The term 'leakage current' has been used to express several different concepts, such as contact current, protective conductor current, insulation characteristics, etc. At present, equipment standards still commonly use this term to refer to the current flowing through the human body when it comes into contact with electrical equipment, but in reality, it refers to the contact current. To comply with industry usage habits, this specification continues to use the term "leakage current". In the past, equipment standards used two traditional techniques to measure leakage current, whether it was measuring the actual current in the protective conductor or using a simple resistor capacitor network (representing the impedance of the human body), which defined leakage current as the current flowing through the resistor. The following conclusions have been drawn from the study of the effect of leakage current: - In terms of safety, the main consideration is the harmful current that may flow through the human body (this current may not necessarily be equal to the current flowing through the protective conductor); - It has been found that the effect of current on the human body is more complex than was recognized in the early formulation of standards. The most important human effects that serve as the basis for setting limits for continuous waveform currents are: perception; Reaction; Get rid of; Electric burns. Each of these four human effects has a separate threshold, and some of these thresholds vary greatly with frequency. With the widespread application of electronic switching technology in power systems and equipment, more and more high-frequency harmonic voltages and currents have been generated. Various equipment standards gradually refer to the more representative measurement network defined in GB/T 12113-2003, in order to scientifically and reasonably measure leakage current