How does an electromechanical relay work?

An electromechanical relay uses a physical moving part to connect contacts within the output component of the relay. The movement of this contact is caused by using electromagnetic forces from the low-power input signal, allowing the completion of the circuit that contains the high-power signal.

When a circuit energizes the coil, the armature moves toward the coil and “breaks” its connection with the upper contact and then “makes” a new connection with the bottom contact. Construction does not allow any electrical path between the contacts and the current that controls the coil, which allows the control circuit to remain electrically isolated from a device that the relay contacts turn on or off.

A diagram of the components of a general-purpose electromechanical relay.

An electromechanical relay has two main components: an electromagnet – a coil of wire that become magnetized when electricity is flowing through it – and a set of electrical contacts. When energized, the coil generates a magnetic field that attracts a movable contact or armature, causing it to make or break the electrical connection with other stationary contacts. Within the electromechanical relay class, there are three major sub-groups: general purpose relays, machine tool relays, and reed relays.