The **JR28-R-4MFP1** is a thermal overload relay commonly used in industrial automation and motor control circuits. It is designed to protect electrical motors from overheating, phase failure, and sustained overcurrent conditions. --- ### ## Technical Specifications The following table summarizes the key electronic and physical characteristics of the JR28 series (specifically the 4MFP1 variant): | Feature | Specification | | :--- | :--- | | **Product Type** | Thermal Overload Relay | | **Frame Size** | JR28 (Compatible with LC1-D series contactors) | | **Current Range** | Typically adjustable (Check label for specific range, e.g., 2.5A - 4A) | | **Tripping Class** | Class 10A (Trips within 10s at 7.2x rated current) | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Reset Mode** | Manual or Automatic (Switchable) | | **Phase Failure Protection** | Yes (Differential mechanism) | --- ### ### Key Electronic Components & Functions #### 1. Bimetallic Strips The heart of the relay consists of three bimetallic strips (one for each phase). When current flows through them, they heat up. Because the two metals have different expansion coefficients, the strips bend. If the current is too high, the bending triggers a mechanical linkage to open the circuit. #### 2. Auxiliary Contacts (1NO + 1NC) These are secondary switches used for signaling: * **NC (95-96):** Usually wired in series with the contactor coil. When a fault occurs, this contact opens, cutting power to the motor. * **NO (97-98):** Used for fault indication. It closes during a trip to light up an error lamp or send a signal to a PLC. #### 3. Current Adjustment Dial This allows the user to set the trip current to match the **Full Load Amps (FLA)** of the motor being protected. It ensures the relay does not trip during normal operation but reacts precisely to minor overloads. #### 4. Temperature Compensation The relay includes a compensation bimetal strip that adjusts the trip threshold based on the ambient room temperature, preventing nuisance trips in hot environments. --- ### ### Installation & Wiring The JR28-R-4MFP1 is typically "plug-in" style, designed to be mounted directly onto the bottom of a 3-pole AC contactor (such as the LC1D09 through LC1D32 series). ```mermaid graph LR L1[Line 1] --> C[Contactor] L2[Line 2] --> C L3[Line 3] --> C C --> JR28[JR28 Overload Relay] JR28 --> M((Motor)) ``` ---