Wrong.
There is no minimum. You can set it at floor level, if you like. No disconnect - main or branch - can have its' center more than 6'7" above grade. That is, above whatever you're standing on when you're in front of it.
I clarify as I saw one service set directly above the basement stairs - it may have been 6' above 'grade,' but you needed a ladder in the stairwell to reach it!
