High Resistance Ground System and the application of 250.122

[No Shortz]

We have a 480 wye connected secondary feeding a 2000A bus. The system is using a Post Glover HRG. We have 6 parallel feeders running in PVC conduits in a concrete duct bank.I am having trouble determining what is required to be in the conduit with the feeder cables and how to size them. Does 250.122 even apply? Can these feeder cables be run with just the 3 phase power and no ground in each conduit? 250.36 (D) allows for the Neutral point to grounding Impedance Conductors to be installed in a separate raceway. Does this imply that the phase conductors are the only conductors in that raceway?
Why would we size the EGC using 250.122 if ground current is limited to 5-10A?
Any help understanding this would be greatly appreciated!
Thanks!

 

[mayanees]

I say size the EGC using 250.122 and the rationale is that the 2nd fault on the system would be large enough to need the higher ampacity cable.
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250.36(D) only applies to the single cable that connects the neutral lug to the ground resistor.

 

[No Shortz]

I say size the EGC using 250.122 and the rationale is that the 2nd fault on the system would be large enough to need the higher ampacity cable.
...
250.36(D) only applies to the single cable that connects the neutral lug to the ground resistor.

How would ground fault current be higher if there is 2 or more ground faults on an HRG system? The resistor would limit fault current no matter the quantity of faults, correct?

 

[don_resqcapt19]

How would ground fault current be higher if there is 2 or more ground faults on an HRG system? The resistor would limit fault current no matter the quantity of faults, correct?

A second fault of another phase to ground is really a line to line fault if the first fault has not been cleared.

 

[kwired]

If you have a high resistance ground or even an ungrounded system - you still must run equipment grounding conductors as well as a grounding electrode system just like you do with a solidly grounded system. You don't want to have isolated non current carrying components floating at their own voltage level should something fault to them, you want all those components solidly bonded together. The only thing that is high impedance is the resistor link to the source neutral. Your fault monitoring equipment will not indicate a fault on an isolated piece of equipment frame - it will if that frame is bonded to the grounding system.