how do i tell if 50 amps is coming through plug.

Love it how everyone becomes an electrician. This was an interesting thread. We have a storage owner was trying to accommodate an RV owner. IMHO, when it comes to electricity, if you have any doubt what so ever what you are doing or if you don't understand how electricity works or think you know how electricity works, then your best bet is to hire a licensed Electrician to assess your situation.