30 amp is really 20amp

Debbie, maybe it is the way you worded your initial post. Obviously you were not looking for an arguement, but maybe asking why you are getting the same voltage reading from your 30 amp plug you would get from your 20 amp plug. The answer is simple. Pretty much every appliance in the US uses 110-120 volt current. If you look at how the 50 amp plug is wired in the above diagram you will notice that even that only provides 120 volts from line to load. The 120 volts is there but not doing anything until you provide a path for it to "move". Now amps is a totally different measurement. The thickness or gauge of the wire determins how large of a circuit breaker and how much current (amps) can safely flow through it. Basically the current coming in to the box is limited by large circuit breakers up the line. And the current available at the box is much more than any one item in your camper can use. So as you start turning things on they They allow current to pass. 5 amps here, 10 amps there, 15 more when you run pretty much anything with a heating element. When these add up to more than the designed electrical system the breaker will kick to protect the system and prevent an unsafe condition. I know others here have more electrical knowledge than I do but that should somewhat correctly cover the basics.