25kV isolated phase arrangement underground

[dontexplode]

Proposed design is for an isolated phase arrangment consisting of 25kV cables with 3-500 kcmils and a #4/0 ground routed underground embedded in conduit.

there is no ferrorous, or steel encircling only one phase, but rebar around the entire duct bank.

The cables are shielded with a tape shield and was thinking that the shield will get hot because it encircles the conductors similar to rebar or steel. will that happen? last time i did one of these is was bussing from a generator.

also i don't believe the equipment ground is required to be in each conduit but can be run in a seperate conduit or exposed in the duct bank

thoughts?

 

[jghrist]

As long as the cable shield is non-ferrous, there will be no heating from eddy currents like in a steel conduit. There will be current induced in the shields from the conductor current, and it will be higher if the cable spacing is greater. The induced shield current will heat the cable, but it will be offset somewhat by being further from adjacent hot cables.