Gerald J. - 1/1/2014 08:58
Old codes did allow a reduced size ground but I think that's no longer true. The function of the ground is to carry current IF there is a short to the case and to do that with a low enough voltage drop to prevent a shock hazard to people and critters and a fire hazard from the ground wire heating up. A reduced size ground does NOT accomplish that.
Gerald J.
A properly sized circuit breaker will trip long before a reduced size ground wire will heat up. That is why the NEC allows reduced and shared grounds... They only carry current in an emergency fault situation.
That being said... I find it interesting that all wires in romex are of equal size. Probably to make things more idiot proof for the residential week end warriors. | 
What size ground wire on a 50 amp 230V four wire circuit?
