electrical units in which EACH of the following test results would be
expressed.
a) Insulation resistance.
b) loop impedance.
c) Tripping time of an RCD
Megohm (MΩ)
Ohm's (Ω)
Milli-seconds (mS)

35) Identify the type of circuit that would require the following applied voltages
when conducting an insulation resistance test.
a) 250v
b) 500v
c 1000v
a SELV or PELV
b Systems upto and including 500v
c Systems over 500v but under 1000v
36) List the first three tests that should be carried out during periodic inspection
and test of an installation.
Continuity of protective conductors, continuity of bonding conductors, continuity of ring
circuit, insulation resistance
37) Name the protective conductors that connect together the following.
a) An electrically heated towel rail and exposed metal pipework in a bathroom.
b) The earthing terminal of a socket outlet and the main earthing terminal.
c) Mains Gas and Water services to the main earthing terminal.
Supplementary protective bonding conductor
Circuit protective conductor
Main protective bonding conductor
38) State the essential action to be taken before disconnecting a main protective
bonding conductor for test purposes during a periodic inspection and test and
danger that would arise if this action is not taken.
Persons affected should be informed. Supply should be isolated if not fault protection is
compromised which could but people livestock or property in danger. Consideration should
also be taken with regard to potentially dangerous test voltages which may be present
during testing
39) State the
a) Equipment required to conduct a ring final circuit continuity test b) other test that
is automatically completed when the test in a) is carried out c) significance of the
reading obtained between Line conductor and CPC at each socket outlet.
Low ohm meter, polarity checks, Circuit R1+R2 value

40 In the test required to verify the electrical separation of a SELV circuit
a) instrument to be used
b) test voltage to be applied.
Insulation resistance meter,
250v
41) With regards to polarity testing of an installation, state a) the instrument to be
used b) in which conductor all single pole devices should be connected c) to which
part of an Edison screw landholder the neutral conductor should be connected.
Low Ω meter for dead tests and a dedicated test lamps or volt meter both compliant to the
GS38 specification,
Line conductor,
Screw or outer part.

42) The diagram below shows the layout of the electrical installation in a detached
garage. The owners have, for some time been using it for a business venture
repairing lawnmowers, electric and petrol driven. Heating is provided by two 2 kW
convector heaters plugged in when needed. The three Way metal clad consumer
unit houses a double pole main switch and BS 1871 type 2 M.C.B.'s. All surface
wiring is multicore PVC. non-armoured cable clipped direct, and all socket outlets
(these have been raised from their original position to bench level) and lighting
switches are made from moulded plastic.
43) State the a) documentation and information it would be useful to have regarding
this installation b) action to be taken if such documentation is unavailable c)
documentation that will need to be completed for this inspection and test d) test
equipment needed.
Any diagrams charts or tables, Periodic inspection report, schedule of inspections
schedule of test results,
An exploratory investigation would be undertook,

A Low ohm meter, insulation resistance meter, earth loop impedance meter, dedicated test
lamps or voltmeter to GS38 specifications
44 ) State THREE general causes for concern regarding the use of this installation
that would be revealed during a visual inspection.
Briefly explain the reasons for EACH of the concerns listed and for each one
suggest a possible solution.
Lack of RCD protection for use of hand tools, increases shock risk, could rectify by fitting a
30mA RCD.
Mechanical protection on surface mounted cables, again increases risk of shock by
inadequate mechanical protection of a live part, could rectify by installing trunking or
conduit.
Two 2kw heaters if both on equate to 4kw / 240v = 16.6 amps usage, if other appliances
are been used then the ring is close to an overload condition. Install new fixed circuits for
heating.
Mechanical protection for switches and sockets being plastic could be improved. Increases
risk of shock by inadequate mechanical protection of a live part, could rectify by installing
metal clad switches and sockets.
45) Why is it necessary to carry out a ring circuit continuity test in this garage
installation? Describe how the test in a) should be carried out. Indicate the
instrumentation to be used. Which of the test results would be recorded on the test
schedule?
To ensure ring continuity and the existence of no interlinks, loose connections or identify
spurs.
Ensure during visual inspection that no damage will occur to People, Livestock or
Property.
Check meters and leads .
Check meter operation against a known source.
Isolate supply and lockout and place isolation notice on isolator
Confirm isolation using voltage meter that confirms to GS38
Remove the ring circuit ends from the terminals
End to End resistance test are carried out at the ends of each of the ring circuits
Line conductor 1 to Line conductor 2
Neutral conductor 1 to Neutral conductor 2
Circuit Protective conductor 1 to Circuit Protective conductor 2

Line conductor 1 is now connected to Neutral conductor 2
Line conductor 2 is now connected to Neutral conductor 1
Resistance readings are taken at each socket between the Line and Neutral sockets,
these readings should be equal to each other and around half the end to end resistance
figures
The test is repeated using the CPC conductor rather than the Neutral conductor.
Line conductor 1 is now connected to CPC conductor 2
Line conductor 2 is now connected to CPC conductor 1
Resistance readings are taken at each socket between the Line and CPC sockets, these
readings should be equal to each other and around half the end to end resistance figures.
Instrument used was a low ohm meter 4-24v and generating 200mA .
This final test gives us our R1 and R2 values and can be entered in our Schedule of Test
Results and if the results are as required the tick for Ring circuit Ok can be ticked
46) State pre-test precaution before insulation resistance test undertook
insure no danger to persons livestock or property. Isolate supply, insure fuses in place and
switches and are in the on position, remove any lamps, capacitors in circuit. Remove any
sensitive equipment from circuit.
47) Test voltage to be used is 500 volts and minimum expected value would be 1 MΩ for
individual circuits or 2 MΩ for complete circuit
48) Individual circuits give readings of 80M ohm 60M ohm and 30M ohm what is
expected overall resistance. We need to consider that the circuits will be in parallel
with each other when connected to the supply
1 + 1 + 1 = 0.0625 1 = 16M ohm
80 60 30 0.0625
1/80 = 0.0125
1/60 = 0.0166
1/30 = 0.0333
0.0125 + 0.0166 + 0.0333 = 0.0625
1/ 0.625 = 16 which equates to 16 MΩ

49)An inspection is required of a change in builder owner ship. State the
Type of inspection required?
Documentation that will need to be completed?
Periodic inspection report
Periodic inspection report, Schedule of test results, Schedule of inspection.
50) State the three items of technical information that must be recorded on the
Schedule of Test Results, and relate to the incoming supply to the installation.
Type of supply TNC, TT TNC-S
Ze at origin
Prospective Fault Current
51) State with who should the extent and limitations of the inspection and test
should be agreed with?
The person ordering the work.
52) Where should this be recorded?
On the Periodic Inspection Report under the Extent and limitations of the Inspection.
The name of the person ordering the work should be entered in the deceleration section
under the For and behalf of section.

2391 questions sample 5

Sample questions
1) Indicate three main items for which you would require relevant information about
in order to undertake an initial inspection on a new installation.
2) State relevant documentation that relate to the inspection and test of a system
Name one statutory and two non statutory.
3) An Electrical Installation Certificate and a Periodic Inspection Report should be
accompanied by two other documents what are they?
4) State three areas of inspection you would check when carrying out a periodic
inspection.

5) State three human senses used when carrying out a Periodic Inspection Report
6) List the instruments which provided the measurements 20 Megohms, 8KA and
22mS.
7) Insulation resistance testing requires different test voltages for certain circuits,
identify what circuits require the following voltages 250v, 500v and 1000v.
8) State the first three tests that should be taken during the initial verification of a
new installation.
9) The test for continuity of the CPC in a radial circuit with one socket requires a
link and a Milli-ohmmeter state: were link is connected, where the meter is
connected, what the meter reading represents.

10) State three different protective conductors that need to be connected to the
main earth terminal.
11) The following results were obtained during the initial test on a healthy ring
circuit.
P1 > P2 = 0.8 ohms
N1 > N2 = 0.8 ohms
CPC1 > CPC2 = 0.8 ohms
What readings would you expect after cross connection
Between Line and neutral at each socket?
Between Line and CPC at each socket?
What does the Line and CPC represent? The following results
12) State the effect on, Conductor resistance when cable length increases.
Conductor resistance when CSA increases. Insulation resistance when cable length
increases.
13) State three precautions to be taken before an insulation resistance test on a
circuit.

14) An enclosure has been fabricated on site state the minimum IP rating, it is not
affected by liquids.
15) State the protection offered by the following IP ratings IP4X, IPX8, IPXXB.
16) State three reasons for conducting polarity checks on a circuit.
17) ID earthing system that is connected with overhead cables, a multi core supply
cable with separate earth and neutral, supply in which earth and neutral are
performed in one conductor.
18) State three location were there are additional requirements for an electrical
installation
19) From the formula Zs = Ze+(R 1 + R 2 ) x 1.2 x L state what is Ze, R2 and 1.2
1000

20) State three functional test to be carried out on an installation.
21) Carry out initial verification of the installation.
a. what information/documentation is required
b. were should it be found
c. what particular uncommon details should be recorded on this installation.
d. what consideration should be given to the existing installation from which the new one
is fed.

22) List five areas of inspection that should be undertook before testing
23) The electronic door/sensor/motor is wired on its own radial circuit.
List ALL the component parts of the earth fault current loop path associated with
this circuit in the event of a fault to earth
If the maximum value of Earth Loop Impedance for this circuit is 2.4Ω and an earth
fault causes a current of 120A show by calculation if this value will disconnect the
circuit in the required time.
In questions like this please consider a diagram to help explain to the examiner and
to help you recognise any areas you may have missed.

24) The test results shown below were obtained from a ring final circuit continuity
test. State whether the readings for each socket are satisfactory or not satisfactory
giving reasons for those readings deemed to be unsatisfactory. The line, neutral
and the circuit protective conductors have loop test results of 0.5Ω
Socket Line to Neutral Line to CPC
A 0.25 0.26
B NO READING 0.25
C 0.35 0.24
D 0.24 NO READING
E 0.26 0.26
25) Describe in detail how you would carry out an insulation resistance test on this
installation.
26) The test result indicates an overall value of 1.75 MΩ. State with reasons, what
actions if any should be taken.
27) A loop impedance test on the lighting circuit cannot be carried out because the
6A MCB is tripping under the test voltage, why?
28) How can this be overcome?
29) State THREE circumstances that would require a periodic inspection and test to
be carried out on an installation.

30) There are various documents that are relevant to the Inspection and Testing of
an installation. State a) one statutory item of documentation b) two non-statutory
items of documentation.
31) A Electrical Installation Certificate should be accompanied by signed
documentation regarding thee stages of an installation. Identify
TW0 of these stages
The status of the person signing.
32) List THREE areas other than wear and tear and ageing that should be
considered when carrying out a periodic inspection and test of an insulation.
33) BS 7671 gives a list of 18 items to be checked, where relevant, during an initial
inspection. List THREE of these.
34) State the electrical units in which EACH of the following test results would be
expressed.

35) Identify the type of circuit that would require the following applied voltages
when conducting an insulation resistance test.
a) 250v
b) 500v
c 1000v
36) List the first three tests that should be carried out during periodic inspection
and test of an installation.
37) Name the protective conductors that connect together the following.
a) An electrically heated towel rail and exposed metal pipework in a bathroom.
b) The earthing terminal of a socket outlet and the main earthing terminal.
c) Mains Gas and Water services to the main earthing terminal.
38) State the essential action to be taken before disconnecting a main protective
bonding conductor for test purposes during a periodic inspection and test and
danger that would arise if this action is not taken.
39) State the
a) Equipment required to conduct a ring final circuit continuity test b) other test that
is automatically completed when the test in a) is carried out c) significance of the
reading obtained between Line conductor and CPC at each socket outlet.

40 In the test required to verify the electrical separation of a SELV circuit
a) instrument to be used
b) test voltage to be applied.
41) With regards to polarity testing of an installation, state a) the instrument to be
used b) in which conductor all single pole devices should be connected c) to which
part of an Edison screw landholder the neutral conductor should be connected.

42) The diagram below shows the layout of the electrical installation in a detached
garage. The owners have, for some time been using it for a business venture
repairing lawnmowers, electric and petrol driven. Heating is provided by two 2 kW
convector heaters plugged in when needed. The three Way metal clad consumer
unit houses a double pole main switch and BS 1871 type 2 M.C.B.'s. All surface
wiring is multicore PVC. non-armoured cable clipped direct, and all socket outlets
(these have been raised from their original position to bench level) and lighting
switches are made from moulded plastic.
43) State the a) documentation and information it would be useful to have regarding
this installation b) action to be taken if such documentation is unavailable c)
documentation that will need to be completed for this inspection and test d) test
equipment needed.

44 ) State THREE general causes for concern regarding the use of this installation
that would be revealed during a visual inspection.
Briefly explain the reasons for EACH of the concerns listed and for each one
suggest a possible solution.
45) Why is it necessary to carry out a ring circuit continuity test in this garage
installation? Describe how the test in a) should be carried out. Indicate the
instrumentation to be used. Which of the test results would be recorded on the test
schedule?

46) State pre-test precaution before insulation resistance test undertook
47) Test voltage to be used
48) Individual circuits give readings of 80M ohm 60M ohm and 30M ohm what is
expected overall resistance. We need to consider that the circuits will be in parallel
with each other when connected to the supply.

49)An inspection is required of a change in builder owner ship. State the
Type of inspection required?
Documentation that will need to be completed?
50) State the three items of technical information that must be recorded on the
Schedule of Test Results, and relate to the incoming supply to the installation.
51) State with who should the extent and limitations of the inspection and test
should be agreed with?
52) Where should this be recorded?

2391 questions sample 4

City and Guilds 2391 Sample Paper D
Page 1 of 5
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 An installation has been seriously overloaded and needs investigation.
State the
a) type of inspection and test that would be required (1 mark)
b) certificate that will need to be completed (1 mark)
c) documentation that must accompany the certificate in b) (1 mark)
2 State the
a) statutory document that is relevant to electrical systems (1 mark)
b) non-statutory document that details the use of electrical test
equipment
(1 mark)
c) non-statutory document that sets out the requirements for electrical
installations
(1 mark)
3 State who
a) should decide when the first periodic test on an installation should be
carried out
(1 mark)
b) should decide when further periodic tests on an installation should be
carried out
(1 mark)
c) the extent and limitations of a periodic inspection and test should be
agreed with.
(1 mark)
4 State the form of shock protection offered by the following
a) placing out of reach (1 mark)
b) EEBADS (1 mark)
c) class II equipment (1 mark)
5 State the instruments required for the following tests
a) continuity of ring final circuit conductors (1 mark)
b) insulation resistance (1 mark)
c) live polarity (1 mark)
City and Guilds 2391 Sample Paper D
Page 2 of 5
6 State, apart from loose connections, three circumstances that would result
in an increase in conductor resistance
(3 marks)
7 The c.p.c. continuity of a radial circuit comprising four socket outlets is to
be tested. If the test method uses a temporary link between phase and
earth in the distribution board, state
a) at which points in the circuit the test should be conducted (1 mark)
b) the conductors between which the test should be made (1 mark)
c) the significance of the reading at the farthest point (1 mark)
8 State THREE wiring systems that would not normally require a separate
thermoplastic (p.v.c.) insulated conductor as a CPC
(3 marks)
9 For a ring final circuit, state
a) why the test between P and N is conducted (1 mark)
b) the reason why phase to neutral readings at each socket would
increase towards the mid point of the ring then decrease again
(1 mark)
c) the other test that is automatically conducted (1 mark)
10 For the insulation resistance test on a 230 V installation, state the
a) test voltage to be applied (1 mark)
b) minimum value of resistance acceptable (1 mark)
c) value below which further investigation is required (1 mark)
11 The insulation resistance of 600 V discharge lighting installation is to be
tested, state the
a) test instrument to be used (1 mark)
b) test voltage to be applied (1 mark)
c) minimum value of insulation resistance (1 mark)
12 For an installation in a bathroom, state the
a) type of socket outlet permitted, excluding shaver sockets (1 mark)
b) location of zone 0 (1 mark)
c) rating of an r.c.d. protecting an item of equipment in zone 1 (1 mark)
13 To what IP codes should the following comply?
a) Accessible horizontal top surfaces of enclosures. (1 mark)
b) An intermediate barrier inside an enclosure (2 marks)
City and Guilds 2391 Sample Paper D
Page 3 of 5
14 For the testing of polarity, state why
a) single pole devices should be in the phase conductor only (1 mark)
b) certain modern E14 and E27 lamholders do not require testing (1 mark)
c) a live polarity test is required (1 mark)
15 The total loop impedance of a circuit may be calculated using the following
fomula
1000
( 1+ 2) × ×1.2
Zs = Ze + R R L
a) Ze (1 mark)
b) R2 (1 mark)
c) 1.2 (1 mark)
16 State the
a) important check to be made regarding equipotential bonding carrying
out a loop impedance test on a circuit
(1 mark)
b) action to be taken regarding the earthing conductor prior to
conducting an external loop impedance test
(1 mark)
c) precaution that should be taken before conduction the test in b). (1 mark)
17 A test is to be conducted on a lighting conductor earth electrode. State the
a) instrument to be used (1 mark)
b) other two electrodes used in the test (2 marks)
18 State three circumstances under which an r.c.d. having an operating
current of 30 mA, or less, must be used in an installation
(3 marks)
19 State
a) why a test on an r.c.d. must not be conducted before a loop impedance
test
(1 mark)
b) the reason for a functional test on an r.c.d. (1 mark)
c) the maximum test current that needs to be applied to a 100mA r.c.d. (1 mark)
20 A single-phase T.N.C-S installation has a measured value of external loop
impedance of 0.015 ohms. Show by calculation the expected value of the
prospective fault current.
(3 marks)
City and Guilds 2391 Sample Paper D
Page 4 of 5
Section B Questions 21 to 26 refer to the following scenario. Answer ALL SIX questions. All questions
carry equal marks.
A 15-year-old dry-powder coating factory is situated adjacent to an 11kV/415/240V Regional Electricity
Company substation. The earthing system is T.N-C-S with an external earth fault loop impedance (Ze) of
0.012Ω and a prospective fault current of 20 kA.
The dry-powder coating process involves cleaning metallic components in an acid bath, washing off with water
sprays, drying with hot air blowers, spraying with electrostatically charged powder and finally baking in a
tunnel oven.
The existing installation, which are all radial circuits, is wired with (p.v.c.) conductors in metal conduit and
trunking. Six new lighting circuits supplying high-bay 300W SON luminaires have been installed using a
similar wiring system to the existing installation. The new circuit breakers are fed from a metal clad
distribution board housing BS EN 60898 circuit breakers.
An inspection and test of the whole installation is to be carried out.
21 State
a) the type/s of overall inspection and test required (4 marks)
b) the certification/documentation that needs to be completed by the
inspector
(4 marks)
c) who should receive the originals of these documents (1 mark)
d) who decides when the first periodic test should be conducted on the
new lighting
(1 mark)
e) One statutory and two non-statutory documents relevant to this
inspection and testing process
(3 marks)
f) the status of the inspector (2 marks)
22 State
a) apart from wear, tear and safety, five installation conditions that
would need to be considered during the inspection process
(5 marks)
b) Five items from the BS 7671 schedule of inspections that would need
to be considered
(5 marks)
c) Three human senses that would be used in the inspection process (3 marks)
d) with whom the extent and limitations of an inspection should be
agreed
(2 marks)
23 List
a) the first four relevant tests, in sequence, to be conducted on the new
lighting installation
(7 marks)
b) All relevant test equipment needed for a) (8 marks)
24 a) Describe how an Insulation Resistance test would be carried out on the
new lighting circuits
(5 marks)
b) If an Insulation Resistance test between live conductors and earth on
the whole installation resulted in a test value of 1.6Ω, explain, giving
reasons, any actions to be taken.
(3 marks)
City and Guilds 2391 Sample Paper D
Page 5 of 5
c) Describe how an external loop impedance test should be conducted. (4 marks)
d) Describe how a prospective fault current test should be conducted at
the origin of the installation
(3 marks)
25 The Maximum and measured values of loop impedance for four circuits are
as follows
Max values Measured values
3.43Ω 2.7Ω
2.29Ω 1.7Ω
2.4Ω 1.9Ω
3.75Ω 3.2Ω
a) Explain the reasons for the use of the ‘rule of thumb’ (3 marks)
b) Using the above method, determine if the measured values are
acceptable. (Show all calculations).
(4 marks)
c) For any circuit that fails to comply, indicate two methods of
overcoming the problem.
(6 marks)
26 a) Draw a labeled diagram of the earth fault loop path for any circuit in
the installation.
(8 marks)
b) Explain why it would be appropriate to use BS 3036 fuses in a
distribution board at the origin of this installation
(4 marks)
c) Most standard PSCC testers are designed for single-phase use. How
could an appropriate value of short circuit current between phases be
determined?
(3 marks)

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