Precautions for the Practical Use of Fuses

The key precautions for the practical use of fuses are specified as follows:

First, the protection characteristics of the fuse must match the overload characteristics of the protected equipment. Fuses with sufficient breaking capacity shall be selected to withstand potential short-circuit currents in the circuit.

Second, the rated voltage of the fuse shall be compatible with the voltage level of the operating circuit, and the fuse’s rated current shall be no less than the actual operating current of the circuit.

Third, graded matching must be realized for the rated current of fuse elements at all circuit levels. The rated current of the upper-level fuse element shall always be higher than that of the lower-level one to ensure staged protection.

Fourth, only standard and matching fuse elements are allowed for installation and use. It is prohibited to arbitrarily upgrade the specification of fuse elements or replace formal fuse elements with other conductive materials.

The following key factors shall be fully considered during fuse type selection:

1. Select the fuse model based on circuit operating requirements and on-site installation conditions. Semi-enclosed or non-filled enclosed fuses are suitable for small-capacity circuits; filled enclosed fuses are applicable for circuits with high short-circuit current. Fast-acting fuses are specially designed for the protection of semiconductor components.

2. Determine the rated voltage of the fuse according to the nominal voltage of the circuit to ensure voltage matching.

3. Select the fuse rated current in accordance with the actual load characteristics of the circuit.

4. Hierarchical coordination of fuse elements at all levels is essential, with the rated current of lower-level fuses set smaller than that of upper-level ones. The current parameters of the main circuit and each branch circuit differ, so the matching fuse specifications must be adjusted accordingly. If 15A and 25A fuse elements are improperly configured in upper and lower circuits, simultaneous fusing may occur during a short circuit, completely invalidating the selective protection function.

This problem can be effectively avoided by maintaining a specification difference of 2 to 3 grades between the main circuit and branch circuit fuses. For instance, the low-voltage outlet of a transformer adopts RT0100/800 fuses, while supporting motors are equipped with RT0400/250 or RT0400/350 fuses. The upper and lower level rated current ratios reach 3.2 and 2.3 respectively, achieving excellent selective protection. In the event of a branch circuit short circuit, only the branch fuse will blow, and the power supply of the main circuit will remain unaffected.

5. Avoid selecting fuse elements with excessively small rated current. Undersized fuses are prone to single-phase fusing faults, which will cause motors to operate in single-phase mode and eventually burn out. Relevant statistical data shows that 60% of motor burnout failures are caused by improper fuse configuration.