In message . com,
stevelup writes
Hi

Disconnect everything from the ring, and disconnect the ring from the
CU.

With your multimeter set to the ohms range, do the following
measurements:-

LL (should read low)
NN (should read low)
EE (should read low)

That proves your ring is intact from end to end.

Next, on either of the cables measure between LE, LN, and EN. They
should all read open circuit.

If you get any low resistance readings, perform the same test on the
other leg of the ring as whichever gives the lowest reading indicates
the fault is nearer that end of the ring.

Thanks for that Steve.

A quick lunch break update.

OK, checked over the circuits again, but could not find anything lurking
in the woodpile.

So been trying the above tests.

Looks like a Live to Earth fault- Low resistance/continuity between Live
and Earth. I think I've now managed to narrow down the section of the
ring that the fault is on - there is probably a junction box lurking
somewhere as there is a spur off that probably comes off this leg
somewhere.

I'm thinking that maybe my RCD isn't doing it's job properly? (We have a
TT earth system with just one main incoming RCD - about as old looking
as the CU) The test button works ok though.
--
Chris French