See 310.15 (B) (4) regarding the neutral as a current carrying conductor. Except when carrying only the imbalance from the other conductors, the neutral is a current carrying conductor and must be accounted for.
As far as derating ampacity goes..
110.14(C)(1)stipulates which column to use for ampacities based on conductor size & equipment temp. ratings.
But for derating purposes, look under the appropriate column (310.16) to find the initial ampacity for your conductor type. Then derate.
Example: If you had a 3, 50 amp, 3 phase loads and used #6 THHN in a single raceway. (total 9 #6 THHN in raceway.)
1) Table 310.16(90c column) allows 75 amps for #6.
2) 310.15(B)(2) requires derating to 70%.(9 conductors).
3) .7 x 75 = 52.5 amps.
Note that if you used the 75c column for your derating, your ampacity at 70% would be only 45.5 amps,(7 x 65) and you would need a larger conductor.
Anyone else?
[This message has been edited by Redsy (edited 05-20-2002).]
