Mcb trips but tests clear

[Morsey]

Evening all
Let’s see if anyone can solve this one.
Recently wired a new extension. Today connected up ring circuit to 32amp mcb, all relevant dead testing done ir +999mohms and ring continuity.28 .28 .48. So all good turn mcb on and pop it trips off. Rechecked testing removed sockets just to double check for any small nicks etc all fine. Reconnect and turn on all seems fine. Hour or so later same problem. Replaced mcb all fine. Hour or so later same problem. Any ideas????
FYI nothing plugged in yet so no load whatsoever

 

[Deleted member 9648]

The 1000v IR test will sometimes find a fault when nothing shows up at 500v, especially if you zap it for 10 seconds or so. Regardless of whether it's right or wrong it's done the business for me on numerous occasions over the years.

 

[Deleted member 9648]

Not creative at all Rpa07, fact.

 

[Toneyz]

Sounds like a cable between both points has been nailed/screwed etc catching the live and going into the fabric of the building what work has been carried out between the two points in time?