What Do Electrician Interviews Actually Test?

Who you're actually talking to

For most contracting jobs, the person across the table is not HR. It's the contracts manager or a senior electrician who has to live with your work on their sites, and who will be the one signing off your certificates if you're not yet qualified to self-certify. On smaller domestic firms it might be the owner, often still an NICEIC or NAPIT-registered contractor themselves, sitting in on their own interview because there's nobody else to do it. Industrial and M&E contractor interviews sometimes add a technical manager who will ask about three-phase distribution, panel work, or SWA termination specifically because that's what their contracts run on.

If the role is through an agency for a subcontract position, the first conversation is often a phone screen about your ECS card grade, your JIB grading if you have one, and whether you hold a current 18th Edition (BS 7671:2018 plus amendments) qualification. That call decides whether you get put forward. The actual interview, when it happens, is shorter and more practical than people expect, because the paperwork has already answered most of the box-ticking questions.

The practical or technical part

Not every interview includes a hands-on test, but a meaningful number do, and it's worth assuming one will. What it looks like depends on the size of the employer.

Smaller contractors often run something informal: a consumer unit or a distribution board in the workshop, and you're asked to demonstrate safe isolation from start to finish. This is not a trick question, it's a filter. They want to see you prove the supply is dead using an approved voltage indicator to GS38, not just flip the breaker and start pulling cores. If you don't mention proving your tester on a known source before and after, that's noticed.

Larger contractors, especially those doing commercial or industrial work, sometimes run a bench exercise close to what you'd see on the AM2 or AM2S: wire a small installation from a drawing, terminate correctly, then be asked to test it. If testing and inspection is part of the job — and for anyone working towards or holding a Level 3 in Inspection and Testing it usually is — expect to be handed a schedule of test results, or blank one, and asked to talk through what you'd record and in what order.

That order matters more than people think. Guidance Note 3 sets a sequence for a reason: continuity of protective conductors and bonding first, then insulation resistance, then polarity, then earth fault loop impedance, then RCD operation, and functional testing last. An interviewer who does testing for a living will notice immediately if you jump straight to Zs without doing insulation resistance first, because doing it out of order can mean you're testing a circuit that isn't actually safe to energise yet.

The questions that are actually checking something

A lot of interview questions sound like small talk but are doing real work. Here's what they're actually testing, and what a shallow answer sounds like.

"Talk me through your safe isolation procedure." This is the single most common competence check in the trade, asked at every level from apprentice to approved electrician, because it's the thing that gets people hurt when it's skipped. A shallow answer says "I switch it off at the board and lock it off." A real answer identifies the correct means of isolation, locks off and tags, proves the tester on a known live source, tests dead, then proves the tester again afterwards. If you leave out proving the tester before and after, someone who does this job will hear the gap immediately.

"What's the maximum Zs you'd expect for a 32A Type B MCB, and does it change on a TN-C-S supply versus TT?" This isn't trivia. It's checking whether you actually understand disconnection times under BS 7671 rather than having memorised a pass/fail number off a test meter. A shallow answer quotes a figure with no context. A real answer explains that the tabulated value already includes the correction factor and that on a TT system you're relying on RCD protection rather than Zs alone, because loop impedance is usually too high for the overcurrent device to clear the fault in time.

"Tell me about a fault you diagnosed that wasn't obvious." This is the one that separates people who fix things from people who replace things until it works. A shallow answer is "there was a loose neutral, I found it and fixed it." A real answer walks through the logic: what the symptom was, what you ruled out and why, what test confirmed it, and — this is the part people skip — why you checked what you checked in that order rather than starting somewhere else. Interviewers who do fault-finding themselves are listening for the reasoning, not the ending.

"A customer asks you to sign off work you didn't inspect properly, or wants you to leave an RCD out to stop nuisance tripping. What do you do?" This tests judgement and whether you understand your own legal position under Part P and BS 7671, not just technical knowledge. A shallow answer is "I'd just do what they want, it's their house." That answer ends interviews at any competent contractor, because it says you'll sign your name to something that could get someone killed, and get the company deregistered with NICEIC or NAPIT in the process. A real answer explains you'd investigate the cause of the tripping rather than remove the protection, and that you wouldn't issue an EIC or minor works certificate for something you hadn't tested properly regardless of who's asking.

"How would you test a ring final circuit?" A shallow answer says "check continuity and insulation resistance." A real answer describes the end-to-end test at the board, then the cross-connection test to confirm there isn't a break in the ring hidden behind correct readings at the socket, because a ring with a break can still show plausible resistance values if you only test superficially.

What separates a real answer from a rehearsed one

The pattern across all of these: shallow answers describe the outcome, real answers describe the sequence and the reasoning behind the sequence. Someone who has actually done the work for a few years talks in terms of what could go wrong if you did it differently — a break in a ring hidden by a false-positive reading, an RCD masking a fault instead of catching it, a Zs reading that looks fine but ignores that the supply type changes what "fine" means. Someone who has crammed the theory but not lived it tends to give you the correct-sounding vocabulary with the steps in a slightly wrong order, or the right steps with no explanation of why they matter.

The other tell is scope. A shallow candidate answers every question at the same level of detail regardless of what's actually being asked. Someone who does this for a living will naturally go deeper on the parts of the question that carry the actual risk — safe isolation, correct test sequence, anything to do with signing a certificate — and stay brief on the parts that don't.

Before you go in

Bring your ECS card, your qualification certificates, and if you hold BS 7671:2018 with the current amendment, say so specifically rather than "I'm up to date on regs." Refresh the GN3 test sequence in your head the night before even if you've done it hundreds of times, because interview nerves are exactly when people start it in the wrong order. If you're weak on Zs values or disconnection times for different supply types and protective devices, that's a half-hour of revision that closes the most common gap in these interviews. And have one fault-finding story ready that you can walk through step by step, not just the ending.

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