Faulty appliances
Kettles, toasters, washing machines, fridges and heaters with worn elements or damaged cords are the most common cause, especially older ones.
Start at the switchboard. A safety switch, also called an RCD, has a small Test or T button. It switches the power off when it senses electricity leaking to earth, which is what happens when someone gets a shock.
A circuit breaker has no test button. It trips when a circuit is overloaded or shorts out, for example with too many heaters or kettles running on it at once. Some newer boards use combined devices (RCBOs) that do both jobs, one per circuit. If the one that went off has a test button, this guide is for you.
- Switch off and unplug everything on the affected circuit. If you’re not sure which power points it covers, unplug everything you can.
- Reset the safety switch by pushing it back up to on. If it won’t stay on with everything unplugged, go straight to step 5.
- Plug appliances back in and switch them on one at a time, waiting a minute or so between each.
- When the switch trips again, the last appliance you plugged in is the likely cause. Leave it unplugged and have it checked or replaced.
- If it trips with nothing plugged in, or you can’t find a culprit, the fault is probably in the fixed wiring or a hard-wired appliance such as the oven, hot water system or an outdoor light. Leave the switch off and call an electrician.
Reset the switch once or twice to test, not over and over. Never tape, wedge or hold a safety switch on: it’s the thing standing between a fault and a shock.
Water and moisture
Outdoor power points, garden lights and exterior fittings can let in water. If it trips after rain or a heavy dew, start looking outside.
Electric hot water
A failing element in an electric storage hot water system often trips the safety switch, sometimes overnight when the off-peak heating switches on.
Damaged wiring
A nail or screw through a cable, rodents chewing wires in the roof, or old insulation breaking down can all leak current to earth.
Too much on one switch
Many appliances leak a tiny amount of current. When one safety switch covers lots of circuits, those small leaks can add up enough to trip it.
A worn-out safety switch
Safety switches can wear out with age and start tripping for no clear reason. An electrician can test whether the switch itself is the problem.
If it trips at night, think about what switches on by itself: the fridge or freezer compressor, an electric hot water system on off-peak, heaters or pool pumps on timers, and outdoor lights as the dew settles.
If it’s the lighting circuit, the usual suspects are outdoor and garden lights, a light fitting with water in it, or a failing LED driver or transformer. Exterior lights are worth checking first.
- You can smell burning, or see scorch marks or melted plastic at a power point, switch or the switchboard
- The switchboard is wet, buzzing or warm to touch
- Anyone has had a tingle or a shock from an appliance, tap or metal fitting
- The safety switch trips the moment you reset it, with everything unplugged
If it looks unsafe, don’t touch the switchboard. Keep people clear and call Joel on 0413 548 944. If someone is hurt by an electric shock, call 000.
Is it safe to keep resetting a safety switch?
Once or twice to test, yes. If it keeps tripping, there’s a fault it’s protecting you from, so leave it off and have the circuit tested.
Why does my safety switch trip when it rains?
Water is getting into something outside, usually an outdoor power point, a garden or wall light, or a cable joint. It often settles down once things dry out, but the fault is still there and tends to get worse.
Why does it trip with nothing plugged in?
Then the fault is in something that’s always connected: the fixed wiring, a light fitting, or a hard-wired appliance such as an oven, cooktop, hot water system or pool pump. That needs an electrician to test the circuits.
How often should I test my safety switch?
Press the test button every few months. The switch should turn off straight away; push it back on afterwards. If it doesn’t trip when tested, it needs replacing.
Can an old switchboard cause nuisance tripping?
Yes. An old safety switch can wear out, and older boards often have one safety switch covering many circuits, so small leaks add up. A switchboard upgrade can give circuits their own protection, so one fault doesn’t knock out half the house.
How does an electrician find the fault?
By testing each circuit and appliance with an insulation resistance tester, which shows where current is leaking, then repairing or replacing the faulty part.
LENNELEC is a local electrician based in Somerville, covering the Mornington Peninsula and south-east Melbourne. More guides
Still tripping?
Tell Joel what’s tripping and when it happens, or call him for a chat about the fault.