How to choose a drop-out fuse

In the 10 kV power grid, drop-out fuses are generally used as overcurrent protection devices for branch lines and distribution transformers. In order to achieve the purpose of safety and reliability, the following two points must be considered when selecting a melt：

1.The rated current of the selected melt should be less than the primary setting current of the overcurrent protection device of the outgoing switch of the substation, so as to realize the selectivity between the upper and lower protection devices.

2. The melting time of the melt should be shorter than the setting time of the overcurrent protection device of the outgoing switch of the substation, so as to achieve the coordination and cooperation between the upper and lower protection devices. When installing the melt, it is not allowed to connect multiple small-sized melts together as a large-sized melt. Because the melts of different specifications or the same specifications are produced by different manufacturers, the resistance value may not be based on the shunt principle of parallel resistance, and the current flowing through each melt is also different. When the total current flowing through the melt has not yet reached the total rated value, the melt with a small rated current may be blown first due to too large a shunt, and an arc will be generated to blow other melts, resulting in a power outage accident.