Identifying exact cause of earth leakage

[LuckyBenski]

So, 2 weeks ago I came home to find several ring mains off. It had been really REALLY stormy while we were out - but I didn't connect the two. I investigated and basically we have a secondary consumer unit feeding the upper half of the house - its RCD had tripped taking that entire section out.

It happened again during rainy weather and I started suspecting it was a leak into the loft, affecting lighting rings. Long story short - the cause is two exterior lights on a roof terrace in my landlord's room. His builders mounted the light switch upside down so I didn't identify it when testing the first time

Recently (past month) the walls bearing these lights and cables have been modified (neighbour removing shared chimney stacks and adding air bricks).

So - given the fault is directly affected by rain (only trips literally while it's being rained on heavily) - and it's only a short stretch from the doorway, along to one fitting and then the next... How do I identify which bit is causing leakage to ground?

I'm guessing this isn't something a normal multimeter can do. I'm an electronic engineer and would rather not raise the dispute with neighbour so, if I can identify it myself I'll happily sort it.

Suggestions?

 

[Adam_151]

You need an insulation tester, now come high end multimeters do have the functionally built in, but its very few. A decent one costs a fair amount, but second user and no name ones are available on ebay. You do also need to know how to use it without blowing up electronics.....

 

[LuckyBenski]

You need an insulation tester, now come high end multimeters do have the functionally built in, but its very few. A decent one costs a fair amount, but second user and no name ones are available on ebay. You do also need to know how to use it without blowing up electronics.....

Cheers, I've considered it although it would be one of those tools taking up space for very occasional use. Like a lot of things!

But would it help me find the exact issue? I know exactly which section of the ring is failing (the outdoor bit!). I suppose visual inspection is best at this stage.

 

[b0rn2sk8]

Unless you have an obvious leaks in the house all signs point to any electrical items which are outside, so the lights themselves or any exposed wiring.

I doubt you’ll be able to reliably use testing equipment to find the fault because it’s the water bridging the insulation.

 

[gc123]

Cheers, I've considered it although it would be one of those tools taking up space for very occasional use. Like a lot of things!

i use the old addage when trying to explain this to the wife...yes it cost a lot, no i dont use it all the time, but when i need it nothing else will do the job always works and yes i have lots of rarely used items/tools

 

[BigBoy]

I would be looking at the termination on the light fittings them selves, my bet is poor insulation within a metal fitting. Water ingress will then make it trip.

 

[LuckyBenski]

I would be looking at the termination on the light fittings them selves, my bet is poor insulation within a metal fitting. Water ingress will then make it trip.

Both lights are metal bodied and look poorly sealed so hopefully you're right. Weirdly they looked bone dry inside but it's still going to be my first port of call.

 

[NoobCannon]

You need an insulation tester, now come high end multimeters do have the functionally built in, but its very few. A decent one costs a fair amount, but second user and no name ones are available on ebay. You do also need to know how to use it without blowing up electronics.....

you dont test earth leakage with a insulation tester. You need a clamp meter.

@LuckyBenski If the cables have been moved theres likely some connections somewhere, tripping like that is likely water on the terminals or inside the light itself Some pics would help but you really need an electrician