I hope someone can help.

I want to get the mathematical formula to calcutate the spark over or flash over distance between 2 conductors / busbars.

I was taought the rule of thumb is 25mm per 1000 volt i.e 22000 volt the flash over distance is then 550 mm if the conditions is favourable.

Do I have this correct or am I totally off the point.

I will be glad if someone can help

Thanks