This is a drawing of the 50A-30A standard dogbone adapter which you can see only is connected to one HOT leg of the 50A service. Having the correct wiring you could use two 30A circuits from one connection. Of course my question is where are going to park the second 30A RV trailer. I have also heard alot of camp grounds are policing the use of the split cable adapters... Some are not safe to use I guess...
This is a RV50A MALE to RV30A FEMALE dogbone adapter drawing from DMBRUSS.
I do this all the time at camp ground location with my 30A trailer setup. The first thing I do is look at the condition of the Pedestal 30A Service receptacle and if it shows any signs of burned contacts etc i will use my RV50A-30A dogbone adapter and hook up to the 50A service if available.
The only drawback is the 30A Shore Power Cable will most likely have a 120VAC 50A source present on it at all times even when a 30A circuit trip has occurred in the 30A Trailer. These 30A trailer overloads will probably NOT ever trip the Camp Ground Pedestal 50A service circuit breaker. Lots of recent posts on RV NET Forum on this subject as being SAFE to do or not.
Just my 2-cents