Can the distribution box of the unit building be connected to the power supply of the charging car of the external unit?

Yes . If you want to connect an external power box, it depends on what the distribution box is. If it is a distribution box in a public area, there is no problem, as long as the property agrees. The distribution box in public areas is separated from the residents' electricity consumption, which will not occupy the residents' electricity consumption. Whether or not to pay the electricity bill is to pay the electricity bureau. If so, that's the best. If it is to hand over real estate, it will be considered. Although the lines are separate.