Practice Test GeeksPart P Electrical Practice Test
← All PART P Flashcard Decks

Circuit Protection 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 Circuit Protection flashcards as text

  1. What is the maximum Zs permitted for a 32 A Type B MCB protecting a socket outlet circuit?

    Answer: 1.44 Ω (as per BS 7671 Table 41.3 for 0.4 s disconnection)

    BS 7671 Table 41.3 specifies maximum Zs values for each protective device type and rating to ensure 0.4 s disconnection on socket circuits; for a 32 A Type B MCB this is 1.44 Ω (at the standard Table temperature).

  2. What is the purpose of a 'neutral link' in a consumer unit?

    Answer: To provide a common connection point for all circuit neutral conductors, connected to the supply neutral

    The neutral link (neutral bar) in a consumer unit connects all circuit neutral conductors to the supply neutral; in single-phase installations it is typically an insulated bar rather than a terminal connected to earth.

  3. In a dual-RCD consumer unit, why might a fault on one circuit cause another unrelated circuit to lose supply?

    Answer: If both circuits are on the same RCD, a fault on one will trip the shared RCD, disconnecting all circuits on that RCD including the unrelated circuit

    In a dual-RCD board, circuits are split into two groups each sharing an RCD; a fault tripping one RCD disconnects all circuits in that group. An RCBO board avoids this by giving each circuit its own individual device.

  4. What is a 'main switch' (isolator) in a consumer unit?

    Answer: A switch that disconnects all circuits from the supply simultaneously for safe maintenance and emergency isolation

    The main switch (main isolator) in a consumer unit provides a means of isolating the entire installation from the supply for safe maintenance; it is separate from individual circuit protective devices.

  5. What test is performed to verify that the main protective bonding conductor is correctly connected and effective?

    Answer: Continuity test using a low-resistance ohmmeter from the main earthing terminal to each bonded service

    A continuity test measures the resistance of the bonding conductor path from the MET to each bonded service; a low resistance confirms the conductor is correctly connected and will conduct fault current effectively.

  6. What is the correct procedure before working on a live circuit in an existing installation?

    Answer: Isolate the circuit at the consumer unit, lock off (or secure) the MCB, prove dead using an approved voltage indicator, and post a notice; only work live if absolutely necessary with written risk assessment and permit to work

    Safe isolation requires switching off, locking off (securing the MCB or removing the fuse), proving dead with an approved voltage indicator, fitting a warning notice, and only re-energising after work is complete and safe.