My MCB trips randomly with nothing obviously on — how do I find the cause?

Question

One breaker trips at seemingly random times — sometimes at night with nothing obvious running. Resetting works until it trips again. How do I actually track down what's causing it?

Bilal H. · Accepted Answer

A trip is the breaker doing its job — three usual causes: overload, short circuit, or earth leakage (the RCD/ELCB type). To find it:

Note which breaker trips and what's on that circuit.
Unplug everything on that circuit, reset, and see if it holds.
Reconnect one appliance at a time, waiting between each. When it trips again, the last thing you plugged in (or its socket) is the fault — common culprits are a water heater, washing machine, or an old fridge leaking to earth.
If it trips with nothing plugged in, the fault is in the wiring/socket itself — stop and get a licensed electrician.

Random night-time trips often point to a thermostatically-controlled load (heater, fridge, AC) switching on — which is why it seems random. Don't just keep resetting an RCD; earth leakage is a shock risk.

Priya N. · Answer

The one-appliance-at-a-time method found ours — an old water dispenser was leaking to earth and tripping the RCD overnight when it heated.

Omar K. · Answer

Chasing one of these random trips is exactly what pushed us to rethink the whole board. Once you've found the culprit, if you're on an old single-RCD board where one earth fault kills half the house at once, it's worth deciding on the protection layout while you're at it. There's a good thread on whether to fit RCBOs on every circuit or stick with one RCD and a bank of MCBs — RCBOs mean only the faulty circuit trips instead of everything going dark together. Wish we'd sorted it sooner.

My MCB trips randomly with nothing obviously on — how do I find the cause?

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