The **JR28-R-4LDP2** is a specific model of a **Thermal Overload Relay**, commonly used in industrial automation to protect electric motors from overheating, phase failure, and overcurrent conditions. It is typically designed to be compatible with LC1-D series contactors. --- ## 1. Core Technical Specifications The following table outlines the primary electronic and mechanical characteristics: | Feature | Specification | | :--- | :--- | | **Relay Type** | Thermal Overload | | **Model Series** | JR28 (Compatible with LR2-D) | | **Current Setting Range** | Typically 23A - 32A (Verify on unit) | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Tripping Class** | 10A (Standard protection) | | **Reset Mode** | Manual or Automatic | --- ## 2. Key Electronic Components & Functions ### A. Bimetallic Elements The heart of the JR28 is the **bimetallic strip**. * **Function:** As current flows through these strips, they heat up. Because the strips consist of two different metals with different expansion rates, they bend when heated. * **Protection:** If the current exceeds the set threshold for a specific duration, the physical bending triggers a mechanical linkage that opens the control circuit. ### B. Auxiliary Contacts (1NO + 1NC) These are the electronic signal terminals used for control logic: * **NC (95-96):** Connected in series with the contactor coil. It opens during a fault, cutting power to the motor. * **NO (97-98):** Closes during a fault. Usually connected to an indicator light or an alarm to notify the operator of a trip. ### C. Phase Failure Protection The JR28-R includes a differential mechanism. If one phase loses current while others are under load, the relay trips faster than a standard overcurrent event to prevent "single-phasing," which quickly destroys motor windings. --- ## 3. Physical Interface & Controls 1. **Current Adjustment Dial:** A rotary pot on the front allows the user to set the exact Amperage corresponding to the motor's Full Load Amps (FLA). 2. **Test Button:** Manually simulates a trip to verify that the auxiliary contacts (95-98) are functioning correctly. 3. **Reset Button:** A blue button used to restore the circuit after a trip has occurred (once the bimetal has cooled). 4. **Stop Button:** A red button that manually opens the NC contact to test the control circuit stop function. --- ## 4. Wiring Diagram Concept ```text [Main Power L1, L2, L3] | [Contactor (LC1-D)] | [JR28-R-4LDP2 (Overload Relay)] ----> [97-98: Alarm/Light] | ----> [95-96: Series with Coil] [Electric Motor] ``` ---