Difference Between Shunt Trip, Undervoltage Release and Closing Coil

Shunt trip, undervoltage release, and closing coil are the accessories of circuit breakers. Let’s have a look at their definitions and differences. After reading the article you will fully understand their differences.

Shunt trip

The shunt trip is an electrical accessory used for the instantaneous opening of the circuit breaker. It is generally controlled through normally open contact. It is also referred to as opening coil or shunt release. By energizing the shunt trip you can open the circuit breaker remotely.

The range of shunt trip proposes various supply voltages. (For example from 24 V to 415 V)

Q1 selenoid of a circuit breaker that actuates a release mechanism when voltage is applied. When de-energized the system is in the rest position. A normally open contact actuates the system. Tripping does not occur in the event of wire breakage, loose contacts, or Undervoltage.

Undervoltage release

Undervoltage release is an electrical accessory used for triggering the instantaneous opening of the circuit breaker if the supply voltage drops below a certain level and in particular if the control contact opens. It is generally controlled by normally closed contact.

A passive electromagnetic relay (Q1) actuates a release mechanism when the supply voltage drops or is interrupted. (For example To prevent the automatic restarting of motors) The system is in the rest position when energized. Actuation is produced by a normally closed contact. Undervoltage releases are always designed for uninterrupted operation.

Time-delayed Undervoltage release

Time-delayed Undervoltage release is equipped with an electronic device that delays its operation for around 3 or 4 seconds. It is designed to be used in unstable supplies, where the supply voltage of the release may be subject to variations or micro-breaks, to avoid unwanted opening of the circuit breaker.

Delayed Undervoltage release (Q1) is a combination of a separate delay unit and the respective release. This release is used to prevent brief interruptions in power leading to disconnection of the circuit breaker. The delay time can be set between approximately 0,06…..16 seconds.

Closing coil

The closing coil is an electrical accessory used for controlling the closing of the power contacts of the circuit breaker. The springs of the circuit breaker are to be loaded before the action of the closing coils. It is controlled by NO contact.