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.
Safety first
An RCD that won't trip on test may not protect against a real earth fault — a serious safety issue. Treat the protection as not functioning and prioritise correcting it.
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.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
Faulty / seized RCD mechanism
Most likelyThe RCD's internal trip mechanism has failed or seized and won't operate.
- 2
No supply through the RCD
#2The test button needs the RCD energised; if there's no supply through it, the test does nothing.
- 3
Wiring fault (test circuit needs correct supply/neutral)
#3The test function relies on correct line/neutral connection; a wiring fault can stop the test working.
- 4
End-of-life RCD
Least likelyRCDs age; an old one can stop responding to its own test.
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.
Confirm the RCD is energised (supply present through it) before relying on the test.
RCD energised with supply through it.
Energised but test fails — strongly suspect a faulty RCD.
No supply — restore it, then re-test.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Test button won't trip RCD
→ step 2 - 2decision
Is the RCD actually energised (supply through it)?
Yes→ step 3No→ step 4 - 3decision
Is the line/neutral wiring through the RCD correct?
Yes→ step 5No→ step 6 - 4result
Restore supply through the RCD, then re-test.
- 5result
RCD won't trip on test — replace it (safety priority).
- 6result
Wiring fault disabling the test — correct it, then re-test.
Common mistakes apprentices make
- Ignoring a failed test button result — it's a real safety flag.
- Testing an RCD that isn't actually energised.
- Overlooking a neutral wiring fault that disables the test.
- Leaving an end-of-life RCD in service.
When to stop & escalate
An RCD that fails its own test should be treated as not providing protection — correct or replace it promptly per the wiring rules, and verify operation after. This is a safety priority.
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.
Related faults
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.
RCD won't reset at all
The RCD won't stay reset — the toggle won't latch up, or it trips instantly every time, so the circuit can't be restored.
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.
Learn the theory
How the gear and circuits behind this fault actually work.