Lets say I have a 200A service on a single family dwelling. T310.15(B)(6) permits me to use 2/0 cu conductors for the service entrance and main power feeders. But lets say I use T310.16 instead and install 3/0 cu conductors. Does this represent an increase in the ungrounded conductor size and thus require an increase in the feeder EGC per 250.122(B)?

I would have to say -- yes.

I say not necessarily. The neutral conductor is sized by calculation, and the EGC is sized per breaker size.

This is good. We may finally disagree again. It's been so long.............

I'm putting my head on the pillow now, will post more tomorrow.

ns

I'm with Mike, 250.122 for the EGC

Go for it

Okay, same idea different example.

Let’s say I have a 100A feeder of THHN insulation. T310.16 permits #3 awg cu. If the specifications call for TW insulation, I would be required to use #1 awg cu.

Same question - does this mean I have increased my ungrounded conductor size and now T250.122 needs to be amended per part (B) of that section?

My point is that part (B) doesn't indicate what the "normal" ungrounded conductors are and what constitutes an increase in their size.

Please excuse my first answer. 250.122 clearly governs.


However Bryan raises an interesting question and I believe that 250.122(B) would apply when ungrounded conductors are increased in size [to compensate for voltage drop]. Then, the equipment grounding conductor would have to be resized accordingly.