What factors should be considered when selecting a fuse?

1. Determine the size and shape of the fuse according to the circuit space

SMD, micro, ultra-small, ceramic, glass tube, etc.

2. Determine the required safety certification

C-UL, VDE, SEMKO, PSE, CCC, KC, BSI, etc.

3. Rated voltage

When the fuse works normally in the circuit, its power consumption is very small, so its voltage drop is also very small, but when the circuit fails and the fuse blows, the two ends of the fuse will bear the rated voltage of the circuit. Greater than or equal to the rated voltage of the circuit is one of the factors for selecting the fuse.

4. Rated current

The rated current of the fuse is the current that the fuse can work normally under laboratory conditions. Since the North American (UL, CSA) standard and the European (IEC) standard have different views on fuse design, the following formula should be followed when selecting the fuse current value:

North American standard fuse:

Fuse current value >= normal working current of the line / 0.85

IEC standard fuse:

Fuse current value > = normal working current of the line

5. Breaking capacity

When the fault current passes through, the fuse will melt and break, cutting off the fault current and then flowing. However, if the fault current is much greater than the voltage and current that the fuse can withstand, the fuse itself will explode and endanger the surrounding environment or components. The maximum fault current that the fuse itself can withstand under the rated voltage is called the breaking capacity of the fuse. The fuse manufacturer will indicate the maximum fault current that the fuse can withstand. When selecting a fuse, the user should estimate the maximum fault current value that may appear in the line, and the fault current must be less than the breaking capacity of the fuse

6. Ambient temperature attenuation rate

When the fuse is used under 25±5℃ environment, the rated current value of the fuse is not affected by the ambient temperature. When the fuse is used under an environment greater than 30℃, the ambient temperature has a great influence on the rated current carrying capacity of the fuse.

7. Melting characteristics of fuse link

Due to the presence of inductance or capacitance in the line, surge current often occurs when the line is switched on and off. The surge current may be 7 to 10 times the normal working current. The pulse width and waveform vary with the line. The surge current will appear every time the circuit is switched on and off. It is necessary to select a time-delay fuse link. According to the degree of surge resistance, there are medium delay (M), delay (T) and long delay (TT). Sometimes, in order to protect important components, such as thyristors and ICs, it is hoped that the fuse link will be quickly opened when there is a fault current. At this time, a fast (F) fuse link or (FF) fast fast fuse link should be selected.