The one in the HW heater is so when it is drained you can insure that no one accidently turns it on from inside the RV. If switched on while empty it will immediately burn out the element.I have 2 buttons for hot water on my panel. 1 is for gas the other is for electric. But I also have a button on the outside water heater panel. If the 1 on water heater is for electric and the one on the inside panel is fir electric? Why 2 buttons?