Why must dead tests be carried out with the installation isolated?

Isolation prevents electric shock to personnel and protects test instruments, which apply their own test voltage, from damage by the supply.

To prevent electric shock and equipment damage

To allow the cables to cool to ambient temperature

To reduce the prospective fault current at the board

To ensure the RCD does not trip during the test

What is the correct sequence for safe isolation?

Regulation 462.1 requires the means of isolation to allow the full sequence: identify the supply, isolate it, SECURE IT AGAINST RE-CONNECTION, then prove dead. Securing comes BEFORE proving dead — lock off after testing and the circuit can be re-energised in the gap between the two, which is the exact scenario the procedure exists to prevent. The voltage indicator is proved on a known source before AND after the test, so a tester that failed mid-check cannot read as a dead circuit.

Identify, isolate, secure the isolation, then prove dead with a tester proved before and after

Identify, isolate, prove dead, then secure the isolation once the circuit is confirmed dead

Isolate the supply, prove dead, start work, then secure the isolation before leaving site

Prove dead with the tester first, then identify the circuit, isolate it and secure the isolation

When proving dead, the voltage indicator should be tested:

Voltage indicators must be proven on a known live source before and after use.

Free mock exam

Safe Isolation — 18th Edition (BS 7671) Practice

Free topic-focused mock exam: all 10 questions on Safe Isolation, 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: 10
Time limit: 60 min
Pass mark: 70% · 7/10
Question bank: 10

Free, no sign-up. Retake as many times as you like — the questions are reshuffled, with the answer order changed.

Sample questions

01Why must dead tests be carried out with the installation isolated?
- ATo ensure the RCD does not trip during the test
- BTo allow the cables to cool to ambient temperature
- CTo prevent electric shock and equipment damage
- DTo reduce the prospective fault current at the board
Why: Isolation prevents electric shock to personnel and protects test instruments, which apply their own test voltage, from damage by the supply.
02What is the correct sequence for safe isolation?
- AProve dead with the tester first, then identify the circuit, isolate it and secure the isolation
- BIdentify, isolate, prove dead, then secure the isolation once the circuit is confirmed dead
- CIdentify, isolate, secure the isolation, then prove dead with a tester proved before and after
- DIsolate the supply, prove dead, start work, then secure the isolation before leaving site
Why: Regulation 462.1 requires the means of isolation to allow the full sequence: identify the supply, isolate it, SECURE IT AGAINST RE-CONNECTION, then prove dead. Securing comes BEFORE proving dead — lock off after testing and the circuit can be re-energised in the gap between the two, which is the exact scenario the procedure exists to prevent. The voltage indicator is proved on a known source before AND after the test, so a tester that failed mid-check cannot read as a dead circuit.
03When proving dead, the voltage indicator should be tested:
- AOnce immediately before use
- BBefore and after use
- COnce after use only
- DOnly if it appears faulty
Why: Voltage indicators must be proven on a known live source before and after use.

Common questions

Is the Safe Isolation mock exam free?

Yes — 100% free, 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 towards the real qualification?

No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.