The following Y capacitor has two markings on it, labeled as X1 and Y2.
Also you can see the capacitance and safety approvals.
This means that the capacitor can be used both as an X capacitor and as a Y capacitor. In practical applications, the requirements for Y capacitors are generally higher. This can be seen from the voltage rating markings on the capacitor. The voltage rating when the same capacitor is used as a Y capacitor is usually lower than when it is used as an X capacitor.
Y capacitors are typically blue in color. In terms of connection, Y capacitors are usually connected between the live wire and ground, or between the neutral wire and ground. Therefore, they are typically found in pairs in the circuit.
The naming is also similar because the connection method somewhat resembles the letter "Y", so it is called a Y capacitor.
Like the X capacitors, the number following the Y (such as Y1, Y2, etc.) indicates the rating. Let's take a look at an actual circuit board; you can see that Y capacitors appear in pairs, typically located at both ends of the power supply interface.
However, Y capacitors can also be connected differently. Instead of being placed between the live wire and ground or between the neutral wire and ground, they may be placed at the end of the bridge rectifier filtering circuit, then connected in series to the hot ground and cold ground. This setup can still filter the live and neutral wires to ground. In this case, only one Y capacitor is needed.
Connection Methods
As the names suggest, the connection methods are distinct. X capacitors are directly connected in series between the live wire and the neutral wire, resembling the letter "X," and function to filter out interference between the live and neutral wires. Y capacitors, resembling the letter "Y," typically appear in pairs in circuits: one between the neutral wire and ground, and the other between the live wire and ground. This setup performs a ground filtering function for both the live and neutral wires, and this symmetric filtering is also called common-mode filtering.
Appearance
X capacitors are usually yellow and have a rectangular shape, while Y capacitors are typically blue and have a flatter, oval shape.
Component Markings
Both X and Y capacitors are marked with designations like X1, X2, Y1, Y2, indicating their specific ratings.
Voltage Requirements
Y capacitors have higher voltage requirements in the circuit. Although the voltage rating on the capacitor may show 400V or other values, the actual withstand voltage of Y capacitors is much higher and can typically handle several thousand volts of pulse voltage. In comparison, X capacitors have lower voltage requirements.
Substitution Rules
Due to the difference in voltage ratings, a Y capacitor can be used in place of an X capacitor, but the reverse is not true. You cannot substitute an X capacitor for a Y capacitor.
Consequences of Breakdown
Safety regulations ensure that safety-rated capacitors do not cause harm to humans if they break down. However, if X and Y capacitors fail, the effects are different due to the differences in their connection methods. If an X capacitor breaks down, it will directly short-circuit the live and neutral wires, causing overcurrent, which may lead to blown fuses or tripped circuit breakers.
Y capacitors are grounded, so if they break down, they will cause a short circuit to the device's ground. This may connect the live or neutral wire to the device’s outer shell. If the device is not properly grounded, the outer shell may become electrified, posing a safety hazard to people. This is why Y capacitors have higher voltage standards than X capacitors.
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