The **JR28-R-DMCT115** is a specific model of an **Overload Thermal Relay**, typically manufactured by brands like Chint or similar industrial electrical components suppliers. It is designed to protect three-phase AC motors from overheating due to overloads or phase failures. --- ## 1. Core Technical Specifications Below are the primary electrical characteristics of this specific component: | Feature | Specification | | :--- | :--- | | **Model Series** | JR28 (Compatible with LC1-D series contactors) | | **Current Setting Range** | 80A to 93A (Typical for DMCT115 variant) | | **Rated Insulation Voltage (Ui)** | 660V / 690V | | **Tripping Class** | 10A (Standard protection) | | **Number of Poles** | 3 Poles | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | --- ## 2. Key Electronic & Mechanical Parts The device operates using a combination of bimetallic strips and mechanical linkages. ### A. Bimetallic Elements The heart of the relay consists of three bimetallic strips (one for each phase). When current flows through them, they heat up. If the current exceeds the set limit, the strips bend sufficiently to trigger the trip mechanism. ### B. Current Adjustment Dial On the front face, there is a rotary dial that allows the user to set the precise current trip point (e.g., matching the Full Load Amps of the motor). ### C. Auxiliary Contacts (1NO + 1NC) * **NC (95-96):** Usually wired in series with the contactor coil. It opens during a fault to stop the motor. * **NO (97-98):** Usually used for an alarm or indicator light to signal that a trip has occurred. ### D. Reset & Test Buttons * **Blue Reset Button:** Can be set to "Manual" or "Auto" reset mode. * **Red Stop/Test Button:** Manually opens the NC contact to test the control circuit. --- ## 3. Wiring Diagram Overview The JR28 is usually mounted directly beneath a contactor. ```text L1 L2 L3 (Power In from Contactor) | | | +-----------+ | JR28 |--> [95-96] Control Circuit (NC) | Relay |--> [97-98] Alarm/Fault (NO) +-----------+ | | | T1 T2 T3 (To Motor) ``` --- ## 4. Protection Functions 1. **Overload Protection:** Protects against sustained high current that would damage motor windings. 2. **Phase Failure Protection:** Features a differential mechanism that trips the relay faster if one phase is lost, preventing unbalanced heating. 3. **Temperature Compensation:** The internal mechanism adjusts for ambient temperature changes so that it only trips based on the heat generated by the motor current.