The **FRN-R-400** is a high-capacity power fuse commonly used in industrial and commercial electrical systems. It belongs to the Fusetron™ family manufactured by **Eaton (Bussmann Series)**. --- ## 1. Technical Specifications The following table outlines the core electronic and mechanical parameters of the FRN-R-400: | Parameter | Specification | | :--- | :--- | | **Current Rating** | 400 Amps | | **Voltage Rating (AC)** | 250 Volts | | **Voltage Rating (DC)** | 125 Volts | | **Interrupting Rating (AC)** | 200,000 Amps RMS Symmetrical | | **Interrupting Rating (DC)** | 20,000 Amps | | **Fuse Class** | Class RK5 | | **Mechanism** | Dual-element, Time-delay | | **Mounting Style** | Blade / Bolt-on | --- ## 2. Key Features & Components ### A. Dual-Element Design Unlike standard "one-time" fuses, the FRN-R-400 features two distinct components within the casing: 1. **Thermal Element:** Handles temporary overloads (e.g., motor startups). It allows a brief period of high current without blowing. 2. **Short-Circuit Element:** A high-speed element that reacts instantly to catastrophic faults or short circuits to prevent equipment damage. ### B. Time-Delay Functionality This fuse is specifically engineered to ignore "inrush currents." When an electric motor starts, it can pull up to 500% of its normal operating current. The FRN-R-400 is designed to stay intact during this surge but will trip if the high current persists long enough to indicate a genuine fault. ### C. Rejection Feature (Class RK5) The "R" in FRN-R indicates a **rejection feature**. The fuse has a specific physical notch in the blade. This prevents a user from accidentally replacing it with a lower-rated fuse (like a Class H fuse) that doesn't have the same interrupting capacity, ensuring the safety level of the circuit remains high. --- ## 3. Typical Applications The FRN-R-400 is primarily used in high-load environments where large motors or heavy machinery are present: * **Main Power Feeders:** Protecting the primary electrical lines entering a building or large workshop. * **Branch Circuit Protection:** Safekeeping specific heavy-duty equipment. * **Motor Protection:** Ideally suited for AC motors due to its time-delay characteristics. --- ## 4. Safety and Maintenance > **Warning:** Fuses should only be replaced by qualified personnel. Always verify that the power is disconnected before attempting to inspect or replace a 400A fuse. * **Visual Check:** The fuse body is usually made of fiberglass or high-grade phenolic resin. Inspect for signs of charring or discoloration. * **Testing:** Use a multimeter in the **Ohms (Ω)** setting. A functional fuse will show near-zero resistance (continuity); a "blown" fuse will show infinite resistance (Open Line/OL).