This begs another question. Arriving at a new camp ground and standing plug in hand, what do you do next. I am picturing pooring water on the ground and pressing a large screw driver into the ground and metering from ground to each conductor to find, hopefully, one hot wire. Then challenge that finding with a load such as a 100 watt bulb. Next would be the challenge of finding which of the remaining two is the common. Last. I think I would ignore the ground and drive my own ground rod or use the bed of nails ground.
This is incomplete. Please add to it.