Can I install a 12-2 nmc cable to an AC that has a min circuit ampacity 22amp on a 30amp breaker. The AC draws about 17amps. The 22amps is at 125%.The name plate states the 22amp min circuit ampacity and a maxium 30 breaker. 2002 NEC 310.16 12cu 60c 25amps with* *240.4d 12cu only 20amps unless permitted in 240.4e through 240.4g 240.g permitts AC article 440 parts III, VI 440.22a Rating or setting 175% branch circuit
[This message has been edited by abode electric (edited 01-08-2003).]
i would run at least 10 gauge wire. 12 gauge is only good for 20 amps, also AC is considered a continous load and 80% rules apply here. Other things to consider are voltage drop and ambient temperatures which also mean derating. With these other factors you may even have to run #8s.
[This message has been edited by spyder (edited 01-08-2003).]
Spyder, (1)310-16 12cu 25amps (2)240.40d allows higher than 20amps on 12cu (3)AC isn't considered a continous load, it's a motor load, 125% of motor load. 17 amps X125%= 22 amps (4)voltage drop and ambient temperatures are not factors here I haven't found a reason why I can't do this. I know this may not be the best way but it complies with the code.
You said voltage drop not a factor so the run must be short. Unless you got couple of hundred to do, how much are you going to save buy using #12. Plus anyone that goes into the panel after you is going to ask questions on this, I am thinking "Home inspectors" or the GC who thinks he knows that 30 amp breakers need #10s
Bob Badger Construction & Maintenance Electrician Massachusetts
I wouldn't normally run a #12. The hvac guy didn't have his compressor on the job and told me it was a smaller unit. When it came to final inspections the inspector said I wasn't compling with the code. I knew the #12 I already ran meets code requirments of this unit. Why should I have to take that out and run a new one? There is sheetrock already in place.