National Electrical Installation Standards

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Thursday, May 7, 2020

Question:

Hello Code Nuts,

I have a simple question. What is the minimum size equipment grounding conductor needed for a 15,000-volt, 3-phase, 100-ampere feeder? The system is a single-point grounded system. Each of the cables in the feeder have a copper tape shield that appears to be okay to use for this purpose. Is that acceptable? Any guidance would be very helpful, before we pull the feeder conductors into the duct bank raceways.

 

Jim Tracey
A

Answer:

Hi Jim,

 his system is 15kV so the requirements in Part X of Article 250 apply. Section 250.180 indicates that Section 250.1 through 250.180 apply unless modified by Section 250.182 through 250.184. That said, for a single point grounded neutral system, an equipment grounding conductor is required in accordance with 250.184(B)(8). The minimum size equipment grounding conductor required is found using Table 250.122 based on the rating of the overcurrent protective device for the feeder, which based on the question, is 100 amperes. Section 250.122 applies, and Table 250.122 indicates that, a minimum 8 AWG copper conductor is required to be used with this feeder. The tape shields in each cable serve a different purpose as indicated in 311.44 (2020 NEC)

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