Thermal fuse LS 90 is meant to be used in e.g. heating stations using oil as their energy source. There are two circuits in LS 90 of which one is used to control the oil burner and the other one makes the alarm. In case of fire the fuse will cut off the oil burner control circuit thus stopping oil pumping to the station. At the same time the other circuit makes the alarm.

LS 90 consists of two parts: contact block and fuse block. The metal in the fuse block melts in 90 °C temperature allowing the contact block to change state.

NOTE: Never assemble LS 90 to a place where temperature rises in normal conditions higher than 40 °C. The metal used in the fuse softens by ageing in this temperature and might cause false alarm.