The AC power input is divided into three terminals: live wire (L), zero wire (N), and ground wire (G). The capacitance connected in parallel between the live wire and the ground wire, as well as between the zero wire and the ground wire, is generally referred to as the Y capacitance. The connection position of these two Y capacitors is crucial and must comply with relevant safety standards to prevent electronic equipment leakage or case electrification, which can easily endanger personal safety and life. They all belong to the category of safety capacitors, which requires that the capacitance value should not be too large and the withstand voltage must be high. In general, machines operating in subtropical regions are required to have a ground leakage current not exceeding {{0}}.7mA; Working on temperate machines, it is required that the leakage current to the ground should not exceed 0.35mA. Therefore, the total capacity of Y capacitors generally cannot exceed 4700PF (472).
It is particularly pointed out that as a safety capacitor, Y capacitors must obtain certification from a safety testing agency. The appearance of Y capacitors is mostly orange or blue, and they are generally marked with safety certification marks (such as UL, CSA, etc.) and the words' withstand voltage AC250V or AC275V '. However, its true DC withstand voltage can reach over 5000V. It must be emphasized that Y capacitors should not be arbitrarily replaced by ordinary capacitors with nominal withstand voltage of AC250V or DC400V.
The capacitance in parallel between the live line and the zero line suppression is generally referred to as the X capacitance. Due to the critical location of the capacitor connection, it is also necessary to comply with relevant safety standards. The X capacitor is also one of the safety capacitors. According to actual needs, the capacitance value of capacitor X is allowed to be larger than that of capacitor Y, but at this time, a safety resistor must be connected in parallel at both ends of capacitor X to prevent the power cord plug from being electrified for a long time due to the charging and discharging process of the capacitor when unplugging. According to safety standards, when the power cord of a working machine is unplugged, the voltage (or ground potential) charged at both ends of the power cord plug must be less than 30 percent of the original rated working voltage within two seconds.
As one of the safety capacitors, X capacitor also requires certification from a safety testing agency. X capacitors are generally marked with safety certification marks and the words' withstand voltage AC250V or AC275V ', but their true DC withstand voltage can reach 2000V or above. When using them, do not use ordinary capacitors with nominal withstand voltage AC250V or DC400V as substitutes.
