The main function of the fuse is short-circuit protection.

The selection requirements for fuses are:

During the normal operation of electrical equipment, the fuse should not be blown out; In the event of a short circuit, it should be fused immediately; When the current changes normally (such as the motor starting process), the fuse should not be blown out; When the electrical equipment continues to be overloaded, the fusing should be delayed. The rated voltage of the fuse should be greater than or equal to the rated voltage of the circuit.

The selection of fuses mainly includes the selection of fuse type and the determination of melt rated current.

There are many varieties 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, which are not repeated here. Low-voltage fuses are commonly included in three categories: plug-in type, tubular type and spiral type. It can be divided into three types: open type, semi-closed type and closed type.

R - fuse; C - plug-in; L - spiral; M-Closed tube type; S-Fast; T-With packing tube type. For example, RC1 and RC1A are plug-in types; RM-No packing tube type; RT0, RL1 and RLS are packed tube type and packing spiral type, respectively. Low-voltage fuses have three melts with different structures, one as overload and short-circuit protection (gG) for electrical circuits; the other as short-circuit protection (aR) for semiconductor devices and their complete devices; It can also be derived as motor short-circuit protection (aM).

The principles of fuse selection are:

A. Select the model of fuse according to the line requirements and installation conditions. Circuits with small capacity choose semi-enclosed type or closed type without packing; The choice of large short-circuit current is packing closed type; Fast fuses are selected for semiconductor component protection.

B. Select the rated current of the fuse according to the load characteristics.

C. The selection of melts at all levels needs to cooperate with each other, the latter stage is smaller than the previous stage, the current on the main gate and each branch line is different, and the choice of fuse is also different.

D. Select the rated voltage of the fuse according to the line voltage.

E. The protection melt current of AC asynchronous motor cannot be selected too small (it is recommended to be 2~2.5 times the rated current of the motor). If the choice is too small, it is easy to appear after the one-phase fuse is fused, causing the motor to run out of phase and burn out, and must be equipped with thermal relays for overload protection. Note: The fuse current includes two aspects, one is the rated current of the seat and shell frame where the fuse is installed, and the other is the rated current of the fuse, and the two should not be confused. This is similar to a circuit breaker.