I am sure you have all heard this before
Anyway, i had an issue with a property were the earth leakage would trip for no reason, randomly. But more often when the garden lights were being used, So i had to put on my thinking cap and actually go do some work.
One of those jobs. I tested all the cables and lights made sure everything was clear then left. That night my phone rang, earth leakage tripped again.
I stripped the entire garden light circuit, removed all the lamps and tested again, all clear over 10 Meg. I disconnected the garden lights from the main (house) earth leakage and fitted an earth leakage unit next to the switch as a temp measure.
Then i did mA leakage readings, first on the earth and then across live and neutral. The leakage on the earth wire was so little it wasnt worth wasting time on it. However the live and neutral leakage was 14.6 mA on the main DB without anything switched on and 5.6 mA when testing the garden lights. So what i assume was happening is the mA added together plus leakage current once other devices were switched on exceeded the threshold of the earth leakage. the highest leakage recorded was traced back to an element in the stove disconnected and bingo problem solved. No more earth leakage tripping for now. The earth leakage is an old unit which trips at around 20 mA when I recorded tests with the earth leakage plug test.
Normally when i do domestic fault finding I dont really pay much attention because it is such basic stuff, but every now and again you get one of these interesting faults which test you.