Winnie, you are corect- it is that one of the connections between two transformers is grounded.
As for marking this conductor white: Don, I agree that the wording of the code supports your position. However, the code does only requires this where the conductor is insulated- and I see no requirement that it be insulated at all! For example, 200.2 states "the grounded conductor, where insulated...."
I think the idea of having this particular conductor uninsulated would never occur to an electrician. Nor, for that matter, connecting this conductor directly to the case of the equipment.
Perhaps the code needs to re-consider this %$# power set-up.
I will admit to my ignorance regarding corner-grounded deltas. The only place I've seen then is at wells- where the only single-phase load is the control circuit, whose neutral is created at a transformer in the panel.
I fail to see the advantage of this system. Heck, you've already got three transformers- why aren't they connected in a "wye" to begin with?
With each leg being 240 to ground, there is also the issue of whether the breakers are suitably rated.
This is a "three phase" system. Yet, when using two pole breakers, you may set them up as follows:
- 240 leg to 240 leg; in essence, similar to our usual 240 circuit; or,
- 240 leg to 0 leg; in essence, similar to our usual 120 circuit, but with double the volts.
Now, these two circuits cannot be equivalent, unless we are also somehow drawing current from the "0" leg. That would make for an interesting "neutral!"
I just don't like this arrangement. Does anyone know what the advantages are, as compared to a "wye"?
