Knowing that many devices can generate unwanted EMI, how is EMI reduced as to not affect other devices? This is where AC line filters are commonly used. But how do EMI filters work? In this example here, an EMI filter is used at the input of the dryer’s power circuit and contains inductors and capacitors. EMI filter inductors are commonly called chokes, as they choke or prevent sudden current changes. The inductor has a low impedance at 50 and 60 Hz which allows the useful power to pass on through to the dryer. But at high frequencies where the EMI is present, the inductor has a high impedance which helps block the EMI from passing through. In addition to the inductor, capacitors are placed between the line and neutral and line to ground. Capacitors that are connected from line to line or line to neutral are called “X” capacitors. Capacitors that are connected from line to ground are called Y capacitors. At 50 and 60 Hz, the capacitors have a high impedance which has no effect on the AC voltage. But at high frequencies, the capacitors have a low impedance which shunts transient currents to either neutral or ground. An important observation in this example is that the ground connection of the filter is connected to chassis ground of the dryer which is the external metal enclosure.