How to Reset a Tripped Safety Switch (RCD) and Find the Faulty Circuit

By Ash — licensed electrician, Adelaide SA.

The safety switch trips. You walk to the switchboard, flick it back up, it holds for ten seconds, then trips again. So you flick it again. And again. Eventually you give up and ring me, and I charge you $180 to do something you could have done in five minutes with a notepad.

Aussie safety switches (RCDs, residual current devices) are required by AS/NZS 3760 and AS/NZS 3000 to trip at 30 milliamps within 30 milliseconds. That’s much more sensitive than a US GFCI, which trips at 5 mA but only on bathroom and outdoor circuits — ours protect every powerpoint and lighting circuit added since 1991 in most states. The upside: they save lives. The downside: they’re paranoid. An old fridge motor with worn brush insulation, a 15-year-old pool pump, or a kettle with a damp element will all trip a healthy RCD.

What follows is the appliance-by-appliance isolation method I use on call-outs. Same method a sparky uses, except you do it for free. If you find the faulty appliance, replace or repair it. If the RCD trips with everything unplugged, then yes, ring me — that’s a wiring fault and it’s mine to fix.

Quick note on terminology — Aussies use “safety switch” loosely. Strictly: an MCB (miniature circuit breaker) is the small switch protecting against overload and short-circuit; an RCD (residual current device) is the bigger one with the test button protecting against earth leakage; an RCBO combines both functions in a single device. When this article says “safety switch” I mean the RCD or RCBO — the one that trips when something leaks current to earth, not when you’ve simply overloaded the circuit. Knowing which is which at your switchboard saves a lot of confusion.

What you’ll need

• A torch (the switchboard cupboard is always the worst-lit cupboard in the house)
• A pen and notepad — old school, works
• Knowledge of which RCD covers which circuits (we’ll work this out in Step 2)
• Patience — this takes 20 minutes if you do it methodically

Step 1: Reset once and watch what happens

Open the switchboard. Find the RCD — it’s the bigger switch with a “T” or “TEST” button on it. Push the switch firmly to OFF, then back to ON. Does it stay on? If yes, the trip was a momentary spike (lightning, neighbour’s air-con starting, a globe blowing). Note the time and move on. If it trips again immediately, or within a few seconds, you’ve got a real fault. Continue.

Step 2: Map your RCD’s coverage

Modern Aussie boards usually have one RCD per circuit (called RCBOs) or one RCD covering multiple MCBs. Look at the labels. Common groupings: “RCD1: Power upstairs, Power downstairs” or “RCD1: All Power, RCD2: All Lights”. If unlabelled, with the RCD off, walk through the house with the torch — anything that’s still working is on a different RCD. Note which rooms/circuits are dead.

Step 3: Unplug everything on the affected RCD

Walk through every room covered by the dead RCD and unplug literally everything. Fridges, microwaves, phone chargers, lamps, fish tanks, the lot. If a powerpoint has a switch, turn the switch off too. Don’t forget the obvious culprits — washing machine, dishwasher, kettle — and the not-so-obvious ones — the pool pump in the back shed, the bore pump in the laundry, the 4-way board behind the TV unit.

Step 4: Reset the RCD with everything unplugged

Push the RCD back to ON. Does it hold? Two outcomes:

• It holds: Good. The fault is in an appliance, not the wiring. Continue to Step 5.
• It trips: The fault is in the fixed wiring (a bathroom fan, a ceiling light, a hardwired oven). That’s licensed work — call me. Skip to Step 9.

Step 5: Plug appliances back in one at a time

Now the methodical bit. Plug in one appliance, turn it on, wait 30 seconds. Still on? Plug in the next one. Write each one down as you go. The key is to wait long enough — a fridge compressor doesn’t kick in for a couple of minutes after plugging in, and a faulty fridge will only trip when the compressor starts.

Step 6: Watch for the usual suspects first

From 15 years of call-outs, here are the appliances that trip RCDs in order of frequency:

• Old fridges and chest freezers — worn motor windings leak current to earth. Anything pre-2010 is suspect.
• Pool pumps — the ones sitting outside in the weather have water-ingressed terminals. Davey, Onga, AstralPool — doesn’t matter, they all suffer.
• Kettles and toasters — heating elements crack, water gets in. A $25 Kmart kettle will outlast a $300 Smeg if you’re unlucky.
• Bathroom heated towel rails — moisture intrusion at the cable gland.
• Garden lights and outdoor extensions — slug-eaten cable, water in the join, pegs through buried Cordtech.
• Cheap phone chargers — yes really, especially the unbranded $4 jobs from a service station.

Step 7: When the RCD trips, you’ve found it

Whichever appliance you plugged in last is the culprit. Unplug it. Reset the RCD. Plug everything else back in to confirm. The faulty appliance gets either thrown out, repaired, or in the case of a fridge or pump, taken to a service tech who can re-Megger it.

Step 8: Test the RCD itself, monthly

While you’re at the switchboard — push the TEST button on the RCD. It should trip immediately. If it doesn’t, the RCD itself is faulty and that IS a sparky job (about $150 to replace). AS/NZS 3760 actually requires you to test it every six months in a residential setting; do it on the first of every quarter and you’ll never forget.

Step 9: When to actually call a sparky

Three scenarios where this method ends and mine begins:

• RCD trips with everything unplugged (fixed wiring fault — could be a nail through a stud, a rodent in the roof, or a degraded cable in a wet wall)
• RCD won’t reset at all, even with no load (faulty RCD or earth fault)
• You found the appliance but it’s hardwired (oven, cooktop, hot water system, ceiling fan)

Quote a sparky $150–$300 for fault-finding plus repair time. Worth it — chasing a wiring fault without a Megger and a thermal camera is like fishing without a rod.

Step 9a: The “intermittent trip” gotcha

Hardest fault to find: the trip that happens once a week at 3am for no obvious reason. Two common causes I’ve chased to ground over the years. First — the fridge defrost cycle. Old fridges run a defrost heater every 6–8 hours that draws current through a thermostat. If that heater has degraded insulation, it’ll trip the RCD only when it cycles on. Solution: leave the fridge plugged in overnight on its own circuit and watch when it trips. Second — the hot water system. Aussie storage HWS heat overnight on off-peak tariff (Tariff 31/33 in NSW, controlled load 1/2 in VIC). If the element has a slow leak to earth, it’ll trip when it switches on at 11pm. Both faults are diagnosable by the timing alone.

Step 10: Document what you found

Write the appliance and date in the switchboard cupboard with a Sharpie or a label-maker. “Aug 2026 — old beer fridge in garage tripped RCD2, replaced.” Next time something trips, you’ve got a maintenance log. Sounds anal. Saves you an hour next time.

Step 11: Storms, lightning and the false trip

Aussie summer storms are a special category. Direct lightning strikes within a few hundred metres can induce voltage spikes on the supply that trip RCDs even when nothing’s wrong with your appliances. If your RCD trips during a storm, reset once after the storm passes. If it holds, it was a spike — note the date and move on. If it trips again, run through the isolation method properly. Surge protection at the switchboard (a Type 2 surge protector, $250–$400 supply and install) is worth considering if you’re in a high-strike area like the Sunshine Coast hinterland or the Adelaide Hills.

Step 12: When to upgrade the whole switchboard

If your board has a single RCD covering the whole house, every trip kills the lights AND the fridge AND the home office. Modern boards split this — typically one RCBO per circuit so a faulty kettle only kills the kitchen GPOs, not the whole house. Upgrading from old single-RCD to a per-circuit RCBO board costs $1,500–$3,500 depending on circuit count, and is one of the better safety upgrades on an older home. If you’re already getting other electrical work done, ask for a quote in the same visit.

The Ash rule

An RCD that keeps tripping is doing its job. It’s telling you 30 mA of current is leaking somewhere it shouldn’t — almost always to earth via a degraded appliance. Don’t tape over the test button, don’t replace the RCD with a regular MCB, don’t ring “an electrician mate” who’ll bypass it. The 30 mA threshold is what stops the leak from becoming the lethal 100+ mA that stops your heart. Find the leaky appliance instead.

Got a switchboard mystery you’ve cracked? Send us a write-up.