Fuse selection principle - Solutions - Huaqiang Electronic Network

Photocoupler

1. Choose the fuse type based on the circuit requirements and installation conditions. For low-capacity circuits, use semi-enclosed or non-filled fuses. For high short-circuit current applications, opt for filled fuses. When protecting semiconductor components, it's best to use fast-acting fuses.

2. Select the rated voltage of the fuse according to the circuit voltage to ensure compatibility and safe operation.

3. Determine the rated current of the fuse based on the load characteristics to avoid overloading and ensure proper protection.

4. Ensure coordination between fuses at different levels. The lower-level fuse should have a smaller rating than the one above. If the main and branch lines have different currents, using fuses with similar ratings can cause both to blow simultaneously during a short circuit, leading to loss of selectivity. To prevent this, maintain 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 uses RT0 400/250 or RT0 400/350, the current ratio is 3.2 and 2.3 respectively, ensuring good selectivity—so that only the branch fuse blows in case of a fault, without affecting the main supply.

5. Avoid selecting fuses that are too small. A fuse that is too small may blow easily, causing a single-phase failure in motors, which can lead to damage. According to statistics, about 60% of burned-out motors result from improper fuse configuration. Always follow recommended guidelines and ensure the fuse rating matches the circuit requirements for optimal performance and safety.