When I worked transmission in the uk. Our engineers ( national grid ) knew the max potential and we grounded with the appropriate amount of grounds ( that were a certain dimension appropriate to the situation) . Don't know how they new ( probably a mathematical / electrical theory ).
Heres an example... When we were removing jumpers from a 400 , ooo kva line ( four wires ) it took 148 grounds " earths plus all the X arms were bonded together with the top earth wire
they called it a " double dress earthing procedure. "
They reckoned ( and still do ) that this was required to produce an equipotential zone that was safe to work on with one circuit live and the other switched out .