Fuse selection principle - Solutions - Huaqiang Electronic Network

Photocoupler

1. Select the type of fuse according to the line requirements and installation conditions. The circuit with small capacity is semi-closed or non-filled closed; the choice of large short-circuit current is filled with packing; the protection of semiconductor components selects fast-fuse.

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

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

4. Select the melts at all levels to cooperate with each other. The latter level is smaller than the previous one. The current on the main gate and each branch line is different, and the fuse is not the same. If the line is short-circuited, the 15 A and 25 A fuses will blow at the same time, and the protection characteristics will lose their selectivity. Therefore, this phenomenon does not occur only if the total gate and branch maintain a 2-3 level difference. For example, if the low-voltage side outlet of a transformer is RT0 1000 / 800 and the motor is RT0 400 / 250 or RT0 400 / 350, the ratio of rated current between the upper and lower stages is 3.2 and 2.3 respectively, so the selectivity is good, that is, the branch circuit is short-circuited, and the branch line is insured. Fuse does not affect the main gate supply.

5. The melt cannot be chosen too small. If the selection is too small, it is easy to appear that the fuse of one phase is blown, causing the motor to run in one phase and burn out; according to statistics, 60% of the burned motors are caused by improper insurance configuration.