No ground in duct bank

[sberger3]

I just saw a set of drawings that show 35KV,3 phase conductors in a duct bank to a downstream 15KV substation. The distance is about a mile and a half. The conduit does not have a ground conductor in it: is this legal?

Thanks in advance.

 

[rcwilson]

Yes. The copper tape shielding onthe HV cables may be supplying a ground path if they are grounded at both ends adn are continuous.

This sounds like a utility application. Utilities do not have to follow NEC. Using earth as a ground return path is common for utilities.

 

[BJ Conner]

Cable Shields

Cable Shields

I just saw a set of drawings that show 35KV,3 phase conductors in a duct bank to a downstream 15KV substation. The distance is about a mile and a half. The conduit does not have a ground conductor in it: is this legal?

Thanks in advance.

Legal maby but not smart.
The ususal ground in a duct bank is the fault return. Earth doesn't work very well and maby not at all depending how dry the ground gets when it's hot and doesn't rain for a while.
How many vaults in that run 6 or 7? Every one should have ground loop and a couple of ground rods.
The cable shields will have to be grounded periodically to drain shield currents.
Cable shields may not be able to take fault currents without being damaged.

http://www.okonite.com/engineering/shielding-currents.html

http://www.okonite.com/engineering/shielding.html

Concentric neutral cables work better but copper tape shields can be damaged in 8 or 10 cycles of fault currents. :roll: