Feeding your 30 amp RV from a 50 amp circuit will do no more harm, then the Edison line with virtually unlimited amperage (relatively) to your home that has a say 100 hundred or 200 amp service. Your house is protected by the main breaker, which is appropriately matched to the circuits inside your house. You could feed your 30 amp RV with a 200 amp service, if available, and still that 30 amp main breaker will not allow more than a 30 amp draw through your RV electrical system.
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