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#194362 - 05/26/10 01:04 PM Conductor Size for AC compressor  
SJT  Offline
Member
Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
There is an outside Air Conditioning compressor for Central Air. The name plate running Amps says 19amps. 30 amp breaker at the Panel. Even though the code says #12 is good for 25 amps, the unit should be wired in #10 wire, right? Is there an exception in the 440 section of the code? As far as I know #12's limit is 20 amps. No exceptions? Thanks - Good Day


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#194363 - 05/26/10 01:49 PM Re: Conductor Size for AC compressor [Re: SJT]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,056
Estero,Fl,usa
If the "19 Amps" is labeled as the "minimum circuit ampacity" or words to that effect.
Grab a hold of your hat. You could use #14. (per 310.16, 60 degree column).
There was a question on the inspectors test about a 1hp motor on a 120v circuit where the right answer was "40a breaker, 14 ga wire". Strange sounding things happen around motors and HVAC units.
The exception is in 240.4(G) (2008 code or in 240.4(D)ex in earlier versions).


Greg Fretwell

#194368 - 05/26/10 04:55 PM Re: Conductor Size for AC compressor [Re: gfretwell]  
SJT  Offline
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Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
I seen 240.4(D)(5), saying 12 AWG Copper - 20 amperes. I thought I had to go with that? Is 240.4(G) only refer to Overcurrent Protection, so I would have to go to a #10?
Could I leave #12's? The Electrician already wired the unit with 12's.


#194369 - 05/26/10 05:04 PM Re: Conductor Size for AC compressor [Re: SJT]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,056
Estero,Fl,usa
It says

Quote
240.4(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.
so the whole issue is about overcurrent protection.


Greg Fretwell

#194370 - 05/26/10 05:06 PM Re: Conductor Size for AC compressor [Re: SJT]  
SJT  Offline
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Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
Table 310.16 (left side) has the * next to #'s 14, 12, and 10. Does the asterik mean you have to keep #12 at 20 amps?


#194371 - 05/26/10 05:11 PM Re: Conductor Size for AC compressor [Re: SJT]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,056
Estero,Fl,usa
No that just refers you to 240.4(D) which then further defines the necessary overcurrent protection for small conductors in any use not excepted by 240.4(G) or (E).


Greg Fretwell

#194375 - 05/26/10 06:46 PM Re: Conductor Size for AC compressor [Re: gfretwell]  
SJT  Offline
Member
Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
Thanks, I'll go through Article 440 parts 3 and 6.


#194377 - 05/27/10 02:17 AM Re: Conductor Size for AC compressor [Re: SJT]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,056
Estero,Fl,usa
The short answer is the label on the condenser rules.
Another interesting read is the U/L marking guide for HVAC equipment. Unfortunately they don't have it online without paying for it.


Greg Fretwell


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