Why does my fuse box keep tripping?

It is 9pm. Half the house has gone dark, the washing machine has stopped mid cycle, and you are stood at the fuse box with your phone torch wondering which switch to push. This is one of the most common calls we get, and most of the time it is not an emergency. A tripping board is a safety device doing its job. Something on that circuit has a problem, and the board has cut the power before the problem could become a fire or a shock.

The good news is you can usually narrow down the cause yourself in ten minutes, without touching anything more technical than a plug. Here is how to do it, what tends to be behind it, and the point where you should stop and ring someone.

First, work out what has actually tripped

Open the fuse box, or consumer unit to give it its proper name, and look at the row of switches. What has dropped tells you a lot.

• One small switch is down. That is a single circuit breaker, and it means one circuit has the problem. Maybe the kitchen sockets, maybe the upstairs lights. Everything else in the house should still be on.
• A bigger switch is down and several rooms are dead. That is usually an RCD, a switch that protects a whole bank of circuits. It trips when electricity is leaking somewhere it should not, often through moisture or a failing appliance.
• The whole board is off. Rarer, and worth checking whether your neighbours have power too, because it might be a supply problem rather than your wiring at all.
• Nothing on the board has moved but one appliance is dead. Then it is probably the fuse in the plug, not the board. Unplug it, check the fuse, and replace it with one of the same rating if it has blown.

The ten minute check you can do yourself

This is the same first step we would take, and it is safe because it only involves plugs and the switches on the front of the board.

1. Unplug everything on the dead circuit. Every socket, every appliance. If it is a lighting circuit, switch every light on that circuit off at the wall.
2. Go back to the board and reset the tripped switch. Push it firmly all the way down first, then back up. Some breakers will not reset unless they have been pushed fully off.
3. If it holds, plug things back in one at a time. Give each one a minute of actually running, not just sitting there plugged in.
4. When the board trips again, the last thing you plugged in is your culprit. Leave it unplugged and the rest of the circuit should behave.

That is as far as it goes. Never take the cover off the consumer unit, and never poke about inside a socket or a light fitting. The checks above involve nothing you were not already touching every day.

What usually causes it

In rough order of how often we find them:

• A failed appliance. Comfortably the most common cause, and kettles and washing machines lead the field. Anything with a heating element in it wears out eventually, and when the element breaks down it leaks current and the board cuts it off. Dishwashers, tumble dryers and old fridge freezers are regulars too.
• Moisture outside. Outside sockets, garden lights, pond pumps, hot tubs. If the board trips after rain, or every time you use something in the garden, water has found its way in somewhere. The RCD is doing exactly what it is there for.
• An overloaded circuit. Too much running on one circuit at once. Plug-in heaters are the usual suspects in winter, especially several of them on one extension lead. If the trip only happens when everything is on together, this is a likely candidate.
• A damaged cable. A nail or screw through a wall that clipped a cable, a rodent that has been chewing, or simply old wiring giving up. This one you cannot find by unplugging things, because the fault is in the fixed wiring itself.
• A faulty breaker. Rare, but real. Breakers are mechanical and they do wear out. If a circuit tests clean and the breaker still will not hold, the breaker itself can be the problem.

When it stops being a DIY job

The unplug and reset routine solves a good share of these. But there are clear lines where you should stop.

• The switch will not reset at all, even with everything on the circuit unplugged.
• It trips instantly the moment you push it up, with nothing plugged in. That points at the fixed wiring, not an appliance.
• It trips at random, with no pattern you can pin to any appliance.
• There is any burning smell, scorching, buzzing, or warmth at the board or at a socket.

If you can smell burning, see smoke or sparks, or anyone has had a shock, ring 999 first. Then switch off at the consumer unit if it is safe to reach, and call us after that. Electrical fires move fast and the fire brigade would always rather come out to nothing.

For everything short of that, this is what fault finding is for. We test the circuit properly, split it down section by section, and find the fault rather than guess at it. Fault finding is £80 to £180 depending on how deep the fault is hiding, and there is no VAT on domestic work. Our full price guide covers what the other common jobs come out at.

One more thing worth saying. A board that trips constantly, week in week out, can be a symptom of wiring that is coming to the end of its life rather than one bad kettle. If that sounds like your house, have a read of 7 signs your home needs a rewire before you spend money treating the symptoms.