The melt is not equal to fuse rated current, rated current melt rated current according to the protected equipment choice, load current fuse rated current shall be greater than the rated current, melt determined in conjunction with the main electrical appliance.
The fuse is mainly composed of melt, shell and support. The melt is the key element to control the circuit breaker. The material, size and shape of the melt determine the circuit breaker. Melt materials are classified into two types: low melting point and high melting point. Low melting point materials such as lead and lead alloy, its melting point and low fusing, easily because of its resistivity is bigger, so it made the melt is larger, the section size of metal vapor generated in fusing more, is only applicable to low ability to fuse. High melting point materials such as copper, silver, and its high melting point, is not easy to fuse, but because of its low resistivity, melt the cross section of small size can be made than low melting, fusing the metal vapor produced in less, suitable for high marks broken ability to fuse. The shape of the melt is divided into two types: filaments and ribbons. Changing the shape of the variable section can significantly change the fuse characteristics of the fuse. The fuse has a variety of fuse characteristic curves, which can be applied to the needs of different types of protection objects.
The ampere characteristic:
The action of the fuse is realized by the fusion of the melt, and the fuse has a very obvious characteristic, which is the ansecond characteristic.
In the case of melt, its action current and action time feature, namely, the ampere second characteristic of the fuse, also called the reverse time delay characteristic, namely: overload current hour, long fuse time; When overload current is large, fuse.
Time is short.
Understanding of Ann s features, we can see from the joule's law Q = I2 * R * T, in a series circuit, the fuse of the R value basically remain unchanged, calorific value and is proportional to the square of the current (I), is proportional to the heating time T, that is to say: when the current is bigger, shorter time it takes to melt fuse. And current is small, the melt fuse need time is longer, even if the speed is less than the speed of thermal diffusion heat accumulation, temperature fuse would not rise to the melting point, will not even fuse fuse. Therefore, in a certain overload current range, when the current returns to normal, the fuse will not fuse and can continue to be used.
Therefore, each melt has a minimum melting current. The minimum melting current is different for different temperatures. Although the current is affected by the external environment, it can not be considered in practical applications. General definition of the smallest fusing electric current of the melt and the ratio of the rated current of the melt to A minimum melting coefficient, the melting coefficient of commonly used melt is greater than 1.25, which means the rated current of 10 A melt fuse while under current 12.5 A.
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 it is necessary to use in overload protection, it is necessary to carefully match the rated current of line overload current and fuse. For example, the melt of 8A is used in the circuit of 10A for short circuit protection and overload protection, but the overload protection feature is not ideal at this time.
The selection of fuse is mainly based on the protection characteristics of the load and the type of the short-circuit current. For small motor and lighting feeder, the fuse is often used as overload and short circuit protection, so the melting coefficient of the melt is expected to be less. The RQA series fuse with lead tin alloy melt is usually selected. For larger motor and lighting mains, the short circuit protection and breaking capacity should be considered. The fuse of RM10 and RL1 series with high resolution is usually selected. When the short circuit current is large, it is appropriate to use the fuse of RT0 and RTl2 series with limited flow.
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