One of the RCDs in the split consumer unit tripped yesterday. It was the
side I'd previously had a problem with concerning the lighting wiring.
Not a good time for a wiring check...

However, a quick check turning off and then on each MCB in turn on that
side showed it wasn't the lighting wiring. I'd got out a 10" desk fan
which hadn't been used since last summer, and that had been on an hour
when it tripped the RCD. Resetting the RCD and turning on the fan had it
tripping again in a few minutes.

I've just dismantled the fan (not easy - many hidden plastic catches and
unreachable circlips) and put it on in free air. After an hour the
outside of the windings were at 87 deg C, and the laminations furthest
from them were at 67 dec C. I assume that if left on the enamel on the
wires would have reached a high enough temperature to fail and rubbed
against the laminations (which are earthed), so tripping the RCD.

Fortunately, I've always got a couple of spare fans and the tip is now
open for electrical goods.

--

Jeff