Paper 7

Question 1

During a periodic inspection
a, the inspector must ensure the safety of persons. State three practical actions that the inspector can take in order to maintain a safe environment during this process

Answer 1

I. Safely isolate circuits and lock off
II. Inform the people within the building about work being carried out where it might affect their safety, i.e. lifts stop working or lighting going off in areas with no natural light.
III. Post warning signs where necessary, such as trip hazard when using long lead for continuity testing

Question 2

state four items that may be inspected , when considering fault protection provided by ADS

Answer 2

I. Presence of earthing conductor
II. Presence of main protective bonding conductor
III. Presence of overcurrent protective devices
IV. Presence of residual current devices
Or any provision of automatic disconnection of supply

Question 3

state four methods of Basic Protection

Answer 3

Insulation
Barriers or enclosures
Placing out of reach
Limitation of discharge energy

Question 4

identify four situations where additional protection is required

Answer 4

General purpose socket outlets not under the supervision of skilled or instructed persons and not specifically labelled for nominated equipment.

Question 5

State one human sense that would be best used to detect each of the
following conditions and describe how.
A i)	Overloaded electric motor.
A ii)	Loose connection.
A iii)	Suitable cable routing.

Answer 5

i) Smell or touch
ii) Touch
iii) Sight

Question 6

State three areas of inspection that would be specific to an electrical installation within a bathroom. (Not just zone 1, zone 2 & zone 3)

Answer 6

Presence of supplementary bonding
IP rating of equipment and enclosures
presence of RCDs
Or any other relevant point
Zone 0, zone 1 etc not accepted.  Specific item for a relevant zone is ok.

Question 7

C when conducting insulation resistance testing;
State the test voltage and minimum acceptable test values to comply with BS7671 for each of the following circuits,
i) SELV down lighters
ii) FELV motor control
iii) 1600v exterior lighting

Answer 7

i) 250v dc and 0.1 MΩ
ii) 500v dc and 1.0 MΩ
iii) 1000v dc and 1.0MΩ

Question 8

When testing between line and neutral conductors on three individual single-phase circuits. State the circuit conditions that are revealed for each of the following values.
A) 0.00 M.
b) 0.25 M.
c) >500 M.

Answer 8

iv) Short circuit (fail is not acceptable)
v) Something connected (e.g. neon) or damaged insulation
vi) Clear (circuit ok!)

Question 9

State whether the Earthing Conductor should be connected or disconnected from the installation when carrying out the following tests.

i) Earth electrode resistance test.
ii) External earth fault loop impedance test.
iii) Earth fault loop impedance test on a socket-outlet circuit.

Answer 9

i) Disconnected
ii) Disconnected
iii) Connected

Question 10

State the instrument to be selected for each of the following tests.

i) Earth electrode resistance test.
ii) Insulation resistance test on a domestic immersion heater circuit.
iii) Continuity of main protective bonding conductors.

Answer 10

i) Earth electrode resistance tester or EFLI tester
ii) Insulation resistance tester
iii) Low resistance ohmmeter

Question 11

C While verifying the continuity of a ring final circuit as part of an initial verification the measured loop resistance of the line, neutral and circuit protective conductor were 0.9, 0.91 and 1.5 respectively. All sockets are connected directly in the ring. State;

i) The most likely reason for the cpc resistance being greater than the line and neutral resistance.
ii) The expected test value at each socket-outlet when the line and neutral are correctly interconnected at the distribution board
iii) The expected test value at each socket-outlet when the line and cpc are correctly interconnected at the distribution board.
iv) Explain the standard procedure, which confirms correct polarity during a continuity of ring final circuit test.

Answer 11

i) Smaller csa = 1 mark
ii) 0.45 ohms = 1 mark
iii) 0.6 ohms = 1 mark
iv) Following stages 2 and 3 = 3 marks
If candidate states “at the end”, 1 mark only

Question 12

D Guidance Note 3 states that the PFC is to be determined at the origin and at other relevant points in the installation. State

i) Two instances or circumstances where a test at other relevant points would be required
ii) When testing for the PFC what consideration should be taken regarding the earthing conductor?

Answer 12

i) Presence of remote distribution boards etc (1)
and where the protective device’s breaking capacity is less than the devices at the intake (1)
ii) all earthing and bonding must be connected

Question 13

a) List five possible defects which could be identified using your senses, inside the plastic consumer unit

Answer 13

1. Sight; no fly lead/cpc from SWA earth tag to earth bar
2. Touch; loose connections
3. Sight; blanks missing where not all circuit breaker ways have been used
4. Sight; incoming tails reversed
5. Sight; line and neutral conductors not in the same sequence so incorrectly identified
6. Sight; conductors too small for the rating of a protective device
   Any suitable alternatives

Question 14

b) Identify which Code would attributed to each deficiency 1. Sight; no fly lead/cpc from SWA earth tag to earth bar
2. Touch; loose connections
3. Sight; blanks missing where not all circuit breaker ways have been used
4. Sight; incoming tails reversed
5. Sight; line and neutral conductors not in the same sequence so incorrectly identified
6. Sight; conductors too small for the rating of a protective device
Any suitable alternatives

Answer 14

1. C2
2. C2
3. C1
4. C2
5. C3
6. C2

Question 15

Describe how you would prove the continuity of cpc, correct polarity and earth fault loop impedance to the socket outlet feeding the trough water heater without de-energising the whole installation

Answer 15

This is a live test so all earthing and bonding must be in place.
Ze (RA) will already have been measured confirming the existence of the earth.
A plug lead will be used so there will be no exposed live parts
Using an earth fault loop impedance tester, a check will be made before pressing the test button to confirm earth presence and correct polarity
The expected results will be around the same value as Ze (RA) as the R1 + R2 will likely be tiny in comparison
record results as compliant if RA was 100Ω then Zs at this socket is likely to be around 102Ω
Zs would be compliant if it is no more than touch voltage divided by I∆n 50/0.1 = 500Ω
But a figure greater than 3 or 4Ω larger than Ze would imply a problem with R1 + R2

Question 16

Describe how the RCD testing would be carried out including expected results.

Answer 16

SIMER;
This is a live test with the installation energised so;
All earthing and bonding in place
Check with the user it is safe to isolate, as the power will repeatedly go off.
The tests will be undertaken at a socket outlet so there will be no issues with exposed live parts.
The tester lead has a BS1363 plug and will comply with GS38.
The instrument used is an RCD tester, set to 100mA.
Method; Plug RCD tester into a socket outlet; use same measured value for all circuits.
Apply the following tests
0° at ½ times, must not operate for 2000ms
180° at ½ times, must not operate for 2000ms
0° at 1 times, must operate within 300ms (BS EN type)
180° at 1 times, must operate within 300ms
Mechanical test = push button marked “test” or “T” to confirm mechanical operation last.