When must the fuse be used? What are the situations where fuses should be used?

The main function of fuse is short circuit protection. The requirements for fuse selection are: when the electrical equipment is in normal operation, the fuse should not be blown; In case of short circuit, it should be blown immediately; When the current changes normally (such as motor starting process), the fuse should not be blown; When the electrical equipment continues to be overloaded, it should be delayed to fuse. The rated voltage of the fuse should be greater than or equal to the rated voltage of the circuit. The choice of fuse mainly includes the choice of fuse type and the determination of melt rated current. There are many kinds and types of fuses according to different occasions, voltage levels, protection objects and requirements. High-voltage fuses High-voltage fuses are divided into indoor and outdoor types, so I won't go into details here. Low-voltage fuses are usually divided into plug-in, tubular and spiral types. It can also be divided into three types: open, semi-closed and closed. R fuse; C- plugin; L helix; M- closed tube; s-fast； T-tube with packing. For example, insert RC 1 and RC1a; RM- no packaging tube; RT0, RL 1 and RLS are filled tubes and filled spirals respectively. Low-voltage fuses have three kinds of melts with different structures, one is used for overload and short-circuit protection (GG) of circuits; The other is short circuit protection (AR) as a semiconductor device and its complete set of devices; It can also be derived as motor short circuit protection (aM). The selection principles of fuses are as follows: a. Choose the fuse model according to the line requirements and installation conditions. Small-capacity circuits are semi-closed or unfilled; The choice of large short-circuit current is closed packaging; Fast fuses are selected for semiconductor element protection. B, according to the load characteristics, choose the rated current of fuse. C, choose fuses at all levels need to cooperate with each other, the latter level is smaller than the previous level, the current on the main brake and each branch line is different, and the fuse selection is also different. D. Select the rated voltage of the fuse according to the line voltage. E. The protective fuse current of AC asynchronous motor should not be too small (it is recommended to be 2~2.5 times the rated current of the motor). If the selection is too small, the motor will burn out easily after the one-phase fuse is blown, so thermal relay must be equipped for overload protection. Note: the fuse current includes two aspects, one is the rated current of the seat shell frame where the fuse is installed, and the other is the rated current of the fuse, so don't confuse it. This is similar to a circuit breaker.