On 06/08/2013 09:58, Lobster wrote:
Currently being driven nuts by the above... I have a split load CU. When
the RCD trips, it's only that which goes; ie none of the MCBs trips at
the same time which means there's not much for me to go on.

Question 1: if, for diagnostic purposes, I switch off each circuit in
turn by manually flipping its MCB, does that actually isolate the
circuits for the purpose of elimination?

It may prevent the trip, but you can't be certain, since switching off
the circuit leaves the neutral connected. If the cause of the problem
was say for example a neutral to earth short, then the trip could still
manifest.

Or would I need to open the CU
and physically disconnect all the cables from each circuit in turn,
completely?

That would ensure the circuit is isolated.

Question 2: what does the fact that no MCBs are tripping; and the trips
occur at apparently random intervals (4-5 times in the last day, with
interval of up to ~10 hours so far, and including an overnight trip; and
no problem with reinstating the RCD immediately) tell me about the
nature of the fault, if anything?

It tells you there is no associated overcurrent trip. It probably
indicates that you have high leakage that is "sensitising" the RCD (i.e.
using most of its trip current budget, and leaving it close to the point
of tripping), and hence it does not take much to put it over the edge.
Even transients on the mains that could originate outside of the house
may trigger the trip.

Thanks for any pointers!

Try he

http://wiki.diyfaq.org.uk/index.php?...Nuisance_trips


--
Cheers,

John.

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