Precautions for safety capacitors:

Capacitors for Suppression of Power Supply Electromagnetic Interference When using capacitors in power supply cross-line circuits to eliminate noise, not only normal voltages but also the generation of abnormal pulse voltages (such as lightning) must be considered, which may cause smoke or fire from the capacitors. Therefore, the safety standards for cross-line capacitors are strictly regulated in different countries, so safety-certified capacitors must be used. DC capacitors are not allowed to be used as cross-line capacitors. For X2 type capacitors for suppressing power supply electromagnetic interference, it should be suitable for occasions where the failure of the capacitor will not cause the danger of electric shock. For example, if the power supply is connected across the line, it can withstand a pulse voltage of 2.5kV. The Y2 type capacitor for suppressing electromagnetic interference of power supply should be suitable for occasions where the failure of the capacitor will not to the danger of electric shock.​​

Safety capacitors, using IEC standards, advanced production technology, and strict quality assurance system, according to IEC 60384-14, capacitors are divided into X capacitors and Y capacitors,

1. Y capacitors are capacitors that span between L-G/N-G. (L=Line, N=Neutral, G=Ground) The X capacitor is further divided into X1, X2, and X3, the main differences are: 1. X1 high voltage resistance is greater than 2.5 kV, less than or equal to 4 kV,

2. X capacitor refers to the capacitor across the L-N, X2 high voltage is less than or equal to 2.5 kV,

3. X3 high voltage resistance is less than or equal to 1.2 kV Y capacitors are divided into Y1, Y2, Y3, and Y4, the main differences are: 1. Y1 high voltage resistance is greater than 8 kV, 2. Y2 high voltage resistance is greater than 5 kV, 3. Y3 high voltage resistance n/a

4. The Y4 high voltage resistance is greater than 2.5 kV. The X and Y capacitors are all safety capacitors, the X capacitor between the live wire and the neutral wire, and the Y capacitor between the live wire and the ground. They are used in the power filter to play the role of power filter, Filter the common mode and differential mode interference respectively. Safety capacitors are used in such occasions, that is, after the capacitor fails, it will not cause electric shock and will not endanger personal safety. The allowable peak pulse voltage in the application of safety capacitor safety grades Overvoltage class (IEC664) X1 >2.5kV ≤4.0kV Ⅲ X2 ≤2.5kV Ⅱ X3 ≤1.2kV —— Safety capacitor safety class Insulation type Rated voltage range Y1 Double insulation or reinforced insulation ≥ 250V Y2 Basic insulation or supplementary insulation ≥ 150V ≤250V Y3 Basic insulation or supplementary insulation ≥150V ≤250V Y4 Basic insulation or supplementary insulation <150V The capacitance of the Y capacitor must be limited, to control the size of the leakage current flowing through it under the action of rated frequency and rated voltage and the purpose of impact on system EMC performance. GJB151 stipulates that the capacity of the Y capacitor should not be greater than 0.1uF. In addition to complying with the corresponding power grid voltage withstand voltage, the Y capacitor also requires sufficient safety margin in terms of electrical and mechanical properties to avoid breakdown short-circuit phenomenon under ly harsh environmental conditions. Protecting personal safety is important

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There is an X capacitor on the filter circuit, which is connected across the L-N line; the Y capacitor is the N-G line. In the safety standard, capacitors are divided into X1, X2, and X3 according to the pulse voltage; Y1, Y2, and Y3 are divided according to the insulation level. (These are not divided according to what material, I will learn more in the future.) As for the safety standards, there are some differences in various countries, but the rated voltage is nothing more than 250 and 400. The safety capacitors made by major manufacturers are to meet the requirements of this safety standard. A safety capacitor can meet the requirements of Y capacitors, and some can also be made to meet the requirements of X capacitors. So there are safety capacitors marked with X1Y1, X1Y2...

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A capacitor between the live wire and the 0 wire is X, and a capacitor between the live wire and the ground wire is like a Y. Due to the direct capacitance between the live line and the 0 line, it is affected by the voltage peak to avoid short circuits. The more important parameter is the withstand voltage level, and there is no fixed limit value on the capacitance value. The direct capacitance of the live wire and the ground wire involves the problem of leakage safety, so the parameter it focuses on is the insulation level. As James bai said, too large a capacitance value will affect the device after the power is cut off.