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Question DetailsAsked on 7/27/2013

3rd wire on smoke alarms not tied in to buss bar. Will this cause the alarms to continually chirp?

Alarms are wired in series but the third wire was added after installation and not tied into the breaker box.
The third wire was added after using 12-2 wire with a ground. Batteries have been replaced but alarms continue to chirp. Will not having the third wire tied into the buss bar cause the chirping?

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1 Answer


Hard to tell without seeing your wiring.

Here is a link to the normal wiring (NOT every single type of alarm, especially European designs, some of which use a digital signal over the neutral to trigger the others, instead of using a separate alarm wire) for interconnected multiple alarms. There should be a wiring diagram inside the cover or on the back of your alarm housings, or find your make and model number on the back and check for wiring instructions in the instruction manual on their website.

Basically, if the above diagram is your proper wiring scheme, normal 12-2 wire plus bare ground would come from the breaker (and ground bus) to one alarm. From that alarm to all others, there would be 12/3 + ground to each alarm, either in line parallel or as stub branches. I presume in line in parallel is what you meant when you said in series, not actually "in series" - though looking at an individual wire path (as opposed to the electricity flow in the circuit) I guess you could say the alarms are in series on the circuit - just not electrically "in series".

That way, each has a ground and neutral (bare copper and white) of course which is connected to all others, and a live wire (normal black wire) connected to all others to keep the alarms "live" and able to detect fires. When any one alarm triggers, that activates power into the second live wire (red) - the "alarm" wire, and power goes through that wire to all the other alarm horns or bells also, causing them to sound also.

In some alarm models, the chirping can mean both dead battery and alarm circuit not correctly connected, so maybe that is what is happening.

The third wire does NOT go back to the breaker - if you did that it would be powered all the time, so all the alarms would sound continuously (if wired between alarms right).

I would test each alarm with the test button (if there is one) or with test smoke in a can (about $5 at Radio Shack, fire supply and safety stores, most home improvement stores), then find which alarm(s) do not sound - there is probably the problem.

If no alarm sounds when you test one, then that one is probably missing a neutral or live connection. If the tested alarm sounds but no others, then red connection problem. If at least one other but not all sound, then the not-sounding ones have bad red or neutral connection. As you work from one to the next, you should be able to narrow it down pretty easily.

Good luck

Answered 7 years ago by LCD

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