Neutrals current carring?

[WirenutNH]

In a 120/208v and 277/480v 3 ph service is the neutral conductor considered a current carring conductor and need to be included in the count for derating purposes?

 

[GoldDigger]

In a 120/208v and 277/480v 3 ph service is the neutral conductor considered a current carrying conductor and need to be included in the count for derating purposes?

Only if the circuit is known to be serving primarily non linear loads.
If you try to reduce the wire count by running only two phases and the neutral, you then have to count the neutral instead.
The wording in the relevant section is quite specific. Take a look at 310.15(B)(5) [2011] or the corresponding in your code cycle.

 

[mbrooke]

No, especially if the single phase loads connected phase to neutral is small. However, as said below a large number of non linear harmonic rich loads will require it be counted as a current carrying conductor. However, in any case if harmonics are an issue I really recommend the neutral be upsizes be it 200% or less.