The **JR28-R-4MCT115** is a specific model of a **Thermal Overload Relay**, typically used in industrial motor control circuits. It is designed to protect electric motors from overheating due to overload conditions or phase failures. --- ## 1. Technical Specifications The following table highlights the core technical characteristics of the JR28 series, specifically the 4MCT115 variant: | Feature | Specification | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Model Number** | JR28-R-4MCT115 | | **Rated Current (In)** | 115A (Typical maximum for this frame) | | **Current Setting Range** | Often adjustable (e.g., 80A - 115A) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Tripping Class** | Class 10A (standard motor protection) | | **Compatibility** | Usually mounts to LC1-D series contactors | --- ## 2. Key Internal Components The electronic and mechanical parts work together to trigger the protection mechanism: 1. **Bimetallic Strips:** The heart of the device. These consist of two metals with different expansion coefficients. When current flows through them, they heat up and bend. 2. **Differential Mechanism:** Monitors the balance between the three phases. If one phase fails (Single Phasing), the differential slider moves to trip the relay faster than a standard overload would. 3. **Auxiliary Contacts:** * **95-96 (NC):** Normally Closed contact used to break the control circuit of the contactor coil. * **97-98 (NO):** Normally Open contact used for fault signaling (e.g., turning on an alarm light). 4. **Current Adjustment Dial:** A rotary potentiometer-style dial on the front that allows the user to set the trip current to match the motor's Full Load Amps (FLA). 5. **Reset Button:** Allows for manual or automatic reset after a trip has occurred and the bimetal has cooled down. --- ## 3. Working Principle The JR28 operates on the **Electro-Thermal Effect**: 1. **Heating:** As motor current passes through the relay, the bimetallic strips heat up. 2. **Deflection:** Under normal load, the heat is insufficient to trip the mechanism. During an overload, the strips bend significantly. 3. **Tripping:** The bending pushes a trip lever that opens the **95-96 NC contact**. 4. **Protection:** This cuts power to the contactor coil, which in turn opens the main power contacts and stops the motor before the windings burn out. --- ## 4. Typical Wiring Example Below is a conceptual representation of how the control pins are integrated: ```markdown Control Circuit: [L1] ---- [Emergency Stop] ---- [Stop Button] ---- [Start Button] ---- [95 (NC) 96] ---- (Contactor Coil A1) ---- [N] | (Relay) [Aux Holding] ```