Re: Separate Building-Minimum Feeder?
225.39 Rating of Disconnect.
The feeder or branch-circuit disconnecting means shall have a rating of not less than the load to be carried, determined in accordance with Article 220. In no case shall the rating be lower than specified in 225.39(A), (B), (C), or (D).
(A) One-Circuit Installation. For installations to supply only limited loads of a single branch circuit, the branch circuit disconnecting means shall have a rating of not less than 15 amperes.
(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or branch-circuit disconnecting means shall have a rating of not less than 30 amperes.
(C) One-Family Dwelling. For a one-family dwelling, the feeder disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.
I would say if you are setting a panel in this building, the minimum size feeder is 60 amps. As for the ground rod, I believe (correct me if I'm wrong) that you will be required to driva a rod no matter if your feeder is 3 or 4-wire. Bond N-G if 3-wire, do not bond if 4-wire. In the 4-wire case the ground rod would connect to the Equipment Ground Bar.