1. Safety certification: Determine the safety certification of fuses based on the required safety certification for the entire machine, such as UL or IEC specifications. 2. Structural size: The size is determined based on the space in the circuit design, such as length, diameter, and whether there are leads. 3. Rated voltage: It must be greater than or equal to the actual application voltage, generally including 24V, 32V, 63V, 125V, 250V, etc. 4. Breaking capacity: should be greater than the maximum fault current in the circuit. 5. Rated current: Based on the following items: (1) Normal working current, the rated current of UL specification fuses operating at 25 ℃ is ≥ normal working current/0.75; The rated current of IEC standard fuses is ≥ normal working current/0.9. (2) Environmental temperature: The current carrying capacity test of a fuse is conducted under the ambient temperature of 25 ℃. The higher the ambient temperature, the shorter the lifespan of the fuse, and the lower the carrying capacity. Therefore, when selecting a fuse, environmental temperature should be considered. The impact of environmental temperature on the current carrying capacity is shown in the following figure:
(3) Pulse: Pulse generates thermal cycling and mechanical fatigue that affects the lifespan of the fuse. When designing, the pulse I2T should be smaller than the nominal melting heat energy of the fuse, taking into account the pulse factor. The rated I2T of the fuse is greater than the actual pulse I2T/Pf Pf: The pulse factor varies depending on the number of pulses it can withstand, as shown in the following figure:
6. The samples selected through the above procedures need to be tested in actual circuits to verify the suitability of the selected fuse. This verification should include testing under normal and fault conditions to ensure that the selected fuse plays a protective role in the protected circuit.
According to electrical performance, it can be divided into two types: disposable fuses and self restoring fuses.
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