The **JR28-R-4LFP1** is a thermal overload relay designed primarily for motor protection. It is often used in conjunction with magnetic contactors to prevent electric motors from burning out due to overloads or phase failures. --- ### ## Technical Specifications Below are the primary electronic and physical specifications for the JR28 series (specifically the 4LFP1 variant): | Feature | Specification | | :--- | :--- | | **Current Setting Range** | Typically adjustable (e.g., 0.63A to 1A or 1A to 1.6A) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Auxiliary Contacts** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Tripping Class** | Class 10A (Standard trip within 2-10s at 7.2x current) | | **Reset Mode** | Manual or Automatic (Switchable) | | **Phase Failure Protection** | Yes (Differential mechanism) | --- ### ### Key Electronic Components & Functions 1. **Bimetallic Strips:** The core of the relay consists of three bimetallic strips (one for each phase). When current exceeds the set threshold, the heat causes these strips to bend at different rates, eventually triggering the internal trip mechanism. 2. **Current Adjustment Dial:** A calibrated knob on the front allows the user to set the exact "Full Load Amps" (FLA) of the motor. The relay will not trip if the current stays below this setting but will begin the timing curve if it exceeds it. 3. **Auxiliary Contact Block:** * **95-96 (NC):** Usually wired in series with the contactor coil. When a fault occurs, this opens, cutting power to the coil and stopping the motor. * **97-98 (NO):** Usually wired to a signal lamp or PLC input to notify the operator of a "Tripped" status. 4. **Test/Stop Buttons:** * **Red Button:** Manual stop/test function to ensure the NC contacts are working. * **Blue/Reset Button:** Resets the device after a trip has occurred and the bimetallic strips have cooled down. --- ### ### Wiring Logic Example To protect a 3-phase motor, the relay is typically wired as follows: ```mermaid graph TD Power[L1, L2, L3] --> Contactor[Magnetic Contactor] Contactor --> JR28[JR28-R Thermal Relay] JR28 --> Motor[AC Motor] JR28 -- Control Circuit --> Coil[Contactor Coil] ``` --- ### ### Comparison: Thermal vs. Electronic While the JR28 is a **Thermal** relay, it differs from purely **Electronic** Overload Relays (EORs) in the following ways: * **Heat Sensitivity:** It relies on physical heat; therefore, it requires a "cool down" period before it can be reset. * **Power Supply:** It does not require an external power source to operate (self-powered by the line current). * **Cost:** Generally more affordable and robust for standard industrial environments compared to digital microprocessor-based relays.