The Y capacitance is a capacitor that is connected between the two lines of the power line and the ground (L-E, N-E), usually in pairs. Due to the limitation of the leakage current, the Y capacitor value cannot be too large, generally the Y capacitor is nF level.

Y capacitor: The location where these two Y capacitors are connected is more critical, and they must meet the relevant safety standards to prevent leakage of electronic equipment or energization of the chassis, which is likely to endanger personal safety and life. They are all safety capacitors, which requires that the capacitance value cannot be too large, and the withstand voltage must be high. Under normal circumstances, machines working in the subtropical zone require ground leakage currents not to exceed 0.7mA; machines operating in temperate zones require ground leakage currents to not exceed 0.35mA. Therefore, the total capacity of Y capacitors generally cannot exceed 4700PF (472).

The capacitance of the Y capacitor must be limited, so as to achieve the purpose of controlling the size of the leakage current flowing through it and the impact on the EMC performance of the system under the action of the rated frequency and rated voltage. GJB151 stipulates that the capacity of Y capacitor should not be greater than 0.1uF. In addition to complying with the corresponding voltage withstand voltage of the power grid, Y capacitors also require such capacitors to have sufficient safety margins in terms of electrical and mechanical performance to avoid breakdown short circuits under extreme harsh environmental conditions. Protecting personal safety is of great significance. Specially pointed out: Y capacitors as safety capacitors must be certified by safety inspection agencies. The appearance of Y capacitors are mostly orange or blue, generally marked with safety certification marks (such as UL, CSA, etc.) and the voltage of AC250V or AC275V. However, its true DC withstand voltage is above 5000V. It must be emphasized that Y capacitors should not be replaced with ordinary capacitors such as nominal voltage AC250V or DC400V at will