LTLFTcomposite wrote:One more question, this is feeding a small (four space) sub panel, is the "calculation" the sum of the amps of the breakers in the sub panel?
No, the calculation is done per Article 220 of the NEC. As a practical matter, the sum of the breakers will be an overestimate of the load, often a very large overestimate. On the other hand, if the run is long, you will need to upsize the conductors to account for voltage drop.
As a practical matter none of these loads is continuous, eg a boat lift. Basically we have 6/3 romex feeding a string of LED Christmas lights on the dock
This 6/3 Romex is only for the indoor portion of the run? Because NM cable is only for use in dry locations, and any outdoor location (even inside conduit) is considered a wet location.