250.190 and 250.100

[Isaiah]

We have 1/C 15kV, 3 Phase feeders coming from an outdoor utility substation SF6 CB. They run underground direct buried to a 3MVA XFMR Primary w/480V secondary which feeds a 480V switchgear. The MV cable is not MC cable BUT it does have a shield. Looking at 250.190 and 240.100, it looks like I can use the shield as an EGC; we have Schweitzer relays for protection and the upstream transformer 69kV to 13.8kV has a resistor. Do I still need to run a separate EGC with with the phase conductors or will the shield suffice?


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[electrofelon]

We have 1/C 15kV, 3 Phase feeders coming from an outdoor utility substation SF6 CB. They run underground direct buried to a 3MVA XFMR Primary w/480V secondary which feeds a 480V switchgear. The MV cable is not MC cable BUT it does have a shield. Looking at 250.190 and 240.100, it looks like I can use the shield as an EGC; we have Schweitzer relays for protection and the upstream transformer 69kV to 13.8kV has a resistor. Do I still need to run a separate EGC with with the phase conductors or will the shield suffice?


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Is the 13.8 system a delta or wye system? MGN? Where is the service point? What kind of shield does the cable have?

 

[Isaiah]

Is the 13.8 system a delta or wye system? MGN? Where is the service point? What kind of shield does the cable have?

System, incoming service is 69kV Delta-Wye with neutral resistor on the secondary of the power transformers. Power originates from a local power plant.
Cable is Okonite Okoguard-MV-105 15kV Shielded Power Cable
Copper Conductor/105°C W/133% Insulation Level
Shield is 5 mil bare copper tape helically ap- plied with 12.5% nominal overlap. The protective relays have all the bells and whistles including 50/51, 87, 27 etc


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[electrofelon]

System, incoming service is 69kV Delta-Wye with neutral resistor on the secondary of the power transformers. Power originates from a local power plant.
Cable is Okonite Okoguard-MV-105 15kV Shielded Power Cable
Copper Conductor/105°C W/133% Insulation Level
Shield is 5 mil bare copper tape helically ap- plied with 12.5% nominal overlap. The protective relays have all the bells and whistles including 50/51, 87, 27 etc


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It does seem that if the 15kv system is not solidly grounded then you could use the tape shield as the EGC. I assume you have researched whether the shield is rated for the fault current?

Just curious, is the 13.8 to 480 transformer delta wye?

 

[Isaiah]

It does seem that if the 15kv system is not solidly grounded then you could use the tape shield as the EGC. I assume you have researched whether the shield is rated for the fault current?

Just curious, is the 13.8 to 480 transformer delta wye?

Yes - and the 13.8kV to 480V is delta wye.
Many thanks
Isaiah


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