8. Inspection & Testing

An insulation resistance test is carried out on a circuit in 2.5/1.5 mm² cable, supplying a heater. If the value of insulation resistance between live conductors is 300 MΩ, the expected value between live and earth would be

• a) 100 MΩ

• b) 300 MΩ

• c) 500 MΩ

• d) 1000 MΩ

Answer explanation

The expected value between live and earth is typically one-third of the insulation resistance between live conductors, so it would be 100 MΩ (300 MΩ / 3 = 100 MΩ). Therefore, the correct choice is a) 100 MΩ.

If the length of a cable is doubled the insulation resistance will

• a) Be doubled

• b) Remain the same

• c) Be halved

• d) Be quartered

Which one of the following tests is carried out to conform that all accessories are correctly connected?

• a) Polarity

• b) RCD function

• c) Phase sequence

• d) Additional Protection

The continuity of circuit protective conductors should be verified and recorded using

• a) A continuity tester

• b) A high resistance ohmmeter

• c) An earth fault impedance tester

• d) A low resistance ohmmeter

A test of insulation resistance on a number of circuits produces the following results: 10 MΩ, 5 MΩ, 4 MΩ and 2 MΩ. The insulation resistance measured at the distribution board, with all the circuits connected in parallel will be

• a) 26 MΩ

• b) 10 MΩ

• c) 5.2 MΩ

• d) 0.8 MΩ

The measurement of conductor resistance would not be affected by the

• a) Thickness of conductor insulation

• b) Conductor temperature

• c) Conductor csa

• d) Conductor length

Which one of the following, for reason of safety, should be verify prior to conducting test of an RCD using an RCD test instrument?

• a) Suitably low earth fault loop impedance

• b) Suitable insulation resistance values

• c) The operation of the RCD integral test button

• d) The prospective fault current at the point where the RCD is fitted

The maximum permitted measured value of Zs for a particular circuit is 1.09 Ω and the measured value of Ze at the origin of the installation is 0.6Ω. Which of the following is the maximum permitted value of R1 + R2 ensure compliance with BS 7671?

• a) 0.19 Ω

• b) 0.49 Ω

• c) 0.84 Ω

• d) 1.03 Ω

If the CSA of a copper conductor is doubled, its resistance will

• Quadruple

• Double

• Stay the same

• Halve

Functional tests are to be carried out on a general purpose RCD using an RCD tester. At which point during the testing process would the effectiveness of the test button on the RCD be checked?

• Before all instrument tests

• Following all instruments tests

• Following the 0.5 × IΔn test but before the 1 × IΔn test

• At no point, as the instrument tests will carry out this function