Why is my RCD tripping but the electrician can't find the fault?
Quick answer
An RCD that trips but leaves electricians baffled usually has an intermittent or low-level earth leakage fault — often from ageing appliances, damp wiring, or cumulative leakage across multiple circuits. Ask your electrician to perform a full insulation resistance test on each circuit individually, check every connected appliance, and consider a time-of-day pattern. If it only trips at night or in wet weather, suspect moisture ingress. Do not ignore repeated tripping — it indicates a genuine fault that could cause electric shock or fire.
🏠Homeowner view
Why Your RCD Keeps Tripping But the Electrician Can't Find the Fault
This is one of the most frustrating electrical problems a homeowner faces. Your RCD (Residual Current Device) is doing exactly what it should — detecting a leakage of current to earth — but the fault is either intermittent, very small, or spread across multiple sources, making it hard to pin down during a routine visit.
What an RCD actually does
An RCD monitors the difference between current flowing out through the live wire and returning through the neutral. If more than 30mA escapes (to earth or through a person), it trips instantly to protect you. Something doesn't have to be dramatically wrong for it to trip.
Common reasons it's hard to find
The fault only appears under load or heat — wiring insulation that's fine when cold can break down when warm
Damp or moisture — a wet garden cable, a damp outdoor socket, or condensation in a light fitting can cause leakage that dries out before the electrician arrives
Ageing appliances — washing machines, dishwashers, electric ovens, and immersion heaters develop small earth leakage over time
Cumulative leakage — each appliance on a circuit may pass individual tests, but together they exceed the RCD threshold
Time-of-day patterns — if it trips at night, suspect a storage heater, overnight appliance, or moisture build-up
Faulty RCD itself — RCDs can become oversensitive with age and trip at leakage levels well below 30mA
What you can safely do
Note the pattern — what time does it trip, what's running, what's the weather?
Unplug appliances one by one — if it stops tripping after removing a specific appliance, you've likely found the culprit
Check outdoor sockets and cables for visible damage or waterlogging
Look for recently installed items — a new appliance, extension lead, or DIY wiring job may be the cause
When to call an electrician (again)
If it trips repeatedly and you cannot identify the appliance
If it trips even with everything unplugged (points to fixed wiring fault)
If you notice scorch marks, burning smells, or flickering lights
Ask specifically for an insulation resistance test (IR test) on individual circuits — this is different to a basic visual check and far more likely to find hidden faults.