line filter

In power equipment, a noise filter is inserted to block input feedback noise, external noise, and conducted noise, such as external surges, from the power circuit to the AC power supply. It is required to reduce noise to within the standards specified by the Electrical Appliance and Material Safety Act. A line filter can mitigate common mode noise that occurs between the power lines and the ground, but cannot mitigate normal mode noise that occurs between the power lines.