You have what is commonly referred to as a split phase system. This is the standard 50 amp hookup in the RV industry. There are 4 prongs on your plug and they contain two hot phases, one neutral, and one ground. If you measure voltage between the two hot phases you'll see 240 volts. If you take either of the hot phases and measure voltage between one of them and the neutral terminal, you'll see 120 volts. This is basically the same principal as the breaker panel in your home.
A 30 amp RV service only has one hot phase and uses a 3 prong connection, which only gives you 120 volts. You will have the ability to pull up to 30 amps between these two terminals on a 30 amp service, which gives you 3600 watts (30 amps times 120 volts = 3600 watts). On a 50 amp service you have two hot phases that EACH can produce 50 amps. So, in effect you have 12,000 watts (50 amps times 120 volts time two phases = 12,000). That's why the 50 amp service has so much more power than a 30 amp service.
Your RV's breaker panel is wired to accept both of these feeds as in-phase power so you really do not have the ability to run a 240 volt item in your coach. If you did, it would cause problems when the 120 volt in-phase generator would be on.
If you are wanting to set up a shore power receptacle at home, be sure to wire up a 4 wire 120/240 volt feed to the standard 4 prong 50 amp RV outlet and you'll be fine. Do not wire it up to a 3 wire 240 volt outlet, such as used for a welder or clothes dryer. You will need that 4th wire for an RV application.
Mark & Leann Quasius
2016 Cornerstone 45A
2007 Allegro Bus 42QRP (Sold)
2012 Jeep Wrangler Unlimited - Rubicon