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.
Safety first
An RCD trips because of earth leakage — a real shock risk. Don't defeat it or keep forcing it on. Find the leakage; treat any circuit it protects as potentially faulty.
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
A genuine earth-leakage fault on a connected circuit/appliance
Most likelyDamaged insulation, a faulty heating element, moisture ingress, or a failing appliance is leaking current to earth.
- 2
Accumulated leakage from many devices on one RCD
#2Lots of electronics/filters each contribute a small standing leakage; together they can push a sensitive RCD over its threshold, especially at switch-on.
- 3
A neutral-earth fault or shared/borrowed neutral
#3A neutral touching earth, or neutrals shared between circuits, creates leakage paths that trip the RCD.
- 4
Moisture or water ingress
#4Water in fittings, outdoor sockets, or junctions creates a leakage path that often appears after rain or wash-down.
- 5
Faulty RCD itself
Least likelyLess common, but a worn or faulty RCD can become over-sensitive or nuisance-trip. Prove the leakage is real before blaming the device.
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 ModeNote the pattern: trips instantly on reset, randomly, or only when specific equipment runs? Record what's connected.
A pattern that points at a circuit or appliance (e.g. only trips when the kettle/heater/pump runs).
A clear trigger narrows it to one circuit/appliance — isolate that and confirm.
If it trips with everything off, suspect wiring (neutral-earth) or the RCD itself.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
RCD/RCBO keeps tripping
→ step 2 - 2decision
Does a specific circuit/appliance trigger the trip?
Yes→ step 3No→ step 4 - 3result
Isolate that circuit/appliance and insulation-test it. Repair the leakage.
- 4decision
With all load split off, does it still trip?
Yes→ step 5No→ step 6 - 5decision
Does fixed-wiring insulation test good (no neutral-earth fault)?
Yes→ step 7No→ step 8 - 6result
Likely cumulative leakage — reintroduce loads one at a time; consider splitting across more RCDs.
- 7result
Verify the RCD itself; if it operates out of spec, replace it.
- 8result
Insulation/neutral-earth fault in the wiring — repair and retest.
Common mistakes apprentices make
- Strapping out or replacing the RCD with a non-RCD device to 'fix' the tripping — that removes vital protection.
- Not splitting the load to localise the fault before testing everything at once.
- Forgetting neutral-earth faults and shared neutrals as a leakage source.
- Blaming the RCD before proving the leakage isn't real.
When to stop & escalate
Confirmed insulation faults in fixed wiring should be repaired by a qualified person and the circuit retested. Persistent cumulative-leakage problems may need the installation's RCD arrangement reviewed. Always follow local wiring rules and site procedures — never remove earth-leakage protection as a workaround.
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
Three-phase equipment single-phasing (lost a phase)
Three-phase equipment is misbehaving — motors humming, struggling, overheating, or tripping — because one phase has been lost somewhere between the supply and the load.
Heater bank drawing uneven current across phases
A multi-element heater bank pulls noticeably different current on each phase. Heating is uneven, output is low, or a phase reads much lower than the others.
No control voltage in the panel
Nothing in the control circuit will operate — contactors won't pull in, indicators are dead, the PLC may be off. The control voltage that should be there simply isn't.
Learn the theory
How the gear and circuits behind this fault actually work.
RCD (safety switch)
Detects earth leakage and disconnects fast to protect people from electric shock.
RCBO
Combines an RCD and a circuit breaker in one device — earth-leakage plus overload/short-circuit protection.
Earthing & bonding
Connecting exposed metal to earth so a fault blows protection fast and metalwork can't become live.
How an RCD protects you
An RCD compares current out and back; any imbalance means leakage to earth, so it disconnects fast.