It is made up of the following parts:1. Melt striker, 2. Micro switch (with one normal close contact and one normal open contact), 3. A base for the striker and the switch. Fuse monitoring devices are usually paralleled under the lid fastening screws at the ends of the fuse. When the fuse breaks, the striking pin springs out of the striker, the microswitch pushed and signal sent out or circuit cut down. Then distance between the two fastening ends can be adjusted in a certain range for paralleling to fuses with different heights.