IMO, no. All equipment ground conductors in each cable must be full sized. Fault currents may not divide equally depending on where the fault is and this could exceed the rating of the equipment ground if not full sized. AFAIK, there is no exception to the requirement.

Last edited by Tom; 06/24/13 01:52 PM. Reason: spelling
Few things are harder to put up with than the annoyance of a good example.