Connecting existing 120v smoke detectors together with low voltage wire.

[jgarciat]

Hi everyone, long time lurker first time poster.

I'm doing a residential remodel in the California. There are existing smoke detectors in the correct locations and all the smoke alarms are tied to the same lighting circuit. The problem is that there was no additional wire ran for communication between detectors. I've done some research and found that the alarms communicate via low voltage. My question is , would it be possible to connect all the alarms by running some low voltage wire?

 

[Rick 0920]

The answer is yes. I worked for a contractor once who wired all his interconnected smoke detectors with 14-2 and ran a #16 TFFN alongside each run. The interconnect of smoke detectors works off the 9 volt battery. This raised eyebrows for sure but it was a code compliant installation. At the time, 14-3 was much more expensive than 14-2.

 

[hbiss]

The answer is yes. I worked for a contractor once who wired all his interconnected smoke detectors with 14-2 and ran a #16 TFFN alongside each run. The interconnect of smoke detectors works off the 9 volt battery. This raised eyebrows for sure but it was a code compliant installation. At the time, 14-3 was much more expensive than 14-2.

installation instructions

From Kidde:

WIRING REQUIREMENTS • This smoke alarm should be installed on a U.L. listed or recognized junction box. All connections should be made by a qualified electrician and all wiring used shall be in accordance with articles 210 and 300.3(B) of the U.S. National Electrical Code ANSI/NFPA 70, NFPA 72 and/or any other codes having jurisdiction in your area. The multiple station interconnect wiring to the alarms must be run in the same raceway or cable as the AC power wiring. In addition, the resistance of the interconnect wiring shall be a maximum of 10 ohms.

So, to answer the OP, the answer is no. I would suggest that you look at the ones that communicate wirelessly. They work well.


-Hal

 

[Rick 0920]

installation instructions

From Kidde:

WIRING REQUIREMENTS • This smoke alarm should be installed on a U.L. listed or recognized junction box. All connections should be made by a qualified electrician and all wiring used shall be in accordance with articles 210 and 300.3(B) of the U.S. National Electrical Code ANSI/NFPA 70, NFPA 72 and/or any other codes having jurisdiction in your area. The multiple station interconnect wiring to the alarms must be run in the same raceway or cable as the AC power wiring. In addition, the resistance of the interconnect wiring shall be a maximum of 10 ohms.

So, to answer the OP, the answer is no. I would suggest that you look at the ones that communicate wirelessly. They work well.


-Hal

Hal, I agree with you. I was stating what a contractor did and inspector did not have a problem with it. If the interconnect conductor only has 9 volts on it and is run alongside the 14-2 (maybe even secured to it by cable ties), then the way it was installed years ago may have been perceived as fine. This was years ago back when it first required to have your smoke detectors interconnected. It is possible that those requirements were not in the instructions at that time. I appreciate you bringing the instructions to our attention and correcting my response.

 

[kwired]

It is basically a class 1 control and signaling circuit and needs to utilize class 1 wiring methods.

You can't have a circuit with just one conductor and one the other power conductors is also the second conductor of this control circuit.

Had they made these things with four wires it may be possible to have a two wire class 2 circuit as the interconnect circuit.