The **JR28-R-4MCT1** is a specific model of an **Overload Relay**, commonly used in industrial electrical control systems to protect electric motors from damage caused by overheating, phase failure, or current overload. --- ## 1. Core Technical Specifications Below are the primary electrical characteristics of the JR28 series (specifically the 4MCT1 variant): | Parameter | Description | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Trip Class** | 10A (Standard protection) | | **Setting Range** | Typically adjustable (e.g., 2.5A to 4A or similar depending on the specific sub-range) | | **Contact Configuration** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Mounting** | Compatible with specific AC contactors (Direct plug-in) | --- ## 2. Key Electronic & Mechanical Components The device functions through a combination of thermal mechanics and electrical switching: ### A. Bimetallic Elements The heart of the JR28 is the **bimetallic strip**. As current flows through these strips to the motor: * **Thermal Expansion:** Excessive current causes the strips to heat up and bend. * **Tripping Mechanism:** Once the bend reaches a certain threshold, it triggers a mechanical lever that opens the control circuit. ### B. Auxiliary Contacts (95-96 / 97-98) * **95-96 (NC):** Usually wired in series with the contactor coil. It opens during a fault to stop the motor. * **97-98 (NO):** Usually used for an alarm or indicator light to signal that a trip has occurred. ### C. Adjustment Dial A physical potentiometer-style dial on the front allows the user to set the exact "Full Load Amps" (FLA) of the motor. This calibrates the sensitivity of the bimetallic strips. --- ## 3. Protective Functions The JR28-R-4MCT1 provides three main layers of protection: 1. **Overload Protection:** Prevents the motor from running at currents higher than its rated capacity for extended periods. 2. **Phase Failure Protection:** If one phase of a three-phase system drops out, the relay detects the resulting imbalance and trips. 3. **Temperature Compensation:** It is designed to maintain consistent tripping characteristics regardless of the ambient temperature in the control cabinet. --- ## 4. Operation Modes * **Manual/Auto Reset:** A blue selector button allows the user to choose between manually resetting the device after a trip or letting it reset automatically once the bimetallic strips cool down. * **Test Button:** A red button (usually) that manually simulates a trip condition to verify that the auxiliary contacts are working correctly.