50 to single 30a cord to single 30a inlet is not the problem. The parallels is not problem when you plug into a 30a pedestal. The problem is feeding 50a into a 30a cord that is parallels to two 30a breakers. Neither of those 30a breakers will trip if each load is less than 25a~. But you now have 50a total feeding through a 30a cable.
Exactly, although the 50 to single 30A to single 30A inlet (or 50A 125/250V split to 2x 30A) has a very slight risk if a boat-side breaker fails to trip, as the shore-side breaker is too big to protect the shore power cables.
If you have a set up that allows a gen and even one cord you have a bigger problem than a Y splitter. I wouldvdoubtnthat was an OEM factory set up?
If you mean either I get it and that's the way mine is set up. I do not believe you can exceed 30A when 1&2 combined... atheist I know on mine it will trip if/ when I exceed 30A. Somehow I doubt that was an "oversight" by ABYC and Mfgrs allowing 60A through one cord/inlet.
The setup on my boat is factory. It doesn't allow use of the gen and one inlet at the same time, there are 3 distinct positions on the transfer switch (1 at a time as you're expecting). And my inlets are 50A/125V (the old style 3 wire ones), so my boat isn't susceptible to the 30A issue (unless I managed to find an outlet good for more than 50A and an adapter to use it). But a similarly configured boat with twin 30A inlets would be at risk if using an adapter to a 50A pedestal and only using 1x 30A cord to feed the boat (I see people do this regularly in cases where they don't need more than 30A total).
For this purpose we'll call the 2 sides of my panel L1 and L2. Each side of the panel has a 50A main breaker. However, these are not input breakers, as they're downstream of the transfer switch. The transfer switch positions do the following: "Both Inlets" feeds Inlet 1 to L1, Inlet 2 to L2. "Generator" feeds the generator output to L1 and L2 in parallel (generator provides 120v single phase, not 120/240 split phase, so it's a single output). "Inlet 1" connects Inlet 1 to L1 and L2 in parallel, Inlet 2 is disconnected internally.
Being an older boat and with the shore power connections within 10' of the panel (which means no inlet breakers are required at the inlets according to ABYC), there are no "source" breakers before the transfer switch. I haven't seen anything in the ABYC docs I've read that would actually require these (and the generator manufacturer actually states that no breaker is required on the output if the wiring is sized according to their recommendation, as the generator is incapable of supplying enough power to harm appropriately sized wiring).
Realistically, if I were designing the AC wiring, I would have done it differently. There would be a source breaker and a "source available" light for each source (inlet 1, inlet 2, generator). And then the transfer switch setup and the panel breakers.
