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sootybuttercup 09-19-2006 07:46 AM

12 Smoke Alarms
I am installing Kidde brand smoke alarms in a new home. There are 16 smoke alarms and 1 carbon monoxide sensor that are all interconnectable to a maximum total of 18 untis according to Kidde. I have read that there should be no more than 12 smoke detectors interconnected. I am wondering if this is a "U.S. only" rule (I am in Canada) and what the reason is for this. I would think that it would be better to have all 16 units connected together. Anyone know more about this? Thanks!

redline 09-19-2006 12:00 PM

How many square feet is this home?

I would think that if 12 smoke alarms were to sound at once then that should get your attention.


sootybuttercup 09-19-2006 01:15 PM

3000 sq ft with detector in every room/hallway except baths. No problem to split the circuits but seems like less protcetion to not have all alarms sounding. Example: basement electrical room fire sounds only basement alarms while people sleeping on 2nd floor don't get warned. Too late to split system 1/2 per floor. Wondering why the rule for max 12 was developed?!

mdshunk 09-19-2006 03:35 PM

The 12 max rule is a limitation of the detectors. The way around this is to put a relay accessory (available from kidde) and do two circuits of smokes and all your smokes will still sound at once.

sootybuttercup 09-19-2006 03:58 PM

Actually it isn't a limitation of these detectors. The manufacturer states that 24 can be interconnected with up to 18 initiating (ie: 16 alarms and 8 relays) but "should not exceed NFPA limit of 12".

mdshunk 09-19-2006 04:09 PM

That manufacturer instruction might be referring to NFPA document 72, which does not have the force of law for dwellings in most of the US.

darren 09-19-2006 05:21 PM

Up here in Canada we are only allowed 12 devices on a circuit. So if they are 120V smoke dectors you are allowed only 12. I will have to look through my code book and see if i can find the reference for it.
So you could cheat and put 16 on one circuit, but this is against code.
The only other way I can think to do it for they are all connected is to run 14/3 to the first one then run 14/4 between sm1, sm2, sm3, sm4. Use the black to power the first four detectors, the red would get marreted at each detector for your second circuit, and the blue would be the common between them. Then between the rest of them you could run 14/3. Using the black(which would be tied onto the red in detector 4) this would become your hot and then use the red to link the rest together.
Hope this makes sense and not confuse you more.

14/3(SM1)-14/4(SM2)-14/4(SM3)-14/4(SM4)-14/3(SM5)-14/3(SM6) and so on

sootybuttercup 09-19-2006 05:34 PM

darren...i know about the "12 devices on a circuit" thing but i don't think that is where the limitation is coming from...especially from devices rated at 80 mA the manual says "maximum 24 devices on the long as maximum 12 are smokes". This 12 thing is coming from somewhere else....and I'm curious as to why this rule was made...and by whom. thanks you see anything in the CEC about this?

darren 09-19-2006 08:06 PM

hey there
This is what I found in the code, if you have a code book it is rule 12-3000.

Subrule 1 says that there should be no more then 12 outlet on one circuit. Not sure by outlet if they mean just outlet or outlet and lights. I have always been told lights fall in there to. So 8 plugs and 4 lights would fill a circuit. A side note a light switch does not count as one of the 12 because it use no power.

Subrule 2 says Such outlets shall be considered at no less then 1A per outlet. This is where the 12 rule comes in. 12 outlets rated at 1A each equals 12A and accodiring to our code you can not load a breaker to more then 80%. Hence 15x.8= 12A

Subrule 3 says when the connected load is known, the number of outlets shall be permitted to exceed 12 providing the load current does not exceed 80% of the rateing of the overcurrent device protecting the circuit. According to this rule I think you would be allowed to put all 16 on one circuit since you no the load and it is well under 12A.

So I hope this helps answers some of your questions

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