208/120 wye over 3 current carring calculation

[Joe livewire]

my question is simple it seems but i get so many different interpritation.400amp main service breaker 4 wire wye system.several 3 phase balanced circuits with more single phase mixed 120volt circuits.does the 310.15 b2 a apply and is the neutral concidered a current carring conductor.

 

[Dennis Alwon]

First off does you install meet part (4)(a,b,or c)of art 310.15(B)(2)????

Secondly, it probably doesn't matter anyway if you only have 4 conductors and are using 90C rated wire-- unless you have parallel conductors.

4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).
(b) In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(2)(a).
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.

 

[infinity]

Joe you need to provide some further information. Are the single phase circuits MWBC's? (do they share a neutral).