12.5 kv Cable Grounding?

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Goroon

Member
This is not my area. looking for thoughts.
We have a firm doing MV Service work. He Has indicated that the 12.5KV cable shields are only grounded at the Main 12.5KV Service. He indicates that they should be also grounded at the receiving Switchgear. The 12.5KV is a 3PH System. I find nothing on this in the NEC in Over 1KV. We have 12.5KV to 480V Xformers that are double ended at the ends of the 12.5KV Cables.
Would this not create more ground loops?:-? All was inspected and approved when installed and as upgraded since 1974.
 

wirenut1980

Senior Member
Location
Plainfield, IN
I believe the shield and EGC's should be connected on both ends. If you want a firm answer, contact the cable manufacturer. If they are connected at both ends, the shield would carry a portion of ground fault current. I'm not sure if that is a problem or not.
 

quogueelectric

Senior Member
Location
new york
This is not my area. looking for thoughts.
We have a firm doing MV Service work. He Has indicated that the 12.5KV cable shields are only grounded at the Main 12.5KV Service. He indicates that they should be also grounded at the receiving Switchgear. The 12.5KV is a 3PH System. I find nothing on this in the NEC in Over 1KV. We have 12.5KV to 480V Xformers that are double ended at the ends of the 12.5KV Cables.
Would this not create more ground loops?:-? All was inspected and approved when installed and as upgraded since 1974.

This is how we do it around here there is a drawing on page 11 of the pdf showing specifically how we are to connect. http://www.lipower.org/pdfs/commercial/trade/3phase.pdf
 

jghrist

Senior Member
Grounding at both ends creates circulating currents that reduce the ampacity of the cable.

Leaving one end ungrounded creates high voltages on the ungrounded end and a possible safety hazard.

Take your pick. Most choose to have a somewhat reduced ampacity over a high voltage.
 
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