The **JR28-R-4MCM1** is a thermal overload relay commonly used in industrial automation and motor control circuits. It is designed to protect electric motors from overloads and phase failures. --- ### 1. Technical Specifications The following table highlights the core electrical characteristics of the device: | Feature | Specification | | :--- | :--- | | **Series** | JR28 (Compatible with LC1-D series contactors) | | **Current Setting Range** | Typically adjustable (e.g., 2.5A to 4A or similar depending on variant) | | **Contact Configuration** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Tripping Class** | Class 10A (Standard industrial protection) | | **Reset Mode** | Manual or Automatic reset options | --- ### 2. Key Electronic & Mechanical Components The JR28 relay operates based on electro-thermal principles rather than purely digital logic. * **Bimetallic Strips:** The heart of the device. As current flows through these strips, they heat up. If the current exceeds the set limit, the different expansion rates of the two metals cause the strip to bend. * **Trip Mechanism:** A mechanical linkage triggered by the bending bimetallic strips. It acts upon the auxiliary contacts to break the control circuit. * **Auxiliary Contacts:** * **95-96 (NC):** Used to disconnect the contactor coil, stopping the motor. * **97-98 (NO):** Used for signaling or alarm lights to indicate a fault trip. * **Current Adjustment Dial:** A potentiometer-style dial on the front face that allows the user to set the precise current limit based on the motor's Full Load Amps (FLA). * **Test/Stop Buttons:** * **Red Button:** Used to manually stop or test the trip mechanism. * **Blue/Reset Button:** Used to reset the relay after a trip event occurs. --- ### 3. Connection Diagram (General Layout) ```mermaid graph TD A[Power Supply] --> B[L1, L2, L3] B --> C[Contactor LC1-D] C --> D[JR28 Thermal Relay] D --> E[Electric Motor] subgraph Control Circuit F[95-96 NC Contact] --- G[Contactor Coil] H[97-98 NO Contact] --- I[Fault Lamp] end ``` ### 4. Application Use Case The **JR28-R-4MCM1** is specifically designed to plug directly into the bottom of a **Chint** or **Schneider-style (LC1-D)** AC Contactor. This creates a compact motor starter that protects against: 1. **Sustained Overcurrent:** When the motor is overloaded mechanically. 2. **Phase Loss:** When one phase of the three-phase supply goes missing, causing the other two to overheat.