Fuse Question

Whether the rated current of the fuse is the fusing current of the fuse? 　　

The answer is no. The rated current of the fuse is only nominal specification, and how big current the fuse can bear and when the fuse blows out are not regulated in detail in the fuse standard, and the regulations are different due to different standards. The fuse has a fusing factor, the fusing factor is over 1, normally between 1.1 and 1.5; the fusing factor is the specific value of common non-fusing current and rated current. Therefore, even the current flowing through the fuse is higher than the rated current but not higher than the common non-fusing current, the fuse will not blow out.

How to understand the rated voltage of the fuse? 　

Whether the fuse blows out depends on the strength of the current flowing through the fuse, but has nothing to do with the working voltage of the circuit.The rated voltage of the fuse is come up with in an angle of safely using the fuse and is the maximum working voltage at which the fuse can work at a safe state. This means the fuse can be only installed in the circuit, of which the working voltage is less than or equal to the rated voltage of the fuse, so that the fuse can safely and effectively work, otherwise, when the fuse blows out, the phenomena of continuous flash over and voltage puncture occur, which will cause damage to the circuit.

What does the voltage drop of the fuse show? 　　

The voltage drop of the fuse is the voltage drop at both ends of the fuse under a condition of rated current, and shows the internal resistance of the fuse; the voltage drop should not too high; if the fuse with too high internal resistance (voltage drop) is installed in the circuit,the system parameters of the circuit will be affected,so that the circuit can’t normally working.In the standard, the upper limit and the consistency of the voltage drop are both regulated.

Why do we research temperature rise of the fuse? 　　

The temperature rise of the fuse is the temperature increase value of the fuse when the specified current through the fuse, namely difference value of measured temperature and ambient temperature.In the IEC standard, the upper limit of the temperature rise is 135℃, and in the UL standard, the upper limit of the temperature rise is 75℃. Because the fuse-element is quite sensitive to the temperature, the melting point and the resistance of the melt will be changed if the fuse is used at a certain temperature for a long time, and this change will affect the accuracy of the fuse. This is called the aging of the fuse. The aging fuse is quite dangerous when used in the circuit, therefore, we must pay attention to the temperature rise of the fuse when manufacturing and using the fuse. Meanwhile, we also notice even the fuse doesn’t blow out after being used for a long time, the fuse is quite possible aged, you’d better replace it.

What is the breaking capacity of the fuse? 　

When the current between common non-fusing current and the rated breaking capacity current flows through the fuse, the fuse can normally operation and doesn’t cause any damage to the ambient environment. The anticipated fault current of the circuit, in which the fuse is installed, must be less than the rated breaking capacity current,otherwise, the phenomena of continuous arcing,burning of fuse, fusing of parts contacting the fuse, blurred fuse markings,etc.will occur when the circuit fault happens and the fuse blows out. Of course, the breaking capacity of poor-quality fuses can’t meet requirements of the standards, and the dangers mentioned above will also occur if they are used.

What is the slow-fusing fuse? 　　

The slow-fusing fuse is also called the time-lag fuse; its time delay characteristic is that when the non-fault pulse current exists in the circuit, the fuse can still be kept well so as to protect the circuit overloaded for a long time. For some circuits, the current generated at the moment when the circuit is switched is several times higher than the normal working current, although the peak current is very high,the period when this kind of current occurs is quite short,we call it pulse current, or surge current.The common fuse can’t bear this kind of current, the machine can’t be started if the circuit with the pulse current is installed with the common fuse, but if the fuse in higher specification is used, the circuit can’t be protected when overloaded. The melt of the time delay fuse is processed by a special method and can absorb energy, and the fuse not only resists the surge current, but also provides overload protection by adjusting the amount of energy absorbed.