Mains Smoke Detector

[Stroppy]

Nope, no requirement for separate isolation. I suppose it could be handy in the once-in-a-blue-moon event of changing an alarm in the hours of darkness, but don't think most people would bother.

Yes they can come straight off the mains feed for the lights continuing the 1.0/1.5mm t+e mains cable to the first alarm, then carrying on to the others in the same CSA 3core.

Think of your circuit as a 6 amp circuit, which happens to have lights and alarms on, rather than a lighting-only circuit that has been hijacked with alarms.

 

[oldtimer]

Coz there's no point in having another fuse!

Yes there is if you are testing the circuit or you need to isolate it to say change a battery. I do work for letting agents and for some reason a lot of detectors indicate a low battery during the night with tenant hauling them of the ceiling because they turned off the circuit when they went to remove the head leaving them in the dark lol

 

[Stroppy]

Isn't that the argument in favour of a DP switch for isolation? I just don't see the value in introducing a fuse into the circuit.

(All I need now is for someone to point out the smoke alarms instructions demand they are protected by a 3 amp fuse, like those stupid bathroom fans!)

 

[oldtimer]

Isn't that the argument in favour of a DP switch for isolation? I just don't see the value in introducing another fuse into the circuit.

Yep I agree and as I said this subject is full of urban myths thats because say a local council decides it wants a DPFCU but another says no put it on with the same lighting circuit so its open to debate mind I am not complaining if the tenant hauls it off the ceiling its a job for me lol

 

[Tuttle]

I've wondered about that as well. Approved Document B (Fire safety), Volume 1 (Dwellinghouses), section 1.19 says "There should be a means of isolating power to the smoke alarms without isolating the lighting" but manufactures instructions I have looked at say "The circuit used to power the alarm must be a 24 hour voltage circuit that cannot be turned off by a switch". Not sure how you are supposed to comply with both of those, an unswitched FCU maybe. I think I'd prefer no separate isolation for the smokes but I'm not sure that is allowed.

 

[oldtimer]

Tuttle I think the mentality is as long as there is a smoke detector fitted then they can discuss the detail later a bit like Part P lol

 

[lauriehurman]

As others have said "best practice" is to power them from a "well used lighting circuit" with an isolation so that they can be worked on in the dark.

In practice, giving the tenant the means to turn them off when they go off is a bad idea.

Personally I wire each one from an adjacent light junction and use a radio interlink. Expensive but much cheaper than trying to run a new cable up three levels of an old house. Lets face it - if you can't get the punter to pay for it then you're wasting your time anyway.

Laurie

 

[Stroppy]

In practice, giving the tenant the means to turn them off when they go off is a bad idea.

Double pole key-switch?