I have a vessel with an existing 50amp isolation transformer, single coil input and center tapped two phase output. 50 amp shore cable, two phase. I’d like a way to use 30amp single phase shore power. I’m thinking of an auto transformer fitted with an input from a 30a 120v shore cable, and receptacle for taking 240v output into my standard 50a shore cable. Shore neutral and hot 240 connected to L1 and L2 of my isolation transformer. The setup could be portable but usually on the boat. I’d get my normal split phase 240 into the vessel circuit panel. Loads would be concentrated on one leg generally but I might occasionally use a bit of 240. Anything wrong with this setup? Case would be grounded to the vessel ground on the isolated side. I figure I can use up to about 27 amps on one leg on the vessel, provided I use nothing on the other phase.
That’s hazardous.
Anything on the shore side of the isolation transformer needs to use the shore side Ground/PE. If the unit is on the boat, then it should be inaccessible in normal use, as the case will not share the same local ground as the boat.
Better to either replace the isolation transformer, or to reverse it, and use the auto transformer on the output side of the isolation transformer.