This installation doesn't involve isolated grounding, it is a routine installation with multiple 3 phase 480volt circuits in one raceway about 80 feet in length.
I will increase the ungrounded conductor size for each circuit to compensate for derating due to the number of current carrying conductors in the EMT.
The maximum OCPD will be 60 amps which calls for a #10 EGC when installed. The EMT is a suitable equipment grounding means according to 250.118
I have always installed a EGC in my metalic raceways. An extra step to insure an effective ground fault path in my mind, I guess. I loose locknut, or the helper forgets to tighten a set screw on a coupling and you all know that it happens.
Iwire...I agree that the code does say to increase the size
So I will...
Redsy...There is nothing in the NEC that restricts the lenght of a EMT run that is used for an equipment grounding conductor.
George Little...Although the EGC I'm installing is optional, I must follow rule 250.122(B)...You see, with my reason for installing it in the first place, for a back up to a loose locknut or the forgotten tightening of the setscrew on a EMT coupling, I would want it properly sized as if the metalic pipe was not the grounding means at all