Designed for surge and impulse protection, safety certified capacitors shunt impulse energy to ground and protect the circuit and user from high voltage surges.
Certified Safety Capacitors are vital components for safety critical across-the-line and line-to-chassis applications. X-class capacitors are used across the line where failure would not lead to an electrical shock. X-class capacitors are divided into sub-classes by its rated and pulse voltage. See Table 1. Table 1.
X-class safety capacitors classification Y-class capacitors are used in “line-to-ground” applications where failure could lead to an electrical shock. It is also divided into sub-classes by their AC voltage and peak surge voltage ratings. See Table 2.
The function of these capacitors is to protect against surges and transients, as well as providing EMI filtering. Safety capacitors are circuit-specific and serve to protect the circuit and the user from high-voltage surges by shunting the impulse energy to ground. One common cause of such surges is lightning strikes.
Subclass X2 and Y2 are the most common type of subclass for applications that use 120VAC (USA) or 220/240VAC (Europe). X/Y combination capacitors are also available, so you might consider using one of these, as well. Whichever safety capacitor you choose, make sure that it has all the proper safety-approval logo markings.
Are Y capacitors safe?
According to the safety level, Y capacitors are divided into 4 categories: Y capacitors are mostly orange or blue and are generally marked with safety certification (such as UL, CSA, etc.) and withstand voltage AC250V or AC275V. However, from the above table, its actual DC withstand voltage is 5000V (Y2) or more.
The most ideal capacitor is an oil-filled iron-case capacitor. (3) Safety capacitors can not be used for high power. (4) The safety capacitor step-down is not suitable for dynamic load. (5) When DC is required, half-wave rectification should be used to meet the constant load. Bridge rectification is not recommended. Recommended Article: