how to check volts in plug

[Bryan]

hey guys,
I recently plugged in my bus for the first time, and some of the electronics inside didn't seem to be working properly. I was told the plug at the building was recently installed. We decided to disconnect and use generator because I certainly didn't want to under power and damage anything inside. I have a 50amp plug, and of course adapters to change it to a 30amp 3 pin plug. But how would i know if the building is supplying proper to me, and would my breaker box protect me from under power or damage? Thanks for your input!