A PW-ZW has all four ground posts bused together, so you only need one connection. Do NOT parallel PW-ZW outputs! There will result in a direct short of the windings between the two wipers, and there's no fuse or breaker protection for that configuration! Doing this will pretty quickly cook something in the transformer, and when you overheat the windings and burn the enamel coating off the windings, the transformer is junk!
Follow the red lines, if you were to connect the A & B posts together, note the current flow! Note that the circuit breaker isn't anywhere in the current path! It's the same situation for any of the A thru D posts, the circuit breaker in in the common U path.
