Upsize equipment grounding conductor

[hhsting]

I have a 70A breaker feeding #4 awg phase and neutral. The engineer has provided #8 awg ground for it. Would #8 awg ground be undersized based on NEC 2017 Article 250.122(B) or not?

 

[Greentagger]

#8 CU for an EGC is good up to 100A.

 

[infinity]

I have a 70A breaker feeding #4 awg phase and neutral. The engineer has provided #8 awg ground for it. Would #8 awg ground be undersized based on NEC 2017 Article 250.122(B) or not?

#8 is the correct minimum size.

 

[suemarkp]

This is an unclear part of the NEC. To me, the 60C ampacity is the normal size for circuits under 100A. So 70A on #4 seems normal and not upsized so the EGC should be normal and not have to be upsized.

 

[infinity]

Since it's a 70 amp circuit #4 is the minimum size conductor (you are not required to use the next size up rule) so nothing has been upsized. Since 250.122(B) does not apply you can use the #8 as the minimum size EGC from T250.122.