A Residential AC unit was installed with the following nameplate info Minimum Circuit Ampacity: 22 amps Minimum Fuse/Breaker: 35 amps Maximum Fuse/Breaker: 35 amps My question is whatis the minimum size conductors that can be used. The circuit is only 10-12' long. A code section would also help. Thanks
With a circuit selection current of 22 amperes and the branch circuit serving only one motor compressor the branch circuit conductors must be sized to 125% of that ampacity or the motor compressor rated load current whichever is greater. 125% of 22 amperes is 127.5 amperes which brings us back to #10 AWG Cu conductors.
440.32 Single Motor-Compressor. Branch-circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of either the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater. -- Tom
"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
If he is looking on the name plate of the compressor only then you would need to follow 440.32 but I would guess that his is looking at the name plate on the "box" sitting outside which would be a multimotor load (fan and compressor) so the conductors need to be sized based on the minimum circuit ampacity on the name plate. #12 wire would be sufficient size for the short distance your going but I would recommend using at least #10 from the branch breaker to the disconnect to prevent excessive voltage drop if this circuit was much longer.
Re: A/C overcurrent protection#81125 07/15/0207:58 AM07/15/0207:58 AM
Jerry, Please, can you give us all of the nameplate information?
Caselec & tdhorne, Yes, I was talking about the visible nameplate on the outside of the entire A/C unit. Which on the new units I have seen list the FLA of the fan motor along with Min. Circuit Amps, etc. And I thought this would then require you to use 440-4(b) of 1999 NEC.
I agree #10 is fine but Jerry asked for the minimum size wire allowed and I believe it to be #12.
Anyone else have any thoughts on this subject?
Re: A/C overcurrent protection#81126 07/15/0209:47 AM07/15/0209:47 AM
I agree that the NEC permits #12 copper for this application. I am assuming that this is a multimotor (condenser fan and compressor) unit and the nameplate markings are per 440.4(B). If so the minimum circuit ampacity marked on the nameplate can be used directly size the conductors. See 440.35. Don
I don't recall ever seeing the "Minimum Fuse/HACR Breaker" designated.I think that is what raised my original question. My thinking was if the manufacturing has a Min and a max of 35 amps, does he want the wire sized based on 310-16?