10-2NM B

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nickelec

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Good afternoon all I had an inspective family on a recent house we did scenario is

10/2 NMB feeding an AC condenser rated at a minimum circuit and capacity of 31.5 with a max OCP of 40 .

Inspector is saying I need a number eight He's siting 334.80 which I'm aware of for the old NM but 334.80 specifically states the capacity of types NM , NMC, and NMS does not mention anything about NMB.

What say you guys

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NM-B is 90C rated for derating purposes only. You are limited to its 60C ampacity. That 90C derating limit helps if cables are bundled or you have high ambient temperatures. But it is limited to a 30A MCA.
 
If you change to another wiring method, check the termination temperature rating on your condenser. Some are marked at 60°C termination which would eliminate your using #10 of any type.
 
nickelec said:
Good afternoon all I had an inspective family on a recent house we did scenario is

10/2 NMB feeding an AC condenser rated at a minimum circuit and capacity of 31.5 with a max OCP of 40 .

Inspector is saying I need a number eight He's siting 334.80 which I'm aware of for the old NM but 334.80 specifically states the capacity of types NM , NMC, and NMS does not mention anything about NMB.

What say you guys

Sent from my SM-S906U using Tapatalk
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Doesn’t really help you on this one, but SER cable #8 and larger you can use the 75C ampacities. #10 and smaller still follows the NM ampacity rules
 
augie47 said:
If you change to another wiring method, check the termination temperature rating on your condenser. Some are marked at 60°C termination which would eliminate your using #10 of any type.
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Listed equipment should not have 60°C marking unless it is very old. The listing standard has required the use of 75°C rated terminations for at least a decade.
 
Looking at Art. 440.32, I'm seeing that if you have a MCA of 31.5, your circuit conductors must have an ampacity of 39.375 A. So even if you are figuring this at 75° C., the operating temperature of a #10 would exceed 75° C. The only way I could see this as acceptable would be if all terminations were listed for 90° C.
 
Rick 0920 said:
Looking at Art. 440.32, I'm seeing that if you have a MCA of 31.5, your circuit conductors must have an ampacity of 39.375 A. So even if you are figuring this at 75° C., the operating temperature of a #10 would exceed 75° C. The only way I could see this as acceptable would be if all terminations were listed for 90° C.
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A mca is the minimum circuit ampacity which already has 125% built into it. Thus 31.5 amp conductor is all that is required.
 
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