The interesting part is where you have a circuit protected at 30 amps or less....the EGC must be the same size as the circuit conductors. This often comes into play for parking lot lighting where you may be using a #4 or 6 on a 20 amp circuit. Don
The conflict described by Don also occurs on equipment such as motors and air conditioning equipment that may have conductors that are permitted to be sized smaller than the branch circuit overcurrent device.
In many cases, the contractor will install conductors sized based on the max overcurrent device instead of the minimum branch circuit size and NOT increase the EGC in proportion.
The contractor doesn't understand why the EGC has to be increase when a smaller EGC is normally permitted for that circuit rating.
There were a couple proposals submitted this past code cycle that tried to clear up this issue, but none were accepted.
I have tried to come up with a good rewrite of 250.122(B) myself without much luck.
Bryan P. Holland, ECO. Secretary - IAEI Florida Chapter