The **JR28-R-4** is a thermal overload relay designed primarily for the protection of AC motors. It is commonly used in industrial automation and motor control circuits to prevent damage from overheating caused by overload or phase failure. ### 1. Technical Specifications The "4" in the model name typically indicates a specific thermal setting range. Below are the general specifications: | Feature | Specification | | :--- | :--- | | **Model** | JR28-R-4 (Equivalent to LR2-D13) | | **Trip Class** | 10A (Trips within 2-10 seconds at 7.2x current) | | **Current Setting Range** | Typically 0.4A to 0.63A (varies by sub-series) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Compatibility** | LC1-D series contactors | --- ### 2. Internal Electronic & Mechanical Components While primarily electromechanical, the JR28-R-4 functions through the interaction of several key parts: 1. **Bimetallic Strips:** The core sensing element. Three strips (one per phase) bend when heated by current. If the current exceeds the set limit, the physical deformation triggers the trip mechanism. 2. **Differential Mechanism:** Detects **Phase Failure**. If one strip bends significantly less than the others (due to a lost phase), the internal linkage trips the relay faster than a standard overload. 3. **Adjustment Dial:** A potentiometer-style knob on the front face that allows the user to calibrate the trip current to the motor's Nameplate Full Load Amps (FLA). 4. **Auxiliary Contacts:** * **95-96 (NC):** Usually wired in series with the contactor coil to cut power during a fault. * **97-98 (NO):** Usually wired to an alarm or PLC input to signal a fault state. 5. **Test/Reset Buttons:** * **Blue Button:** Reset (Manual or Auto modes). * **Red Button:** Stop/Test (Manually opens the NC contact). --- ### 3. Connection Diagram Logic The device acts as a "bridge" between the contactor and the motor. ```mermaid graph LR A[Power Supply] --> B[Contactor] B --> C[JR28-R-4 Relay] C --> D[AC Motor] C -. Fault Signal .-> B ``` ### 4. Key Features * **Temperature Compensation:** Ensures the relay doesn't trip prematurely due to high ambient temperatures in the factory. * **Plug-in Design:** Designed to plug directly into the bottom terminals of an LC1-D09 through LC1-D32 contactor, saving wiring time and space. ---