Case Study — Tracking Down an Earth Leakage Fault in a Residential Kitchen
Case Study — Tracking Down an Earth Leakage Fault in a Residential Kitchen
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The brief: A homeowner called us out after a residual current device (RCD) on the switchboard wouldn't reset. They'd already done the right first step — disconnected every appliance on that circuit, one by one. The RCD still wouldn't hold. That meant the fault was in the fixed wiring itself, not in an appliance.
Day 1 — Isolating the fault
On the first visit (28 April), we found the switchboard had multiple circuit conductors connected to a single RCD. That's a common setup but it makes fault-finding harder.
The diagnostic sequence:
Disconnect circuits one at a time from the shared RCD, testing after each disconnect.
Narrow the fault to two specific conductors — both feeding into the same physical wiring run.
Place the suspect circuit onto its own dedicated RCBO so the rest of the house could power up normally.
The homeowner had power back to the rest of the house at the end of Day 1, with the faulty circuit safely isolated.
Day 2 — Finding and replacing the faulty cable
On the return visit (30 April), we did insulation resistance testing along the suspect circuit. The reading came back low on the section of cable between the kitchen island bench and the kitchen socket on the wall. That meant the cable had degraded between those two points — buried in the ceiling cavity above.
The repair:
Entered the ceiling cavity above the kitchen.
Located the faulty cable run by following the route from the island bench.
Drew a replacement cable through the same route.
Joined the new cable into the existing wiring at both ends, using a code-compliant ceiling-mounted junction box.
Re-connected the circuit, energised, and tested. All clear.
The outcome
Total: 5 hours of on-site work across two visits by a two-person team, plus the replacement cable, RCBO and junction box. Total invoice including GST: $1,163.61.
The homeowner left with a properly diagnosed and repaired circuit, the faulty section isolated on its own RCBO going forward, and a Certificate of Compliance for the work.
Why fault-finding like this isn't a one-visit job
An earth leakage fault that's already had appliances ruled out is almost always inside the fixed wiring. That means a methodical isolate-and-test sequence:
Narrow down which circuit it's on
Split that circuit so the rest of the house can run
Come back to test, locate, and replace the faulty section
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