New twin RCD board install, replacing wylex rewireable one.
Energised the board.. trip.
Id tested the whole house prior to the job with not too many faults...
However, it'd had lots of work done to it over the last 20 years.
The main culprit was one of the RFCs. However, there were other circuits which seemed to add to the problem.
Took the RFC in question, split into 2 radials to narrow the fault. Identified the half causing the problem and split that down even more.
Eventually found this in a socket, spurred off the ring. The little nick in the wire was
just touching the earth terminal of the socket. Snipped it out and re terminated.. hey presto everything fine..
The annoying thing is it didnt show out on IR test, even when testing just that spur from the other side.
The only explanation I can give is that it must have been a fraction away from the contact, but when energised it was close enough to jump the gap..!!
3 hours of hunting... but got there in the end.