Redsy,
Many older residential sections of a PoCo's distribution grid will have a single Ø of primary high tension line snaking down the alleys for many blocks (one conductor sitting on an insulator right on top of the pole - no cross arm). Each of these lines will carry as many transformers as needed for the installed load in the dwellings and small commercial occupancies along its path. The basic PoCo owned, pole mounted transformer supplying 120/240 1Ø to these buildings has a primary hooked up as one leg of wye. The transformer primary winding has one end connected to the high tension primary line, and the other end connected to a very busy grounded conductor. The secondary center tap is connected to the same grounded conductor.
This transformer is an economical choice as it has only one high voltage insulator leading into its primary winding (cheaper to manufacture), and the line crew only has to mount one cutout to the primary line (less labor).
The turns ratio, for 8 KV to ground, is roughly 33:1, making the return current small by comparison to the secondary neutral currents.
