On 28/02/2019 12:21, bert wrote:
In one bedroom we have a ceiling fan supplied from the lighting circuit.
It's been there for over 10 years no problems.
In the past few nights a couple of times when switching it off the RCD
protecting the ring mains has tripped. But the lighting circuits don't
go through it and the lights are still on including the one which is
part of the fan and the fan itself can be switched back on.
Puzzled as to how this can happen - and where to start looking.

Possibly a suppressor in the motor has failed and the resulting
inductive spike is coupling into an adjacent circuit. Makes sense as
you say it doesn't always happen, probably only when the voltage happens
to be on a high part of the AC cycle.

Cheers
--
Clive