Ditto that you should check your shore power connection before use. As Al pointed out, you can do so with most surge protectors. Keep in mind you must NOT plug the bus into these until they indicate it's safe to do so. You're better served with an active power management device that has an internal relay that disconnects power to the coach if there are any faults in voltage while connected. Too many parks suffer brownouts or low voltage situations in the peak of summer air conditioning use. Progressive Industries, TRC (Surge Guard Brand), and now CAMCO have power protection devices.

I'm surprised no one has a plug-in quick tester for a 50A/240V outlets like those that exist for 120V outlets. The testing is easy with a multimeter, but not everyone is comfortable using a multimeter.