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Wednesday, 13 July 2011

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
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
Priority given to
Safety of person's
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

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
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.
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.
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.
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
Circuit Protective Conductor (CPC)
Earthing conductor
Main protective bonding conductor
11) The following results were obtained during the initial test on a healthy ring
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
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
Resistance increases
Resistance decreases
Resistance decreases
13) State three precautions to be taken before an insulation resistance test on a
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
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.
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
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
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
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
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
C 0.35 0.24
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

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
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.
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
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
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,
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
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
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
To ensure ring continuity and the existence of no interlinks, loose connections or identify
Ensure during visual inspection that no damage will occur to People, Livestock or
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
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.

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