NEC 555.12

[Steve@sei]

I have been told by engineers that it is perfectly sound to use demand factors in 555.12 for sizing a main breaker in a Marine setting.

Here is the design criteria.
Dock mounted sub station distribution panel #1 480/240 single phase with a connected secondary load of apx 170 amps
Dock mounted sub station distribution panel #2 480/240 single phase with a connected secondary load of apx 415 amps

Both are being fed from a 400 amp 480/3 phase distribution board which is fused at apx 300 amps, bussed at 600 amp.
So we have a main breaker in MDP at 300/3 480 volt. Calculated load at 204 amps
sub breaker in the MDP at 250/2 480 volt
sub breaker in the MDP at 600/2 480 volt

What is wrong with this picture?

 

[buzzbar]

You have to count the number of boat slips in order to figure out the derating. Without that information, nothing can be calculated.