Roger wrote:


Well I certainly managed to trip the RCD in my sisters house while
working on a disconnected ring main. I put it down to the fact that the
MCB only isolates the live and the neutrals are all linked thus a
neutral/earth short anywhere on the system will give an alternative
return path for any device drawing current.

Exactly so. Congratulations: you've managed to say in 5 lines what
usually takes me several screenfuls - and just took Andy W nearly as
long, but with more cases more thoroughly considered - on the frequent
occasions that this FAQ comes up!

Stefek