The **JR28-R-4LMP1** is a specific model of an **Overload Relay** (often compatible with Chint or similar industrial automation brands). These devices are designed to protect electric motors from overheating due to overcurrent or phase failure. --- ### 1. Technical Specifications Below are the primary electronic and physical specifications for the JR28 series: | Feature | Specification | | :--- | :--- | | **Model** | JR28-R-4LMP1 | | **Current Setting Range** | Typically 23A - 32A (varies by sub-frame) | | **Number of Poles** | 3 Poles | | **Auxiliary Contacts** | 1NO (Normally Open) + 1NC (Normally Closed) | | **Tripping Class** | 10A (Standard industrial protection) | | **Reset Method** | Manual or Automatic (Switchable) | | **Mounting** | Direct mounting to Contactor or DIN Rail | --- ### 2. Key Electronic Components & Functions #### A. Bimetallic Strips The heart of the JR28 is the **bimetallic element**. Three strips of two different metals are bonded together. As current flows through them, they heat up. Because the metals expand at different rates, the strips bend. If the current exceeds the set limit for too long, the bend triggers the mechanical linkage to open the circuit. #### B. Auxiliary Contacts (1NO + 1NC) * **NC (Normally Closed):** Used in series with the contactor coil. When a fault occurs, this contact opens, cutting power to the coil and stopping the motor. * **NO (Normally Open):** Used for signaling. It closes during a fault to trigger an alarm lamp or a PLC input signal. #### C. Phase Failure Protection This relay includes a **differential mechanism**. If one of the three phases loses current, the mechanical sliders inside move unevenly, causing the relay to trip faster than a standard balanced overload. This prevents the motor from "single-phasing" and burning out. --- ### 3. Interface Controls 1. **Current Adjustment Dial:** A rotary dial used to set the trip current to match the motor's Full Load Amps (FLA). 2. **Test Button:** Manually simulates a trip to ensure the auxiliary contacts are functioning correctly. 3. **Reset Button:** Used to restore the circuit after a trip (once the bimetal has cooled). 4. **Stop Button:** Manually opens the NC contact to stop the motor, but does not "trip" the overload logic. --- ### 4. Wiring Diagram Concept ```mermaid graph TD Power_In[3-Phase Power] --> Relay_Main[JR28 Main Terminals] Relay_Main --> Motor[Electric Motor] Control_Circuit[Control Power] --> NC_Contact[NC Contact 95-96] NC_Contact --> Contactor_Coil[Contactor Coil] Fault_Signal[Alarm/PLC] --- NO_Contact[NO Contact 97-98] ``` ---