| Instructor says on 3p, 4-wire, delta-connected system the wild leg is | usually connected to Bravo terminal. It's almost always that way. | | Mike Holt's "Understanding NEC" says "High-leg conductors are required by | the National Electric Safety Code (utility code) to be terminated to the "C" | phase, and not the "B" phase. So take the extra time when working with | these types of systems to confirm just where the utility company connected | the high-leg." | | Does NESC not have authority to enforce or what is the deal?
here's what I've read and learned about it (I am not an electrician or an engineer):
What's called A, B, and C might be different on each side of the boundary between where NEC and where NESC have their say. It might be called "B" in the breaker panel, but be called "C" by the linemen. Since 240 delta is effectively an extension of 120/240 single phase, there would already be "A" and "B" for single phase. Then as two (or one with Scott-T) more transformers are added to bring it up to three phase, there's a new wire and it could be called "C", but be connected inside the building to "B".
We tend to write "A" on the left and "B" on the right for a horizontal depiction of single phase 120-0-120. Then the wild leg is added in the up direction, and we tend to think clockwise and label the high leg after the "A" so then it becomes "B". These are different approaches to the determination of labels, which, unfortunately, have different results. So thus confusion. I've never been able to really sort it out. One has to always check and be sure.