Operating Principles of Fuses
Fuses utilize metallic strips as fusible links wired in series within electrical circuits. When overloading or short-circuit currents pass through these links, the heat buildup from electric current will melt the fusible part and disconnect the circuit. Boasting a compact structure and simple installation, fuses are extensively deployed in power supply systems, industrial electrical machinery and domestic electrical appliances.
A complete fuse assembly is composed of three core parts: fusible element, outer casing and mounting bracket. The fusible element serves as the decisive component that governs fusing behavior. Its raw material, physical size and geometric profile collectively determine the overall fusing properties of the fuse.
Fusible link materials are categorized into low and high melting point variants:
Low melting point substances like lead and lead alloys melt readily under heat. However, their high electrical resistivity demands thicker cross-sections for fusible links. A large volume of metal vapor will be released during melting, restricting their application to fuses with limited fault breaking capacity.
High melting point metals such as copper and silver feature a high melting threshold and resist premature melting. Their low resistivity allows production of slim fusible cross-sections, and far less metal vapor is generated during rupture. This makes them perfect for high breaking capacity fuses. Fusible elements come in wire and ribbon forms; modifying their cross-sectional geometry can greatly adjust the fuse’s fusing response.
Widely Used Fuse Variants
Plug-in Fuse
Mostly fitted at the terminal end of circuits rated 380V or lower, delivering short-circuit safeguarding for distribution branch circuits and electrical machinery.
Screw Mount Fuse
Equipped with a fault indicator on its top porcelain cap. The indicator springs out instantly once the fusible link blows, visible via a glass observation window on the cap. It is widely used within machine tool control panels. Thanks to its robust breaking performance, it provides short-circuit protection for circuits up to 500V and 200A.
Enclosed Cartridge Fuse
Split into sand-filled and hollow non-filled types:
Sand-filled cartridge fuses adopt square porcelain tubes filled with quartz sand and internal fusible links. They deliver powerful fault breaking performance for circuits below 500V and 1000A.
Hollow enclosed fuses house fusible links inside sealed cylinders with relatively weaker breaking capacity, suited for power grids and distribution gear rated under 500V and 600A.
High-Speed Fuse
Specially engineered to protect semiconductor rectifier modules and rectifier units against short circuits. Semiconductor components feature extremely weak overload endurance and can only sustain large overload currents for a split second, calling for ultra-fast response short-circuit protection. While sharing a similar overall structure with enclosed cartridge fuses, they adopt distinct fusible link materials and profiles: V-shaped deep-groove deformed cross-section silver sheets.
Self-Recovering Fuse
Metallic sodium acts as its conductive core, which offers outstanding electrical conductivity at ambient temperature. Upon circuit short-circuit failure, extreme heat from fault currents vaporizes sodium rapidly; sodium vapor becomes highly resistive to suppress excessive short-circuit current. Once the short-circuit fault clears and temperatures cool down, sodium reverts to its original conductive state.
Self-recovering fuses only restrain short-circuit current rather than fully isolating the circuit. Their standout merit is repeatable operation without needing replacement of fusible components.
During operation, each fuse is wired in series with the equipment or circuit it safeguards. Should a short circuit or severe overload arise, the internal fusible link will melt automatically to activate circuit protection. Ordinary household safety fuses are the most commonplace example of this protective device.