John. Cambridge UK wrote:
Had a similar problem recently where there was nuisance tripping about 3
times a week. Had trouble putting the RCD back online. Checked the
Earth-neutral and found a lot of leakage on a SWA exterior connection (using
a standard multimeter). Disconnected this feeling very good and no trips for
a week, then occasional trips started again. Bit the bullet and changed the
RCD - bingo, no trips now for over two months.So it can be just a faulty
RCD.

It could simply be that the old RCD was near maximum sensitivity and
the new one near minimum. A 30mA RCD *must* trip at or below 30mA
leakage but may trip all the way down to 15mA and still be within
specification.

A large installation (as ours was before I replaced consumer units and
installed multiple RCDs) may well cause nuisance tripping of a single
30mA RCD simply because of its size. Even when all insulation
resistance etc. is within specification if there's enough little bits
of leakage they will add up to something that trips the RCD,
especially on wet days and/or when a number of PCs are turned on.

--
Chris Green )