> Technical Data > Operation principle of thermal fusesThermal fuses are circuit breakers in temperature sensing devices to cutoff the circuit by detecting overheat caused from fire, short circuit, or abnormal electronic operation. Thermal fuses are not reusable once they were used, but they work once only in the function temperature.
SW-1, 3, 5 series thermal fuses
SW-1, 3, 5 series thermal fuses are composed of sliding contact, spring, and electrically non-conductive thermal pellet. Before it is operating, current flows from the left lead to the sliding contact and then to the right lead through the metal case when tempeature reached to the designed functioning point, thermal pellet changes into liquid states and spring compression looses. That is, the spring expands and the sliding contact moves away from the left lead. The circuit is opened and the current between the sliding contact and the left lead is stopped.
SW-2 series thermal fuses
SW-2 series thermal fuses are composed of axial symmetric leads, the thermal element of metal compound that is melting in a defined temperature, special compound to prevent the oxidation of the element, and ceramic insulator. The special resin compound begins liquefaction when the ambient temperature rises, and it generates a surface tension when the temperature reaches to the melting point of the thermal element. Followed by the melting of metal compound that linked two leads, pulling back to the leads, and breaking the circuit permanently
