ARWadsworth wrote:

"On net" wrote in message
...
Our house upstairs lighting circuit has decided to start tripping it's
circuit breakers - with no obvious cause. First suspect was that a
wire had come loose in the last light fitting installed which was a
tight fit for all the connections when it was replaced. I've removed
the light fitting and the dimmer switch, but still the problem persists.

Secondly, we have an alarm system whose power is derived from this
lighting circuit and is doing some rather strange things (spurious
alarms and modes). This alarm has been installed for years and hasn't
been seen by the installer for years either and I suspect the original
installers are no more. I know alarms have a lead-acid battery that
will eventually deteriorate.

It could be a malfunction in the alarm triggering the circuit breaker,
so calling out an electrician could be a complete waste, or it could
just be the alarm is spooked by a circuit fault.

Generally, the circuit breaker can be set, but after a while shuts
off, so I guess that would indicate some form of leakage rather than a
direct contact short.

Current plan is to disconnect the alarm from the lighting circuit and
see if the breaker still has a problem.

Any other thoughts?

Paul

Alarms usually have an internal fuse of around 1A and they should not
cause the MCB to trip. The power loss to the alarm is causing the alarm
to play up not the other way around

That would be good news.

MCBs may fail and become weak in old age. Swap the MCB over with the
downstairs lighting MCB and see what happens.

Is there any chance that the upstairs lighting circuit is overloaded?

Nothing has has changed about the circuit for some time. The unit will
trip even if nothing is active (besides the alarm).

I've just remembered that we also have an exterior security light wired
to this.

I've gone into the loft and removed some of the taps of the junction box
that powers the alarm, loft lights and security light. It's behaving so
far..

...tripped again. The alarm is innocent!

The upstairs circuit hasn't changed for almost a year and it seems to
trip even with the lights off.

I'll just keep isolating bits until it behaves.

Thanks for the suggestions.

paul




Adam