Free mock exam
Protection & Devices — 18th Edition (BS 7671) Practice
Free topic-focused mock exam: 30 random questions from a pool of 35 on Protection & Devices, drawn from the wider 18th Edition (BS 7671) bank. 60-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.
- Questions
- 30
- Time limit
- 60 min
- Pass mark
- 70% · 21/30
- Question bank
- 35
Free, no sign-up. Retake as many times as you like — different questions each time.
Sample questions
01Which regulation requires that circuits supplying portable outdoor equipment be RCD protected?
- ARegulation 643.1
- BRegulation 521.8
- CRegulation 314.1
- DRegulation 411.3.3
Why: Regulation 411.3.3 mandates RCD protection for circuits supplying portable outdoor equipment.
02What is the acceptable maximum disconnection time for a 30mA RCD on a TT system?
- A200 milliseconds
- B40 milliseconds
- C300 milliseconds
- D5 seconds
Why: For a TT final circuit up to 32 A at 230 V, Table 41.1 sets a maximum disconnection time of 0.2 s, and Reg 411.5.3 requires the RCD to achieve it. 300 ms is the verification criterion for an RCD tested at IΔn (NOTE to Reg 643.8), not the circuit's maximum disconnection time.
03How does BS 7671:2018+A4:2026 require the effectiveness of a 30mA RCD to be verified?
- ATests at ½x, 1x and 5x IΔn on both half-cycles only
- BThe integral test button pressed once only
- CA test at 5x IΔn on each half-cycle only
- DA single AC test at IΔn, whatever the RCD type
Why: Amendment 2 (2022) deleted Table 3A (time/current performance criteria for RCDs) from Appendix 3. Regulation 643.8 now calls for a single alternating current test at the rated residual operating current, IΔn, regardless of RCD type — AC, A, F or B. A general non-delay device must operate within 300ms. The 5x IΔn test still has a place in fault-finding, but it is no longer part of the required verification.
Common questions
Is the Protection & Devices mock exam free?
Yes, it is free with no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.
Can I retake the mock exam?
Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.
Does this count as a qualification?
No. This is independent practice material and does not award a qualification, card or certificate. Where a subject has a formal qualification or card, you gain it through an approved provider.