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#81119 - 07/12/02 09:46 AM A/C overcurrent protection
JERRY0129 Offline
Junior Member

Registered: 07/12/02
Posts: 3
Loc: Hamilton, Ohio , USA
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

2014 / 2011 NEC & Related Books and Study Guides
#81120 - 07/12/02 10:05 AM Re: A/C overcurrent protection
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
See Art.440--primariy 440-6b. Use 10AWG conductors, and they'll not be a problem.

#81121 - 07/12/02 10:33 AM Re: A/C overcurrent protection
Joe Tedesco Offline

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
Look at the following link:

[This message has been edited by Joe Tedesco (edited 07-29-2002).]
Joe Tedesco, NEC Consultant

#81122 - 07/13/02 09:31 AM Re: A/C overcurrent protection
MikeW Offline

Registered: 06/03/02
Posts: 39
Loc: Michigan
Hello Jerry,

Based on 1999 NEC I’m going to give my opinion and if anyone sees I’m wrong please step in.

Section 440-4(b) says the manufacturer shall provide a nameplate with the minimum supply circuit conductor ampacity, along with other info. 110-3(b) requires equipment to be installed to this minimum.

Since you say the nameplate info given is, “Minimum Circuit Ampacity: 22 amps” I would use #12 AWG CU and I believe this would be code compliant with (310-16).

[This message has been edited by MikeW (edited 07-13-2002).]

#81123 - 07/14/02 03:58 PM Re: A/C overcurrent protection
tdhorne Offline

Registered: 03/22/01
Posts: 344
Loc: Maryland, USA
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 Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

#81124 - 07/14/02 07:17 PM Re: A/C overcurrent protection
caselec Offline

Registered: 04/14/02
Posts: 557
Loc: San Jose, CA
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.
Curt Swartz

#81125 - 07/15/02 05:58 AM Re: A/C overcurrent protection
MikeW Offline

Registered: 06/03/02
Posts: 39
Loc: Michigan
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?

Thanks, MikeW

#81126 - 07/15/02 07:47 AM Re: A/C overcurrent protection
resqcapt19 Offline

Registered: 11/10/00
Posts: 2209
Loc: IL
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.

#81127 - 07/15/02 12:04 PM Re: A/C overcurrent protection
wolfdog Offline

Registered: 10/24/01
Posts: 135
Loc: Dallas,TX
I agree with Don. The minimum amps marked on A/C units includes the 125%.

#81128 - 07/15/02 12:23 PM Re: A/C overcurrent protection
JERRY0129 Offline
Junior Member

Registered: 07/12/02
Posts: 3
Loc: Hamilton, Ohio , USA
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?

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