Romex

[wayne123]

When using table 310.16 to size conductors, what insulation type should I use to size romex?(THHN,THWN, or what?)

 

[dana1028]

Re: Romex

(1999) Section 336-26
"The 90 degree rating shall be permitted to be used for ampacity derating purposes provided the final derated ampacity does not exceed that for a 60 degree rated conductor."

 

[charlie]

Re: Romex

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. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.

 

[tom baker]

Re: Romex

You can use the 90 Deg C rating for derating only, but the final ampacity can not exceed the 60 Deg C rating. The conductors are rated at 90 C but jacket is rated at 60 Deg. NEC Section 334.80 lays it out very clearly.

 

[charlie]

Re: Romex

Sorta looks three of us were answering at the same time. At least we agree.

 

[templdl]

Re: Romex

And about 3 minutes apart, that is replies at 01:11, 01:14, and 01:18. Not bad.