My MCB trips randomly with nothing obviously on — how do I find the cause?
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?
3 answers
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. If isolating each circuit doesn't pin it down, Al Ghubaiba's electricians can meter it out properly.
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.
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.
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