general wiring of ground or neutral

sam spade gave you the answer. You are only to switch the 120v from one side to the other. The other wires are coupled together (ie. neutral to neutrals and ground to grounds). You run your "hot" from the breaker to the center of the switch (either L1 or L2, it doesn't matter) and then connect the one charger input power wire to the A side (of the same choice of the L1 or L2) and the other charger's input to the B side (of the same choice of the L1 or L2). Thus when the switch is operated one direction, it connects the center to one side, and when flipped the other way, it connects the center to the other side.

NOTE: you are switching AC and the 55 amp versus 30 amp doesn't apply directly... you will likely be switching less than 10 amp AC.