Got called out to an odd one. Dual RCD board and the left hand RCD went off and wouldn’t come back on. Nothing was being done at the time, couple were watching TV.
So went today and had a look. No shared neutrals.Narrowed it down to the kitchen ring and left hand side upstairs lights and utility extractor fan.
Both circuits had a dead short on IR test.
On the socket ring the L-N was a dead short but the L-E and N-E was fine. End to ends were fine.
The light and fan circuit was a dead short on all 3 for both cables.
However these circuits feed diagonally opposite sides of the building (it’s a huge farm conversion). There’s no loft space as it’s vaulted ceilings. So there’s about 40-50mm of space between the upper floor ceiling and roof at the apex. And approx 30-40mm between downstairs ceiling and upstairs floors
Initially I thought rodent damage, and could still be. But given the seperation of the circuits then I can only guess the rodent damage is close to the consumer unit. Or that it is poor workmanship with some errant capping/dodgy junction boxes.
Going back next week to try and locate the issue.
Anyhoo, after a long winded explanation. I noticed something else today when I had the cover off. See if you can spot it.
To help, the circuits from R-L (starting at the RCD) are
Kitchen ring (with the dead shorts)
Lounge and studio ring
Utility sockets
Integrated oven and microwave
Central heating
Kitchen and patio lights
Lounge, studio and rear patio lights
Upstairs left hand side bedroom and bathroom lights and utility extractor fan. (Again circuit with dead short in both the light and extractor fan circuit)