An RCD that trips at random

A residual current device compares the current going out on a circuit with the current coming back. When some of it leaks away — through damp insulation, a faulty appliance element or a damaged cable — the RCD switches off to protect people from shock. Random tripping usually means the leakage comes and goes: an appliance that only leaks when its heater runs, a cable that only leaks when it is damp, or several small leakages that add up when many things are on at once.

This guide describes what people notice and what is safe to do. It does not diagnose your installation; only someone who has seen it can.

The useful owner checks are about patterns. Does it trip at night when the water heater runs? After rain or irrigation? When the dishwasher reaches its heating stage? Keeping a short log of when it trips and what was running makes the electrician’s testing much quicker, because insulation and leakage tests can then focus on the likeliest circuits and appliances.