In summary, Johanson Safety Certified Capacitors are designed for surge and impulse protection and are used as EMI filters in telecom and AC/DC power supply applications. Capacitors are rated based on their use in a circuit, X for line-to-line and Y for line-to-ground, as well as their impulse rating. Johanson Dielectrics has a variety of Safety Certified Capacitors suitable for any EMI filter or isolation needs.