6. Inspection & Testing 2

For a circuit having a R1 + R2 reading 0.37Ω the test instrument and range should be

• An insulation resistance test instrument set to the minimum range

• A low resistance Ohmmeter set to the maximum range

• An insulation resistance test instrument set to the maximum range

• A low resistance Ohmmeter set to the minimum range

Answer explanation

A low resistance Ohmmeter set to the minimum range is the correct choice to measure the combined resistance of R1 + R2 at 0.37Ω.

A 30mA RCD when tested at 150mA, will operate within

• 40ms

• 200ms

• 240ms

• 100ms

Answer explanation

A 30mA RCD will operate within 40ms when tested at 150mA, as it should trip within 1/3 of the rated current, which is 100ms for 30mA.

On a TN-C-S single phase supply, the Ze is measured as 0.5 Ω. What will be the PFC value recorded at the same point?

• 200 A

• 460 A

• 1600 A

• 240 A

Answer explanation

Given Ze = 0.5 Ω, PFC = 230V / 0.5 Ω = 460 A. Therefore, the correct choice is 460 A.

The measured Earth Loop Impedance of a circuit having fault protection by means of a 20A Type C circuit-breaker is 1 Ω. The circuit-breaker has a maximum tabulated earth fault loop impedance of 1.15 Ω. Will the circuit meet the requirements of BS 7671 for disconnection?

• No - fails to meet 0.75 correction factor

• No - Fail to meet 0.8 correction factor

• Yes - meets 0.8 correction factor

• Yes - meets 0.75 correction factor

Answer explanation

The circuit fails to meet the 0.8 correction factor required by BS 7671 due to the measured Earth Loop Impedance being 1 Ω, exceeding the maximum tabulated earth fault loop impedance of 1.15 Ω.

Phase rotation instruments can be of the rotating disc type or

• Buzzer

• Indictor lamp

• Klaxon

• Siren

Answer explanation

Phase rotation instruments can be of the rotating disc type or indicator lamp, making the correct choice indicator lamp.

A Minor Electrical Installation Works Certificate should issue for

• Additions to existing circuits and new single circuits

• Additions or alterations to existing circuits only

• Alterations to existing circuits and new single circuits

• Additions to existing circuits only

Answer explanation

A Minor Electrical Installation Works Certificate should issue for Additions or alterations to existing circuits only.

In what method of earthing is PME used?

• TN-C-S

• TT

• TN-S

• TN-C

Answer explanation

PME (Protective Multiple Earthing) is used in the TN-C-S method of earthing, making TN-C-S the correct choice.

When a cable’s length is reduced, the effect on the insulation resistance will be to

• Increase

• Stay the same

• Fluctuate

• Reduce

Answer explanation

When a cable's length is reduced, the insulation resistance will increase due to less surface area for leakage current, improving the resistance.

Isolating supplies for long periods of time will cause

• Standby batteries to charge

• Lighting conductors to corrode

• Standby batteries to drain

• Cables to overheat

Answer explanation

Isolating supplies for long periods of time will cause standby batteries to drain.

What percentage of the installation’s sockets must be checked for polarity on a periodic inspection?

• 100%

• 25%

• 50%

• 75%

Answer explanation

100% of the installation's sockets must be checked for polarity on a periodic inspection, ensuring thorough examination.