Interlinked alarms - power supply

[John Mulrooney]

Hello,

I'm starting to install some interlinked smoke and heat alarms. Can they use L & N from different circuits, or sgould they have a seperate dedicated one.

John M

[spuorgelgoog]

All alarms must be on the same circuit.

It doesn't have to be a dedicated alarm-only circuit and there are good reasons for it not being so; but the alarms should then have battery or capacitor back-up.

On a mixed use circuit you are likely to notice a supply failure more quickly than if only the alarms are affected.

Owain

[Bob Eager]

Or do what I do and put a prominent non-maintained emergency light on the same circuit. Useful in its own right.

[John Rumm]

Yup that was my preferred solution as well. I also fitted a centralised switch so that the alarms can be tested or silenced from one place easily (since some are well out of reach on 10' high ceilings)

[Tim Watts]

The must be on the same circuit and generally are put on a lighting circuit (ground floor preferred) so that circuit trip is immediately apparent (evening/night at least).

[ARW]

If you do that then there should be a means of isolating the smokes whilst still leaving the lights powered up.

[Tim Watts]

Is there a recommended way? I presume it should not be *too* easy? Emergency key type test switch or just an out of the way normal isolator?

[John Mulrooney]

Thanks all inc. Tim & Adam, got the idea

John

[spuorgelgoog]

Perhaps in theory, but I'm unhappy about having isolators on smoke alarms in case it's left off.

Anyway, I didn't fit an isolator as I used the smoke alarm circuit to back feed half the lights.

Owain

[ARW]

For a RCD protected circuit I would suggest a double pole key switch. For a non RCD circuit (16th edition) an unswitched fused spur would be fine on a TN supply.

[The Natural Philosopher]

My BCO insisted I have a seperate smoke alarm circuit. They have green LEDS in em - obvious when the wife has left the bath running and tripped em again by letting water cascade through the floor

[Tim Watts]

OK -

Can I just query the rationale though? I was just thinking that it would not shut them up as they've all got batteries of some sort and if it's a matter of replacing them, most of the ones I know of plug into a base.

Sorry for being thick - I assume there is a good reason, just not one I know of!

[Dave Liquorice]

Good idea, there is a non-maintiand emergenct light above the strairs but I think it's on a lighting circuit not the dedicated smokes one. I'm not going to play just at the moment...

Yep, ours has "locate", "test" and "silence".

No one has mentioned that the smokes wiring ought to be done in red three core and earth. I'd also do it as a seperate circuit for the smokes only even if the power comes of a lighting circuit rather tahn just picking up the nearest bit of lighting power.

[John Rumm]

Yup, that's the beastie - three rocker switches on a single faceplate.

Should be 3&E certainly... not sure if the colour requirement applies to domestic though?

[ARW]

Possibly because it is not required for a grade D LD2/LD3 domestic install:-)

One of the troubles with smoke detectors is that there are 3 different regs to refer to

You have BS 5839-6 BS 7671 and Part B of the building regs.

[ARW]

Oh and there is the NICEIC who make up whatever rules they want to when doing inspections.

[Dave Liquorice]

I did say "ought" not "must". B-) Makes sense to me to use red so it's obvious its the smokes circuit when faced with a gert bundle of cables.

Isn't the red PVC stuff a bit tougher than bog standard grey?

[ARW]

Do you mean red fp cable?

If you want a bastard cable to work with try the LSZH ones.

Cheers

[charles]

Pyro is even more fun.

[spuorgelgoog]

And then the Scottish Government housing office, and the local council housing office, and the local fire service, etc etc who all make up their own versions too.

Owain