wiring diagram for shunt trip circuit breaker
**Shunt Trip Circuit Breaker Wiring Diagram: A Comprehensive Guide**
**Core Components and Functionality**
A shunt trip circuit breaker integrates a **shunt trip coil** into a standard circuit breaker, enabling remote or automatic tripping via an external control signal. Key components include:
- **Shunt Trip Coil**: An electromagnet that triggers the breaker to open when energized.
- **Control Circuit**: Connects the coil to a power source (e.g., 24V DC, 120V AC) and control devices (e.g., emergency buttons, fire alarms).
- **Safety Mechanisms**:
- **Short-Time Operation**: Coils are designed for brief activation (≤1 second) to prevent overheating .
- **Microswitch**: Automatically disconnects power to the coil after tripping to avoid burnout .
**Wiring Diagrams by Application**
**1. Basic Manual Trip Setup**
**Components**:
- Shunt trip breaker (e.g., Eaton Cutler-Hammer, Siemens).
- Normally Open (NO) emergency push button.
- Power supply matching the coil voltage (e.g., 24V DC or 120V AC).
**Wiring Steps**:
1. **Power Connection**:
- Connect the coil’s **positive terminal (C2)** to the live wire of the control power supply.
- Connect the **negative terminal (C1)** to the emergency button’s **common terminal (COM)**.
2. **Control Circuit**:
- Link the button’s **NO terminal** to the power supply’s neutral/ground.
3. **Safety Check**:
- Ensure the circuit is de-energized during installation. Test by pressing the button— the breaker should trip immediately.
**2. Automatic Tripping with Fire Alarm System**
**Components**:
- Shunt trip breaker.
- Fire alarm control panel (e.g., Siemens Cerberus).
- 24V DC power supply.
- Intermediate relay (e.g., Honeywell R7243).
**Wiring Steps**:
1. **Fire Alarm Interface**:
- Connect the alarm panel’s **relay output** to the relay’s **coil terminals**.
2. **Relay Activation**:
- Link the relay’s **NO contacts** to the shunt trip coil’s **C1** and **C2** terminals.
3. **Power Supply**:
- Connect the coil to a **24V DC source** via the relay.
4. **Feedback Signal**:
- Use the breaker’s **auxiliary contacts** to send a trip confirmation back to the alarm panel .
**Diagram**:
**3. Industrial PLC Control**
**Components**:
- Shunt trip breaker.
- PLC (e.g., Siemens S7-1200).
- 24V DC power supply.
- Solid-state relay (SSR).
**Wiring Steps**:
1. **PLC Output**:
- Configure a PLC digital output (e.g., Q0.0) to send a 24V signal.
2. **SSR Activation**:
- Connect the PLC output to the SSR’s **control input**.
3. **Coil Connection**:
- Link the SSR’s **load contacts** to the shunt trip coil and 24V power supply.
4. **Safety Interlock**:
- Add a **manual override switch** in series with the PLC signal for emergency use.
**Diagram**:
**Critical Considerations**
# **1. Voltage Compatibility**
- **Coil Ratings**: Match the control voltage (e.g., 24V DC, 120V AC) to the breaker’s specifications. Mismatched voltages can damage the coil or prevent tripping .
- **Power Source**: Use a dedicated power supply for reliability. Avoid daisy-chaining with other high-current devices.
**2. Control Signal Types**
- **Manual Control**: Use NO push buttons for momentary activation.
- **Automatic Control**: Connect to sensors (e.g., smoke detectors) or control systems (e.g., PLC) via relays.
- **Intermediate Relays**: Essential for isolating low-voltage signals (e.g., 24V DC) from high-voltage coils (e.g., 120V AC) .
**3. Safety and Code Compliance**
- **Short-Time Operation**: Ensure the control circuit includes a timer or microswitch to limit coil energization to ≤1 second .
- **NEC Requirements**:
- Mark the breaker’s **short-circuit current rating (SCCR)** and available fault current at the installation site .
- In fire alarm systems, use **Class A signaling** for redundant control paths .
- **Grounding**: Connect the breaker’s frame to the equipment ground per NEC 250.118.
**4. Maintenance and Testing**
- **Periodic Checks**: Verify coil resistance and contact alignment annually.
- **Functional Testing**: Trip the breaker manually and automatically at least twice a year.
- **Documentation**: Keep records of wiring diagrams, voltage settings, and test results.
**Troubleshooting Common Issues**
| Problem | Possible Cause | Solution |
| Breaker fails to trip | Low control voltage, open circuit, or faulty coil. | Test voltage, check continuity, replace coil. |
| Coil overheats | Prolonged energization or voltage mismatch. | Add a timer or replace the power supply. |
| False tripping | Loose connections or electromagnetic interference. | Secure wiring and shield control cables. |
**Example: Westinghouse Shunt Trip Breaker**
For Westinghouse breakers (e.g., DB-15 model), the shunt trip accessory mounts on the breaker’s top panel. Wiring steps:
1. **Power Connection**:
- Connect **C2** to the live wire of a 120V AC supply.
- Connect **C1** to the control switch’s COM terminal.
2. **Control Circuit**:
- Link the switch’s NO terminal to the neutral wire.
3. **Testing**: Press the switch to verify tripping.
**Diagram**:
*(Courtesy: [ManualsLib](https://www.transformerandswitchgear.com
**Conclusion**
Shunt trip circuit breakers enhance safety and control in electrical systems. Proper wiring requires careful attention to voltage compatibility, control signal integration, and code compliance. Always consult the manufacturer’s documentation and local electrical codes for specific installations. For complex systems (e.g., fire alarms or PLC control), seek guidance from a licensed electrician to ensure reliability and safety.
