Ycapacitors

Y capacitors, also known as safety-rated line-to-earth capacitors, are used in electrical equipment to suppress electromagnetic interference (EMI) by providing a path from the mains conductors to earth. They form part of the input EMI filter alongside X capacitors, which connect line to line rather than to ground. Y capacitors help reduce common-mode noise that travels from the power line to the chassis or to grounded parts of the circuit.

Most Y capacitors are film types, using polypropylene or polyester dielectric, and are encapsulated in epoxy or other protective housings. They come in radial or axial lead configurations and are manufactured to safety standards that govern capacitors used between live parts and earth. Within the Y category, two common classifications are Y1 and Y2. Y1 capacitors are designed to withstand higher surge voltages and transients and are often used for direct line-to-earth connections, while Y2 capacitors are rated for standard mains operation with slightly lower transient withstand. Working voltage ratings typically range up to about 250 V AC for Y2 and up to around 300 V AC or higher for Y1, with precise values depending on the maker and standard.

Capacitance values for Y capacitors are generally small, ranging from a few picofarads up to several tens or hundreds of nanofarads, chosen to achieve the desired EMI suppression without compromising safety. They are designed to fail safely, tending toward an open circuit rather than maintaining a short to earth in fault conditions. Compliance with international safety standards includes considerations of creepage and clearance distances, humidity resistance, and temperature performance.

Applications for Y capacitors include EMI suppression in power supplies, televisions, audio equipment, and other appliances where a connection to earth helps suppress conducted and radiated interference.