Fuse selection process
  1. Safety certification: Determine the safety certification of the fuse according to the safety certification required by the whole machine, such as UL specifications or IEC specifications.
  2. Structure size: Determine the size of the fuse according to the space in the circuit design, such as length, diameter, and whether it has a lead or not.
  3. Rated voltage: must be greater than or equal to the actual application voltage. Fuses generally include 24V, 32V, 63V, 125V, 250V, etc.
  4. Breaking capacity: the fuse should be greater than the maximum fault current in the circuit.
  5. Rated current: Refer to the following items:
  (1) Normal working current, running at 25℃
   Rated current of UL specification fuse ≥ normal working current/0.75;
  The rated current of the IEC specification fuse is ≥ normal working current/0.9.
(2) Ambient temperature: The current carrying capacity test of the fuse is carried out at an ambient temperature of 25℃. The higher the ambient temperature, the shorter the life of the fuse and the lower the carrying capacity. Therefore, the ambient temperature and environment should be considered when selecting the fuse. The influence of temperature on current carrying capacity is as follows:


(3) Pulse: Pulse will produce thermal cycles and produce mechanical fatigue that will affect the life of the fuse. The pulse I2T should be designed to be less than the nominal melting heat I2T of the fuse under the premise of considering the pulse factor.
   Fuse rated I2T>actual pulse I2T/Pf
Pf: Pulse factor, which varies according to the number of pulses that can be tolerated. The specific value is shown in the figure below:


6. Test
  The samples selected by the above procedure need to be tested in the actual circuit to verify whether the selected fuse is suitable. This verification should include tests under normal conditions and fault conditions to ensure that the selected fuse plays a protective role in the protected circuit.