Apparatus for reducing the current drain on the sacrificial anode in a

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. In another embodiment, a voltage breakdown material may be applied directly as the insulating layer between the heating element jacket and the tank wall. The material remains an insulator until it is caused to breakdown at an appropriate overvoltage level, where upon it becomes irreversibly conductive.