The **JR28-R-4MFP115** is a specific type of thermal overload relay, typically used in industrial motor control circuits to protect motors from overheating and phase failures. ### Product Overview This component is designed to be mounted alongside an AC contactor to provide comprehensive protection for electrical motors. --- ### Technical Specifications | Feature | Description | | :--- | :--- | | **Product Category** | Thermal Overload Relay | | **Model Series** | JR28 (Compatible with LC1-D series contactors) | | **Setting Range** | Typically 0.1A to 630A (Specific range depends on the sub-model) | | **Control Voltage** | 115V AC (indicated by the P115 suffix) | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Mounting Type** | Direct plug-in or Independent mounting | --- ### Key Internal Components The "electronic" and mechanical parts of this device work together to interrupt the circuit during a fault: #### 1. Bimetallic Strips The heart of the relay. These are strips made of two different metals bonded together. As current flows through them, they heat up. Because the metals expand at different rates, the strip bends. When it reaches a specific deflection point, it triggers the trip mechanism. #### 2. Current Adjustment Dial A physical potentiometer-style dial on the front face that allows the user to set the "Trip Current" to match the motor's Full Load Amps (FLA). #### 3. Auxiliary Contacts (1NO + 1NC) * **95-96 (NC):** Usually wired in series with the contactor coil. It opens during a fault, cutting power to the motor. * **97-98 (NO):** Closes during a fault, usually used to trigger an alarm or signal a PLC. #### 4. Test and Reset Buttons * **Test:** Manually simulates a trip to check internal mechanical integrity. * **Reset:** Can be set to "Manual" or "Auto." In manual mode, a technician must press the button after the bimetallic strips have cooled down. --- ### Protection Features 1. **Overload Protection:** Protects against sustained current levels above the motor's rating. 2. **Phase Failure Protection:** A differential mechanism inside detects if one phase drops out, tripping the device faster than a standard overload. 3. **Temperature Compensation:** Ensures the relay trips accurately regardless of the ambient temperature in the electrical cabinet.