Choose the instrument for the task, establish a safe test condition and recognise a suspect reading.
A meter reading zero does not mean a circuit is safe to touch. Identify every supply, isolate and secure against reconnection, then prove dead using suitable equipment and the correct procedure. Check the voltage indicator on a proving unit or suitable known source before and after proving dead. A non-contact detector is not a substitute.
Check the whole measuring system
Inspect the instrument, leads, probes and insulation. The measurement category, voltage rating and probe protection must suit the work; a familiar brand does not make damaged leads acceptable. Prefer dead testing wherever it answers the question safely.
For low-resistance measurements, account for lead resistance using the instrument's specified method. Check that moving a lead does not produce erratic readings.
Accuracy is an ongoing check
A calibration certificate records a check at a particular time. Keep instrument identity and routine comparison records so drift or damage can be detected between formal checks.
Decision check: a continuity reading changes sharply whenever one lead moves. Stop and investigate the lead or connection; averaging unstable results does not create a reliable measurement.
GS38 and the right instrument for each test
- HSE's guidance GS38 covers the leads, probes and indicators held near live conductors. Probe tips expose no more than 4 mm of metal, preferably 2 mm or less, to reduce bridging risk. Finger guards and shrouds reduce contact risk. Fusing or current limitation reduces fault energy where required; compliant two-pole detectors may provide the protection internally. These precautions do not make every slip harmless. Look for damaged insulation, check the tip shrouds and hand barriers, and confirm the specified protective arrangement. Take damaged leads or probes out of service rather than taping them.
- An instrument's measurement category and voltage rating must suit the point where it is used, because the expected transient overvoltages depend on the location; an underrated instrument can fail dangerously.
- Prove dead with a dedicated two-pole voltage detector, checked on a proving unit before and after; the proving unit supplies the known voltage for prove-test-prove. A multimeter on the wrong range or function can show dead on a live circuit.
- Before dead testing, consider every source that could backfeed an apparently isolated circuit, and lock off to prevent re-energisation. Work dead unless live testing is justified and controlled.
- Use the relevant parts of BS EN 61557 or equivalent performance, with suitable safety ratings. A continuity tester has a no-load voltage of 4 V to 24 V and a short-circuit current of at least 200 mA. An ordinary multimeter generally lacks that test output; check measurement performance as well. Lead compensation removes the lead contribution, not every contact error.
- Select the appropriate function, whether in a dedicated or multifunction instrument: a low-resistance ohmmeter for continuity, an insulation resistance tester applying the specified DC voltage, a loop impedance tester for Zs on a live circuit, an RCD tester for disconnection times, and an earth electrode tester for a TT electrode. Common installation multifunction testers offer continuity, insulation resistance, loop, RCD and prospective fault current functions. Check the particular model and select the right function; the facilities are not identical on every tester.
- Keep a system for confirming and recording continuing instrument accuracy and consistency, for example using a suitable check box. Choose the check frequency for the instrument’s use, handling, maintenance and previous results; investigate a suspect reading before relying on it. This ongoing system is separate from proving a voltage indicator immediately before and after each proving-dead check.