I remember seeing a photo in an old book of a pole mounted transformer: it had four secondary bushings and four wires extending down to feed the secondary rack. There where both four wire and three wire service drops extending from the secondary rack. I thought immediately that it was a three phase pole mounted transformer. The weird thing was that I could only see two primary bushings (the side mounted kind) and two primary wires extending down from the primary crossarm and cutouts. How could that work? I have observed that modern single phase (and single primary bushing) transformers that are connected phase to neutral have the primary grounded neutral conductor tied to the center tap of the secondary. (essentially the primary and secondary neutrals are the same wire) But I didn't think that the three phase transformer in the old photo would be wired this way. (It looked to be connected the same way as a single phase transformer would be to a delta primary)
Any Ideas?
(digging deep in my memory, I believe the book was on appliance repair, early sixties vintage, and it had a few pages on how electricity is delivered to homes)
Sounds like it might have been an open delta with one primary leg grounded. Either either that, or the other bushings were just hidden from view.
