Guidelines for Selecting Low Voltage Fuses

The main function of a fuse set in a circuit is to safely and reliably cut off when a fault occurs, thereby providing protection for individual components or the entire circuit. The following are the relevant conditions that users need to consider when choosing fuse links.

Normal working conditions and installation conditions
Surrounding ar temperature: -5C-+40C
Altitude: not exceeding 2000m
Atmospheric. conditions: Humidity: The relative humidity, of the air at the installation site should not exceed 50% at a maximum temperature of+40 C. Higher
relative humidity is allowed at lower temperatures, and the average minimum temperature in the wettest month should not exceed+25 C. The average maximum relative humidity in that month should not exceed 90%. Due to temperature changes causing condensation on the product, measures must be
taken.
Pollution levet Level 3
Installation category: Class III

Ambient temperature
The air temperature directly surrounding the fuse link should not be confused with room temperature. In many practical situations, the temperature of the fuse link is quite high, because the fuse link is configured in different structural supports/bases and the entire fuse link is enclosed in the distribution/ control cabinet.

Reduced capacity usage
At an ambient temperature of 20 C, we recommend that the actual operating current of the fuse should not exceed the rated current value. When selecting a fuse link, consideration should be given to environmental and working conditions, such as changes in sealing degree, air flow, cable size (length, cross section), instantaneous peak value, etc; The current carrying capacity test of the fuse link is conducted at an ambient temperature of 20 C, and is affected by changes in ambient temperature during actual use. The higher the ambient temperature, the higher the operating temperature of the fuse, and the shorter its lifespan. On the contrary, operating at lower temperatures will prolong the lifespan of the fuse link. The following figure shows a typical curve of the influence of environmental temperature on current carrying capacity
For example, in a certain usage scenario where the ambient temperatureis20 C, the
rated current of the ordinary type (gG class) fuse link is In=63A. Now that the above
fuse link is used in a high temperature environment of 70 C, it is necessary to
additinally reduce the working current. According to the left figure of the ambient
temperature carrying capacity curve A, the percentage of the rated valueat 70 Cis
0.78. To ensure that the fuse link does not malfunction, the rated current value of the
fuse link should be re selected:n==80.77A Select In :80A according to the standard current level of the fuse Link

Environmental temperature carrying capacity curve

Among them: Curve A: Ordinary type (gG) fuse link curve for line protection:
Curve B: Rapid type (aR) fuse curve for semiconductor equipment protection.

Malfunction
Misconduct is often caused by incomplete analysis of the designed circuit. In the selection of fuse links, special attention must be paid to three factors: 1), 3), and 6) Normal operating current, ambient temperature, and overload increment. For example, a common cause of misoperation
during regular operation is the failure to fully consider factors such as the starting current of the motor circuit, surge current and harmonic current of the capacitor circuit, and air temperature around the fuse link.