Intermittent RCD tripping is one of the most frustrating faults a homeowner can live with, because by the time you have gone out to the board and reset it, everything appears to be working perfectly.
This was a call-out in Milton Keynes to a split-load board protected by two RCDs that was tripping at random times, with no obvious pattern and nothing that reliably reproduced it.
Finding the cause
Rather than guessing, I used an earth leakage clamp meter to measure what was actually flowing. That showed a collective background leakage of 20mA on each RCD, bringing the total system earth leakage to 40mA.
That number explains the whole fault. A standard RCD is designed to trip somewhere between 15mA and 30mA. Every appliance in a house leaks a tiny amount of current to earth by design — the filters in washing machines, dishwashers, computers, TVs and induction hobs all contribute. On a split-load board, everything on one side pools onto a single RCD. At 20mA of standing leakage, that RCD is already sitting most of the way to its trip threshold before anything has happened. A fridge starting up, a shower switching on, a bit of damp in an outdoor circuit — any small surge pushes it over, and the RCD does exactly what it was designed to do.
This is why the fault seems random and why nothing ever looks wrong afterwards. There is no single faulty appliance to find. The leakage is cumulative.
The fix
I upgraded the consumer unit to individual RCBOs on every circuit. An RCBO combines the RCD and the MCB in one device, so each circuit gets its own protection rather than sharing it.
That stopped the leakage pooling, because each circuit’s small amount of leakage is now measured on its own instead of being added together. It also isolated each circuit independently, so a genuine fault on one circuit no longer takes out half the house — a real benefit if a fault develops while you are away, and the freezer is on the same side of the board.
The nuisance tripping was resolved completely, and the installation is now stable and future-proof.
If your RCD trips for no apparent reason, it is worth having the leakage measured rather than living with it. Get in touch with Chilvers Electrical Services, or read more about electrical fault finding.