Using MV Cable Shield for Equipment Ground Conductor

[philly]

Is there anywhere in the NEC or elsewhere that permits the use of the internal cable shield on an MV cable to be used as an equipment ground conductor and satisfy the requirements of 250.122?

A project I am involved with has an MV feeder (4 sets of 750 MCM) between an feeder breaker and the downstream equipment with no separate EGC's run with the feeders. It appears that they are using the internal cable shield for any grounding or ECG requirements.

This is a 4.16kV LRG system (400A) so perhaps this is permissible on an LRG system with reduced fault current as opposed to a solidly grounded system?

 

[roger]

Read 250.190(C)

Roger

 

[Ingenieur]

do you have single individually shielded conductors or a cable assembly?

you a 3 ph mv cable without a ground? (other than the shields)
don't think I've ever seen one
do you have a mfg/pn?

looks acceptable if the lrg limited current can be carried without damage for the requied trip time

what is your ngr ohmic value?
whatgf trip value? any time delay?

 

[philly]

Read 250.190(C)

Roger

OK I see now that this section permits the shields to be used as the EGC on an impedance grounded system provided that the ground fault current and duration is less than the damage point of the shield.

 

[philly]

do you have single individually shielded conductors or a cable assembly?

you a 3 ph mv cable without a ground? (other than the shields)
don't think I've ever seen one
do you have a mfg/pn?

looks acceptable if the lrg limited current can be carried without damage for the requied trip time

what is your ngr ohmic value?
whatgf trip value? any time delay?

Yes the feeder is 1/C cables with shielsds but no separate EGC's. I don't have a manufacturer or part #.

Ohmic value is 5.98ohms limiting ground fault current to 400A.

I need to look into relay settings for delay setting.