NEC 210.122 @ 15kA 34.5kV

[beanland]

According to NEC 250.122, a #4 copper wire is an adequate EGC for a 300A circuit. However, I was reviewing a design where this #4 AWG copper is proposed for a 34.5kV underground line where the available fault current exceeds 15,000A. Per my Southwire Power Cable manual, #4 AWG Copper will be damaged in about 1 cycle at 15kA. Since even the fastest 34.5kV circuit breaker takes 3 cycles, I would expect this #4 ground to be damaged on the first through fault. However, the designer is saying "per NEC 250.122." From what I can find NEC 250.122 applies at all voltages and all AFC. Is there some other clause in NEC that would tell the designer not to use a #4 cu EGC in this application?

 

[don_resqcapt19]

250.122 gives the minimum size of the EGC. You can use 110.10 to require one suitable for the available fault current.