Relay-controlled circuits play a vital role in the everyday electrical systems. Relay-controlled circuits have application ranging from the early telephone exchanges to the present-day applications in the monitoring of processing operations in factories such as the Coca-Cola plant.
A simple switch is a simple circuit component that is used to allow or disconnect the flow of electric current through a circuit by means of an open circuit. A switch has a wide range of application one of which is the relay-controlled circuit. A relay-controlled circuit is in its simplest form, an electrically controlled switch. Most relay circuits make use of an electromagnet to manually (mechanically) operate a switch while others were purely solid-state relays.