Why does my electricity keep tripping?

If your electricity keeps tripping, one of the safety switches in your fuse box is doing its job. It has sensed something wrong on a circuit, such as a faulty appliance, water getting into a fitting or a damaged cable, and cut the power before it could hurt someone or start a fire. The cause is often simple to find, but a switch that trips again and again is telling you something needs fixing.

This post explains what the different switches do, the most common reasons they trip, and why it often starts as the weather turns damp. You can make a few safe checks yourself, but never take the cover off your fuse box or open up sockets and fittings.

What has actually tripped

Most homes now have a consumer unit, the modern name for a fuse box. Inside are two main kinds of switch, and knowing which one has tripped tells you a lot.

• An MCB (miniature circuit breaker) protects one circuit, such as the upstairs sockets or the kitchen lights. It trips when a circuit draws more current than it should, or when there is a short circuit, where live and neutral touch.

• An RCD (residual current device) watches for current leaking to earth, which is what happens when electricity finds a path it shouldn't, through water or a person. It cuts the power in a fraction of a second. One RCD often covers several circuits at once, which is why half the house can go off together.

Newer boards may have RCBOs instead, which combine both jobs in one switch for each circuit. If yours does, only the circuit with the problem goes off.

The most common reasons a switch trips

Most trips come down to one of a handful of causes:

• A faulty appliance. Kettles, toasters, washing machines, dishwashers and immersion heaters are frequent culprits. A worn element or a damp seal can leak a small current to earth and trip the RCD.

• Too much on one circuit. Running a heater, tumble dryer and kettle off the same set of sockets can overload it and trip the MCB.

• Water getting in. Outside sockets, garden lights and bathroom fittings are most at risk.

• A damaged cable. A nail or screw through a wire in the wall, or a cable chewed in the loft, can cause a trip that comes back every time you reset.

• Ageing wiring or an old board. Insulation breaks down over decades, and an old switch can become over-sensitive or worn.

Why it often starts in autumn and winter

We tend to see more tripping as the nights draw in. Rain and condensation find their way into outdoor sockets, security lights and garden lighting that sat dry all summer. Heaters and tumble dryers come back into use, adding load to circuits that have had an easy few months. And from late November, strings of festive lights, often outdoor ones plugged in through extension leads, add both load and damp.

If the trips started when the weather changed, or when you switched on something you haven't used since last winter, that is a strong clue.

Safe checks you can make at home

You can narrow down the cause without touching any wiring. Work through these in order:

1. Look at the consumer unit. Note which switch is down. If it is an RCD, several circuits will be off. If it is an MCB, the label should tell you which circuit.

2. Unplug everything on the affected circuits. Switch appliances off at the wall and pull the plugs. For an RCD, that means everything on every circuit it covers.

3. Reset the switch. Push it firmly back up. If it stays up with nothing plugged in, the fault is likely to be in an appliance.

4. Plug things back in one at a time. Switch each one on and wait a moment. When the switch trips again, you have found the likely culprit. Stop using it until it has been checked or replaced.

5. Check the outside. If you have outdoor sockets or lights, look for water in the covers or cracked fittings, but don't open them up.

It is also worth testing your RCD every six months by pressing the button marked "T" or "Test" on the board. It should trip straight away. Reset it afterwards. The regulations that cover home wiring ask for a label at the board recommending exactly this.

When to stop and call an electrician

Some signs mean you should stop resetting and get a qualified electrician in:

• the switch trips again straight away with everything unplugged

• it won't reset at all

• you can smell burning, or see scorch marks, melting or sparking at a socket, switch or the board itself

• the board feels warm, or you hear buzzing or crackling

• the trips are getting more frequent with no obvious cause

These point to a fault in the fixed wiring, the fittings or the board, and that needs proper testing equipment to find safely. If there is burning or sparking, leave the circuit off and treat it as urgent. Our emergency electrician service is there for exactly that.

Never keep resetting a switch that won't stay up, and never tape or wedge one in the on position. It is the only thing standing between the fault and you.

How we track down a tripping fault

When we visit, we start by asking when the trips happen and what was on at the time, because that pattern often points straight to the cause. We then test the circuits with specialist equipment, measuring how well the insulation is holding up on each one, so we can find a leak to earth even when nothing looks wrong. Once we know where the fault is, we explain what we found and what we recommend before any work starts.

Sometimes the fix is a single fitting or an outdoor socket replaced with a properly weatherproofed one. Sometimes it shows that an old board without modern protection is due for an upgrade, which our page on fuseboard installation explains in more detail. Either way, as NICEIC Approved Contractors, we test our work when it is finished and give you the right paperwork for it.

If your electricity keeps tripping and the simple checks haven't found the cause, JM Electric can track it down and put it right. Book a visit through our domestic electrician service and we'll find the fault and talk you through the options.