Why does my safety switch trip when the power comes back on?

Many appliances have small built-in filters that pass a tiny current to earth by design. On their own they are harmless, but a safety switch covering several circuits sees the total. At the moment power returns, every one of them switches on together, motors start and electronic power supplies charge up, and that brief jump in leakage can be enough to trip it. If the supply came back with a bump, or flicked on and off a few times, it adds to the effect.

Storm outages often come with rain. Water in outdoor points, garden lights, a shed supply or a damp cable joint leaks current that the safety switch sees as soon as it's switched back on. Circuits that sat off and cold for hours can also gather condensation.

A safety switch that is wearing out may refuse to reset, or trip even with every circuit under it switched off. Either way, the device itself or the wiring right next to it is the likely problem, and it needs a licensed electrician to test it.

Unplug or switch off the bigger appliances first. Then, through the open switchboard door and without removing covers, switch off the circuit breakers grouped with the tripped safety switch, reset the safety switch and switch the breakers back on one at a time, a few seconds apart. If it trips as one breaker goes on, that circuit has the problem: leave it off and turn the others back on. Then plug appliances back in one by one on the circuits that hold.

If it won't reset even with all its breakers off, leave it off. Energy Safe Victoria advises calling a licensed electrician if a safety switch won't reset. It also suggests unplugging appliances at the power point during an outage to help prevent surge damage, and fewer things restarting at once makes a trip less likely too.