Thermal fuses, also called thermal cutoffs, are temperature-sensing circuit cutoff devices. Thermal fuses can sense the overheating generated in the abnormal operation of electrical and electronic products, and thus cut off the circuit to avoid the occurrence of fire. Thermal fuses have a delicate structure, good sealing, sensitive and reliable operation temperature, small current impact, vibration resistance, and are mainly used for overheating protection of household electrical appliances and industrial equipments, commonly used in: hairdryer, electric iron, electric rice cooker, electric stove, transformer, electric motor, water dispenser, coffee maker and so on.

The working principle of thermal fuses

When the temperature of the circuit exceeds a certain limit, the thermal fuse will blow and the circuit will be broken. A thermal fuse usually contains a small pellet or has a thin wire that melts at a certain temperature. When the pellet or thin wire melts, the circuit breaks. This is known as “melting” or “blowing”. A thermal fuse cannot be used again after it has operated and will only act once at the melting temperature.

Three common types of thermal fuses

First: Organic type thermal fuses

An organic type thermal cutoff consists of a sliding contact, a spring, and an electrically nonconductive thermalpellet. Before the thermal fuse is activated, current flows from the left lead to the sliding contact. The spring expands and the sliding contact separates from the left lead. The circuit is opened and the current is cut off between the sliding contact and the left lead.

Second type: Porcelain tube type thermal fuses

By the axisymmetric lead , in the specified temperature can be melted fusible alloy and in order to prevent its melting and oxidation of special compound and insulating ceramic insulator composition. Around the temperature rise when the specific resin mixture began to liquefy, when it reaches the melting point in the resin mixture with the help of , the melted alloy has been under the action of surface tension quickly to the ends of the lead as the center of the contraction of the ball, thus permanently cutting off the circuit.

Third type: Square case type thermal fuses

When the temperature around the thermal fuse rises to its operating temperature, the fusible alloy melts and shrinks into a ball attached to the end of the two pins under the action of surface tension and the help of the special resin. Thus, the circuit is permanently cut off.