I have an installation where we pulled in 3- 15kV #4/0 cables in a duct bank. The cables are between a step up transformer (480V x 12.5kV) and HV switch feeding to a step down transformer 12.5kV x 480V.
We have ground grids installed at both ends of the feeder located at both transformers (bonded through the HV switch also).
The HV cable is single conductor, insulation level 133%, 105deg, full copper tape shield. The copper shield is connected internally to a grounding strap in the load breaks on each end of the conductor. The grounding straps are then bonded to the ground grid at both ends.
We are being instructed by the electrical engr. to install a #4/0 ground in the duct bank to clear any faults that may occur. My thoughts are the shields which are bonded to the ground grids at both ends shoud suffice and we would not be required to pull the #4/0 ground. Am I correct in my thinking or is this not acceptable. My foreman, who has many years of experience, does not agree with having a separate ground and the local inspector does not see the need but I need code and theory to back myself.
We have ground grids installed at both ends of the feeder located at both transformers (bonded through the HV switch also).
The HV cable is single conductor, insulation level 133%, 105deg, full copper tape shield. The copper shield is connected internally to a grounding strap in the load breaks on each end of the conductor. The grounding straps are then bonded to the ground grid at both ends.
We are being instructed by the electrical engr. to install a #4/0 ground in the duct bank to clear any faults that may occur. My thoughts are the shields which are bonded to the ground grids at both ends shoud suffice and we would not be required to pull the #4/0 ground. Am I correct in my thinking or is this not acceptable. My foreman, who has many years of experience, does not agree with having a separate ground and the local inspector does not see the need but I need code and theory to back myself.