RV Tech Library - Shore Power Connections
If you plug an RV into a 50 amp service you have an X and a Y phase. Each phase is capable of 50 amps therefore you have a total power capacity of 12,000 watts from these two poles (50 amps x 2 poles x 120 volts = 6,000 watts each). A 50 amp shore power receptacle contains 4 wires - the X phase, Y phase, neutral, and a ground lug. The X phase feeds one side of your breaker panel while the Y phase feeds the other half. Remember between the Red and the black wire is 240 volts 2 phase. But we split it and either wire only carries 120volts to ground single phase.
The long version is here:
http://www.myrv.us/electric/Pg/50amp_Service.htm
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