Small CU with DP switch + 20A Type B MCB ->
100m of 10mm SWA ->Garage CU with DP switch + 2 RCBOs (16A & 6A)
The first third of the SWA is buried under tarmac & grass. The last two thirds are above round, running through rough scrub land (brambles, small trees, rhododendron etc). The intention is to bury this in the next couple of years when I get around to clearing the land. The earth at the head end is connected to the SWA armour. This is not connected to anything at the garage end; I've fitted an earth rod at that end.
Recently (the last 4 months or so), the 20A MCB at the house end has been tripping. It doesn't trip immediately; it may be a couple of hours or a couple of days after reset that it trips. I've done various tests, but the most poignant ones are:
- With SWA disconnected at the head end, it doesn't seem to trip
- With SWA disconnected at garage end it does trip
- With SWA disconnected at both ends, using a simple DMM on highest resistance mode, I measure open circuit between all conductors
So, it looks like the problem is an intermittent short in the SWA somewhere, I guess caused by moisture getting into a damaged area. I've examined the portion of cable that's still above ground which seems fine. The ground near the buried section has not been disturbed since installation. My question is where do I go from here? Any other tests I can do?