The **JR28-R-DMDP3** is a specific model within a series of **Thermal Overload Relays**, typically designed for use with Chint (CHNT) or similar industrial contactors. These components are essential for motor protection. --- ### 1. Key Technical Specifications The model suffix "DMDP3" often denotes specific current ranges or terminal configurations. Generally, the JR28 series features the following attributes: | Feature | Description | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Phase Protection** | 3-Phase (Triple-pole) | | **Control Circuit** | AC 50/60 Hz | | **Mounting** | Direct plug-in to contactor or independent mounting | | **Protection Type** | Phase failure protection and overload protection | | **Reset Type** | Manual or Automatic reset options | --- ### 2. Functional Components The "Electronic" and mechanical parts of this relay work together to provide circuit safety: * **Bimetallic Strips:** The core sensing element. As current flows through, heat causes these strips to bend. If the current is too high (overload), the strips bend enough to trigger the trip mechanism. * **Adjustment Dial:** A rotary knob on the front face that allows the user to set the **Full Load Amps (FLA)** to match the specific motor's nameplate. * **Auxiliary Contacts:** * **95-96 (NC):** Normally Closed contact used to cut power to the contactor coil during a fault. * **97-98 (NO):** Normally Open contact used for fault signaling (e.g., turning on a warning light). * **Test/Stop Buttons:** Allows for manual testing of the trip mechanism and emergency stopping of the connected load. --- ### 3. Protection Mechanism The JR28 series is designed to handle two primary fault conditions: 1. **Overload Protection:** When the motor draws more current than the rated value for a sustained period, the bimetallic strips heat up and disconnect the circuit. 2. **Phase Failure Protection:** If one of the three phases is lost, the relay detects the imbalance and trips faster than a standard overload to prevent motor burnout. --- ### 4. Typical Application Diagram In a standard motor starter circuit, the wiring follows this logic: ```mermaid graph TD A[Power Supply L1/L2/L3] --> B[Contactor] B --> C[JR28 Overload Relay] C --> D[Electric Motor] C -.->|95/96 NC Contact| E[Contactor Coil Control] ``` ---