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I will relate all information that I can possibly give as I have no idea how to even diagnose this issue.

I live in a hot, dry country with 240V supply. The house I just bought here, has it's lights wired through 2 separate 10A circuit breakers. For some reason earth leakage was bypassed for the lights when I bought the house. A electrician rewired the entire lights circuit and made sure that earth leakage is not bypassed anymore.

After the rewiring we started to have a weird issue. The main earth leakage circuit breaker trips randomly.

With randomly I mean that I am unable to detect a pattern.

Times between this happening have been 1 week, 1 week, 4 weeks, 2 weeks and 2 days. 2 times it was raining at other times it was dry and hot. Once it happened in the morning while other times it happened in the afternoon. 3 times it happened without ANY lights being on.

When this happens, I am unable to reset the earth leakage breaker unless I switch off one of the lights breakers. (Always the same breaker) If I try to reset the breaker without switching off the lights breaker earth leakage trips again.

None of the lights have any timer functionality. They are all just light switches connected to standard lights. (Some LED)

The only odd wiring is a 2-way switch for a bedroom.

Now comes the weird part. After the breaker trips I need to wait several hours (more than 3 hours each time, usually overnight), and then everything is fine again. I can reset all breakers and everything works as it should, until the issue happens again some days or weeks later.

Has anyone had a similar issue? Any suggestions on diagnosing the issue would be appreciated.

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  • I think that you have already determined which branch circuit is causing the problem. Tracking down the exact location of the fault can be easy or not, depending upon what test equipment you have available. Start by finding out what the leakage current trip threshold of your breaker. That will allow you to calculate a resistor value that you can use for measuring the leakage current as you disconnect wires from devices on that branch circuit.
    – Dwayne Reid
    Commented Nov 27, 2018 at 19:22
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    I would want to hire an electrician on this or purchase a Megger. Start with all the light switches in the off position and the breaker off then meg the hot wire and see if there is a weak point in the insulation. If that looks good remove any lamps / ballast turn light switches back on and try again. A megger is a high voltage ohm meter I would test at a minimum of 1kv since it is intermittently tripping. Depending on how the wiring was done you can pull the neutral and test it also. If insulation tests good then it is down to possible bad devices like ballasts or xformers.
    – Ed Beal
    Commented Nov 27, 2018 at 23:59

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You have an intermittent earth fault, probably triggered by expanding metal pinching something

From the symptoms described, this sounds like there is some piece of earthed metal that is heating up and pinching/damaging a wire when it does so, causing an intermittent earth fault. The heat source can be either environmental or internal, which makes this hard to troubleshoot.

I would recommend a thorough checkout of the circuit's always-hot cabling, with all devices unplugged and all light switches removed, using an insulation resistance tester from both H-G and N-G at the distribution board. (Your local electrician should have access to one.) From there, the circuit can be divided into sections by way of the junctions in it for further troubleshooting.

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