If you assume that 500A is the largest cable that a user can handle[0], then 2kV per megawatt. If you don't mind actively cooling the part of the cable the user

If you assume that 500A is the largest cable that a user can handle[0], then 2kV per megawatt. If you don't mind actively cooling the part of the cable the user handles, then you could run at higher currents for the same cable size. The biggest problem likely will be the much higher demand charges from the power company (they really don't like sudden large loads), so the charging station will likely need a large battery pack of its own. [0]: You want injured/elderly people to be able to charge without assistance so cable weight/stiffness is a important design factor.