Fuse Keeps Blowing

What's happening?

First work out which fuse it is, because the fix is different. A plug fuse is the small cartridge inside a UK three-pin plug, made to BS 1362 and usually rated 3A or 13A. Electrical Safety First says appliances from about 700 to 3000 watts need a 13A fuse, and lamps, TVs and computers normally use 3A. If a plug fuse keeps going, the appliance or its lead is the usual cause, or the fuse is the wrong rating. A fuse box fuse protects a whole circuit. Older boards use rewirable fuses (a carrier holding a length of fuse wire) or cartridge fuses. When one of those keeps blowing, the circuit is overloaded, or there is a short circuit or earth fault in the wiring or in something plugged into it. Old fuse boxes also rarely have RCD protection, so the fuse may be the only protection on that circuit.

What usually causes it?

• An appliance with an internal fault, such as a failed heating element, motor or power supply
• A damaged appliance lead or plug, including a trapped or crushed flex
• The wrong fuse in a plug: a 3A fuse in a kettle or heater will blow every time
• Too many high-power appliances on one circuit or one extension lead
• A short circuit or earth fault in the fixed wiring, often after drilling, nails or water
• In a rewirable fuse box, fuse wire of the wrong rating or poorly fitted in its carrier

Is it dangerous?

A blowing fuse is the protection working, not the danger. The danger is what people do next: fitting a higher-rated plug fuse, using thicker fuse wire, or wrapping foil or wire around a fuse to stop it blowing. That removes the only thing stopping a cable or appliance overheating and can start a fire. If the fuse blows with a bang, a flash, a burning smell or scorch marks, stop using the circuit and get an electrician.

Can I fix it myself?

For a plug fuse: 1. Unplug the appliance. 2. Check the rating it needs on its label or manual and fit a new BS 1362 fuse of that rating. 3. If the new fuse blows as soon as the appliance runs, stop using that appliance: it needs repair or replacing. For a fuse box: 1. Unplug everything on that circuit. 2. Turn the main switch off before touching any fuse carrier. 3. Replace the fuse or fuse wire with exactly the same rating, once. 4. Switch on and plug items back in one at a time. If it blows again, leave it out and call an electrician. Never fit a higher rating or any other wire.

When should you call an electrician?

Call an electrician if a fuse box fuse blows again after one replacement, blows with nothing plugged in, blows with a bang or smell of burning, or if you are not confident removing fuse carriers safely. It is also worth asking about replacing an old rewirable fuse box with a modern consumer unit with RCD protection. For a plug fuse that keeps blowing on one appliance, the appliance needs repairing or replacing rather than the house wiring.

What will the electrician actually do?

• Identify whether the fault is on the circuit or in an appliance
• Insulation resistance test the circuit to find short circuits or earth faults
• Check the fuse and fuse carrier are the correct rating for the circuit cable
• Repair damaged wiring, sockets or connections found during testing
• Advise on replacing a rewirable fuse box with a consumer unit that has RCD protection
• Label circuits so the right fuse is easier to find next time

Who fixes this

• Electrical fault finding

What it usually costs

Electrical Fault Finding Cost

Priced on survey

Questions people ask

Sources & References

1. Electrical Safety First: Plugs and fuses (BS 1362 fuse ratings)
2. Electrical Safety First: Ratings of electrical appliances
3. Electrical Safety First: Overloading sockets
4. BS 7671: IET Wiring Regulations (18th Edition)