mattotto

Equipment Ground Protection

Discussion created by mattotto on Jul 25, 2019
Latest reply on Jul 26, 2019 by rcramereleceng

I know NEC 250.122 takes you straight to a table that has had equipment grounds sized as long as I've been an engineer, but I recently came across a situation where I wanted to plot a conductor damage curve and a circuit breaker TCC curve.  The conductor, an equipment ground, is #8 CU THHN and the circuit breaker is a 100A branch circuit overcurrent protective device (standard fixed trip MCCB).  Now consider what 250.4 (A) (5) says (this is the key to this discussion) and a situation where a phase to ground fault has occurred at the equipment served by the 100A breaker and the #8 EG is in the return path.  The attached TCC plot suggests to me that the #8 is not "...capable of safely carrying the maximum ground-fault current likely to be imposed on it..." in compliance with 250.4 (A) (5).  Any thoughts?

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