ECN Forum Forums Code Related Discussion NEC & other Code issues Smoke Alarms

If they are saying when the white wire and the red wire are at the same (or close to the same) potential the alarm goes off but that implies it floats at 120v normally. If you tagged both sides of the panel with different detectors wouldn't that be 240v?
I tried to find out how my Kidde detectrors worked because I wanted a heat detector in the garage but they seemed very close mouthed about details.

G, I really don't know the internal details.

Nothing inside the detectors operates at 120. There's a battery, remember? You'd have to test one to find out for sure how they operate.

I guess I will look into it. You are right, this has to be 9v or so, which brings us back to where the horn drive comes from. You can use the neutral for a DC common but that puts battery voltage on the signal wire to blow the horn. If this is not buffered by the remote detector (relay or solid state) it still depends on the supply coming from the signalling detector. It even takes a bit of current to pick a relay. Probably more than the horn.

Now, that is one detail I can speak to ... in my testing of smoke alarms (lab setting), it was the horn that gobbled up the power. This, indeed, was the reason the first smokes had to use special batteris (F cells). The entire reason for the change to the higher-pitched electronic horns was that the mechanical ones simply used too much power.

If you need 24 or less devices try these out from Kidde.

http://www.kidde.com/utcfs/Templates/Pages/Template-53/0,8062,pageId%3D4363%26siteId%3D384,00.html

I saw that they say all the alarms must be connected to the same branch circuit "single continous (non-switch) power line, which is not protected by a GFCI". I guess AFCI is fine. It also says 18 ga wire up to 1000' is OK.

Greg- I'm still not comfortable with what I'm reading and I don't see anyone wiring smoke alarms (single station) with #18 wire. I think what was discussed in this thread has to do with a fire alarm system. Set me straight!

I am guessing they are saying the signal wire can be 18ga. That might be an issue with wire in pipe. I haven't seen any (2)14-(1)18/3-wg Romex

The link Rob posted is for the regular residential interconnected single station smoke alarm and it does say "up to 24" on the loop

Greg- I went back to that link and read the data sheets and it's talking about "devices" and includes mainly initiating devices (heat sensors, pull stations etc) and when you read all the data, you are still looking at 12 Smoke Alarm enunciating devices.