The **JR28-R-DMFP115** is an industrial thermal overload relay designed primarily for motor protection. It is commonly used in conjunction with magnetic contactors to prevent motor damage due to phase failure or sustained electrical overloads. --- ## 1. Technical Specifications The following table outlines the primary electrical and physical characteristics of the JR28 series, specifically the DMFP115 variant. | Feature | Specification | | :--- | :--- | | **Current Setting Range** | 80A to 115A (Adjustable) | | **Rated Voltage (Ue)** | Up to 690V AC | | **Rated Insulation Voltage (Ui)** | 690V | | **Frequency** | 50/60 Hz | | **Auxiliary Contacts** | 1NO (Normally Open) + 1NC (Normally Closed) | | **Tripping Class** | Class 10A (Standard industrial trip speed) | | **Reset Mode** | Manual or Automatic (Switchable) | | **Mounting** | Plug-in to contactor or independent rail mounting | --- ## 2. Key Internal Electronic/Mechanical Parts While these units are primarily **electromechanical**, they contain several critical components that govern their operation: ### A. Bimetallic Strips The "heart" of the relay. These are composed of two different metals bonded together. When current flows through them, they heat up. Because the metals expand at different rates, the strip bends. When the current exceeds the 115A limit (or the set threshold), the bend becomes severe enough to trigger the internal mechanism. ### B. Current Adjustment Dial A calibrated potentiometer-style dial located on the front face. It allows the user to fine-tune the trip current between 80A and 115A to match the Full Load Amps (FLA) of the specific motor. ### C. Differential Mechanism (Phase Failure Protection) The "DMFP" designation often indicates enhanced protection. It includes a slide mechanism that detects when one bimetallic strip is bending significantly less than the others. This allows the relay to trip much faster during a **Phase Failure** than a standard balanced overload. ### D. Auxiliary Contact Block * **NC (95-96):** Used to break the coil circuit of the contactor to stop the motor during a fault. * **NO (97-98):** Used to trigger an external alarm or signal a PLC that a fault has occurred. --- ## 3. Visual Layout and Interface * **Test Button:** Manually simulates a trip to verify that the auxiliary contacts are functioning correctly. * **Stop Button:** Manually opens the NC contact to stop the motor without triggering a full "trip" state. * **Reset Button:** Blue button used to restore the circuit after a trip has occurred (once the bimetallic strips have cooled). * **Selector Switch:** Allows the user to choose between **Hand (Manual)** reset and **Auto** reset modes. --- ## 4. Wiring and Integration In a typical control circuit: 1. The three main power phases pass through the **Main Terminals (L1, L2, L3)**. 2. The **NC terminal (95)** is connected to the control power. 3. The **NC terminal (96)** is connected to the Contactor Coil (A1). 4. If the JR28 detects an overload, it opens 95-96, cutting power to the contactor coil and disconnecting the motor.