Why does my fuse board keep tripping?
Short answer
A fuse board trips because something is drawing too much current or leaking current to earth. The most common cause by a distance is a faulty appliance, and you can usually find it by unplugging everything on the affected circuit, resetting, then plugging items back one at a time. If the breaker trips with nothing plugged in, the fault is in the fixed wiring and needs an electrician. Never tape a breaker on or keep resetting one that trips immediately.
What tripping actually means
Your consumer unit contains two kinds of protection, and which one has tripped tells you a lot.
An MCB or the overload half of an RCBO trips when a circuit draws more current than it is rated for. Too much plugged in, or a short circuit.
An RCD, or the earth-leakage half of an RCBO, trips when current is leaking to earth. It is looking for the difference between what goes out and what comes back, and it disconnects in milliseconds when that difference gets big enough to matter. This is the one that protects people.
Look at your board. If a single small switch has dropped, that is one circuit. If a wider switch has dropped and taken half the board with it, that is an RCD covering several circuits, which is why older boards knock out more than they need to.
The check you can safely do yourself
Most tripping is a faulty appliance, and you can find it without any tools.
- Unplug everything on the affected circuit. Everything, including things you are sure are fine.
- Reset the breaker.
- If it holds, plug items back in one at a time, waiting a moment after each.
- The one that trips it is your culprit.
Kettles, washing machines, dishwashers, immersion heaters and outdoor equipment are the usual suspects, because heating elements fail to earth as they age.
If it trips again with nothing plugged in, stop. The fault is in the fixed wiring and there is nothing more you can safely do.
When it is the wiring, not an appliance
Some patterns point straight at the installation:
- It trips when it rains. Water in an outdoor socket, garden lighting, or a shed supply.
- It trips when a specific light is switched on. Often a failed fitting or a damaged cable at a switch.
- It trips at the same time every day. Something on a timer, usually an immersion or heating control.
- It trips randomly with nothing obvious. Often accumulated small leakage across several circuits rather than one big fault, which is common on older installations sharing a single RCD.
- It will not reset at all. A hard fault, most likely a short. Leave it off and call someone.
What not to do
Do not tape, wedge or hold a breaker in the on position. It is there to disconnect a fault, and defeating it turns a nuisance into a fire risk.
Do not keep resetting a breaker that trips immediately. Each reset re-energises the fault.
Do not replace a breaker with a higher rated one to stop it tripping. The rating protects the cable, and a bigger breaker means the cable overheats before the protection operates.
What we do about it
Fault finding is systematic, not guesswork. We isolate circuit by circuit and take insulation resistance readings to find where current is leaking, which turns an intermittent nuisance into a located fault.
If your board is tripping, call 01732 655003. In working hours we get back to you within 2 hours, and fault finding is charged at our published standard rate with no separate call-out fee.
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