The **JR28-R-4MMP115** is a specific model of a **Thermal Overload Relay**, typically used in industrial motor control circuits to protect motors from overheating and phase failures. It is often a direct equivalent or compatible part for the Schneider Electric TeSys D series (LRD style). --- ### ## Technical Specifications The following table outlines the primary electrical characteristics of the device: | Feature | Specification | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Series** | JR28 (TeSys D Compatible) | | **Current Setting Range** | 80A to 93A (Standard for this frame size) | | **Control Voltage** | 115V AC (For auxiliary contacts/tripping logic) | | **Frequency** | 50/60 Hz | | **Mounting** | Direct mounting to LC1D contactors or DIN rail | | **Trip Class** | Class 10A (Standard industrial trip speed) | --- ### ## Core Electronic & Mechanical Components The device functions through a combination of electromechanical and thermal sensing elements: 1. **Bimetallic Strips:** The heart of the unit. As current flows through these strips, they heat up. Because they consist of two different metals, they bend at a predictable rate. If the current exceeds the set threshold, the physical displacement triggers the internal mechanism. 2. **Differential Mechanism (Phase Failure Protection):** It monitors the relative position of all three bimetallic strips. If one phase drops (current becomes zero), the differential slide moves unevenly, causing the relay to trip faster than a standard overload condition. 3. **Auxiliary Contacts:** * **95-96 (NC):** Normally Closed contact used in series with the contactor coil. It opens during a fault to kill power. * **97-98 (NO):** Normally Open contact used for signaling or alarm lights to indicate a fault has occurred. 4. **Adjustment Dial:** A calibrated potentiometer-style dial on the front face that allows the user to set the exact full-load current (FLC) of the motor. --- ### ## Operational Modes The device features a multi-function selector on the front panel: * **H (Hand/Manual):** After a trip, the user must physically press the Reset button to restart the circuit. * **A (Automatic):** The relay will automatically reset itself once the bimetallic strips have cooled down. * **Stop/Test Button:** Allows for manual interruption of the circuit to verify that the auxiliary contacts are functioning correctly. --- ### ## Wiring Diagram (Typical) ```mermaid graph TD Power_In[3-Phase Power] --> L1_L2_L3[Main Terminals] L1_L2_L3 --> Bimetal[Bimetallic Strips] Bimetal --> T1_T2_T3[Motor Output] subgraph Control_Circuit NC_95_96[95-96 NC Contact] -- Series Connection --> Contactor_Coil NO_97_98[97-98 NO Contact] -- Alarm --> Indicator_Light end ``` ---