Electrical appliances refer to all electrical devices that consume electricity. From a professional perspective, they mainly include electrical devices, equipment, and components used for connecting or disconnecting circuits, changing circuit parameters, and achieving control, regulation, switching, detection, and protection of circuits or electrical equipment. From the perspective of ordinary people, they mainly refer to some commonly used electrical devices in households that provide convenience for daily life, such as televisions, air conditioners, refrigerators, washing machines, various small appliances, etc.

The metal parts or live parts in electrical appliances are insulated from each other. In the absence of "applying voltage" and "no obstacles", the current formed on the surface of the insulating parts through the medium is called leakage current. The existence of leakage current is one of the important indicators for evaluating the insulation performance of an electrical appliance. From a safety perspective, people have higher requirements for the performance of electrical appliances, especially household appliances. It is unacceptable for electrical appliances to have current leakage, which would pose a threat to the personal safety of users.

The earliest electrical appliances were knife switches used by physicists when studying the phenomena of electricity and magnetism in the 18th century. In the late 19th century, as the application of electricity gradually spread to society, various electrical appliances were also introduced. However, the capacity of these appliances was small and they were manual. Circuit protection mainly used fuses (commonly known as fuses). Since the 20th century, due to the significant advantages of electricity application in social production and human life and its rapid popularization, various electrical appliances with different requirements have continuously emerged. There are large ones such as two- or three-story high ultra-high voltage circuit breakers used in power systems, and small ones such as ordinary household switches.