Emergency lighting Smoke alarms

[qubit]

Hello if I want to wire up 3 mains smoke alarms (interconnected) would I use 1mm 3 core and earth and a separate 3A MCB? I'm thinking I'd rather connect the smoke alarms to the landing ceiling rose that way if the smoke alarms lose supply I'll know because the lights will go out. Is it okay to go 1mm twin from ceiling rose to first SA 1mm 3 core to 2nd SA 1mm 3 core to 3rd SA (i.e serial from bottom floor to top)

Also would I wire emergency non maintained luminaires to any nearby ceiling rose using 1mm 2 core and e (do they automatically detect loss of supply) and can I run 1mm 2 core and e to an existing lightswitch from luminaire so that if I wanted a key switch in future it would be quite simple (knock out another switch box next to existing lightswitch) any help greatly appreciated pleeeeeese

 

[electronicsuk]

If you can manage it then you should run a dedicated supply back to the CU for the smoke alarms, protected by a 6A (I haven't seen many/any 3A) MCB. Cable conductor size depends upon the length and nature of the run, but generally speaking 1mm T+E from CU to first detector and then 3 core+E from thereon to the last detector.

Wiring emergency lighting to a nearby ceiling rose is fine, this make more sense than putting them on their own circuit as it guarantees that should the lighting circuit lose its supply then the emergency luminaires will come on. They are, of course, automatic in the event of a power failure. Again, running a T+E back to somewhere fairly local for a test switch also makes sense.

 

[Lectrician]

If you are taking the feed from a light fitting for your EM light, I would place a keyswitch on the ceiling butted upto the EM fitting. I wouldn't bother dropping it down the wall.

If you where wiring several EM fittings on the same cable, then one keyswitch somewhere central, or adjacent to one of the EM's would be fine too.

As for the smokes, the rule has always been that mains smokes with battery backup can go on their own circuit or share a well used lighting circuit. Mains smokes WITH NO battery backup MUST be on a local well used lighting circuit.

 

[qubit]

Okay thanks very much for the informative quick replies Mr Lectrician and Mr UK sorry electronics I meant 6A I dunno where I got 3 from but isn't it that if the smoke alarms are connected to the light circuit then their non mains powered time would be minimal and the risk of them having no power and dead batteries (let's face it most people don't pay attention to the batteries I've been to many houses where the alarms are beeping like mad and nobody pays any attention) is minimal avoiding a catastrophic situation.

I was thinking a keyswitch on the ceiling would look very ugly and maybe a little unproffessional and 1mm cable is fairly cheap but thanks for the idea I may use it (especially if I run out of 1mm ) if I did then do these keyswitch thingies use a standard mounting box? Say if I ran 3 smoke alarms in serial over like 8m 1mm should be okay huh?

 

[electronicsuk]

Say if I ran 3 smoke alarms in serial over like 8m 1mm should be okay huh?

I presume by serial you're actually referring to wiring them in a daisy-chain connected in parallel? The current these things consume really is minimal. Unless it's a very large installation then you are unlikely to suffer any volt drop issues, and if it were on such a scale then you would probably be installing a proper fire alarm anyway.

 

[qubit]

I mean like this

Ceiling rose =1mm 2core+e= 1stSA =1mm 3core+e= 2ndSA
=1mm 3core+e= 3rdSA finished with about 5m distance between each

 

[nozspark]

One of my local wholesalers do a EM fitting with a key switch built in!!

 

[electronicsuk]

I mean like this

Ceiling rose =1mm 2core+e= 1stSA =1mm 3core+e= 2ndSA
=1mm 3core+e= 3rdSA finished with about 5m distance between each

Yup, that would be a daisy chain (or radial to coin the correct term) with everything wired in parallel. It should be fine.

 

[securespark]

MK do a 3A MCB.

 

[RF Lighting]

It's like Déjà Vu all over again

 

[qubit]

tanks very much guys