The suppression capacitor is the most effective interference component. Its impedance decreases with the frequency, so that we have a short circuit between the mains terminals and/or between the terminals and ground at high frequency. Capacitors for applications between the mains terminals are called:
Class X-capacitors, X-capacitors for short, are capacitors with unlimited capacitance for use where their failure due to a short circuit would not lead to the danger of an electric shock. Capacitors for applications between terminals and ground are called:
Class Y-capacitors, Y-capacitors for short, are capacitors, which serves to reduce the asymmetrical interference voltage, and are located between a live conductor and the metal case which may be touched.
NOTE: The high electrical and mechanical reliability intended to prevent short circuits in the capacitors. The limitation of the capacitance of all Y-capacitors is intended to reduce the AC Voltage of the current flowing through the capacitor and in the case of DC voltage the energy content of the capacitor to a safe level. In fulfilling their technical function in electrical equipment, machines and installations, Y-capacitors bridge industrial insulating systems whose reliability, in conjunction with an additional protection measure prevents danger to human beings and animals. They are intended for use in circumstances where failure of the protection measures of the equipment could lead to a danger of electric shocks.