Fridge or cool room keeps tripping the safety switch
The RCD goes out and the fridge (or cool room) is on the circuit — sometimes hours apart, often overnight. Refrigeration has two classic leakage sources with their own timing signatures: the defrost heater and the compressor.
Safety first
The RCD is tripping on real earth leakage — never bypass it or move the fridge to an unprotected circuit as a 'fix'. Unplug before any testing at the appliance, and remember food-spoilage pressure makes people do silly things: don't let it rush the diagnosis.
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
Defrost heater element leaking to earth
Most likelyThe classic. The defrost element only energises during its cycle — every several hours — so the trips look random but are actually periodic. Moisture and element insulation breakdown do the leaking.
- 2
Compressor winding insulation breaking down
#2Leakage that appears at compressor start (often after a door-open/thermostat call). Old or moisture-affected windings leak to the earthed shell.
- 3
Moisture in heaters, harness or terminal box
#3Door-frame (anti-sweat) heaters, drain heaters, and wet terminal areas in cool rooms all give intermittent, humidity-linked leakage.
- 4
Cumulative leakage — the fridge is just the last straw
#4A circuit already near the RCD's threshold from other electronics only trips when the fridge's modest leakage joins in. The fridge gets blamed; the circuit's the story.
- 5
Damaged flex, plug or the socket itself
Least likelySquashed flex behind the fridge, a cooked plug, or a wet outlet — check the cheap stuff.
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 ModeGet the timing: when does it trip? Note the hours between trips for a day or two (the owner's account plus the RCD's state each morning is enough).
A roughly regular interval (defrost cycles commonly run every several hours) or a start-linked pattern (trips as the compressor kicks in).
Regular-interval trips scream defrost heater; start-linked trips point at the compressor.
No pattern at all — treat it as general leakage: test the appliance and the circuit both.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Fridge/cool room trips the RCD
→ step 2 - 2decision
Do the trips land at a roughly regular interval (every several hours)?
Yes→ step 3No→ step 4 - 3result
Defrost-cycle signature — test the defrost heater circuit (energised, via leakage clamp).
- 4decision
Does the RCD hold with the fridge unplugged?
Yes→ step 5No→ step 6 - 5decision
Does the appliance IR test low to earth (or leak on a clamp during start/defrost)?
Yes→ step 7No→ step 8 - 6result
Not the fridge — general circuit leakage fault-finding from here.
- 7result
Internal leakage confirmed — appliance/refrigeration tech for the repair.
- 8result
Cumulative leakage — measure standing leakage and split/redistribute the circuit.
Common mistakes apprentices make
- Moving the fridge to a non-RCD circuit to 'stop the nuisance' — that's removing shock protection from a leaking appliance.
- IR-testing cold and declaring the fridge healthy — the defrost element leaks when it's energised.
- Ignoring the trip timing, which practically names the faulty component for you.
- Condemning a healthy fridge on a circuit that was already at the leakage limit.
When to stop & escalate
Internal repairs — defrost element, compressor, refrigerant-adjacent anything — belong with an appliance or refrigeration tech; your job is proving WHERE the leakage lives. Cool room defrost and door-heater faults on three-phase plant may also involve the mechanical contractor. And a genuinely leaky compressor usually means a replacement conversation, not a repair.
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 / 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.
An appliance trips the power the moment it's plugged in or switched on
Plugging in or switching on a particular appliance instantly trips the safety switch or breaker — strongly suggesting an earth fault or short in that appliance.
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.
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.