Circuit Breaker Under Voltage Release – How Does It Work?

Under Voltage Release

An under voltage release is an optional device installed in a circuit breaker that automatically triggers a power trip when the power falls below a preset level, usually between 70 and 35 percent of the UV rating. The circuit breaker does not power it. Instead, it receives its power from an alternative source, such as a battery. It was initially designed for use in coal mines but can now be found in any field employing heavy industry.

How it works

An under voltage release device consists of a solenoid magnet with a moving armature fixed to a spring-loaded latch. This latch restrains a spring-biased plunger, which when released, makes contact with the breaker trip bar to trip the breaker.

As long as the voltage connected to the solenoid magnet remains normal, the magnetic force is strong enough to overcome the spring force and keep the trip bar from releasing. But once the voltage cuts off or falls too far below the preset level, the spring force overcomes the magnetic force. This force unlatches the plunger, which then trips the power.

When the circuit breaker contacts are open, a mechanical reset leaver, powered by a central contact arm, holds the solenoid magnet in a sealed-in position. Once power is restored, the magnet reenergizes and holds the plunger in its position allowing the circuit breaker to be reset and turned back on. If the power has not been restored to the solenoid coil and someone tries to reset the breaker, it will only trip again.


It can be mounted on either the left or right pole and installed next to the operating system of a circuit breaker case. Although attached to the trip unit, the spring-loaded release extends through a knockout in the trip unit case. When installed, it won’t interfere with the standard tripping action of a circuit breaker when it experiences a power surge.

The under-voltage release is available for both AC and DC usage with several different voltage ratings to choose. Connections for a UVR come in four different forms. The standard is pigtail leads (18 inches long minimum), exiting the rear of the base directly behind the UVR. These leads are color coded for identification.

Other configurations available include a terminal block mounted on the same side of the base as the accessory. Another has leads exiting the same side of the base as the accessory. The fourth version has leads coming out on the opposite side of the accessory.

Difference between Shunt Trips

A similar appliance that can be combined with a UVR in a circuit breaker is called a Shunt Trip. It has a similar design and function to a UVR, but is instead activated when there is a power outage. Remote control can enable it, but the solenoid coil only carries a temporary charge and is not rated for continuous use.

Eaton’s Under-Voltage Releases

Although UVR’s are not required by law in most cases, they are still recommended. When sensitive equipment is in use, an under-voltage, such as in brownouts, can cause data loss or fry the entire system. The other danger is one of safety; some industrial equipment can be a safety concern if the power dips below its required level.

Eaton’s under-voltage releases are designed to provide the protection needed for electrical systems with a compact design that is easy to install. They have both terminal magnetic and electronic magnetic units available, as well as a host of other accessories.

Eaton has been working in the industry for many years and continues to produce reliable electrical appliances for both commercial and residential use. Their high level of quality control and commitment to safety make Eaton one of the best brands in electronic devices.

Eaton – UVH4RP03K

The G series is designed for all circuit protection needs around the world. These are factory sealed and must be installed onsite. This high-performance UVR can be used for both regional and industry requirements.

Its compact design allows it to be installed easily while still leaving plenty of panel space. It has a left pole mount and a voltage rating from 525 to 600 VAC. Along with built-in ground fault protection, this makes it one of the best UVR’s for EG and JG circuit breakers.

Eaton – 1228C76G03

This classic UVR is made for standard MARK 75 mining service use, with a 120V LAMH electrical reset under-voltage release. This UVR is popular for its reliability and ease of use in factory settings, making it a prime choice in the mining industry.

Series C Eaton-Cutler Hammer 1373D62G09

This 50Hz under-voltage release has a 240V release mechanism and is designed for use with GD breaker parts and accessories.


Eaton Circuit Breaker under voltage release mechanisms are popular due to their high quality and reliability, whether for commercial or residential use. They’re easy to install and have a high safety record across all appliances.