Mine has two switches. One breaker switch in the main distribution panel which must nbe on, and then a switch (with a locking pin) rdirectly on the unit.
Heed Dave's previous warning about making SURE that the tank stays full when the electric is on. Running it dry is a sure way to burn it up. Also, I do the same as fkent when I'm going to use the electric. Heat the water initially with gass, then switch over. I also put the gas back on when we are taking morning showers, as it recovers so much quickly...
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter