Doc,
It doesn't say anywhere in either (a) or (b) that the overcurrent protection must be in the panelboard. I don't think the exception to (a) is even needed. The rule only says that the panel must have overcurrent protection not exceeding the panel rating on the supply side. The other end of the feeder is on the supply side of the panel and provides the required overcurrent protection for the panel.
Don(resqcapt19)
