Why does my RCD keep tripping?

What an RCD actually does

A residual current device, or RCD, constantly compares the current flowing out along the live conductor with the current coming back along the neutral. In a healthy circuit they match. If some current is leaking away, for example through a damaged cable, water or a person, the RCD switches off in a fraction of a second.

Most homes have RCDs protecting groups of circuits, or RCBOs protecting each circuit individually. Either way, the switch that has flipped down is the one that detected the problem.

The most common causes

In our experience, most nuisance tripping comes from a handful of causes. The good news is that the most common one is also the easiest to find.

• A faulty appliance, often a kettle, toaster, washing machine, dishwasher or immersion heater with a failing element
• Water getting into an outdoor socket, garden light or junction box, especially after heavy rain
• A cable damaged by a nail, screw or rodent
• Old wiring whose insulation is breaking down
• A neutral to earth fault, often after DIY work or a new fitting
• Several appliances that each leak a small amount, adding up on one RCD

How to narrow it down safely

You can usually find out whether an appliance is to blame without touching any wiring. Only do this if the consumer unit is in good condition, there is no burning smell, and nothing is hot or damaged.

• Unplug everything on the affected circuits, including things on timers
• Switch off all the circuit breakers, then reset the RCD
• Switch the breakers back on one at a time. If the RCD trips, note which circuit did it
• With every breaker on, plug appliances back in one by one, waiting a moment after each
• If one appliance trips it every time, stop using it and have it repaired or replaced

When to call an electrician

If the RCD trips straight away with every breaker off and nothing plugged in, the fault is in the fixed wiring and needs testing. The same applies if it trips when a particular circuit comes on even with nothing plugged in, if the fault comes and goes with the weather, or if you notice warm sockets, scorch marks or a burning smell.

An electrician will use insulation resistance testing to find the fault and confirm it is fixed. Please do not keep resetting a device that trips immediately. It is telling you something is wrong.

RCD or circuit breaker?

If a circuit breaker (MCB) trips rather than the RCD, the cause is different. A breaker trips on overload or short circuit, for example too many high power appliances on one circuit, or a fault where live touches neutral. Overloading is common with kettles, heaters and tumble dryers sharing a kitchen circuit.

It is also worth pressing the test button on each RCD every six months, as the label on your consumer unit suggests. It should switch off straight away. If it does not, get it checked.

Common questions

This guide is general information for properties in England and is not a substitute for an inspection by a qualified electrician.