Greg,
I don't think the rule is one bit ambiguous. It is clear that when you are using OCPDs rated 30 amps or less that the EGC must be of the same size as the ungrounded conductors. If you are using a cable wiring method, you will have to get custom cable or use a cable 4 conductor cable in place of a 3 or 5 in place of a 4 to get a full size condutor to use as the EGC.
It is my opinion that the size of the EGC should be based on the size of the ungrounded conductor and not on the size of the OCPD. That would make table 250.122 work like 250.66, but that is not what the code says and a proposal to that effect was rejected by CMP 5.
