bennypass.com - Shunt Release of a circuit breaker

Shunt Release of a circuit breaker - working Principle

A shunt release (or shunt trip) is an optional accessory in a circuit breaker that enables remote, instantaneous opening (tripping) of the breaker via an external, energized signal. When voltage is applied to its internal electromagnetic coil, a plunger is activated, releasing a mechanical latch that forces the breaker contacts open, commonly used for emergency stops, fire alarms, or PLC-controlled shutdowns.

Key Aspects of Shunt Release Operation

Working Principle: The shunt release consists of a coil and a plunger. When an external voltage (AC or DC) is applied to the coil, it produces a magnetic field that moves the plunger, which hits the tripping lever/latch mechanism, forcing the circuit breaker to trip.
Remote Operation: It allows for manual remote tripping via a push-button or automatic tripping through protection relays (e.g., smoke detector, SCADA system).
Short-Time Duty: The coil is not designed for continuous energization. A built-in cutoff switch (or cut-off switch) usually disconnects the coil's power once the breaker has tripped to prevent the coil from burning out.
Voltage Range: It typically operates when supplied with voltage between 70% and 110% of its rated control voltage.
Safety Application: Essential for Emergency Power Off (EPO) systems and reducing arc energy during maintenance, as described in NEC 240.87.

In summary, the shunt release acts as an "electrical finger" that pulls the mechanical trip latch, allowing automatic or remote, safe, and rapid, disconnection of electrical power.

The Shunt Release (or Shunt Trip) is an optional accessory for circuit breakers (such as MCCBs or ACBs) that allows the device to be tripped remotely via an external electrical signal. Unlike the standard internal mechanisms that respond to overcurrent or short circuits, a shunt release acts on an "intentional" command.

Working Principle

The mechanism operates as an electromagnetic actuator integrated with the breaker's internal latch.

Stage	Process
Normal State	The solenoid coil remains de-energized and the breaker operates normally.
Trigger	An external signal (e.g., from a fire alarm or emergency button) applies voltage to the shunt coil.
Activation	The energized coil creates a magnetic field that pulls an internal plunger.
Activation	This plunger mechanically strikes the breaker’s trip bar or latch, forcing the contacts to open immediately.
Cut-off	Once the breaker opens, an internal cutoff switch typically disconnects power to the coil to prevent it from burning out, as most are rated only for momentary duty.

Key Applications

Fire Safety: Automatically cutting power to non-essential loads (like HVAC) when a smoke detector triggers.
Emergency Power Off (EPO): Providing a single "kill switch" for data centers or laboratories.
Remote Control: Allowing operators in a central control room to shut down high-voltage equipment without physical proximity.

Shunt Release vs. Under-Voltage Release (UVR)

While both trip the breaker, they work on opposite electrical logic:

Shunt Release: Trips when voltage is applied. It is used for active, intentional shutdowns.
Under-Voltage Release: Trips when voltage is lost or drops below a threshold. It is a fail-safe against power failure.

Note: A circuit breaker tripped via a shunt release cannot be reset remotely. It must be manually reset at the device to ensure a technician has inspected the cause of the trip.

About

Our Services

Marketing Materials

Marketing Materials1