Consumer Unit Replacement Flashcards
6 cards from real PART P practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Consumer Unit Replacement flashcards as text
What is a 'BS 1363' socket outlet?
Answer: The British Standard for the standard UK 13 A three-pin socket outlet and plug, used on domestic ring and radial circuits
BS 1363 specifies the 13 A rectangular-pin plug and socket outlet system universally used in the UK; the design with safety shutters in the socket prevents children from inserting objects into live terminals.
What protection must socket outlets in a domestic garage have?
Answer: 30 mA RCD protection — garage socket circuits should be protected by a 30 mA RCD as they supply mobile equipment in a potentially damp location
BS 7671 requires 30 mA RCD protection for socket outlets used to supply mobile equipment outdoors or in locations such as garages where the equipment could be used in damp conditions or taken outside.
What does 'double-pole switching' mean for a main switch?
Answer: Both the live (phase) and neutral conductors are switched simultaneously, fully isolating the installation from the supply
A double-pole main switch disconnects both the phase and neutral conductors simultaneously, providing complete isolation from the supply; single-pole switching (phase only) leaves the neutral connected, which can be hazardous.
What is the purpose of a neutral isolation requirement in some consumer unit configurations?
Answer: To ensure that when maintenance is carried out on a circuit, the neutral is also isolated (preventing shock from the neutral conductor, which may be at a hazardous voltage in some fault conditions)
Although neutral is normally at or near earth potential, in some fault conditions (e.g., broken PEN in PME) the neutral can rise to dangerous voltage; double-pole isolation (at circuit level via RCBOs) ensures complete isolation for maintenance.
What is the maximum number of circuits recommended on a single 30 mA RCD in a domestic split-load consumer unit?
Answer: There is no absolute maximum but typically 6–9 circuits per RCD to limit cumulative leakage and the impact of nuisance tripping
Limiting circuits per RCD reduces cumulative earth leakage (preventing nuisance trips) and limits the number of circuits lost if the RCD does trip; good practice keeps 6–9 circuits per RCD in a typical domestic split-load board.
What is a 'Type A' RCBO and why is it used for EV charging circuits?
Answer: A Type A RCBO detects both AC and pulsating DC residual currents — required for EV charging circuits because onboard chargers produce pulsating DC fault currents that a standard Type AC device would not detect
EV onboard chargers (and other electronic equipment with rectifiers) can produce pulsating DC earth fault currents; a Type AC RCD only detects AC residual currents, so a Type A RCBO (which also detects pulsating DC) is required for EV charge point circuits.