I'm not an expert but my Zappi charger shows the kwh going into the house and what is going into the car. It will divert less to the car, if it thinks the house is drawing too much. I've only got a single phase supply in a 4/5 bed house with ample electric devices running all the time.The suggestion is that their 100 amp single phase supply is too near capacity to supply the additional 30ish amps for a 7kW EV charger.