Smoke Alarm General Questions

[daiking]

Could someone give me an idea of the additional wiring required to interlink smoke alarms if they're powered from a local light supply. I also have 2 alarms on their own circuit but it only uses T&E so they don't work together. Do you need to run and addition power cable between them all or just comparable sized cable that carries the signal?

 

I googled but didn't quite know what I was looking for. I'm not intending to do it myself but scoping the work required so that I can determine how I want it run.

Edited August 8, 2016 by daiking

[PeterW]

Usually 3&E and the 3rd core providing the interlink 

[daiking]

1 minute ago, PeterW said:

Usually 3&E and the 3rd core providing the interlink 

 

I know but it's late for that! 

 

Is it possible to retrofit/add the link or is it wireless only now?. I'd prefer not to go wireless if there's another option

[ProDave]

Yes as Peter says. T&E to first alarm, thereafter 3 core & E to second, third, 4th etc. 1mm  is plenty.  Any electrician should know this.
 

[daiking]

8 minutes ago, ProDave said:

Yes as Peter says. T&E to first alarm, thereafter 3 core & E to second, third, 4th etc. 1mm  is plenty.  Any electrician should know this.
 

 

Clearly not. This is a previous over sight, the extension doesn't have any  

Edited August 7, 2016 by daiking

[PeterW]

Not sure what the signal voltage is but you may be able to run a single wire between them ..?

[Onoff]

18. What cable do I need for the interconnect line?

Use the third core of 6243Y cable as stated above. Do NOT use the earth wire of twin and earth cable as this could cause problems of mistaken identity at a later date.

[daiking]

I'll do a sketch later on current layout and see what 'we' think.

[ProDave]

If it's a "mistake" and the system has been wired without interconnects, then if it's to difficult to rewire, consider using RF link bases for the smoke alarms instead.
 

[Nickfromwales]

8 hours ago, PeterW said:

Not sure what the signal voltage is but you may be able to run a single wire between them ..?

I'm sure it's 230v as you'd not be able to run differing voltages in the same ( 3 core + E ) cable   

[ProDave]

I believe the interlink to be 9V (presumably with reference to N)

 

Set up a string of smoke alarms that are mains powered with battery backup, and you will find they all work, and all sound together, even with the mains power off.

 

Also (contrary to manufacturers instructions) I find different makes also interlink together. In fact I have not yet found 2 makes that refuse to work together.
 

[daiking]

So it only needs to be 3&E between the alarms but the bit between the MCB and the first and last alarms is normal T&E? That might be doable now. (Does the cable return in a loop or is it just a single string out from the CU? I am clueless at electrics)

 

the alarms that were fitted (now ruined by dust ingress) only had a L/N/E connector though. Could these not have been interlinked anyway? Some Knightsbridge s*** or something. (That's not true, its not L/N/E the third wire is yellow not yello/green so its the signal for the alarm)

Edited August 8, 2016 by daiking

[daiking]

Now I know what I'm looking for...

 

http://www.aico.co.uk/How-do-I-wire-hard-wired.html

[Onoff]

I've seen it done as a "lollipop" circuit before. That is T&E from the cu to a central junction box then "spoked" off of there via WAGO blocks in 3-core & E to each alarm.

[Nickfromwales]

Apparently your not supposed to do that ( radial ) method. Afaik your supposed to daisy chain from the first to the last and not T / branch off to do any on the way. 

 

@ProDave. Makes perfect sense re the 9V trigger now you mention it. Power cuts being accounted for etc. Cheers. 

[daiking]

3 minutes ago, Onoff said:

I've seen it done as a "lollipop" circuit before. That is T&E from the cu to a central junction box then "spoked" off of there via WAGO blocks in 3-core & E to each alarm.

Raiding my ebuild account has brought up this:

http://www.ebuild.co.uk/topic/18486-hard-wired-smoke-alarms/

(Save your breath, comments previously on ebuild)

 

so the bathroom floor void one is the first alarm and the loft is the second, on a 'string' not a 'loop' as there is only one T&E

 

Bloody hell, almost ready to consider an alarm plan.

[Onoff]

13 minutes ago, Nickfromwales said:

Apparently your not supposed to do that ( radial ) method. Afaik your supposed to daisy chain from the first to the last and not T / branch off to do any on the way. 

 

When I saw it done like that (admittedly only the once) I did wonder but then figured the makers (Aico & Kidde certainly) are happy for you to tee off of the radial run to alarm locator and control switches.

 

EDIT: Could it be that it would generally be expected "historically" that if using a central "JB" it would not be of the maintenance free type and subject to screws loosening and losing power to the whole lot or the interconnects. Hence the WAGOs?

Edited August 8, 2016 by Onoff

[daiking]

Having cleared the brain fog, I'm now looking at a smoke alarm layout here:

 

 

[Temp]

Quote

So it only needs to be 3&E between the alarms but the bit between the MCB and the first and last alarms is normal T&E?

 

T&E from the CU to the first alarm.

3&E between the alarms.

 

Quote

That might be doable now.

(Does the cable return in a loop or is it just a single string out from the CU? I am clueless at electrics)

 

It's not a ring. Just a radial. 

 

About a month after moving in our alarms started beeping in the middle of the night indicating low battery. I replaced the batteries and a month later they started beeping again at 4am.  It turned out our electrician had used 3&E between the alarms and managed to get two wires crossed over between the floors. For two months the alarms on one floor had effectively been running on the internal 9V batteries not mains. Lucky they hadn't been damaged.

 

One day someone will invent an alarm that tests it's batteries at mid day rather than waiting for the voltage to fall when they get cold which usually happens around 4am.

 

Edited August 8, 2016 by Temp