Sure George, yes I mean 3 wire delta / 3 phase. ie 440.
What do I mean by "hidden potential" on such a system?
Well if one leg [A] is ground faulted it floats because it has little or no potential to ground.
Should an electrician accidently touch phase [B/C] and conduit/equipment etc he can receive one hell of a shock at or near 440 volts.
This happened to me. But during another discussion early on I was told not to discuss such things by charlie b. So I wont give details.
I think it was Don who desribed this condition above as a corner grounded fault.
As others ,over time, I have concluded that though we treat a ground rod with much ado, it is much ado about "little" in respects to the interior grounding electrode portion of the system.
It was my mistake to refer to a ground rod as a lightning rod also because a single rod is not of much use in that capacity either IMO.
I have opened panels that were charred black powder and the guts/breakers crumbled out. Same thing for electric ranges and AC disconnects. Internal electronics "smoked" etc.
MO, a # 6 and a single rod wont win the day once the service grounded conductor is lost [seen that one too].
But during a "surge" on a entire city block from lightning, it wont protect
equipment/home/people. Its very humbling. I saw houses on both sides of the street for half a city block with "charred equipment .