This is not a situation in which math will provide any answers. Let's start here:
That is not true, and it leads me to believe that you have a misconception as to the purpose and function of an EGC. Please allow me to explain what I mean, and forgive me if I am not giving you enough credit for your knowledge and experience.
Originally Posted by Dale001289
As far as the physics is concerned, I can run three ungrounded conductors from a panel located on the north wall of a room to a motor located on the south wall of the same room. I can route these conductors in a conduit along the east wall. I can then run the EGC in a separate conduit along the west wall.
EVERYONE PLEASE NOTE: I know this is a code violation, but I am talking about physics here.
Now suppose one of the ungrounded conductors breaks free of its termination point inside the motor and comes into contact with the motor's outer case. This will cause a high current to flow from the ungrounded conductor, to the case, to the EGC, and via the EGC back to the panel. This will cause the breaker to trip and thereby terminate the event. That is, indeed, the EGC's job. The fact that the EGC was nowhere near the phase conductors will not stop it from doing that job.
As far as multiple circuits in the same tray sharing the same EGC, the description I just gave applies here as well. The single EGC will allow the fault current to flow back to the panel, resulting in a trip of whichever circuit breaker serves the load that experienced the fault. I do not see a need for a code change.
Charles E. Beck, P.E., Seattle
Comments based on 2014 NEC unless otherwise noted.