The **JR28-R-4MMP1** (often referred to as the JRS28 series) is a **Thermal Overload Relay**. It is an essential electronic protective component used in industrial automation to protect electric motors from overheating, phase failure, and prolonged overload conditions. --- ## 1. Technical Specifications The "4MMP1" suffix typically denotes specific setting ranges and mounting configurations. Below are the standard electronic and physical specifications: | Parameter | Specification | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Thermal Protection Range** | Adjustable (Typically 0.1A to 93A depending on sub-model) | | **Tripping Class** | 10A (Standard trip speed) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Control Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Compatibility** | CJX2 Series Contactors | | **Reset Mode** | Manual or Automatic (Switchable) | --- ## 2. Key Electronic Components & Functions ### Internal Bimetallic Strips The heart of the JR28 is the **bimetallic element**. * **How it works:** As current flows through the strips, they heat up. * **Reaction:** Because the two metals have different expansion coefficients, they bend. If the current is too high (overload), the bend becomes severe enough to trigger the internal mechanical linkage. ### Auxiliary Contacts (1NO + 1NC) These are the electronic "signal" parts of the relay: * **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, typically used to trigger an alarm light or send a signal to a PLC (Programmable Logic Controller). ### Current Adjustment Dial The device features a graduated dial on the front face. This allows the user to calibrate the relay to the **Full Load Amps (FLA)** of the specific motor it is protecting. --- ## 3. Protective Features 1. **Overload Protection:** Detects when a motor is drawing more current than its rated capacity over a period of time. 2. **Phase Failure Protection:** The relay includes a differential mechanism. If one phase is lost, the imbalance causes the device to trip faster than a standard overload, preventing motor burnout. 3. **Temperature Compensation:** Designed to maintain accuracy even when the ambient temperature of the control cabinet changes. --- ## 4. Wiring Diagram Overview To integrate the JR28-R into a system, the following wiring logic is used: ```mermaid graph TD A[Power Source] --> B[Circuit Breaker] B --> C[CJX2 Contactor] C --> D[JR28 Thermal Relay] D --> E[Electric Motor] D -.->|NC Contact| C ``` ---