Switch and Breaker Accessories Selection Guide
Selection criteria for shunt trips, undervoltage releases, auxiliary contacts, motor operators, and rotary handles for MCCBs and ACBs.
In industrial power distribution switchboards, molded case circuit breakers (MCCBs) and air circuit breakers (ACBs) rely on Switch Accessories for remote tripping, status signaling, and door-interlocked operation. Accessories must match the exact breaker frame size, pole count, and control circuit voltage.
Internal electrical accessories: Releases and auxiliary contacts
- Shunt trip release (MX / YO): Trips the circuit breaker when energized by an emergency stop, fire alarm, or remote control signal. Available in 24 V DC, 48 V DC, 110–130 V AC, and 220–240 V AC coil ratings.
- Undervoltage release (MN / YU): Automatically trips the breaker when supply voltage drops below 35–70% of rated voltage and prevents re-closing until voltage is restored.
- Auxiliary and trip alarm contacts (OF / SD): Report breaker ON/OFF position (OF) or thermal/magnetic fault trip events (SD) to PLC and SCADA inputs.
External mechanical accessories: Rotary handles and terminal kits
Extended door-interlocked rotary handles allow safe operation without opening the enclosure door, while motor mechanisms enable automatic remote charging and closing in transfer schemes.
Breaker accessories comparison table
| Accessory Type | Standard | Primary Function | Key Selection Parameter | Product Link |
|---|---|---|---|---|
| Shunt trip release (MX) | IEC 60947-2 | Remote tripping upon voltage application | Control voltage (24 VDC / 230 VAC) and frame series | Switch Accessories |
| Undervoltage release (MN / UVR) | IEC 60947-2 | Fail-safe tripping on voltage loss | Continuous rated voltage and time-delay option | 3-Pole Breaker Accessories |
| Rotary handle & motor mechanism | IEC 60947-2 | Door-mounted or remote motorized switching | Breaker frame size (160 A, 250 A, 630 A, etc.) | 4-Pole Breaker Accessories |
Frequently asked questions
What is the difference between a shunt trip and an undervoltage release?
A shunt trip is normally de-energized and trips the breaker when voltage is applied; an undervoltage release is continuously energized and trips the breaker when voltage drops or fails.
Are breaker accessories interchangeable across different frame sizes?
Internal contacts and releases are shared only within compatible frame groups defined by the manufacturer, whereas rotary handles, motor operators, and terminal shields are strictly frame- and pole-specific.