Very common. Almost every RV (Recreational Vehicle) has one. Actually most are powered 3-way.1) They run from standard 120VAC when parked and that power source is available. 2) Most also run from 12VDC while the RV is underway. 3) They burn Propane (gas) when parked and 120VAC is not available.
Not all have the 12VDC option but it is safer to turn the propane tank off while driving and use the battery instead.
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