Why is my RCD tripping but my electrician can't find the fault?
Quick answer
An RCD that trips but leaves no traceable fault is almost always caused by intermittent earth leakage — moisture in a cable, a failing appliance, or accumulated leakage current from multiple circuits adding up to the trip threshold. The most common culprit is a faulty appliance plugged in after the last inspection. Unplug everything on the affected circuit and retest. If the RCD holds, reintroduce appliances one at a time. Never bypass or disable an RCD. If the problem continues without a clear cause, request a full insulation resistance test and RCD time-trip test.
🏠Homeowner view
It can be really frustrating when your RCD keeps tripping but your electrician visits and finds nothing wrong. The good news is this is a recognised and very common problem, and there are logical reasons why it happens.
An RCD (Residual Current Device) is the switch in your consumer unit that trips when it detects a small amount of electricity leaking to earth. It is designed to protect you from electric shock. It is extremely sensitive, typically operating at 30 milliamps, which is a very small amount of current.
Why faults can be invisible during a visit
The key word here is intermittent. Some faults only appear when conditions are right. A cable with slightly damaged insulation might only leak current when it is damp, warm, or under load. An ageing appliance might only misbehave after it has been running for 20 minutes. This is why the electrician tests everything, finds nothing wrong, and then the trip happens again the next morning.
Some common reasons the fault hides itself include:
1. Moisture in an outdoor socket, garden cable, or bathroom fitting that dries out before the visit.
2. An appliance such as a washing machine, dishwasher, or electric shower that only develops a fault under heat or load.
3. Accumulated leakage from multiple healthy appliances — each one leaks a tiny amount, and together they nudge the RCD over its threshold.
4. A loose connection that only makes poor contact at certain times.
5. Underground or buried cables that absorb moisture seasonally.
What you can safely do
Before calling your electrician back, try unplugging every appliance on the tripping circuit. If the RCD stops tripping, plug them back in one at a time over a day or two. The one that causes it to trip again is likely your culprit.
Also take note of when the trips happen. Is it always after rain? After the dishwasher runs? In the morning? This pattern is incredibly useful information for your electrician.
What to ask your electrician to do
Ask specifically for an insulation resistance test at 500 volts DC, a full RCD time-trip and ramp test, and a check of accumulated leakage across all circuits. If the installation has not had an Electrical Installation Condition Report (EICR) in the last 5 to 10 years, now is a good time to request one.