Just spoke to a sparky in Screwfix. (well, claims to be a sparky)

Claims you can supply alarm control box mains from light switch !!

 

Surely not ????

You could supply it from whatever you want, that doesn't mean it will conform to standards or safe working practices.

Ideally would have it's own MCB in the CU or a spur from a power circuit, but I have seen all sorts in my time.

 

Also it wouldn't matter about the building being complete, most jobs are retrofits.

a light switch usually has no neutral so id assume either pulling your leg or cretin 

Lighting circuits are fraught with interference, fluorescents, chokes etc. not good practice.

most systems are wired 3 plate, id of took his name and get anything to work of a switch

TBH in the old days, most domestic alarms were in the cupboard under the stairs etc... and that was usually the one place you would find a neutral

behind the light switch, as that fitting wouldn't be part of a loop circuit, in my experience anyway.

 

But yes I've been out to a callout where the report was 'alarm sounds whenever cupboard light turned on', this was 3 months in and some moron

had wired onto the back of a switch. Of course, back then a 60w lamp would have enough of a resistance to provide a relative neutral to a low load

such as a transformer.

 

This was when I worked for a decent setup, but they had used a contractor for the first (and last) time ever on an alarm job. Only the finest...

Edited June 23, 20178 yr by datadiffusion