The **QO2201021** is a specialized molded case circuit breaker manufactured by **Schneider Electric (Square D)**. It is part of the QO (Quick-Open) product line, known for high reliability in residential and commercial electrical panels. The specific suffix **1021** indicates that this unit is a **Shunt Trip** circuit breaker. --- ## Technical Specifications | Feature | Specification | | :--- | :--- | | **Product Type** | Miniature Circuit Breaker (MCB) | | **Poles** | 2-Pole | | **Current Rating** | 20 Ampere | | **Voltage Rating** | 120/240 V AC | | **Interrupting Rating** | 10 kA (10,000 Amps) | | **Mounting Type** | Plug-On | | **Special Feature** | 120/208/240 V AC Shunt Trip | | **Wire Size** | #14 - #8 AWG (Al/Cu) | --- ## Key Components & Electronic Parts While a standard circuit breaker is primarily mechanical, the **QO2201021** includes an electronic/electromechanical sub-assembly to handle the "Shunt Trip" functionality. ### 1. The Shunt Trip Accessory (The "1021" Component) The most critical part of this specific model is the internal **Shunt Trip coil**. * **Function:** This is an electromagnetic coil that allows the breaker to be tripped remotely by an external voltage source (like a fire alarm system or an emergency stop button). * **Operation:** When the coil receives a 120V signal, it creates a magnetic field that moves a plunger, physically hitting the trip bar and opening the circuit. ### 2. Thermal-Magnetic Mechanism The breaker uses two methods for standard protection: * **Bimetallic Strip (Thermal):** Protects against long-term overloads. As current flows, the strip heats up and bends, eventually releasing the trip latch. * **Electromagnetic Solenoid (Magnetic):** Protects against short circuits. High instantaneous current creates a magnetic force that trips the breaker immediately. ### 3. Visi-Trip™ Indicator A signature feature of the Square D QO line is the red mechanical indicator. When the breaker trips, a red window appears, allowing for quick visual identification of the fault. --- ## Common Applications * **Emergency Power Off (EPO):** Used in data centers to shut down power in an emergency. * **Fire Suppression Systems:** Automatically cuts power to kitchen hoods or machinery when a fire alarm is triggered to prevent the fire from spreading or being fed by electricity. * **Interlock Systems:** Used in industrial settings where one piece of equipment must be forced off if another fails. ---