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#81119 - 07/12/02 12:46 PM A/C overcurrent protection  
JERRY0129  Offline
Junior Member
Joined: Jul 2002
Posts: 3
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

2017 / 2014 NEC & Related Books and Study Guides

#81120 - 07/12/02 01:05 PM Re: A/C overcurrent protection  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
See Art.440--primariy 440-6b. Use 10AWG conductors, and they'll not be a problem.

#81121 - 07/12/02 01:33 PM Re: A/C overcurrent protection  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
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 12:31 PM Re: A/C overcurrent protection  
MikeW  Offline
Joined: Jun 2002
Posts: 35
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 06:58 PM Re: A/C overcurrent protection  
tdhorne  Offline
Joined: Mar 2001
Posts: 345
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 10:17 PM Re: A/C overcurrent protection  
caselec  Offline
Joined: Apr 2002
Posts: 558
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 08:58 AM Re: A/C overcurrent protection  
MikeW  Offline
Joined: Jun 2002
Posts: 35
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? [Linked Image]

Thanks, MikeW

#81126 - 07/15/02 10:47 AM Re: A/C overcurrent protection  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
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 03:04 PM Re: A/C overcurrent protection  
wolfdog  Offline
Joined: Oct 2001
Posts: 135
I agree with Don. The minimum amps marked on A/C units includes the 125%.

#81128 - 07/15/02 03:23 PM Re: A/C overcurrent protection  
JERRY0129  Offline
Junior Member
Joined: Jul 2002
Posts: 3
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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