I have ~10 smoke alarms (one per bedroom, one per hall). Somehow the last one isn't working. The green light didn't go on. I've done some troubleshooting - swapped the connectors and swapped the smoke alarm with the previous one on the circuit. This one is at the end of the smoke detector chain.

It seems like the black wire must have been damaged in the wall. I did multi-meter resistance test by hooking all wires at previous smoke together and at last smoke detector checking resistance. White and red seem showed .4, black and red or black and white showed 0. It would be really painful to get a new 3 wire from the alarm back to the previous. The house is modern has few interior walls - the ceiling in this case is a structural panel. The path would go through the studs of a door probably where the wire became damaged. The wire would have been more than 1 1/4" back from the face of any drywall but door jamb get installed with 3" screws and I didn't think about putting a nailing plate anywhere along that stud where a jamb screw could get the wire.

These smoke alarms are from kidde and only do smoke not co. No co devices in house.

Seems like the CEC and NEC handle the smoke detectors differently. CEC requires smoke alarms to be on a circuit with lights and if on an AFCI circuit the smoke needs an integral battery (which I take to mean as something that can't be removed).

I am under the CEC so my plan is to use the red wire to interconnect to the previous alarm(s). I'll cut the black and white of the wiring leading to the non functional back to strain relief in the good smoke detector box. I'll cut the black and white wire back to the strain relief in the non-functional box as well. Then I'll pull a 14/2 for power from a bedroom AFCI outlet circuit up to the non-functional to provide power. I'll get a smoke detector that has a lithium integral battery. The only piece that I may technically fail on would be if the outlet circuit does not have lights on it as well (I haven't checked).

To get a new 3 wire back I'd have to open drywall at the bottom of the wall for 15'. Drill through corner studs and pass through a door header (the previous wire is on the surface of the header which was shimmed out for drywall and then had a large piece of metal as a nailing protector 5" wide x 3' long. The drywall and trim is already painted and caulked.

I wouldn't want to put all smoke detectors on the bedroom AFCI circuit as then I'd need to buy 12 new smoke detectors with integral batteries (one seems reasonable).

I talked to Kidde technical support and the rep claimed that the smoke detectors need to be on their own circuit otherwise they'd be tripped - clearly that is wrong given CEC requires them to have lights on the same circuit.

I tried to address all the comments and I think my plan covers them? Cutting back the black/white in both boxes should prevent anyone in the future from trying to use them and there won't be an exposed hot wire in my wall. I am hoping that the red wire is carrying low voltage so even if there is some damage to it there isn't a worry there? Other thoughts?

  • Are the existing smoke alarms on an AFCI circuit? Also, what make and model is your electrical panel? Commented Dec 16, 2020 at 0:20
  • Existing smoke alarms are not on AFCI. GE TMC4020CCA Commented Dec 16, 2020 at 8:24
  • Can you get a 3-wire cable from the subject box back to any other box on the smoke alarm circuit? Also, is rerouting all power to the smoke alarms to be on this bedroom circuit an option? Commented Dec 16, 2020 at 12:45
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    @TedMittelstaedt "they don't even permit a breaker on the circuit you have to turn off the main breaker to power them down"?!? You better provide a reference for this. You are ludicrously suggesting that a 14 awg wire for smoke detectors gets protected by a 50 or 100 amp breaker????? If this is an attempt to troll then please go elsewhere, this literally affects the safety of a home.
    – MonkeyZeus
    Commented Dec 16, 2020 at 13:37
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    @GeorgeAnderson Thanks for confirming that I'm not crazy, hah. I've read that it's recommended to have them on a lighting circuit because you would quickly notice non-operating lights before realizing the blinky light on the detector is abnormal. Assuming that all of the detectors have a backup 9v battery I think it's really a matter of what you are comfortable with; or just check with your local code officer :-)
    – MonkeyZeus
    Commented Dec 16, 2020 at 14:08

1 Answer 1



It seems like the black wire must have been damaged in the wall.

Well, do you honestly feel comfortable knowing there is an exposed hot wire in your wall?

I understand that if you proceed with your plan then both ends will be capped off but will the next owner of your home understand the necessity for turning off two breakers in order to de-power all of the smoke alarms?

I don't think there is any requirement per se for the circuit to be dedicated. Just make sure a regular light switch does not control them per https://homesteady.com/12359235/what-are-buss-fuses-used-for:

The power circuit providing electricity can be a dedicated circuit, which means it is the only device powered by cables that run directly back to the circuit box. It can also be powered by a circuit that serves outlets and lights if the circuit is not controlled by a switch.

When in doubt, check with your local code officer!

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    Be sure to check local code before proceeding, though!
    – FreeMan
    Commented Dec 16, 2020 at 14:09
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    To address your concern about a broken hot wire in a wall, maybe the OP could disconnect and cap it from the previous smoke in the circuit. It might take a bit of tracing, but that could address your concern. Still doesn't fix the last smoke though. So no answers from me, just a comment (no SOUP FOR YOU! ) Sorry. LOL Commented Dec 16, 2020 at 14:10
  • @GeorgeAnderson Thanks, I addressed that in one of my paragraphs.
    – MonkeyZeus
    Commented Dec 16, 2020 at 14:10
  • Oops, missed that. I should re-read all the posts before commenting. Even the OP said he'd cap it. I just reacted to your comment about leaving an exposed, damaged hot, live in a wall. Take care. Commented Dec 16, 2020 at 14:14
  • @GeorgeAnderson No sweat!
    – MonkeyZeus
    Commented Dec 16, 2020 at 14:17

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