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Fuse safety characteristics

Ampere-second characteristics of fuses:

The action of the fuse is realized by melting of the melt. The fuse has a very obvious characteristic, which is the ampere-second characteristic.

For the melt, its operating current and operating time characteristics, namely the fuse's ampere-second characteristics, are also called reverse delay characteristics, ie: the overload current is small, the fuse-off time is long; when the overload current is large, the fuse-action time is short.

For the understanding of the characteristics of the second and second amps, we can see from the Joule law that Q=I2*R*T. In the series circuit, the R value of the fuse is basically unchanged, and the heat value is proportional to the square of the current I, and the heating time T Directly proportional, that is to say: When the current is large, the time required for melting the melt is shorter. When the current is small, the time required for the melt to melt is longer, and even if the rate of heat accumulation is less than the rate of heat diffusion, the fuse temperature will not rise to the melting point, and the fuse will not even blow. Therefore, within a certain overload current range, when the current returns to normal, the fuse will not blow and can continue to be used.

Therefore, each melt has a minimum melting current. Corresponding to different temperatures, the minimum melting current is also different. Although this current is affected by the external environment, it may not be considered in practical applications. The general definition of the minimum melting current of the melt and the rated current of the melt is the minimum melting coefficient, and the melting coefficient of the commonly used melt is more than 1.25, that is, the melt with the rated current of 10A will not be blown when the current is less than 12.5A.

It can be seen from here that the short-circuit protection performance of the fuse is excellent and the overload protection performance is general. If you really need to use in overload protection, you need to carefully match the line overload current and the fuse's rated current. For example: 8A melt is used in the circuit of 10A, for short circuit protection and overload protection, but the overload protection characteristics at this time is not ideal.

The choice of fuse is based on the protection characteristics of the load and the size of the short-circuit current to select the type of fuse. For small-capacity motors and lighting branches, fuses are often used as overload and short-circuit protection, so it is desirable that the melting coefficient of the melt be appropriately small. RQA series fuses of lead-tin alloy melts are usually used. For larger capacity motors and lighting trunks, short circuit protection and breaking capabilities should be considered. Generally, fuses of series RM10 and RL1 with higher breaking capacity are selected; when the short-circuit current is large, fuses of series RT0 and RTl2 with current limiting effect should be used.