Jimmy,
Please find 2 PDF files attached. This is a job I'm bidding (without engineered drawings at this time) and I'd like to see if you agree or disagree with my understanding of the NEC.
All but 4 of the pedestals will have (2) 30-amp receptacles with circuit breakers in the pedestals. The 4 single loaded pedestals are the ones for the slips nearest the bulkhead on circuits A1 and B1 (see drawing). Each pedestal will have a KWH meter for the individual slip so we will be taking a 10% reduction in feeder calculations per 555.12 note 2.
The circuit that I specifically would like you to comment on is circuit B2. This circuit consists of 4 pedestal each with (2) 30-amp receptacles and individual KWH meters for the slips. The 30-amp receptacles are 120-volts and the feeder is a MWBC consisting of A-phase, B-phase, N, and Gnd from a single-phase 120/240-volt service. In each pedestal, the (2) 30-amps circuits are wired to opposite phases of the feeder. Each phase of the MWBC (from the 1st pedestal in the circuit to the panel) will have a calculated load of 30*4 = 120-amps * 90% (for meter) = 108-amps per phase. 110.14(C) requires us to use table 310.16 for the ampacities at our termination. Table 310.16 lists a #2 copper wire at 75c (our equipment terminations have a minimum of a 75c rating) as having an ampacity of 115-amps. We are thereby OK with this installation at this point.
Here is where I need to know I am understanding the code correctly. The load calculation after the 1st pedestal becomes 30*3 = 90-amps * 90% (for meter) = 81-amps per phase. A #4 copper conductor in table 310.16 has a 75c rating of 85-amps which is greater than the 81-amp load calculation, so use of a #4 type W cable will be in compliance with 110.14(C). Table 400.5(B) has a 75c rating for a #4 W cable of 115-amps (column E) so it is adequately protected by the 110-amp breaker.
Please let me know if you see a fallacy in my thinking.
