Sorry that I mentioned the ungrounded systems; that was just a distraction. In the 2002 code, 250.4(B) for ungrounded systems had a requirement that the EGC be sufficient to facilitate the operation of OCPD...but 250.4(A) did not have a similar requirement for grounded systems. This discrepancy was rectified in the 2005 code. 250.4(A)(5) includes a requirement for 'facilitating the operation of the overcurrent device...' (there is also a confusing use of 'high-impedance grounded systems', which might limit the applicability of 250.4(A)(5), but I really don't want to go there
As I read it, 250.4(A)(5) is an additional requirement, above and beyond the sizing required by 250.122. In 250.122 you are giving a minimum size requirement for the EGC. Additionally, the performance requirement of 250.4(A)(5) must be met, which might require a larger EGC in some situations.
I am trying to understand the performance requirements of 250.4(A)(5), and to understand if GFP changes these requirements. I guess I imagine a situation where with a normal breaker 250.4(A)(5) would require a larger EGC than 250.122, but where the use of GFP would permit using something sized to 250.122.