On 29/05/2020 12:23, Smolley wrote:
On Fri, 29 May 2020 11:52:14 +0100, The Natural Philosopher wrote:

On 29/05/2020 10:41, Jeff Layman wrote:
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.

My last and worst RCD tripper was an earth neutral short.
Other culprit have been wet electrics due to weeping plumbing, a stove
element whose insulation was breaking down, and a burned out washing
machine motor that showed a 2k short to earth on the armature windings.

Its easy enough to pop a meter across a disconnected fan switch it to
'on' and see if it has leakage


Not so obvious when the unit is cold.

I have yet to see a direct short to earth that vanished when cold as a
failure mode on ANYTHING



--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone