AC equipment 440

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implant

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My customer failed a home inspection based on #12 feeding a hermetic compressor unit (residential), the breaker is a 2 pole 30A based on 440.22 175%. Are we in the right direction or should it be based on nameplate?
Thanx
 
Re: AC equipment 440

AC units under Article 440 need to have there OCPD and conductors sized according to the nameplate on the unit. This nameplate must include:
Minimum Circuit Ampacity
Maximum Fuse or Circuit Breaker

It is not uncommon to see #12 wire protected at 30, 35 or even 40 amps. The conductors are sized according to the MCA not the maximum overcurrent protection device size.

According to table 310.16, #12 THHN can supply a minimum circuit ampacity of 25 amp or less.

[ October 20, 2005, 09:45 AM: Message edited by: infinity ]
 
Re: AC equipment 440

careful infinity. we use romex a lot for this and of course its only good for the 60 deg rating of 20.
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If the post mentioned NM cable than I would agree due to 334.80. It did not, but since it was stated that this is residential than maybe I should have made that assumption. However, an AC unit with a 30 amp OCPD would probably be fine with #12 NM cable. Ok, so there is my assumption. Better information would make it easier to properly answer his question without guessing.


Trevor
 
Re: AC equipment 440

stew,
The ampacity of #12 NM is 25 amps. As long as this is greater than the minimum circuit ampacity shown on the nameplate you can use it and you can protect it with the maximum OCPD size shown on the same nameplate.
Don
 
Re: AC equipment 440

and 240.4G

you also mentioned compressor unit..... one might assume "outside"...there have been a lot of discussions in earlier threads as to the use of NM on a compressor in an outside location ie:
is this other than a dry location?
 
Re: AC equipment 440

Read 240.4 (D)

--------------------
Peter
Southern New England
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But how do you get around 334.80? I see no mention of any exception to the 60 degree ampacity except for derating purposes.
 
Re: AC equipment 440

12* @ 60 degrees = 25amps

240.4 (D) Small Conductors. Unless specifically permitted in 240.4(E) or 240.4(G), the overcurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,

BUT

240.3 Other Articles.
Equipment shall be protected against overcurrent in accordance with the article in this Code that covers the type of equipment specified in Table 240.3.
Air-conditioning and refrigerating equipment 440

Well that just put that NM-B cable at #12 = 25 amps for a AC unit
:)
 
Re: AC equipment 440

Sorry, you guys are right. For some reason I glanced at the table and saw 20 amps. Of course this was for #14 wire! Sorry for the brain freeze.

Trevor
 
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