RCD passes test but doesn't trip on a real leakage test
The RCD's own button trips it, but a proper instrument test shows it doesn't trip within the required time/current — so it may not protect adequately in a real fault.
Safety first
An RCD that doesn't trip within spec may not protect people from shock. Treat it as inadequate protection until corrected. RCD instrument testing must follow your procedure.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
RCD aged / mechanism slowing
Most likelyThe RCD has aged and its trip time/current has drifted out of specification.
- 2
Wrong RCD rating/type for the requirement
#2An RCD of the wrong sensitivity or type doesn't meet the protection required.
- 3
Wiring affecting the test
#3Wiring issues (e.g. parallel paths, incorrect connections) affect measured trip performance.
- 4
Test method/setup issue
Least likelyAn incorrect test setup gives misleading results.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeVerify the test setup and that the correct RCD type/rating is being tested to the right criteria.
Correct setup and criteria for the RCD type/rating.
Setup correct — the result reflects the RCD's real performance.
Setup/criteria wrong — correct and re-test.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
RCD out of spec on test
→ step 2 - 2decision
Is the test setup/criteria correct for the RCD?
Yes→ step 3No→ step 4 - 3decision
Is wiring correct with no parallel earth paths?
Yes→ step 5No→ step 6 - 4result
Correct setup/criteria and re-test.
- 5result
RCD genuinely out of spec — replace with a correct device and re-verify.
- 6result
Wiring/parallel-path issue — correct it, then re-test.
Common mistakes apprentices make
- Trusting only the test button and not a proper instrument test.
- Wrong RCD type/rating for the protection required.
- Parallel earth paths skewing the measured trip.
- Leaving an out-of-spec RCD in service.
When to stop & escalate
RCD instrument testing and compliance are governed by the wiring rules and your procedures — an out-of-spec RCD should be replaced and re-verified by a qualified person. This is a safety matter.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
RCD test button doesn't trip the RCD
Pressing the RCD's test button doesn't trip it — a serious sign the RCD may not operate on a real earth fault, even though the circuit is live and working.
RCD / RCBO keeps tripping
An RCD or RCBO trips repeatedly — immediately on reset, randomly during the day, or only when certain equipment runs. The earth-leakage protection is doing its job; something is leaking.
RCBO tripping — telling overload from earth leakage
An RCBO (combined RCD + MCB) keeps tripping and you need to know whether it's tripping on overcurrent/overload or on earth leakage — the fix is very different for each.
Learn the theory
How the gear and circuits behind this fault actually work.