RCD Keeps Tripping? Here's How a Sparky Actually Finds the Fault
RCD Keeps Tripping? Here's How a Sparky Actually Finds the Fault
Call Kris on 021 466 666
You flick the switch on the wall, and the lights in half the house go out. You walk to the switchboard, see the RCD has tripped, push it back up — and it pops straight back down again. You unplug everything you can think of. Still won't reset.
That's an earth leakage fault. And once you've ruled out appliances, the cause is somewhere inside your fixed wiring — the cables in the walls and ceilings.
What an RCD actually does
A residual current device (RCD) — sometimes called an earth leakage trip — is the switch on your board that monitors current flow on a circuit. Specifically, it watches whether the current going out (live) matches the current coming back (neutral). If those numbers don't match, current is escaping somewhere. The RCD detects the mismatch and cuts power in milliseconds.
When an RCD won't reset, it's because the device is still detecting that imbalance. Something on that circuit is leaking current.
Step 1 — Rule out appliances (you can do this)
Identify which circuit the RCD covers.
Unplug every appliance on that circuit.
Try to reset the RCD. If it holds, plug appliances back in one by one until you find the culprit.
If the RCD still won't hold with nothing plugged in — that's when you call a sparky.
Step 2 — A sparky narrows down the faulty section
Open the switchboard. Find which physical conductors are connected to the affected RCD. Disconnect circuits one at a time. After each one, test whether the RCD will now hold. Isolate the faulty circuit onto its own dedicated RCBO.
This is usually the end of the first visit. The customer has power back to everything except the one isolated circuit.
Step 3 — Insulation resistance testing on the suspect circuit
The next visit is the actual fault hunt. Insulation resistance testing uses a meter that puts a small voltage across the wiring and measures how well the insulation is holding. The faulty section is then replaced.
Why it usually takes two visits
The methodical sequence — isolate on Day 1, test and replace on Day 2 — minimises the destruction to the property and is more likely to find the actual fault rather than just swap something on a hunch.
What it should cost
A typical two-visit earth leakage diagnosis and repair is usually $800-$1,500 including GST, depending on how many circuits share the affected RCD, how accessible the fault location is, and whether the switchboard needs extra RCBOs.
How Cosine handles it
We'll come on the first visit with the test gear, isolate the fault, and leave the rest of your house running. We'll come back for the second visit to find and fix the bad section properly. Certificate of Compliance issued for any new work.
Call Kris on 021 466 666
Got an RCD that won't reset? Talk to Kris.
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