I'm trying to settle an argument between myself and a colleague.
We are designing new product. It's 3 phase WYE rated at 343A/phase. (120/208Vac)
We disagree on the cable size needed in the field for installs.
We agree that we need a 450A breaker, but we disagree on the cable sizing.
I was wondering if anybody could explain why (per Chapter 9 Table 1 & 4) you are allowed a greater % of conduit fill for Over 2 Wires than you are allowed for 2 Wires.
Seems counter-intuitive, doesn't it?
I understand the concept of "jamming" explained in FPN No. 2, but as that is fro 3...
when derating wires due to conduit fill, there is exceptions talking about the neutral not needing to be counted as a "current carrying conductor" if it is carrying only the unbalanced load of a multiwire circut.... so when do you not have to count the neutral as a current carrying conductor...