Z31B breaker switch
 

I was reviewing the aeroelectric book and their Z31B ground power solution.
I was wondering if everyone sees this the same way. Once ground power has been applied with correct polarity the diode will allow the coil to clopse the contactor. Once ground power has been removed however, unlike the Z31A drawing the B mechanism will keep the contactor self energized.
To break this you would need to use the switch-breaker (bottom of the schematic) to disengage the contactor.

1. Ground power switch "OFF".
2. Attach external ground power cable.
3. Ground power switch "ON"
4. (external power energizes the relay since ship battery may be dead)
   Then, after charging, etc.:
5. Ground power switch "OFF"
6. remove external ground power cable

you can have a situation where the ship battery will continue to energize the relay if you don't shut off the switch, but I think the idea is to not plug or unplug "Hot".