Campus 15kV underground system

[gerant]

In a campus 15kV underground system a 4/0 AWG bare ground wire was installed (embedded) within the cement of the duct bank surrounding the non-metallic ducts and it is terminated at each manhole ground rod/ring. A typical feeder consists of three shielded phase conductors and an insulated ground conductor. If there is line-to-ground fault the return fault current will divide itself among the metallic shields and ground conductor. What is the purpose of the 4/0 ground wire, that is not bonded to the rebar within the duct bank cement?

 

[dpc]

It is serving as a grounding electrode. Since it is embedded in the concrete, it should provide a fairly low resistance ground, even though it is not bonded to the rebar.

David Castor

http://www.cvoes.com