2014 250.24 (C)(3)

[ronmath]

"Delta-Connected Service. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors."

What grounded conductor are they referring to in a 3-phase, 3 wire delta service?

We have a current 3-phase, 3-wire delta service to a building. I understand that a ground fault on any single phase creates a corner grounded system, but doesn't that also create objectionable current? How is this handled if at all since a single phase ground fault would not trip any breakers?

Thanks,

 

[augie47]

There are such animals as a 3 phase, 3 wire, corner grounded delta where one phase is intentionally grounded (used to be real popular with E I Dupont facilities)
I can't imagine why one would want that phase to be reduced anyway, but apparently it was previously installed that way.

 

[GoldDigger]

That is the reason that an ungrounded delta supply (whether service or SDS) is required to have a ground detector. That detector will not cause a trip but will instead alert you to find and correct the fault before a second fault disables the system.
No fault current (other than capacitive) will flow as a result of the first fault, unless you count the currents flowing in the detector itself.