an electrical device for the switching of electric circuits. It is one of the most common pieces of apparatus in electrical engineering and is made in a very great variety of models. Examples of switches are the knife switch and the packet-type switch. Wafer and toggle switches are examples of the types used in radio equipment and communication apparatus. The supply and control circuits of electric machines and power plants are switched by various kinds of electric switches, controllers, and contactors as well as by contactless electric switches.