Abstract: The sacrificial anode in an electrically-heated water heater is protected against excessive current drain and premature dissolution resulting from the cathodic effect of the metal jacket on the heating element by a protective device which provides an effective insulating separation between the jacket and the tank wall to eliminate current flow to the jacket from the protective anode, and a non-linear semiconductor between the jacket and the tank having a breakover voltage allowing it to become conducting at hazardous overvoltage levels. In one embodiment, the heating element jacket is separately insulated from the tank wall and a discrete semiconductor device is separately attached between the jacket and the tank to maintain the insulated condition unless an overvoltage condition occurs and to then become conducting to shunt to overvoltage current to the grounded tank wall.

Abstract: A common source of DC potential is utilized to simultaneously provide power to the protective anode in an electrically heated hot water heater and to the circuit used to bias the heating element jacket to reduce the current load the jacket would otherwise impose on the protective anode. By utilizing a common DC power source, the desired voltage relationship between the protective anode, the positively biased heating element jacket and negatively biased tank wall may be maintained, regardless of changes in the supply. The need for a second separate power supply is obviated and overall construction of the system substantially simplified. The DC power source may comprise a battery or rectified AC current from the power to the heating element.

Abstract: The adverse effects of the exposed metal jacket on a heating element in an electric water heater on the life and performance of a protective anode are eliminated or substantially reduced with the system that imposes a low voltage differential between the heating element jacket and the tank wall while simultaneously providing a low resistance current path which will provide a direct coductive path between the jacket and tank wall (at ground) in the event of an overvoltage condition. The system includes a potentiometer control which may be adjusted to provide the appropriate low voltage differential sufficient to substantially reduce the anode current. The relatively low resistance path allows an overvoltage current to pass readily to ground.