On Oct 26, 12:27*pm, Jim Stewart wrote:
John wrote:
With 208 single phase two pole transformers were needed, and if three
phase were required you needed to install three transformers to obtain
the star or wye configuration. By using the center-tapped transformer
neutral transformer it eliminated a second transformer. If three phase
was required it was necessary to add only one more transformer rather
than two, except when higher power rating were required and a third
transformer is used. That was the difference between open leg delta and
a full delta secondary. A lot of people are confused by seeing only two
high voltage primary wires and getting fed with three phase into their
building but that is very common.

Do you mean 2 high voltage wires or 2 transformers?

Three phase is possible with 2 transformers, but not
with 2 high voltage lines.

Open Delta. Only two transformers, and ONLY two high voltage lines to
feed the TWO transformers. Pretty common all over.