Abstract: For the safe use of the water storage electrical water heater in the case of poor grounding, a class II electrical water heater using PTC heating elements is proposed, which is independent of the household electrical situation, and can work without ground wire without worrying about the abnormal ground wire. Through the targeted design of the insulation part of PTC heating elements, the requirements for class II appliances in the national standard are met. The leakage current is lower than 41% of the national standard value, and the electrical strength is higher than the national standard value, with high safety. And the double-layer PTC chip heater structure is designed, the heat transfer of the heating element is simulated and analyzed, the heat transfer factors are found. By improving the heat transfer path, reduce thermal resistance, the power of the PTC heater is effectively enhanced. The experimental data indicate that the power of the double-layer PTC heater is increased to 156% of that of the single-layer PTC heater under the condition that the convective heat exchange area with water is unchanged. The research on insulation and power improvement of PTC heating elements provides a reference for the future application of PTC heating elements in class II electrical water heaters.

Key words: PTC, Class II appliance, Electrical storage water heater