Dave..... thanks for the replies
1) In order to be National Electrical Code compliant, a detached building with a sub-panel requires a main breaker panel and not a main lug type. There must be a means of disconnect to the sub, thus the reason for a main breaker.
2) Since a detached building, you also need an 8 foot ground rod at the detached building
3) All subs require a 4 wire circuit, ie , 2 hot's, 1 neutral and 1 equipment grounding conductor.
4) If using Romex as branch circuits, the bare copper grounds land on a separate equipment grounding bar in the sub and not on the neutral bus bar.
DO NOT mix white neutrals with bare copper grounds, that's a code violation and a safety hazard.
5) At the sub, do not insert the green grounding screw or the main bonding jumper. All subs, the neutral must be isolated from the metal cabinet enclosure and be floating.
Hope this helps.........If you have any additional questions, let me know and I'll be glad to answer them for you.
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