NM in hot attic of 142 deg F

[jar546]

Can you install NM in this application?

If you can derate from the 90 deg column but cannot have a rating higher than the 60 degree column, how can you derate from the 90 when it is not allowed in the 60 and there is no number there, only a dash?

"If you always do what is right to others you can't go wrong"

The more I learn, the more I realize just how much I don't know.

 

[jar546]

Use the IRC for this answer.

Would it be different in the NEC?

 

[480sparky]

142°F = 61.1°C. That's why.

 

[jar546]

I think the issue is that NM insulation is rated for 90C even though you cannot rate the ampacity from the 90 deg column, only derate.

 

[480sparky]

334.80 Ampacity. The ampacity of Types NM, NMC, and

NMS cable shall be determined in accordance with 310.15.

The ampacity shall be in accordance with the 60°C (140°F)

conductor temperature rating. The 90°C (194°F) rating

shall be permitted to be used for ampacity derating purposes,

provided the final derated ampacity does not exceed

that for a 60°C (140°F) rated conductor.

I think that means you're SOL.