Per 250.190(C), when installing 5kV-rated, metallic insulation shielded, current-carrying conductors, is it permitted to use the metallic tape insulation shield and drain wire as an equipment grounding conductor for a solidly grounded system?
Note: The metallic insulation shield encircles the conductor.
- No. This is not permitted for a solidly grounded system.
- Yes, as long as the metallic shield is rated for the clearing time of the ground fault current protective device operation without damaging the metallic shield.
- Yes, as long as the minimum size of the phase conductors are 500kmcil or larger.
- Yes, as long as the equivalent area of the metallic shield is equal to or greater than 2 AWG copper.
As noted in this new section of the 2011 NEC [250.190(C)(2)], the metallic insulation shield shall be permitted to be used as an equipment grounding conductor if the metallic shield is rated for the clearing time of the ground fault current protective device operation without damaging the metallic shield as long as the system is not solidly grounded. Because we noted in the question above that we were working with a solidly grounded system, this would result in a Code violation.
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at [email protected].