Shunt Release (Shunt Trip)
A shunt release is a coil that trips the breaker when it is energised. It is the standard release used for remote and protection-initiated tripping: the relay closes a contact, the coil energises, and the breaker opens. It needs control power to operate, so a total loss of control supply means a shunt release cannot trip the breaker.
Undervoltage Release (UVR)
An undervoltage release works the opposite way. It holds the breaker closed while its coil is supplied with sufficient voltage and trips the breaker when that voltage drops or disappears. This makes it a fail-safe device: loss of control supply results in a trip rather than a failure to trip. It is commonly used where an unexpected loss of supply should open the breaker, for example to prevent motors from restarting unexpectedly on voltage recovery.
Choosing and Maintaining Them
- Match the coil voltage and type (AC or DC) to your control supply.
- A UVR that will not stay latched may be seeing low control voltage or a failed coil.
- Test operation periodically as part of routine maintenance.
For related reading, see trip coil versus closing coil. Browse trip coils and releases or request a quote with your breaker model.