Will the VFD allows the use of an 80 amp breaker. In your scenario, a # 6 awg cu. EGC will be needed. You would always use the next closest higher circular mill.
The AHU unit is a factory wired unit with a name plate which states crt -( 59 FLA) &( 60 amp OCP max) it has three fans we were to make a one point connection but the unit from the factory just installed the three VFD,s which now we must connect each individually .
What were trying to do is save the mechanical contractor the cost and still be code smart .
I see your point and thank you for your input I guess will have to change the ECG due to this rule on up sizing I cant change the design of engineer for reasons that cost more so were trying our best to help him and still meet code .
So 60 amp max breaker and we use number 2#awg phase wire and the engineer calls out 8 # ground will up size the ground or ECG that's in our best interest can you make the ground larger in size or is there a rule on that . LOL
We were thinking maybe there was a exception to the rule on motors as far as starting in rush in this case a larger breaker was say needed so that would correct the issue even if the name plate says 60 max if we used a 100 amp breaker in panel and leave the wire EGC at 8 #awg