Interesting.... I think I'm beginning to see this a little more clearly now.
With 120V already established as a common utilization voltage in 120/240V 3-wire set-ups, I was assuming (bad thing to do, I know) that the 120/208-Y system would have been the natural progression when 3-phase started to become common.
You seem to be suggesting that wye systems didn't catch on until the latter half of the century. I think I see my mistake, in that the wye system became common in England so that the same xfmr banks could feed 3-ph commercial with 350-440V and 1-ph 2-wire tapped off of it for residential 200-250V. But with residential service in the U.S. being mostly from smaller 1-ph xfmrs, I see that this wouldn't necessarily have been a factor in favor of adopting wye over delta.
With the preference for 2:1 ratios you mentioned earlier, I suppose it was inevitable that 240V and 480V would become standard, with the 4-w delta being a useful "trick" for the convenience of providing 120V as well. Am I getting near the crux of the matter now?
You mentioned solidly grounded 277/480Y systems with reference to GFI protection, which brings me to another point that occurred to me while pondering this subject.
How do you arrange proper grounding on simple 240 or 480 delta services? If the NEC requires the building ground to be bonded to the neutral on wye or 1-ph 3-w, what happens on a delta service where there is no neutral to bond to?
Obviously 4-w delta and corner-grounded delta wouldn't be a problem, so was corner-grounded delta very common?
Or were many of the straight delta systems floating???
