Here is one thing I've been wondering about for awhile:
The 75 degree column of Table 310.16 says #4 copper is good for 85A. If the conductor is used in a 120/240V, 3-wire service or feeder for an individual dwelling unit, Table 310.15(B)(6) trumps 310.16, and we may use #4 copper for up to 100A.
But suppose we use 4/3 Type NM cable? 334.80 (2005) says that the ampacity of conductors in Type NM cable "shall be in accordance with the 60 C (140 F) conductor temperature rating" of 310.15.
Does 334.80 trump 310.15(B)(6)? If so, I can use #4 Cu for a residential feeder if I am using SER or TC, but I must use #2 if using NM.
I suspect there are differing opinions about this, including among AHJs. Ideas?
