A current relay is switch that utilizes an armature powered by an electromagnet in order to complete an electrical circuit. Relays are commonly used to operate the circuits that provide power to motors and lights.
Relays are simple devices that are comprised of four basic components. Relays make use of an electromagnet, a spring and a set of electrical contacts which are connected to an armature. Without power to operate the electromagnet, the armature is held in position by the spring, which keeps it from making contact with the second electrical circuit that it is designed to operate. The relatively small amount of electricity needed to activate a relay's electromagnet enables it to operate much larger circuits that may be designed to handle much greater levels of power.
Current relays are widely used in a number of common household electronics. Relays may also be found in motorized vehicles, where electrical systems and components require a large volume of current in order to operate. In systems that require a large amount of power, relays may be cascaded, with one or more relays switching the power needed to drive the load. Relays may also be used to implement Boolean logic, and were used in the construction of early computers.