Neutral Conductor Article NEC 310.15

[zabawire]

The following question is in regard to NEC 2008 article 310.15 (B) (4). It is not apparent to me if the neutral conductor for the following voltage systems:

120/240 volt( 3 wire, single phase), 120/208 volt(4w, grounded Wye, three phase), 277/480 volt (4w,grounded Wye,three phase)

is considered a current-carrying conductor or not for the purpose of applying Table 310.15(B)(2)(a). Please advise as appropiate

 

[don_resqcapt19]

For the 120/240 volt single phase, the neutral is never required to be counted as a current carrying conductor when it is part of a 3 wire circuit. For the other two, when part of a 4 wire circuit, with the majority of the loads linear, the neutral is not counted as a current carrying conductor. If a majority of the load is non-linear, then it is counted. Also when using two ungrounded conductors and a grounded conductor from a 3 phase wye system the neutral is always a current carrying conductor.