How it Works: Voltage Relay

A relay refers to an electrically operated switch or component used to break or interrupt a circuit. Voltage relays run based on a preset level of voltage, or the force that drives an electrical current between two points.

Voltage relays manage preset amounts of voltage transmitted through electrical circuits.


Currents flow through the relay coil, creating a magnetic field. The field attracts the switch lever and enables it to change position. Voltage switches typically offer two positions based on whether the coil's current is on or off. Voltage relays can be over-voltage relays, under-voltage relays or a combination.

Over-voltage Relay

An over-voltage relay operates when the current produced by a load, or device connected to the output of a circuit, exceeds a predetermined value.The over-voltage relay connects to a transformer, or device that transfers electrical energy from one circuit to another. The relay is calibrated to operate at or over a preset voltage level. When the relay is switched on, one or multiple contacts trip, or open a circuit breaker.

Under-voltage Relay

An under-voltage relay operates when the voltage that flows through a relay's coil falls below a predetermined value. Under-voltage relays protect loads against voltage drops that can lead to power shortages and brown-outs. The relay contacts trip the circuit breaker when the voltage decreases to a certain level.

Andrea Stein

Andrea Stein has been writing since 2004. She was a features editor for "Hallmark Magazine" and has served as newsletter editor for several nonprofit organizations. Stein has also worked in public relations, marketing and administration. She earned her Bachelor of Arts in English from the College of Dupage in Illinois.