I managed to purchase a second hand "showroom" Zappi charger. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning whereas maintaining average tension on the line. We make use of a present transformer measuring the widespread mode current of the dwell and neutral wires. This is a common mode present and we need to be measuring this! If that is more than 20 mA we want to isolate the car by opening the relays.