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 must be checked about the existing earthing arrangement before replacing a consumer unit?
Answer: The type of earthing system (TN-S, TN-C-S, TT), the condition and size of the earthing conductor, and compliance with the current requirements of BS 7671
The earthing system type determines permissible protections (e.g., TT requires RCDs); the earthing conductor must be verified as correctly sized and connected; deficiencies must be remedied before the new consumer unit is commissioned.
What is the recommended approach if the existing main bonding conductors are found to be undersized during a CU replacement?
Answer: They should be upgraded to comply with the current requirements of BS 7671 Table 54.8 as part of the consumer unit replacement work
Upgrading undersized bonding conductors to current requirements is best practice and should be recommended or carried out as part of CU replacement; deficiencies that affect safety must be addressed.
After fitting a new consumer unit, which test must be performed to check the consumer unit itself?
Answer: Verification that all connections are secure, correct polarity, insulation resistance of busbars, and functional testing of all protective devices (RCD tests, MCB tests)
After installation, the new consumer unit should be verified: all connections checked for security and polarity, insulation resistance tested, and all RCDs tested for correct operation before the installation is handed back to the occupier.
What is the purpose of the neutral bar in a consumer unit with RCDs?
Answer: In an RCD-equipped consumer unit, each RCD has its own neutral bar for the circuits it protects — neutral conductors must be connected to the correct bar matching their circuit's RCD to ensure correct operation
Correct neutral grouping is critical in split-load RCD consumer units; each circuit's neutral must be connected to the neutral bar associated with its RCD, otherwise the RCD will not sense the correct residual current.
Why is it important to identify all circuit cables before removing the old consumer unit?
Answer: To ensure each circuit is reconnected to the correct protective device in the new consumer unit, maintaining the circuit's labelling and protection level
Correct identification ensures each circuit is reconnected to a protective device of the right type and rating in the new unit, maintaining circuit protection and preventing mis-wiring that could leave circuits unprotected or on incorrect RCDs.
What documentation must be issued upon completion of a consumer unit replacement?
Answer: An Electrical Installation Certificate with Schedule of Inspections and Schedule of Test Results, plus a Building Regulations compliance notification
Consumer unit replacement is notifiable work under Part P, requiring an EIC with full schedules and Building Regulations compliance notification (either self-certified via a Competent Person scheme or through Building Control).