Working principle of BlueLight thermal fuse

Release Time: 24 Mar,2026

A thermal fuse, also known as a thermal cutoff device, is a temperature-sensitive circuit-breaking component that serves as a safety safeguard during equipment operation. When abnormal operating conditions cause excessive overheating, the thermal fuse trips, thereby opening the circuit to prevent further malfunctions or potential fires. It is commonly used in applications such as lighting—e.g., lamps; household appliances—including hair dryers, irons, rice cookers, electric stoves, water dispensers, and coffee makers; and industrial equipment—such as transformers and electric motors. Once activated, a thermal fuse cannot be reused; it operates only once at its designated melting temperature to interrupt the circuit and cannot be reset.

Product Construction

Temperature fuses are available in two structural configurations: square-case type and ceramic-tube type, but their operating principles are identical. As shown in the figure above, a temperature fuse consists of a temperature-sensitive fusible alloy connected between two leads, with the assembly encapsulated in a special resin coating, inserted into a plastic housing, and then sealed with epoxy resin.

Operating Principle

This product is a single-use, alloy-based safety protection component. When an abnormal condition occurs in a circuit or electrical appliance and the ambient temperature rises to the set threshold, the temperature-sensitive alloy wire inside the device melts and, under the action of a special resin, rapidly separates, thereby permanently disconnecting the power supply. The product features a compact footprint, highly sensitive temperature response, high operational accuracy, and stable, reliable performance.

A non-resettable device featuring a fusible alloy thermal element for safety protection: when a circuit or appliance experiences an abnormal condition, the temperature rises to approximately the setpoint, causing the thermal element to melt and rapidly separate due to a special resin, thereby permanently disconnecting the circuit. The product is compact, highly sensitive, accurate, and stable.

When designing a thermal fuse for integration into your product, it is essential to strike a comprehensive balance among all relevant factors and conduct field testing of the thermal fuse’s performance characteristics on the actual product.

Caution: The temperature fuse contains a low-melting-point alloy wire as its internal temperature-sensing element, which is connected to two leads. Improper soldering practices—such as excessive soldering temperature, prolonged soldering time, or excessively short leads—can allow heat to conduct through the leads into the fuse body, overheating and damaging the temperature-sensing element (causing it to melt or its end to thin due to thermal shock). This weakens the element and reduces the reliability of its connection to the leads, increasing the likelihood of premature failure at the damaged area when current flows during operation or under other conditions.

Wire-connection rules and soldering prohibitions for thermal fuses: a comprehensive, UL/IEC-compliant hands-on guide.

Essential things to know about fuses

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A professional fuse manufacturer with over four decades of experience, specializing in thermal fuses and current fuses, with an annual production capacity of 1 billion units.Our products are exported to markets in the Americas, Europe, Southeast Asia, and beyond, and the “Hongtian” brand of thermoplastic materials and current fuses enjoy a high level of trust among customers.

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