Mogweed was thinking very hard :
A mate of mine has completely rewired our house so everything in the
installation is brand new, including the split-load consumer unit. We have an
upstairs ring main, downstairs ring main and a kitchen ring main, all of
which are protected by the RCD, and the problem is the kitchen ring.

As soon as *anything* (portable radio, halogen lamp, electric drill or
whatever) is plugged into *any* socket on the kitchen ring, the RCD trips
(plugging the same things into either upstairs or downstairs rings does *not*
trip it).

Splitting the ring at the CU and using a proper Megger (500v insulation
resistance tester, not just a multimeter) to test each leg of the ring shows
the following:

L-N = almost infinity resistance (certainly over 1,000Mohms anyway)
L-E = " " " " " " "
N-E = " " " " " " "

so no short-circuits, but yet the RCD trips. What's the problem - more
importantly, what's the solution to the problem? )

It sounds as if you/he have managed to mix up the ring circuits, such
that - one of the circuits protected by RCD is mixed up with one not on
the RCD. Thus causing an unbalanced load on the RCD, hence it tripping.

Try disconnecting each pair of 2.5mm in turn and make sure you have
continuity between each pair of both reds and blacks.


--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk