The **JR28-R-4MSP1** (often associated with the Chint or generic industrial electrical series) is a **Thermal Overload Relay**. It is designed to protect AC motors from overheating due to overload conditions or phase failures. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Model Series** | JR28 (Compatible with CJX2 contactors) | | **Current Setting Range** | Typically 2.5A to 4.0A (varies by specific sub-model) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Tripping Class** | 10A (Standard industrial protection) | | **Reset Type** | Manual or Automatic (Switchable) | --- ### 2. Main Electronic & Mechanical Components The device operates using a combination of electromechanical principles: * **Bimetallic Strips:** The core sensing element. These consist of two bonded metals with different expansion coefficients. As current flows through them, they heat up and bend. * **Trip Mechanism:** A mechanical linkage connected to the bimetallic strips. When the strips bend beyond a specific threshold (due to high current), they trigger the trip lever. * **Adjustment Dial:** A rotary potentiometer-style dial on the front that allows the user to set the exact current limit (FLA - Full Load Amps) of the motor. * **Auxiliary Contacts (95-96 / 97-98):** * **95-96 (NC):** Usually wired in series with the contactor coil to cut power when a fault occurs. * **97-98 (NO):** Used for signaling or alarm lights to indicate a "Tripped" state. --- ### 3. Core Functions 1. **Overload Protection:** Detects if the motor is drawing more current than its rated capacity over a sustained period. 2. **Phase Failure Protection:** Features a differential mechanism that can detect if one phase is missing, which causes the other phases to overheat rapidly. 3. **Temperature Compensation:** Designed to maintain accuracy even if the ambient temperature of the control panel changes. 4. **Test/Stop Buttons:** Allows manual testing of the trip mechanism to ensure the control circuit is wired correctly. --- ### 4. Typical Wiring Diagram ```mermaid graph TD Power[3-Phase Power] --> Contactor[CJX2 AC Contactor] Contactor --> JR28[JR28 Thermal Relay] JR28 --> Motor[AC Motor] subgraph Control Loop JR28_NC[NC Contact 95-96] -- Interrupts --> Coil[Contactor Coil] end ``` ---