Key points for fuse selection

Release Time:

2020-07-15

Key points for fuse selection   When choosing a fuse, I believe that everyone has a headache, this is because there is no good guide, Below, the editor of Longde Electric will list the factors involved in fuse selection. You can choose the most suitable fuse according to these ideas.   1. Normal working current: The reliable working current of the fuse is usually 75% of the rated current at 25C to avoid failure. For example: In a 25C environment, it is generally not recommended to use a fuse with a rated current of 10A to work above 7.5A. 2. Application voltage (AC or DC): The rated voltage of the fuse must be equal to or greater than the voltage of the application circuit. 3. Ambient temperature: The higher the ambient temperature, the hotter the fuse works and the shorter the life. Conversely, operating at lower temperatures will extend the life of the fuse. The fuse also gets hotter when the normal operating current approaches or exceeds its rating. 4. Overload current: It defines the current that the circuit needs to be protected in the event of a fault. The fault condition can be current, or current and the maximum time to fault that can be tolerated before damage occurs. In fuse and circuit matching, time-current curves should be considered heavily, however keep in mind that curves are based on averaged data. 5. Maximum fault current: The fusing current rating of the fuse must meet or exceed the maximum fault current of the circuit. 6. Pulses (current sudden changes, inrush currents, start-up currents and circuit transients): Electrical pulse conditions can vary widely in different applications. Different fuse constructions may not respond the same to a given pulse condition. Thermal cycling and possible mechanical fatigue from electrical impulses can affect the life of the fuse. The initial or start pulse is normal for some applications where fuses are selected that incorporate a thermal delay design to maintain a normal start pulse and still provide protection during prolonged overloads. For the selection of fuses to deal with starting pulses, we should refer to and compare the time-current curves and I2t ratings of the fuses. 7. Physical size limitations: Refer to the manufacturer's data sheet for fuse length, diameter and height information. 8. Agency Approval Required: Refer to the manufacturer's data sheet for information on agency approvals for a specific device, such as UL, CSA, VDE, METI or MITI. Military requirements require special consideration. 9. Fuse characteristics: For information on mounting type/outline dimensions, ease of disassembly, axial leads, visual indication, etc., please refer to the manufacturer's data sheet. 10. Fuseholder characterization and re-evaluation: Refer to the manufacturer's data sheet for information on clips, mounting blocks, panel mounts, PCB mounts, RFI shielding, etc. 11. Pre-production application testing and validation: Validate selections by requesting samples to be tested in actual circuits. Before evaluating samples, make sure that the fuse has a good electrical connection and that the cables used are properly connected. Testing should include a life test under normal conditions and an overload test under fault conditions to ensure that the fuse is functioning properly in the circuit. The above are the relevant points of fuse selection.