Relay See Also: Carrier Relaying, Relay - Advantages To Simultaneous Fast Clearing Electromechanical Switch in which the variation of Current in one Electric Circuit controls the flow of Electricity in another circuit. A relay consists of a movable contact connected to an Electromagnet by a spring. When the electromagnet is energized by the controlling current, it exerts a force on the contact that overcomes the pull of the spring and moves the contact so as to either complete or break a circuit. When the electromagnet is de-energized, the contact returns to its original position. Relays are used to protect expensive equipment, such as a Transformer, from being damaged under abnormal system conditions.