Free mock exam
Common Faults — Level 3 Fault Diagnosis Practice
Free topic-focused mock exam: 30 random questions from a pool of 77 on Common Faults, drawn from the wider Level 3 Fault Diagnosis bank. 35-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
- 35 min
- Pass mark
- 70% · 21/30
- Question bank
- 77
Free, no sign-up. Retake as many times as you like — different questions each time.
Sample questions
01A common cause of RCD nuisance tripping in damp environments is:
- AMoisture causing earth leakage on circuits
- BReversed polarity at the consumer unit
- CA shared neutral between two lighting circuits
- DA break in the line conductor before the load
Why: Moisture on insulation or in equipment reduces insulation resistance, causing earth leakage current that triggers the RCD.
02LED lamps on a dimmed lighting circuit flicker at low brightness only. What is the most likely cause?
- AA high resistance joint in the protective conductor
- BA missing earth connection at the fitting
- CIncompatible dimmer switch or loose connection
- DA neutral borrowed from the adjacent circuit
Why: LED flickering is often caused by incompatible dimmer switches (designed for incandescent) or loose connections causing voltage variation.
03A circuit breaker that trips randomly, especially in warm weather, may have:
- AA fault in the thermal trip mechanism
- BA protective device of too low a breaking capacity
- CA loose neutral bar screw at the consumer unit
- DA complete open circuit in the protective conductor
Why: Thermal trip mechanisms can become sensitive or fail, tripping at lower than rated current, especially when ambient temperature is high.
Common questions
Is the Common Faults 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.