Shunt Trip Breaker Wiring Diagram

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A shunt trip breaker uses a remote coil to trip the circuit breaker open instantly when energised — allowing fire alarm panels, emergency stop circuits, and interlocks to de-energise a protected circuit from a distance.

A shunt trip breaker (also called a remote trip or shunt release circuit breaker) is a standard moulded-case or miniature circuit breaker fitted with an accessory coil — the shunt trip coil — that electromagnetically releases the breaker's trip mechanism when the coil is momentarily energised. This allows the breaker to be opened remotely by a control signal without manually operating the handle.

The shunt trip coil is a momentary-duty solenoid. This is a critical design point: the coil is rated for a brief energisation pulse only (typically 0.2 to 1 second) and will overheat and burn out if held continuously energised. In practice this means the trip circuit must be designed to interrupt the coil current immediately after the breaker trips — either through a normally-closed auxiliary contact on the breaker itself (which opens when the breaker trips, breaking the coil circuit), or through a pulsed signal from the fire alarm or emergency stop system.

Common applications include: - Fire alarm panel integration: when the fire alarm activates, it energises the shunt trip coil and de-energises power to specific circuits (lift motor feeders, HVAC systems, or entire distribution boards) to prevent fire spread via electrical equipment - Emergency stop (e-stop) circuits: in machinery where the supply to a machine section must be removed by a remote e-stop button or safety relay without requiring someone to physically reach the panel - Utility or building management interlock: remote load-shedding or demand control

The shunt trip coil is available in AC voltages (120 V, 230 V, 277 V) or DC voltages (24 V, 48 V, 110 V) depending on the manufacturer's specification for a particular breaker model. The trip coil voltage must match the control circuit voltage.

The breaker can be reset (re-closed) manually after the triggering condition is cleared — it is not a latching or lockout device by itself. If lockout after tripping is required, an under-voltage release (UVR) accessory is used instead of or alongside the shunt trip, as the UVR prevents re-closure until the control voltage is restored.

Always verify coil polarity for DC versions and check the manufacturer's wiring diagram for the specific breaker model, as auxiliary contact and coil terminal designations vary between manufacturers.

How to wire shunt trip breaker wiring diagram

Confirm the breaker model supports a shunt trip accessory Not all circuit breakers accept a shunt trip coil. Verify that the specific breaker model has an accessory well for a shunt trip unit. Order the shunt trip accessory for the correct breaker model — shunt trip units are not interchangeable between different breaker families or manufacturers. Confirm the available coil voltage matches the control circuit voltage.
Fit the shunt trip coil accessory to the breaker With the breaker de-energised and locked out, fit the shunt trip accessory into the accessory well following the manufacturer's installation instructions. The accessory typically snaps into position and may require a securing screw. Confirm the coil terminals are accessible and correctly labelled (typically Y1 and Y2, or A1 and A2 for DC coils).
Fit a normally-closed auxiliary contact to the breaker Install an NC auxiliary contact accessory on the breaker if not already fitted. This contact is wired in series with the shunt trip coil supply and opens when the breaker trips, interrupting the coil current to prevent coil burnout. Verify the contact is NC when the breaker is closed and opens when the breaker trips.
Wire the shunt trip coil circuit through the NC auxiliary contact Connect the control voltage supply through the NC auxiliary contact and then to the Y1 terminal of the shunt trip coil. Connect the Y2 terminal to the control circuit return (neutral or negative). When the fire alarm or e-stop contact closes, current flows through the NC auxiliary contact and energises the coil. The moment the breaker trips, the NC auxiliary contact opens and interrupts the coil current.
Connect the fire alarm panel or e-stop output to the trip circuit Wire the fire alarm panel's auxiliary relay output or the e-stop safety relay's output contact in series with the shunt trip coil circuit. Confirm the panel output is rated for the coil inrush current at the coil voltage. Some fire alarm panels require a dedicated relay module rated for inductive loads — check the panel's output current specification against the coil inrush current stated in the breaker's datasheet.
Test the shunt trip function before commissioning With the main circuit energised and all personnel clear, test the shunt trip by briefly energising the coil via the control circuit. Confirm the breaker trips open within the specified time (typically under 0.2 seconds). Confirm the NC auxiliary contact interrupts the coil circuit after tripping. Record the test result. Reset the breaker and repeat the test at least twice to confirm reliable operation.

Specifications

Shunt trip coil duty rating	Momentary duty — typically rated for energisation of 0.2 to 1 second maximum; consult manufacturer datasheet for specific coil model
Typical shunt trip coil operating voltages (AC)	120 V AC, 230 V AC, 277 V AC (50/60 Hz) — model-dependent; verify against breaker manufacturer specification
Typical shunt trip coil operating voltages (DC)	24 V DC, 48 V DC, 110 V DC — model-dependent; verify against breaker manufacturer specification
Shunt trip response time (from coil energisation to breaker trip)	Typically < 0.2 seconds (varies by manufacturer and breaker model; verify with manufacturer test data)
NC auxiliary contact rating (typical)	1–6 A at 250 V AC / 30 V DC (model-dependent; verify against manufacturer specification)
Reset method after shunt trip operation	Manual: breaker handle must be moved to the OFF (fully open) position and then re-closed by hand after the triggering condition is cleared
Relevant standards	IEC 60947-2 (circuit breakers for industrial applications); UL 489 (North America); NEC Article 430.72 (motor branch circuit protection); NFPA 72 (fire alarm system design)

Safety warnings

Shunt trip breaker installation and connection to fire alarm systems or emergency stop circuits must be performed by a licensed electrician in accordance with applicable wiring regulations: NEC / NFPA 70 and NFPA 72 (USA), BS 7671 and BS 5839 (UK), AS/NZS 3000 and AS 1670 (Australia/New Zealand), or IEC 60364 and IEC 60839 (international). This content is for reference and educational purposes only.
Isolate, lock out, and verify dead the main circuit breaker and all control circuit supplies before working on shunt trip connections. Both the main power circuit and the separate control circuit supply must be isolated and locked out.
The shunt trip coil is momentary-duty only. Never design a circuit that holds the shunt trip coil energised continuously. Always include the NC auxiliary contact in series with the coil supply to interrupt current automatically after tripping. Continuous energisation will burn out the coil within seconds.
After any shunt trip wiring modification, perform a full functional test of the trip circuit — including confirmation that the NC auxiliary contact interrupts the coil current after tripping — before returning the installation to service. Document all test results.
Verify that the fire alarm panel or e-stop relay output is rated for the shunt trip coil's inrush current, which can be significantly higher than the holding current. Connecting an under-rated output to the coil can cause the output relay to fail or the fire alarm panel to malfunction.

Tools needed

Calibrated voltage tester (for isolation verification)
Digital multimeter
Lockout/tagout (LOTO) equipment
Insulated screwdrivers and terminal tools
Torque screwdriver (for terminal connections to manufacturer torque specification)
Continuity tester (for verifying NC auxiliary contact operation)
Stopwatch or event logger (for timing the trip response)
Cable labels and marker

Common mistakes

Not wiring the NC auxiliary contact in series with the shunt trip coil — this is the most common and most damaging mistake; the coil burns out within seconds of being held energised after the breaker trips.
Connecting a DC-rated coil to an AC control supply or vice versa — the coil will either fail to operate or overheat. Always verify the coil voltage and current type against the control circuit.
Using the shunt trip on the load side of the breaker as the coil supply — if the coil is powered from the load side of the breaker it is protecting, the coil loses power as soon as the breaker trips and cannot complete the trip stroke. The coil supply must be from an independent source.
Selecting a fire alarm panel output that is not rated for inductive loads — fire alarm panel relay outputs may be rated for resistive loads only; an inductive load (relay coil) requires a contact rated for inductive duty, or an RC snubber must be fitted.
Omitting the control circuit fuse — without a fuse on the shunt trip coil circuit, a short circuit in the control wiring can cause a sustained fault current and risk of fire without tripping any protective device.
Assuming the shunt trip mechanism resets automatically after the alarm clears — shunt trip breakers require manual re-closing after a trip. Failure to communicate this to operations staff leads to confusion and unnecessary downtime.

Troubleshooting

Breaker does not trip when the fire alarm activates or e-stop is pressed: Cause: Control circuit not energised — could be a blown control fuse, open wiring connection, fire alarm panel output not activating, or coil wired from the load side of the breaker (coil has no supply before the breaker closes) Fix: With the main circuit isolated, temporarily apply the control voltage directly to the shunt trip coil terminals Y1/Y2 from an external supply at the rated coil voltage. If the breaker trips, the coil and mechanism are functional — the fault is in the control circuit wiring or the panel output. Trace the control circuit from the panel output through the fuse and NC contact to the coil to find the open circuit.
Shunt trip coil burns out repeatedly: Cause: NC auxiliary contact not fitted or wired incorrectly — coil remains energised after the breaker trips. Alternatively, the control circuit has a sustained contact closure that does not release after the alarm clears. Fix: Verify the NC auxiliary contact accessory is correctly installed and wired in series with the coil supply. Confirm the contact opens (continuity test) when the breaker is tripped to the open position. Verify the fire alarm or e-stop output contact opens after the initial activation pulse.
Breaker trips immediately when the control voltage is applied, even without a fire alarm signal: Cause: Shunt trip coil supply is permanently connected without the control signal in series — the coil is energised continuously from installation Fix: Isolate and lock out. Verify the wiring diagram: the control signal contact (fire alarm relay or e-stop button) must be in series with the coil supply. The coil supply must only flow when the controlling contact closes. Correct the wiring so the coil supply path is broken by the normally-open control contact.

Frequently asked questions

What is the difference between a shunt trip and an under-voltage release (UVR) on a circuit breaker?

A shunt trip coil trips the breaker when it is momentarily energised — it requires a positive signal (voltage applied) to trip. An under-voltage release (UVR) holds the breaker closed while control voltage is present and trips the breaker when control voltage is lost. Fire alarm applications often use shunt trip (energise to trip); UVR is used where loss of control power must trip the breaker — for example, emergency generator changeover schemes.

Why must the shunt trip coil circuit be designed to interrupt current after tripping?

Shunt trip coils are rated for momentary duty only — typically a fraction of a second. If the coil remains energised after the breaker trips, the coil will overheat within seconds and permanently burn out. The standard solution is to route the coil supply through a normally-closed (NC) auxiliary contact on the breaker: when the breaker trips, the auxiliary contact opens and automatically interrupts the coil current.

Can a shunt trip breaker be reset remotely?

Standard shunt trip breakers must be reset manually by operating the breaker handle. The shunt trip mechanism only performs the trip function — it has no motorised re-close capability. If remote re-closing is required, a separately motorised operator accessory must be fitted. Some integrated breaker-operator combinations offer both remote trip and remote close, but this is a different product to a simple shunt trip accessory.

What control voltage is typically used for fire alarm shunt trip circuits?

This depends on the fire alarm panel output and the breaker's available coil options. Common fire alarm panel output voltages are 24 V DC (for most modern addressable systems) and 24 V AC or 230 V AC for older conventional systems. The shunt trip coil must be rated for the specific control voltage provided by the fire alarm panel. Always verify both the panel output specification and the coil rating before ordering.

Does a shunt trip breaker provide overcurrent protection in addition to remote tripping?

Yes. The shunt trip coil is an accessory to a standard circuit breaker — it adds remote tripping capability but does not remove the breaker's built-in thermal-magnetic or electronic overcurrent protection. The breaker still trips automatically on overload or short-circuit conditions, independently of the shunt trip circuit.

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