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Savinmoney 10-08-2012 04:55 PM

12/2 vs 12/3
Silly question. Found that my electric fire alarms are wired with 12/3 with a ground. Not a 12/3 in my breaker box, so I'm assuming it is branched off of something else. The alarms are no good (won't go into detail) but will replace with plain battery operated ones. Can I just cap of the wires and put a cover plate on without it affecting whatever it is branched off of?

Speedy Petey 10-08-2012 04:58 PM

No. Replace them with what's there.

12/3 or 14/3 is typical between smoke detectors.

Dierte 10-08-2012 05:03 PM

Its 2 wire to the first smoke and then 3 wire to the other devices. Also here in OH i have to tie smokes onto a bedroom circuit. Its a building code thing not an NEC thing

Savinmoney 10-08-2012 05:15 PM

Thanks guys. It just threw me off seeing 12/3. I have 4 alarms... two that I peeked at. I'm sure one of the other two must be a 12/2 tied into a bedroom circuit. Makes a lot of sense now! Thanks again!

AllanJ 10-08-2012 09:07 PM

You will need the third wire in the cable to properly connect the smoke detectors to each other. You only need 2 wires to provide the power.

patented 10-09-2012 09:23 AM

The 3rd wire is for the "interconnect" between alarms, which is what makes all of them sound at once.

Oso954 10-09-2012 01:11 PM

Replacing a hard wired system with battery operated is like taking air bags and shoulder belts out of your car to use a lap belt.

Hard wired (and interconnected) with battery backup is the way to go.

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