The **JR28-R-4LDP215** is a specific part number for a **Thermal Overload Relay**. These components are essential in industrial automation for protecting electric motors from overheating, phase failure, and sustained overcurrent conditions. --- ### 1. Key Technical Specifications The part number typically breaks down into the series, frame size, and current range. | Feature | Specification | | :--- | :--- | | **Component Type** | Thermal Overload Relay | | **Model Series** | JR28 (Compatible with CJX2/LC1-D series contactors) | | **Current Setting Range** | Typically 9A to 13A (standard for the LDP215 variant) | | **Contact Configuration** | 1 NO (Normally Open) + 1 NC (Normally Closed) | | **Mounting** | Direct mount to contactor or independent DIN rail mounting | | **Reset Mode** | Manual or Automatic (Switchable) | --- ### 2. Main Electronic & Mechanical Parts A thermal overload relay operates on the principle of thermal expansion. Below are the internal components: #### A. Bimetallic Strips This is the "heart" of the relay. It consists of two different metals bonded together. When current flows through them, they heat up. Because the metals expand at different rates, the strip bends. If the current is too high for too long, the bend triggers the trip mechanism. #### B. Current Adjustment Dial A rotary dial located on the front of the unit. It allows the user to set the exact full-load current (FLC) of the motor. The relay will only trip if the current exceeds this threshold based on its time-current curve. #### C. Auxiliary Contacts (95-96 / 97-98) * **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 used for an alarm or indicator light to signal that the relay has tripped. #### D. Phase Failure Protection Mechanism The JR28 series includes a differential mechanism. If one phase loses current while the others are high, the internal linkage shifts unevenly, causing the relay to trip faster than a standard balanced overload. --- ### 3. Wiring and Application To use the JR28-R-4LDP215, it is typically plugged directly into the bottom of a 3-pole magnetic contactor. ```mermaid [Power Supply] --> [Circuit Breaker] --> [Contactor] --> [JR28 Relay] --> [Motor] ``` #### Important Terminals: * **L1, L2, L3:** Main power input (usually via the contactor pins). * **T1, T2, T3:** Load terminals connected to the motor. * **Test/Stop Button:** Used to manually simulate a trip or stop the motor for maintenance checks. ---