12 gauge wire for a 15A Circuit

[tmelo49]

Hello,

I am preparing to extend an used circuit in my attic in order to accomodate my new air conditioner. The AC calls for a 15amp circuit. The circuit I have available is a 20AMP circuit with 12 gauge wiring. Do I have to replace the breaker with a 15A and the wire with 14 gauge? Can I utilize the circuit as is? Or can I replace the breaker and keep the existing 12 gauge wire.

Thanks.

[LazyPup]

Although 14 guage wire is permitted on a 15 amp residential circuit, in fact, the 12 gauage is much preferred. There should be no problem with running a 15 amp load on a 20 amp circuit. (keep in mind, the amp rating of a circuit is the highest load it can safely carry).
While there should not be any problem with running the 15 am ac on a 20 amp circuit, if it is a dedicated circuit the proper thing to do is to install a breaker that matches the load.

[tmelo49]

Thanks LazyPup. I think I'll do it the right way and replace the breaker as well. I'm just glad I don't have to run a new line to the panel since the 12 gauge will do. Thanks again.

[imeduc]

12 gauge is ok for 15 amps for sure . But you say up in the attic. Might want to look into how far a run you will have on this wire. If after the AC runs for a long time. Feel the wire and if it is at all warm I would put in a new #10 wire to the AC.

ED

My mistakes dont define me they inform me.

[HayZee518]

Your house was probably wired right through using 12/2 cable. The contractor just didn't want to incorporate 14/2 in the house. That's the norm now a days.
Consider the distance from the a/c to the panel. If its more than 100 feet you could have a voltage drop problem. It's not supposed to be less than 3%.
For voltage drop you need to consider the total distance - 150 feet out (black wire) and 150 feet back (white wire) total of 300 feet.
I attended a forum once for re-certifying electricians. Given a problem of a dryer 150 feet away from a panelbox. Most guys said that 10/3 would be sufficient to run the dryer. However using a VD formula it was too small, no 6 cable was recommended for a 27 amp load.