50 amp down to 30 amp plug -- still 50 amp?

ECones wrote:
The fellow we talked to said he always plugs his 30 amp trailer into the 50 amp plug through an adapter so he'd have 50 amps available, and being that I'm no electrician I didn't argue. But I did understand that we're really only using half that plug (Roy's post above) so I seriously doubted it.

Luckily, I knew who to ask. ;)

Thanks for all the kind responses and, once again, nobody pointed out my mental deficiencies. ;)

Technically he does have 50A available at the other end of his cord. Using only half of the 50A service just means there is only 50A and not 100A available. As some others have stated, the current coming from the pedestal depends upon what is limiting it. With a 30A pedestal receptacle, the 30A breaker on the pedestal will limit you to 30A.

If you now use a dogbone to connect to the 50A receptacle, there is indeed 50A available. If the trailer does not have a 30A "main" breaker there is nothing stopping it from pulling up to 50A. The setup in the picture a couple of posts above without a main breaker could use (15+20) = 35A if plugged into a 50A dogbone.


This situation is no different than a light-duty extension cord plugged into a 20A receptacle at home. If you then plugged an electric heater into the extension cord, you could overload the cord without tripping the 20A breaker. In this case, just like the RV dogbone into 50A you can't just rely on the receptacle supply's breaker to limit the current if the device plugged into it isn't capable of the load.

Many RV's with 30A cords have 30A main breakers to prevent this.

The reality is his trailer is limited by the lower of his main or the pedestal breaker. By using the 50A service, his effectively now only limited only by his 30A main. This may result in slightly more power available for him if the pedestal 30A breaker would have tripped at something less than 30A.