Tell the three faults apart
Note which device moved, and when.
- Overload. A breaker trips after seconds or minutes of heavy use — kettle plus heater plus microwave on one circuit — then resets and holds until you switch that load on again. The cure is fewer appliances or an extra circuit, never a bigger breaker (MCB ratings and curves).
- Short circuit. The breaker trips instantly, often with a bang, and trips again the moment you reset it with the faulty appliance connected. Something is damaged: a crushed cable, a dead appliance, a miswired socket.
- Earth leakage. The RCD or RCBO trips while the breakers stay on: current is escaping to earth through insulation, water or a person (what is an RCD).
Find the circuit by halving
- Switch every group breaker off, then switch the RCD on. If it will not hold with everything off, the fault is in the panel or ahead of it — call an electrician.
- Switch the groups back on one at a time; with many groups, switch on half, then halve whichever half trips.
- On the guilty circuit, unplug everything and switch it on. If it holds, plug appliances back one at a time until it trips.
- If nothing plugged in causes it, the fault is in the fixed wiring: a junction box, a damaged cable, a wet fitting.
Leakage that is not a broken appliance
Every switched-mode power supply leaks a little current to earth by design: filters inside computers, TVs, LED drivers and induction hobs each send a fraction of a milliampere down PE. Twenty devices on one RCD, plus long cable runs, can add up to 10-15 mA of normal leakage. A 30 mA RCD may trip from 15 mA upwards, so the group sits on the edge and trips at random, usually when the home is busy.
The fix is to divide the leakage, not to weaken the protection: split the circuits across two RCDs, or give the worst leakers their own RCBO (RCD vs RCBO). Fitting a 100 or 300 mA device instead is no option where people are protected — socket and wet-zone circuits stay at 30 mA (why 30 mA).
Moisture is the other classic: outdoor sockets, garden lighting and unsealed junction boxes trip after rain, then work again once dry. That is a genuine fault — water is inside something that should be sealed, and it comes back.
A repeated trip is information
Never tape, wedge or block a tripping device, and never fit a higher rating to make the problem go away. The device is doing its job; defeating it moves the fault from a dead circuit to a hot cable inside a wall (cable cross-sections).
Call an electrician when a circuit trips instantly with everything unplugged, when you smell burning or see scorched plastic, when the RCD will not reset, when the whole home goes dark instead of one group (selective RCDs), or when trips start with nothing changed (when to call an electrician).