Jon- Yor're a smarter man than I am for sure but if I understand your question, you are talking about an "ungrounded" system and the 250.4(A)(5) is under the heading of a "grounded" system. I detect (no pun intended) you are talking about an ground fault dectection on a "ungrounded" system. In either case I could find no provision for reducing the EGC for either a grounded or ungrounded system. If your talking about the conductors used for the ground fault sensor, then I would say they don't need to be sized per 250.122 like the EGC. Hope I'm on the right wave length with your question.
