Open delta saves the poco one transformer.
It is really pretty common around here.
This is the typical installation. The 50KVA is the center tapped one and serves the single phase 120/240v loads in addition to the 240v 3p loads. The 25kva is the wild leg (208 to ground) and only serves 3p loads.
![[Linked Image from gfretwell.com]](http://gfretwell.com/electrical/red_leg_transformers.jpg)
![[Linked Image]](https://www.electrical-contractor.net/theory/D4W_O_SCH_G.gif)
Do power companies follow a rule or a convention as to which phases in your open leg panel is across the 2nd transformer, and which set of phases bridges the open leg? In the diagram, it shows the 2nd transformer as between phases B and C, and the open between A and B. If the phase rotation is always ABC, could one say that the power company always places the 2nd transformer between B and C and never A and B, or is it random? In this case, I will always call the wild leg "phase B" at the particular building I'm in. I realize that one transformer set up on one pole would be say ABC, and one down the street a ways may be BCA, and yet further down the road CAB, to keep the poco power plant equally loaded on all phases.
