Question how to feed residential Air Cond.

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Joe Schweigert

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What size wire is required to feed a residential air conditioner that has a 40 amp max breaker size of 40 amps and a minimum circuit ampacity of 24.9 amps. We have always used a #10-2W/G in this application sizing to the amp draw instead of the breaker size. The inspector will not pass this with out a changing the wire to a #8-2W/G
 
As Bob said, even #12 would be NEC compliant. The inspector is clearly incorrect, and the #10 is more than adequate.

Ask him what he thinks the Min Ckt Ampacity means.
 
The MCA is used to size the circuit conductors. Since your MCA is 24.9 you'll need a conductor rated for 25 amps in table 310.16. #12 is rated for 25 amps even at the 60 degree ampacity so a #12 conductor is large enough for this application. The limitations of 240.4(D) do not apply to this type of circuit so #12 conductors may be used at an ampacity greater than 20 amps.

I agree with Bob, the inspector needs to understand more about Article 240.

Welcome to the forum. :)
 
Many inspectors as well as contractors cannot get over a #10 or #12 wire on a 40 amp breaker. As the others have said it is code compliant because the a/c has built in overload protection. The breaker is strictly there for short circuit and ground fault conditions, not overload.
 
I'll hop in and agree with all the others. Print this out, hand it to your inspector, and ask him to explain to us why 240.4(G) doesn't apply to this situation.

Ask him to read 240.4(D) closely as well, if he tries to throw that at you. :)
 
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