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The short version
- The switch that dropped shows where to look: one breaker means that circuit, an RCD means leakage across several.
- Unplug everything, reset once, then reconnect appliances one at a time to find a faulty one.
- An RCD that trips with nothing plugged in points to a fault in the wiring or a fitting.
- Never hold a switch up or bypass it, and stop resetting if you smell burning.
- Diagnosing a tripping fuse box in London costs from £90, including VAT.
A fuse box that keeps tripping is protecting you from a fault: a circuit drawing too much current, a short circuit, or current leaking to earth. Which switch dropped tells you where to look. One circuit breaker usually means an overloaded circuit or a faulty appliance on it. An RCD taking several circuits off at once points to leakage from an appliance, damp or the wiring.
Most trips have an ordinary cause you can find in a few minutes. Some are a fault that needs an electrician. The checks below show you which, and none of them involves taking the cover off the consumer unit.
The switch that dropped tells you where to look
A modern consumer unit, the current name for a fuse box, has up to three kinds of switch. Open the clear flap, without undoing any screws, and find the one that is down.
| Switch that dropped | What it protects | What it usually means |
|---|---|---|
| One circuit breaker (MCB) | A single circuit, such as the upstairs sockets or the kitchen | Too much load on that circuit, a faulty appliance on it, or a short circuit |
| An RCD, with several circuits off | A group of circuits, against current leaking to earth | An appliance leaking current, damp in a fitting, or a wiring fault somewhere in that group |
| One RCBO | A single circuit, against both overload and leakage | Either of the above, confined to that one circuit |
| The main switch | The whole installation | Usually an on/off switch only. On some boards it is an RCD covering every circuit, so treat it as an RCD trip |
RCDs and RCBOs carry a small test button, usually marked T. A plain circuit breaker has none, which is the quickest way to tell them apart.
Five safe checks, in order
These are the only checks a homeowner should make. None of them means removing the consumer unit cover or touching any wiring.
- Note which switch is down before touching anything, and whether it is an MCB, an RCD or an RCBO.
- Unplug everything on the affected circuits, and switch off fixed appliances such as the cooker, electric shower and outdoor lights at their own switches.
- Reset the switch once. Push it firmly back up. If it will not stay up with everything unplugged, stop here.
- Plug appliances back in one at a time, switching each on for a minute. If the switch drops when one goes on, that appliance is the likely cause.
- Leave the suspect appliance unplugged and have it repaired or replaced. Kettles, washing machines, dishwashers and old extension leads are common culprits.
An RCD that trips with nothing plugged in points to the wiring
If the RCD still drops with every appliance unplugged and switched off, the fault is almost certainly in the fixed wiring or a fitting. This is the point to book fault finding rather than keep resetting.
How an RCD decides to trip
An RCD compares the current flowing out along the live conductor with the current coming back along the neutral. If some goes missing, it is leaking to earth, possibly through a person, and the RCD cuts the supply.
Homes use 30 mA RCDs. In practice one often trips at around 22 mA, well below its rating.
Small leaks that add up
Computers, TVs, chargers and many appliances leak a little current to earth by design. Around 10 mA of that spread across one RCD's circuits leaves only about 12 mA before it trips, so one appliance with a slight fault can tip it over.
Faults in the fixed wiring
- A nail or screw driven through a cable under a floorboard or inside a wall
- A neutral touching earth somewhere on a circuit, which can trip the RCD when you switch off an unrelated breaker
- Damaged cable in a loft, garage or garden supply
Why it trips in the rain, or when the cooker comes on
Water lowers the insulation around live parts, and a small path to earth is exactly what an RCD detects. Tripping in wet weather usually traces back to an outdoor socket, garden lighting, a shed supply or damp plaster around a fitting.
Cookers are a known case. The elements in some cookers absorb moisture while they sit cold, then leak enough current at first switch-on to trip an RCD. If it happens once and settles, that is the likely reason. If it keeps happening, have the cooker checked.
Stop resetting and call an electrician if
- You smell burning, or see scorch marks on a socket, switch or the consumer unit
- You hear buzzing or crackling from a fitting or the board
- The switch trips again the moment you push it up
- It trips with every appliance unplugged and switched off
Repeated tripping means something is faulty, and the fault will not clear itself. Our electricians in London trace the circuit, test the wiring and put the cause right, whether that is one damaged cable or an ageing board. Call 07727 619854.
Older boards with rewireable fuses do not trip at all: the fuse wire burns out instead. The same checks apply, but a board like that has no RCD protection, which is worth fixing in its own right.
Landlords: a tenant reports tripping
Treat a tripping report as a repair to arrange, not something for the tenant to keep resetting. Tripping with nothing plugged in is a wiring fault in a property you are responsible for.
Private landlords in England must have the installation inspected at least every five years and complete any work the report calls for within 28 days, or sooner if it says so. Our landlord EICR service in East London covers the inspection and the remedial work.
What finding the fault costs
Our guide price for diagnosing a tripping fuse box starts from £90, typically £90–£150, including VAT. The repair is quoted once the cause is found, and you decide before any work starts.
| Job | Guide price (VAT included) |
|---|---|
| Diagnosing a tripping fuse box | from £90 |
| Fault finding (minor) | from £100 |
| Replacing a damaged socket or switch | from £80 |
| Replacing the consumer unit | from £400 |
For a price on your own fault, call 07727 619854 or request a quote online.
Frequently asked questions
Up is on for almost every modern consumer unit. A switch sitting down, or partway down, has tripped or been switched off. If it will not stay up after you have unplugged everything on that circuit, leave it off and call an electrician.
They detect different faults. A circuit breaker trips on overload or a short circuit, while an RCD trips when current leaks to earth from a faulty appliance, damp or damaged wiring. An RCD trip with every breaker still up points to leakage, not too much load.
Unplug everything on the affected circuits, reset the switch once, then plug appliances back in one at a time. If it trips with everything unplugged, the fault is in the wiring or a fitting and needs testing by an electrician.
The trip is the protection working, so the danger is the fault behind it. A burning smell, scorch marks or a switch that drops the moment you reset it mean you should stop using that circuit and have it checked.