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Sizing an equipment grounding conductor for high voltage in duct bank

thread238-502586

Sizing an equipment grounding conductor for high voltage in duct bank

Sizing an equipment grounding conductor for high voltage in duct bank

(OP)
Hello all. I had an approach to this question but wanted to see if I'm on the right track.

I'm dealing with a new high voltage cable installation in underground duct bank. 3 750mcm single conductor cables, each in their own conduit, laid in flat formation.

We are required to have an equipment grounding conductor which is transposed in order to provide a low impedance path to ground for a short circuit condition.

Question is, how do I size that EGC. I thought it was as simple as looking at Table 250.122 in the NEC. Based on that table, if the OCPD is set at 300A, I would be going for a #4 EGC.

However, I wasn't sure if Table 250.122 applies to high voltage, and also if there is a way for me to calculate currents expected to run through the EGC. Any suggestions please?

RE: Sizing an equipment grounding conductor for high voltage in duct bank

See NEC
Part X. Grounding of Systems and Circuits of over 1000 Volts
250.190 Grounding of Equipment
(C) Equipment Grounding Conductor
(3) Sizing. Equipment grounding conductors shall be sized in
accordance with Table 250.122 based on the current rating of
the fuse or the overcurrent setting of the protective relay
See also:
IEEE 142/2007 2.7.4.4 Equipment grounding conductor sizing

RE: Sizing an equipment grounding conductor for high voltage in duct bank

(OP)
Thank you very much, forgot there was an entire IEEE book on grounding.

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