The **5HT 3.15-R** is a specific model of a **Miniature Cartridge Fuse**. It is widely used in power supplies, consumer electronics, and industrial equipment to protect circuits from overcurrent and short-circuit conditions. Below is a detailed breakdown of its specifications and electronic characteristics. ### 1. Technical Specifications The part number follows a standard nomenclature used by manufacturers like **Bel Fuse** or **Littelfuse**. | Parameter | Specification | Details | | :--- | :--- | :--- | | **Current Rating** | 3.15A | The maximum continuous current the fuse can carry. | | **Voltage Rating** | 250V AC | Designed for standard mains voltage applications. | | **Fuse Size** | 5x20 mm | Standard miniature cylindrical size. | | **Characteristic** | Time-Lag (Slow Blow) | Designated by the **"T"** (High Surge Withstand). | | **Body Material** | Ceramic | Better heat resistance and higher breaking capacity than glass. | | **RoHS Compliant** | Yes | Indicated by the **"-R"** suffix. | --- ### 2. Key Features and Meaning of Symbols Understanding the alphanumeric code is essential for selecting the correct replacement part: * **5HT**: * **5**: Refers to the physical diameter (5mm). * **H**: High Breaking Capacity. This means the fuse can safely interrupt high fault currents (often up to 1500A at 250V) without the ceramic body shattering. * **T**: Time-delay (from the German *Träge*). This fuse allows for temporary current surges, such as when a motor or power supply capacitor first starts up. * **3.15**: The Ampere rating. * **-R**: Lead-free and RoHS (Restriction of Hazardous Substances) compliant. --- ### 3. Application Use Cases Because this is a **Slow-Blow (Time-Lag)** fuse, it is used where "Inrush Currents" are expected. 1. **Switch Mode Power Supplies (SMPS):** Protects the input stage where large capacitors cause a momentary spike when plugged in. 2. **LED Drivers:** Handles the initial surge of the driver circuit. 3. **Monitors and Televisions:** Protects internal circuitry from power surges. 4. **Small Motors:** Accommodates the high torque startup current that would instantly blow a "Fast-Acting" (F) fuse. --- ### 4. Comparison: Ceramic vs. Glass While a glass fuse of the same rating might fit the holder, the **5HT** is ceramic for specific safety reasons: | Feature | Glass (5ST/5SF) | Ceramic (5HT) | | :--- | :--- | :--- | | **Breaking Capacity** | Low (Low Amps) | High (Up to 1500A) | | **Internal Filling** | Air / Vacuum | Often filled with sand to quench arcs. | | **Safety** | May shatter under high fault. | Contained; will not explode. | --- **Warning:** Always replace a fuse with the exact same rating. Replacing a **5HT 3.15-R** (Slow Blow) with a **5HF 3.15-R** (Fast Acting) will likely cause the fuse to blow immediately upon powering on the device.