What is the difference between a circuit breaker and a fuse?

A circuit breaker (MCB) does the same job as a fuse but can be reset by flipping the switch. Fuses are single-use and must be replaced. Modern consumer units use MCBs rather than rewirable fuses.

Can I replace the circuit breaker with a bigger one?

No. MCB ratings are matched to the cable size on the circuit. Fitting a higher-rated MCB could allow the cable to overheat and cause a fire. Only an electrician should change MCB ratings, and only after confirming the cable can handle the higher current.

Why does the circuit breaker trip when I use the kettle and toaster together?

Your kettle draws around 13A and your toaster around 8A. If they are on a radial circuit rated at 20A, running both together exceeds the circuit capacity. An electrician can check whether you need a dedicated circuit.

How often should circuit breakers be replaced?

MCBs can last 20–30 years but can degrade over time, especially if they trip frequently. If an MCB feels loose, will not stay reset, or trips at loads below its rating, it should be replaced.

Caution

Updated 30 August 2026

Circuit Breaker Keeps Tripping

A circuit breaker in your consumer unit keeps tripping, cutting power to part of your home.

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What's happening?

A circuit breaker (MCB — Miniature Circuit Breaker) protects an individual circuit against overload and short circuit. When it trips, it disconnects the power to that specific circuit. If it keeps tripping, there is either a fault on the circuit or the circuit is being asked to carry more current than it is rated for.

What usually causes it?

Overloaded circuit with too many appliances drawing power simultaneously
Short circuit caused by damaged cable insulation or a faulty connection
Faulty appliance with an internal short circuit
Loose connection at a socket, junction box, or the MCB itself causing arcing
Incorrect MCB rating for the circuit (too low after a circuit modification)
Deteriorating cable insulation in older wiring

Is it dangerous?

A tripping MCB is doing its job and protecting you from a potentially dangerous situation. The fault it is protecting against — whether overload or short circuit — could cause a fire if the protection were not there. Do not replace an MCB with a higher-rated one to stop it tripping, as this removes the protection and could allow cables to overheat.

Can I fix it myself?

Identify which MCB has tripped by checking your consumer unit. Reset it. If it trips immediately, there is likely a short circuit. If it stays on for a while then trips, the circuit may be overloaded. Unplug appliances on that circuit and try resetting. Plug items back in one at a time. If it trips with nothing plugged in, the fault is in the fixed wiring.

When should you call an electrician?

Call an electrician if the MCB trips with nothing plugged in, if it trips immediately on reset, if you cannot identify the cause, or if you notice any burning smell or heat from the consumer unit. Never replace an MCB with a higher-rated one yourself — this is dangerous and against BS 7671.

What will the electrician actually do?

Test the circuit for short circuits and earth faults using insulation resistance testing
Check the loading on the circuit to determine if it is overloaded
Inspect all connections on the circuit for looseness or signs of overheating
Test the MCB itself to confirm it is functioning within specification
Repair the fault — whether a loose connection, damaged cable, or faulty appliance connection
Advise on circuit redistribution if the circuit is genuinely overloaded