Single THHN wire in walls?

Old 11-12-03, 05:09 PM
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Single THHN wire in walls?

As required by code, we have a smoke alarm in each bedroom, and each bedroom is on an individual AFCI circuit.

However, I need to connect the "interconnect" wire of all the smoke detectors so if one goes off they all go off. I only need a single wire between each of the alarms, as they are already powered separately in each room.

Can I make these connections with a single 14 gauge THHN wire?

Or must all wire be bundled (i.e. romex), or in conduit?


Old 11-12-03, 05:47 PM
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I believe that this is a low-voltage signaling wire. If I'm right about that, I would guess that you have a lot of flexibility here. Anybody know for sure?
Old 11-14-03, 07:50 AM
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Firex and First Alert (most popular brands here...) both say minimum #18 single or multi strand wire. Also both/all alarms are supposed to be on the same electrical circuit. I suspect same circuit is not as significant as same 120V leg. My house has a separate smoke detector circuit for all the detectors, which I thought was a code requirement - may be a local revision...

I hate that all detectors now have to be interconnected! According to my sources, the next revision of OSHA regulations will require hearing protection for all False alarms... Kidding, but man, those things are loud!

Doug M.
Old 11-14-03, 01:00 PM
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The NEC is pretty silent on smoke detectors. Other codes require installation and interconnect.
Old 11-14-03, 03:37 PM
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The NEC is quiet on placement and quantity of smokes, but not how they are wired.
The interconnect is not low voltage and is part of the circuit. I feel interconnects are a good thing, even with the occasional false alarm.
The code, and common sense say you CANNOT run a separate conductor for the interconnect. All wies in a branch circuit have to be run together in the same conduit or sheath. Even if not it is a huge code and safety violation to run individual conductors in free air.

How old is this house? You state you have AFCI's which tells me newer house or new re-wiring. Yet the smokes are not interconnected??? Someone missed that day of code class.

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