Safety second characteristic of the fuse
Fuse action by the melt fuse, when the current is larger, the shorter the time required to melt the fuse. Current is small, the melt fuse time is longer, not even fuse. The melt, therefore, its operating current and operating time characteristics fuse safety second characteristic is the inverse time characteristics. High-voltage fuses
Each melt has a minimum melting current. Corresponding to different temperatures, the minimum melting current is also different. Although the current by the external environment, but can be considered in practical applications. Minimum fusing current of the general definition of the melt and melt the rated current ratio of the minimum melt coefficient, commonly used melt melting coefficient greater than 1.25, that is not the fuse rated current of 10A melt below the current 12.5A . The relationship between the fusing current and fusing time, such as shown in Table 1-2.
From here we can see that the fuse can only play the role of short-circuit protection, not from the overload effect. If it proves necessary to use in overload protection, must reduce its use of the rated current, such as 8A of the melt used for a 10A circuit, short circuit protection doubles as overload protection with overload protection features are not ideal.
Fuse selection of the main basis for the protection of the load characteristics and short-circuit current size to select the type of fuse. For small capacity motor and lighting Extension, often use fuses as overload and short circuit protection, and thus hope that the melt melting coefficient appropriate. Usually chosen RQA series of Pb-Sn alloy melt fuse. For a larger capacity motor and lighting trunk, you should focus on to consider the short-circuit protection and breaking capacity. Usually used with the RM10 and RL1 series high breaking capacity fuses; when the short circuit current should be adopted limiting the role of RT0 RTl2 fuse
The rated current of the melt method according to the following options: 1) protection of non-starting the process of steady loads such as lighting circuits, resistors, electric stove, melt the rated current is slightly larger than or equal to the rated current in the load circuit.
2) protection of a single long-term motor melt current can select the maximum starting current, the following formula to select:
The IRN ≥ (1.5 ~ 2.5) IN
Where the IRN - melt the rated current; IN - motor rated current. Frequent motor starters, where coefficient due to increase to 3.5, the concrete should be based on the actual situation.
3) protecting the long motor (supply mains)
IRN ≥ (1.5 ~ 2.5) IN max + ΣIN
In the max-capacity of the largest single motor rated current. And ΣIN the rest of the motor rated current.
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