I am looking at upsizing my AC conductors coming out of my inverter from a #6 to a #4. 250.122(B) says I need to increase the EGC size proportionally according the the circular mil area of the conductors. My ocpd is 60 A so I'm looking at a #10 EGC.

From Chapter 9 Table 8:

#4 circular mils = 41740

#6 circular mils = 26240

#8 circular mils = 16510

#10 circular mils = 10380

41740/26240 = 1.5907013..... x 10380 = 16511.5

Since technically 16511.5 is greater than #8 @ 16510 c-mils I should have to go up to a #6 AWG conductor.

Here is my issue, #4 is only rated up to 95 A at 90 deg C and 85 A at 75 deg C. So the largest overcurrent protection device one would have is less than 100 A and Table 250.122 would let you use a #8 EGC to protect #4 on say a 75 A breaker.

Why is #8 adequate as an EGC for #4 but when I upsize from #6 to #4 for voltage drop #8 is technically insufficient.

Am I allowed to round my ratio of #4 c-mills/#6 c-mills to an even 1.59? If I did this would make #8 adequate.

Am I ok to use #8 as my increased EGC size if I increase my line conductors from #6 to #4 for voltage drop concerns or do I have to use #6 since I'm technically 1.5 c-mils over the limit on #8.

From Chapter 9 Table 8:

#4 circular mils = 41740

#6 circular mils = 26240

#8 circular mils = 16510

#10 circular mils = 10380

41740/26240 = 1.5907013..... x 10380 = 16511.5

Since technically 16511.5 is greater than #8 @ 16510 c-mils I should have to go up to a #6 AWG conductor.

Here is my issue, #4 is only rated up to 95 A at 90 deg C and 85 A at 75 deg C. So the largest overcurrent protection device one would have is less than 100 A and Table 250.122 would let you use a #8 EGC to protect #4 on say a 75 A breaker.

Why is #8 adequate as an EGC for #4 but when I upsize from #6 to #4 for voltage drop #8 is technically insufficient.

Am I allowed to round my ratio of #4 c-mills/#6 c-mills to an even 1.59? If I did this would make #8 adequate.

Am I ok to use #8 as my increased EGC size if I increase my line conductors from #6 to #4 for voltage drop concerns or do I have to use #6 since I'm technically 1.5 c-mils over the limit on #8.

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