Product specifications and parameters of fuses

The rated current is marked on the fuse and indicates its rated operating current. In actual selection, it is often necessary to derate it; for example, UL standards recommend using it at 75% of the rated current. The rated voltage indicates the maximum operating voltage the fuse can operate at, and should be equal to or greater than the effective voltage of the circuit. Cold resistance is the resistance value of the fuse when it is not in operation, and voltage drop is the voltage drop across the fuse at the rated current. Both should be as small as possible, especially in low-voltage circuits. Breaking capacity refers to the maximum current that the fuse can safely interrupt at a specified voltage. High-power circuits require high-breaking-capacity models. Nominal melting heat energy is the energy value required for the fuse to melt, used to assess its ability to withstand high-energy current pulses.

The time-current characteristic shows the relationship between overload current and melting time, and is one of the most important characteristics of a fuse. Based on melting speed, fuses can be classified as extra-slow, slow, medium-speed, fast, and extra-fast. Slow-speed fuses are suitable for circuits with inrush current, such as motor starting, while fast-speed fuses are used for circuits requiring precise protection. Key selection factors include circuit conditions, ambient temperature, certification requirements, and replacement principles. The circuit conditions need to be evaluated, including normal operating current, pulse current, overload current magnitude and duration, and circuit operating voltage. Ambient temperature affects current carrying capacity; as temperature increases, the circuit should be degraded according to the derating curve. Certification requirements should be selected based on the product's export region, such as UL, IEC, AEC-Q, etc.