Modern dishwashing appliances (e.g. dishwashers) typically include a tub defining a wash chamber where, for instance, detergent, water, and heat can be applied in order to clean food and/or other materials from dishes and other articles being washed. Various cycles may be included as part of the overall cleaning process. For example, a typical, user-selected cleaning option may include a wash cycle and rinse cycle (referred to collectively as a wet cycle), as well as a drying cycle. A pre-wash cycle may also be included as part of the wet cycle, and may be automatic or an option for particularly soiled dishes.
It is common to provide dishwashers with rod-type, resistive heating elements in order to supply heat within the wash chamber during one or more of the dishwasher cycles (e.g. during the drying cycle). Generally, these heating elements include an electric resistance-type wire that is encased in a magnesium oxide-filled, metallic sheath.
Such dishwasher heating elements can be exposed to harsh environments that may cause premature failure of the heating elements. For instance, chlorine attack, calcium buildup and/or power surge events can cause premature failure of a dishwasher heating element. Such premature heating element failure may cause a violent ignition due at least in part to high current arcing or sheath rupture. Heating element failure generally follows a measurable increase in current leakage. Ground fault detection can be used to detect current leakage and to prevent such failure. To enable ground fault detection, a means must be provided for electrical dispersion from the heating element to earth ground. However, coupling a heating element sheath to ground can place the heating element at risk of failure due to lightning strikes. Additionally, it can be difficult to detect current leakage at various fault points on the heating element due at least in part to the voltage drop across the heating element.
Thus, it is desirable to provide a system for detecting current leakage with a high level of sensitivity that provides protection from high voltage surges caused by lightning strikes.