Outlet Checker

When I actually worked for a living, I carried an outlet checker like this one in my tool kit, and used it quite often.  It is truly amazing how many electrical outlets are wired incorrectly - usually with the hot and neutral reversed.  Often such miswiring doesn't cause any problem at all, but on sensitive electronic gear, it can spell disaster,
I mention this today because the new refrigerator in the 5th wheel would not work on A-C, and kept blowing the breaker.  The guy who installed it came out, checked everything and disconnected the ground wire from the refrigerator's circuit board.
Once he did that, the refrigerator now works fine, but I would bet the farm that there are some wires reversed somewhere.