The **3AG400-R** is a specific model of a miniature glass cartridge fuse. It belongs to the "3AG" family, which is one of the most common standard sizes for cylindrical fuses used in consumer electronics and industrial equipment. --- ### 1. Technical Specifications The part number can be broken down to understand its electrical characteristics: | Parameter | Specification | Details | |:---|:---|:---| | **Series** | 3AG | Standard size: 1/4" x 1-1/4" (6.35mm x 31.75mm) | | **Current Rating** | 400mA | 0.4 Amperes | | **Voltage Rating** | 250V | Maximum operating voltage | | **Fuse Type** | Fast-Acting | Blows quickly when an overload occurs | | **Material** | Glass Body | Allows for visual inspection of the filament | | **RoHS Compliant** | Yes (-R suffix) | Lead-free and environmentally friendly | --- ### 2. Key Components & Construction The 3AG400-R consists of four primary physical parts: 1. **Glass Tube:** The transparent housing that contains the arc and prevents fire during a "blow" event. 2. **Metal End Caps:** Usually made of nickel-plated brass, these provide the electrical contact points. 3. **Filament (Element):** A thin wire calibrated to melt at exactly 400mA of sustained current. 4. **Air/Vacuum Filling:** Most fast-acting glass fuses are air-filled to allow the wire to snap quickly. --- ### 3. Common Applications Because this is a **low-current (400mA)** and **fast-acting** fuse, it is typically used to protect sensitive components that cannot withstand even brief surges. * **Multimeters:** Protecting the internal circuitry during current measurements. * **Power Supplies:** Secondary side protection for low-power DC rails. * **Audio Equipment:** Protecting internal amplifiers or pre-amp stages. * **Medical Devices:** Ensuring precision instruments fail-safely in case of a short circuit. --- ### 4. Comparison: Fast-Acting vs. Time-Delay It is critical to note that the 3AG400-R is **Fast-Acting**. | Feature | 3AG400-R (Fast-Acting) | 3AG400-S (Slow-Blow/Time-Delay) | |:---|:---|:---| | **Response** | Immediate disconnect on surge | Allows temporary "inrush" current | | **Filament Design** | Thin, straight wire | Coiled wire or wire with a solder "slug" | | **Best For** | Resistive loads (LEDs, ICs) | Inductive loads (Motors, Transformers) | ---