A breaker that trips once and resets is doing its job. A breaker that trips every day, or won’t reset at all, is telling you something is wrong. This guide explains what’s happening, how to narrow down the cause safely, and when to stop and call an electrician.
What is actually tripping?
Open your consumer unit (fuse board) and look at which switch has dropped to the off position. There are usually two kinds:
- An RCD (residual current device), often a wider switch with a “T” test button. It protects people by cutting power when electricity is leaking to earth, for example through damp, a damaged cable or a faulty appliance. One RCD often covers several circuits.
- An MCB (miniature circuit breaker), the narrower switches, one per circuit, labelled things like “sockets downstairs” or “cooker”. An MCB trips when a circuit is overloaded or there’s a short circuit.
Some newer boards use RCBOs, which combine both jobs on a single circuit.
Knowing which one went is the first clue. An RCD trip points towards leakage to earth. An MCB trip points towards too much current on one circuit.
The most common causes
A faulty appliance. This is the cause more often than not. Kettles, washing machines, dishwashers, tumble dryers, immersion heaters, electric showers and outside lights are the usual suspects. Water and heating elements don’t mix well once an element starts to fail.
Too much on one circuit. Running a heater, tumble dryer and oven on the same circuit can overload it. This is more common in older properties with fewer circuits than a modern home needs.
Moisture. Water getting into an outdoor socket, garden lighting, a bathroom fan or a ceiling light under a leak will trip an RCD, often after rain.
Damaged wiring. A nail or screw through a cable, rodent damage in a loft, or old insulation breaking down. This type tends to be intermittent and harder to track down.
An ageing installation. Older boards and wiring are more likely to cause nuisance tripping, and some older boards have no RCD protection at all. If your board is wooden-backed or has rewireable fuses, read our guide to consumer unit replacement.
How to narrow it down safely
You can do these checks without tools and without removing any covers.
- Unplug everything on the affected circuit, or in the whole house if it’s the main RCD that tripped. Switch off fixed appliances like the immersion heater and the electric shower at their isolators.
- Reset the breaker. If it won’t stay on with everything unplugged, the fault is in the fixed wiring or a hard-wired item. Stop there and call an electrician.
- Plug things back in one at a time, waiting a minute or so between each. When the breaker trips again, the last thing you connected is your prime suspect.
- Retest the suspect on a different circuit. If it trips that one too, the appliance is faulty. Stop using it and get it repaired or replaced.
Never hold a breaker in the on position, tape it up or swap it for a bigger one. It’s tripping to protect you from shock or fire.
When to call an electrician straight away
Don’t keep resetting and hoping. Call an electrician if:
- the breaker trips immediately every time you reset it, even with everything unplugged
- you notice a burning smell, scorch marks, buzzing or crackling at the board or a socket
- a socket, switch or plug feels warm
- tripping started after building work, a leak or a flood
- you have an old board with no RCD protection
An electrician will use an insulation resistance tester to find where current is leaking, then repair the cable or circuit at fault. Intermittent faults can take a little detective work, so let them know when the trips happen: after rain, at night, when the heating comes on.
Landlords and letting agents
A tenant reporting repeated tripping should be treated as a priority repair, not a nuisance. It can point to a defect that would show up on an EICR, and you’re responsible for keeping the installation safe between inspections. Our guide to EICR codes explains how defects are graded.
Need it sorted?
Positive Contractors is an NICEIC Approved Contractor based in Chigwell. Our own electricians cover Chigwell, Loughton, Woodford, Ilford, Romford and across London and Essex. Call 020 8227 0035 or request a quote. Find out more about our electrical services.