The most common cause: a faulty appliance
Safety switches monitor for earth leakage, current escaping to earth instead of flowing back through the neutral as it should. A faulty appliance with damaged insulation, exposed internal wiring, or a worn heating element creates exactly this kind of leak, and the safety switch trips to protect you before it becomes a shock risk. Ageing appliances, damaged cords, anything that's gotten wet, and cheap imported electronics are frequent culprits. Kettles, toasters, washing machines and outdoor equipment come up again and again, since they combine water exposure or heat with everyday use.
Moisture is the second biggest cause, especially outdoors
Rain getting into an outdoor power point, a garden light, or a pool pump connection is one of the most common reasons a safety switch trips repeatedly during or after wet weather. Even a small amount of moisture inside a point or a joint creates a leakage path to earth that a healthy safety switch correctly detects. If tripping happens specifically during or shortly after rain, an outdoor circuit is the first place worth checking, not something inside the house.
How to actually find which appliance is causing it
Unplug everything on the affected circuit, reset the safety switch, then plug items back in one at a time, waiting a minute or two between each before adding the next. Whatever's plugged in when it trips again is very likely the cause. If it trips again with absolutely nothing plugged in, the fault sits in the fixed wiring or a hardwired appliance, not something you can simply unplug, and that needs an electrician rather than more testing at home. If that's the situation you're facing, see our guide on a safety switch that won't reset.
When it's the circuit, not one single appliance
Sometimes it isn't one clearly faulty appliance but the combined load of several borderline items running together that tips a marginal fault over the threshold. This shows up more often on older circuits carrying more devices than they were ever designed for. It's a different situation to a single obvious culprit, and it often points to a broader load or wiring issue worth having properly assessed rather than one item to permanently stop using.
When it might be the safety switch itself, not what's plugged in
Safety switches are mechanical devices and can degrade over years of use, becoming overly sensitive and tripping on loads that wouldn't have bothered it when it was newer. NSW Fair Trading recommends testing your safety switch every six months using its built-in test button, since a switch that's starting to fail often shows up as nuisance tripping well before it fails completely. If it trips even with the entire circuit isolated and nothing connected at all, that points to the switch itself, not your appliances.
When repeated tripping is actually worth calling about
An occasional trip you can trace straight to a specific appliance isn't an emergency, that's the safety switch doing exactly its job. Frequent tripping with no clear pattern, tripping that's getting more frequent over time, or a switch that's becoming difficult to reset is worth a proper assessment rather than living with the inconvenience of repeatedly walking to the switchboard.