A metal conductor serves as the fuse element connected in series within the circuit. When overload or short-circuit current flows through the element, the heat generated by the current itself melts the element to cut off the circuit. Featuring a simple structure and easy operation, fuses are widely applied in power systems, various electrical equipment and household appliances.

A fuse mainly consists of three parts: the fuse element, housing and support frame, among which the fuse element is the core component determining the fusing performance. The material, dimension and shape of the fuse element jointly define its fusing characteristics.

Fuse element materials fall into two categories: low-melting-point materials and high-melting-point materials.

Low-melting-point materials such as lead and lead alloys melt easily due to their low melting points. Nevertheless, their high resistivity requires a larger cross-sectional area for the element, and they produce abundant metallic vapor during fusing. Therefore, they are only suitable for fuses with low breaking capacity.

High-melting-point materials including copper and silver have high melting points and are not prone to melting. Thanks to their low resistivity, they can be manufactured into elements with smaller cross-sections, and generate minimal metallic vapor upon fusing, making them ideal for fuses with high breaking capacity. Fuse elements are available in wire and strip forms. Adjusting the cross-sectional shape can drastically alter the fusing performance of a fuse.

Common Types of Fuses

Plug-in Fuse

Commonly used at the end of circuits with a voltage rating of 380V and below, it provides short-circuit protection for distribution branch lines and electrical equipment.

Screw Type Fuse

Its top cap is fitted with a fuse indicator. Once the element blows, the indicator pops out immediately and can be observed through the glass window on the porcelain cap. It is widely adopted in machine tool electrical control equipment. With strong breaking capacity, it offers short-circuit protection for circuits rated up to 500V and 200A.

Enclosed Fuse

Divided into filler-type and filler-free enclosed fuses.

Filler-type enclosed fuses generally adopt square porcelain tubes filled with quartz sand and built-in fuse elements. They feature high breaking capacity and are applied to circuits below 500V and 1000A.

Filler-free enclosed fuses place the element inside an enclosed cylinder with relatively weaker breaking capacity, suitable for power grids and distribution equipment rated under 500V and 600A.

Fast-Acting Fuse

Primarily designed for short-circuit protection of semiconductor rectifier components and rectifier devices. Semiconductor components have extremely poor overload tolerance and can only withstand heavy overload current for an extremely short time, hence fast fusing performance is required for their short-circuit protection. Its structure is basically identical to enclosed fuses, yet the material and shape of the fuse element differ. It adopts V-shaped deep-groove deformed cross-section elements made of silver sheets.

Self-Resetting Fuse

It takes metallic sodium as the conductive element, which boasts excellent conductivity at room temperature. When a short-circuit fault occurs in the circuit, the high temperature induced by short-circuit current rapidly vaporizes sodium, and sodium vapor turns into a high-resistance state to limit short-circuit current. After the short-circuit current disappears and the temperature drops, metallic sodium restores its original high conductivity.

A self-resetting fuse only limits short-circuit current instead of completely breaking the circuit. Its major advantage lies in reusability without replacing the fuse element.

In service, the fuse is connected in series with the protected circuit. In case of short circuit or severe overload in the circuit, the fuse element inside will melt automatically to implement protection. The daily household fuse is the most typical example of this device.