Intermittent fault on power circuit
Hi guys, I’m a newly licensed electrician looking for some advice on an intermittent fault.
Yesterday, I installed a new AC circuit and relocated a 15 A weatherproof GPO for a hot water system for my mates tiny home. Powered on all fine, no dramas.
He has a sub board in the tiny home and the MSB about 20m away.
This morning, he woke up to the POWER circuit RCBO tripped at the sub-board. After resetting it and the supply, it tripped again, and the 63 A three-phase main breaker at the MSB also tripped. The 63 A breaker has only tripped once; since then, it’s been the same POWER RCBO tripping intermittently.
The circuit supplies the kitchen fridge and laundry power points. I IR-tested active-to-earth and neutral-to-earth at 500 V DC and got over 5 MΩ, but after looking into it, the circuit neutrals were still connected to the neutral bar, not sure if that matters? Also the new AC circuit and relocated GPO aren’t supplied by the circuit that’s tripping.
After IR testing both the installation and appliances with results that pass, I decided to swap the RCBO of the power circuit that’s was tripping with a new one, just in case it was a faulty breaker, then put everything back together and left The washing machine and dryer running for about halfa without issue.
However, later the owner switched on the exhaust fan on a separate lighting circuit and the POWER RCBO tripped about a second later.
What would you investigate first? Could this be an intermittent appliance fault, a neutral issue, or something else? How much confidence would you put in those IR readings given the test setup? I’m at a loss here. Not sure what to test next.