Mock exams only help if you sit them the way you would sit an open-book test: your own copy of BS 7671 open, one answer per question, and a check against an answer key that tells you where to look when you were wrong. This page gives you five questions from our question bank, which is not on sale, with the answer, the explanation and the where-to-look line for each. Try each one before you open the answer.
For full-length practice, 18th Edition Amendment 4 Exam Practice has three 60-question papers on BS 7671:2018+A4:2026, 180 original questions in all, on Amazon in paperback and Kindle.
Five free questions from our question bank
Treat them as an open-book test: use your own copy of BS 7671:2018+A4:2026. Each question has one correct answer. Find the answer in your copy of the book rather than from memory, then open the answer.
Question 15
Using Zs × Ia ≤ U0 × Cmin, with U0 = 230 V and Cmin = 0.95, the maximum Zs for a 30 mA RCD providing fault protection in a TN system works out at about:
- A. 728 Ω
- B. 7667 Ω
- C. 1667 Ω
- D. 7283 Ω
Answer and explanation
D: 7283 Ω
Zs ≤ (230 × 0.95) / 0.03 = 7283 Ω. Cmin is 0.95 for a supply given under the ESQCR. Leaving out Cmin gives 7667 Ω, using 50 V instead of U0 × Cmin gives 1667 Ω, and using 300 mA instead of 30 mA gives about 728 Ω.
Where to look: BS 7671 Chapter 41 (automatic disconnection, regulation 411.4.4); IET Wiring Matters 105 (May 2025)
Question 18
Before proving an isolated circuit dead, ESF BPG 2 suggests that, where it is possible and safe, you should:
- A. test with the isolating device ON then OFF, to confirm it controls the circuit
- B. disconnect the neutral conductor first, to prevent any back-feed from other circuits
- C. press the RCD test button to confirm the circuit has been made dead
- D. rely on the circuit chart to confirm the correct device has been used
Answer and explanation
A: test with the isolating device ON then OFF, to confirm it controls the circuit
Identifying the correct point of isolation comes first. Testing with the isolator ON, then OFF, shows the circuit is under that device's control. Never assume a circuit is dead because a device is OFF.
Where to look: BS 7671 Chapter 46; ESF BPG 2 issue 4.3, section 5
Question 33
A circuit protective device is missing from a consumer unit and no securely fitted blanking piece is in its place, so live parts are accessible to touch. Using the examples in ESF BPG 4, this is classified as:
- A. C1
- B. FI
- C. C3
- D. C2
Answer and explanation
A: C1
Accessible live parts are a danger now, so BPG 4 gives C1: the person ordering the report must be told immediately and the danger removed or made safe (for example with a temporary barrier) before leaving site.
Where to look: BS 7671 Chapter 65 and Appendix 6 (condition reporting); ESF BPG 4 issue 7.4, section 9
Question 34
A main protective bonding conductor is 4 mm² and shows no signs of thermal damage. Using the examples in ESF BPG 4, this is classified as:
- A. NC only
- B. Obs
- C. C2
- D. C3
Answer and explanation
C: C2
BPG 4 codes a main bonding conductor of less than 6 mm², or one with evidence of thermal damage, as C2. An undersized conductor that is at least 6 mm² with no thermal damage is 'NC only' and need not be recorded on an EICR.
Where to look: BS 7671 Chapter 65 and Appendix 6 (condition reporting); ESF BPG 4 issue 7.4, section 9
Question 57
What happened to Appendix 17 (energy efficiency) in Amendment 4?
- A. It became normative
- B. It moved into Part 7 as Section 717
- C. It was deleted, and energy efficiency moved to new Chapter 81
- D. It was renumbered Appendix 18
Answer and explanation
C: It was deleted, and energy efficiency moved to new Chapter 81
A4 deleted Appendix 17 and introduced Chapter 81. Section 717 is mobile or transportable units.
Where to look: BS 7671 Chapter 81; A4 table of contents
What the answers give you
Each explanation says why the right option is right and, where it helps, why the other options are tempting. Question 15 above is a good example: the explanation shows how each wrong number comes from a common slip. The where-to-look line then tells you the place in BS 7671 or the published guidance to check, so next time you go straight to it.
What is in 18th Edition Amendment 4 Exam Practice
- Three 60-question multiple-choice papers: 180 original questions
- Every paper covers every Part of BS 7671, from scope and definitions to the appendices, in book order
- An explanation for every answer, with a ‘where to look’ reference to the place in BS 7671 and the published source the answer was checked against
- An answer key for each paper; the paperback adds a printed answer sheet after each paper and a score record by topic
The papers are practice in the style of a 60-question multiple-choice open-book test: confirm the current assessment details with your centre. You will need your own copy of BS 7671:2018+A4:2026.
Get the book
18th Edition Amendment 4 Exam Practice is on Amazon in paperback (£14.99) and Kindle (£9.99): three 60-question papers with answers, explanations and where-to-look references.
Kindle edition free to read with Kindle Unlimited.
For more questions with answers, read BS 7671 A4:2026: 10 free practice questions with answers.
Independent publication. Not produced, endorsed or approved by City & Guilds, EAL, the IET or BSI. Not a past paper and contains no assessment questions.
Written by a City & Guilds 2391-51 qualified electrician.