Fuse selection principle - Solutions - Huaqiang Electronic Network

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When selecting a fuse for an electrical system, it's essential to consider the specific requirements of the circuit and installation environment. For low-capacity circuits, semi-enclosed or non-filled fuses are typically used. In cases where large short-circuit currents are expected, filled fuses are more appropriate. For protecting semiconductor components, fast-acting fuses are recommended due to their quick response time.

The rated voltage of the fuse should match the line voltage to ensure proper operation and safety. Choosing the correct rated current is equally important, as it must be based on the load characteristics of the circuit to avoid unnecessary tripping or failure to protect when needed.

It’s also crucial to coordinate the fuses at different levels in the system. The fuse in the lower level should have a smaller rating than the one above to ensure selective protection. If both the main and branch fuses have similar ratings, a short circuit could cause both to blow simultaneously, leading to loss of selectivity. To avoid this, there should be a 2-3 level difference between the main and branch fuses.

For example, if the transformer’s low-voltage side uses an RT0 1000/800 fuse, and the motor circuit uses an RT0 400/250 or RT0 400/350, the current ratio between the two levels is 3.2 and 2.3 respectively, ensuring good selectivity. This means that if a short circuit occurs in the branch, only the branch fuse will blow, without affecting the main supply.

It’s important not to choose a fuse that is too small. If the fuse is undersized, it may blow even under normal operating conditions, which can lead to a single-phase operation in motors and potentially cause damage. According to statistics, about 60% of burned-out motors are due to improper fuse selection. Therefore, always ensure the fuse is correctly sized for the application to maintain system reliability and safety.