Power supply/Alarm problems

[On net]

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

[ARWadsworth]

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

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?

Adam

[Dave Plowman (News)]

Have you totalled up the maximum load? It's all too easy to add stuff and forget.

[On net]

No, I haven't added up the load - the circuit has been unchanged now for something like nine or ten months and the system trips without any lights on.

[On net]

That would be good news.

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

[Dave Liquorice]

So is the exterior light and loft lights.

Is this an MCB that is tripping or an RCD? If the former leave it tripped and get a new replacement ASAP. MCBs are overload trip devices, one tripping means significant current is going somewhere. Significant current = significant power which could be being disipated as heat somewhere not designed to take that heat. Yes, it could be "tired" in which case you need a new one anyway.

[D.M.Chapman]

Is this a MCB or a RCBO? If it's a RCBO it could be earth leakage - water in an outside lamp? Or in the alarm somewhere?

Darren

[On net]

Update:

Disconnecting the Alarm and security light had no effect on stopping the circuit breaker and left me scratching my head. Even with all lights off the circuit would eventually trip.

Looking at the consumer unit I remembered that we used to have an electrical feed to the garage that had been connected to one of the lighting circuits (before we moved in) but that had been disconnected. On inspection I found that the cabling had been disconnected from the garage but still lay in a covered walkway with some exposure to the elements - this would have been the case for a few years now.

I disconnected that cabling completely and now the upstairs circuit hasn't tripped since about 6:30PM yesterday.

I guess the disconnected cable had been tripping the circuit with the effects on the cable from the weather. One of those cases where the job should have been finished properly.

Thanks for all the great suggestions - much appreciated - I'll be back if it acts up again!

Paul