RCD trips randomly with no obvious pattern
An RCD trips occasionally with nothing obviously changing — not tied to a clear appliance, weather, or time — the frustrating 'tripped again overnight' type.
Safety first
Intermittent earth-leakage is still a shock-risk indicator — don't disable the RCD. Treat any leakage source you find as a real fault.
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
An intermittently-faulty appliance
Most likelyA device that only leaks at certain points in its cycle (heating element, motor) trips the RCD unpredictably.
- 2
Cumulative leakage tipped by a transient
#2Standing leakage near the threshold trips when something switches on (inrush spike).
- 3
Moisture/condensation appearing intermittently
#3Condensation overnight or after weather creates an occasional leakage path.
- 4
Intermittent wiring fault
Least likelyA marginal cable or connection leaks only when disturbed/flexed.
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 ModeLog each trip with time, weather, and what was running/cycling to find any hidden pattern.
A correlation emerges (a cycling appliance, time, weather).
Correlated — target that appliance/condition.
No pattern yet — measure standing leakage and split the load.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
RCD trips randomly
→ step 2 - 2decision
Does logging reveal a correlation (appliance/time/weather)?
Yes→ step 3No→ step 4 - 3result
Target the correlated appliance/condition.
- 4decision
Is standing leakage comfortably below threshold?
Yes→ step 5No→ step 6 - 5decision
Do insulation tests / inspection find an intermittent source?
Yes→ step 7No→ step 8 - 6result
Near threshold — a transient tips it; redistribute circuits.
- 7result
Intermittent leakage source found — repair it.
- 8result
Keep logging to catch the rare event.
Common mistakes apprentices make
- Disabling/swapping the RCD instead of finding the source.
- Not logging conditions to reveal a pattern.
- Ignoring overnight condensation as a cause.
- Testing only when dry/idle and finding nothing.
When to stop & escalate
Genuinely elusive intermittent leakage may need monitoring over time or specialist help. Cumulative-leakage problems may need circuits redistributed — never remove the protection.
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.
Was this guide helpful?
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 nuisance tripping with lots of electronics
An RCD trips intermittently with no single faulty appliance — typically where many electronic devices (with filters/SMPS) share one RCD, each adding a little standing leakage.
Intermittent fault that's hard to reproduce
Something fails occasionally — random trips, dropouts, or stoppages — but works fine when you go to look at it. The classic 'can't fault it on the bench' problem.