The main reason I interpreted 310.15(B)(4)(a) to mean a two wire circuit is because (b&c) specifically mention multi wire. I read (a) to be 2 wire, (b) to be three wire, (c) to be 4 wire. I notice no real mention of single phase service, guess (a) would cover that if unbalanced was changed to balanced.
(b) uses the wording:
"In a three wire circuit consisting of two phase wires and the neutral of a 4 wire 3 phase Wye connected system..."
(c) uses the wording:
"On a 4 wire 3 phase Wye circuit where the major portion of the load consists of nonlinear loads..."
The way I read this is 2 and 3 wire circuits sharing a neutral the neutral must be counted.
But now I am starting to believe unbalanced was meant to be balanced in (a)
When I first started pushing my coworkers to start derating and to be more conscience of what they stuffed into a conduit I made it a point to say "for the majority of our work the neutral will count, period" because I feel this is the safest way to determine conduit loading. Looks like I did mis-interpret (a). They are going to hate me when I bring this up on Monday.
I would like to say that I don't think many circuits are ever balanced consistently and therefore we never truly have a neutral. I also feel that the majority of "round robins" are used to feed nonlinear loads. Therefore we should always count the grounded conductor as a current carrying conductor. At least for the work our shop does this seems to ring true.
What do you think?
