John, But what if the shield is only connected at one end as some other folks are saying? Now, how does flow occur? I agree with the "Possibility" of potential on the ground circuit but I also know that electricity takes the path of least resistance (both voltage and amps---since volts do push amps.) You can see a ground wire (white wire---not the copper ground) spark at the breaker panel when it is connected to a load such as a motor but it has NO potential. Ground faults help with large, potentially dangerous shorts to ground as through your body. You are always going to have a difference in ground potential between a large amp drawing component and something less. You certainly cannot have voltage potential(and flow) without some sort of current, ever how small. No current, no flow.
So, I guess my question remains, since we are dealing with AC, how can wire be directional?