Part P Earthing & Bonding 3

Question 1

What test is performed to verify the continuity of a circuit protective conductor?

Accepted Answer

R1 + R2 test: measuring the combined resistance of phase and CPC conductors from the consumer unit to the furthest point of the circuit

Answer

The R1 + R2 test connects the phase and CPC at the far end of the circuit and measures their combined resistance from the CU; this confirms the CPC is continuous and correctly sized throughout the circuit.

Question 2

What is the purpose of bonding a TV aerial (coaxial) cable screen to earth?

Accepted Answer

To discharge static and induced voltages on the aerial cable screen, preventing dangerous voltages being introduced into the installation or equipment

Answer

The outer screen of a coaxial aerial cable should be earthed at the point of entry to the building to provide a safe discharge path for lightning-induced surges and static charges, preventing them from reaching equipment.

Question 3

What is the minimum cross-sectional area of a supplementary bonding conductor between two exposed conductive parts?

Accepted Answer

2.5 mm² if mechanically protected, 4 mm² if not mechanically protected

Answer

BS 7671 Regulation 544.2 specifies minimum sizes for supplementary bonding conductors: 2.5 mm² when mechanically protected (e.g., in conduit) and 4 mm² when not protected against mechanical damage.

Question 4

What is a PME (Protective Multiple Earthing) warning label and where is it required?

Accepted Answer

A warning label fixed at the origin of a PME installation advising that additional bonding may be required, as required by the electricity supplier's distribution code

Answer

Where a PME supply is used, the electricity supplier's conditions include a requirement to label the installation at the origin with a PME warning, noting that the neutral is used as the earthing conductor and that disconnection of the PEN conductor would energise metalwork.

Question 5

What risk is associated with using PME earth terminals for caravan or boat hook-up?

Accepted Answer

If the PEN conductor breaks in the supply, the caravan or boat metalwork could rise to near line voltage — PME earth must not be used for caravans, boats or temporarily connected equipment

Answer

A broken PEN conductor (common in ageing networks) would cause any PME-earthed metalwork to rise to dangerous voltages. For this reason, BS 7671 prohibits using a PME terminal as the earth for caravans, boats or temporary structures.

Part P Electrical Practice Test

Part P Electrical Practice Test

Part P Earthing & Bonding 3