Can I use a 12-3 romex for 2 different circuits?

[tmelo49]

Ok guys. One more rookie question. Can I use one 12-3 romex to supply power to 2 different circuits? More specifically, the red will be dedicated to a new receptacle for an air conditioner (connected to a 15 amp breaker). The black supplies the garage with power (connected to a 20 amp breaker). Since there is only 1 neutral, is it safe for these 2 circuits to share that same white wire? It would be a pain to run two new 12-2 lines with a 12-3 already in place.

Thanks again.

[Hube]

Sure, go ahead your 12/3 will feed 2 circuits. Red to 1 circuit, Black to the 2nd circuit. The White (neutral will feed both. No problem. Just think about it, that neutral wire coming in to your main panel feeds ALL your circuits.

[tmelo49]

In other words, kill BOTH breakers before doing ANY work to either circuit......right?

[imeduc]

For sure kill the power to work on it. Dont know code for where you are. Here for like the 2 circuits to the kitchen sink. They have to be on a 220 volt breaker so both can be turned off at the same time.If you do go into the box under the sink they both will be dead.

ED

My mistakes dont define me they inform me.

[Rewired]

Just be sure that if you are using two single breakers (if code allows it), you MUST have the breakers on the opposite "legs" of the service!
If they aren't the neutral will be carrying the load of whatever is on in the garage PLUS the A/C load. This could EASILY overload the neutral wire...
If they are on oppsisite "legs" of the panel the neutral will only carry the difference of the two circuits... ZERO chance of overloading the neutral.

A.D

[tmelo49]

Does a tandem breaker satisfy this requirement?

[Rewired]

No, a "Tandem" breaker will not satisfy that, both terminals on the breaker are ultamately connected to the same point in the panel, and therefore the same "leg".
The best and safest way I think to connect your circuts to the panel would be to use a "double pole" 20 amp breaker and make both the garage AND the A/C 20 amp circuits. (even though the A/C is going to be made a dedicated circuit and should be on a 15 amp breaker, being on a 20 wont hurt.)
Connecting it this way you are sure to be on opposite "legs" of the panel, and, should someone decide to work on the wiring at a later time, they only have to turn off one breaker and EVERYTHING is dead....

The only disadvantage is that if you have a problem in the garage say and trip the breaker, the A/C will go down as well, or vice versa.

A.D

[kactuskid]

What you're trying to install is called a Multi-wire branch circuit and they can be dangerous. There is the potential for 240 volts inside the electrical box for each device when wire this way so there are definate rules you MUST abide by, one being the double pole breaker installation that's been pointed out.

The other is "The removal of a wiring device, such as a receptacle, must not cause an interruption of continuity for the grounded (neutral) conductor in a multiwire branch circuit [300.13(B)]. Therefore, the grounded (neutral) conductors must be spliced together, and a pigtail must be provided for device terminations." Per: http://www.ecmweb.com/ar/electric_mu...anch_circuits/

Please be sure this is what you're wanting to deal with before you install, it can be a heck of alot safer to just drill a larger hole size, (3/4" hole) and run 2 cables of 12-2/G instead of a 12-3/G. Here's another link that'll give you a few more details:
http://www.inspect-ny.com/electric/multiwir.htm

[HayZee518]

Install a breaker that has a common trip feature. Shutting off the handle simultaneously opens both circuits.