The conductors in NM cable may look like THHN/THWN but typically don’t have marking on them identifying what type they are. 334.80 requires the ampacity of NM cable to be in accordance with the 60C conductor rating in 310.15 except you may use the 90C rating for temperature and derating purposes provided the final ampacity does not exceed that shown for 60C conductors. Up until the 2002 NEC table 310.15(B)(6) listed specific conductor types that could used and type NM cable is not one of them. There was an errant in the 2002 NEC and the conductor types were not included but should have been.
From the NFPA website:
Table 310.15(B)(6): Add a second sentence to table title to read: “Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2.”
Curt
[This message has been edited by caselec (edited 12-23-2003).]
