Why do fuses should have high resistivity
May 31, 2022
The fuse holder is mainly for overload protection. So why is the resistance required to be large, and does the fuse have a resistance value? Now the 6x30 fuse holder manufacturer will briefly describe it to you.
1. Why do fuses have high resistivity
The fuse is made of a lead-antimony alloy wire with a lower resistivity and a lower melting point, which is called a fuse. The voltage constant resistance comparison is more able to detect the ultra-working range micro-current resistance needs more current to fuse and can burn the electrical appliance without fuse. These principles use the current thermal effect fuse to control the current and allow the current to pass according to the formula Q=IRT resistance produces more heat and is easier to fuse. It has a certain relationship with Joule's law, but things in life are not that simple. The fuse can neither be large nor It should not be too small. If it is too large, it will easily burn the wires in the home and even cause a fire. If it is too small, it will easily fuse and cause unnecessary trouble.
The fuse can directly look at the wire. The reason is simple. The rated current is the same as the wire. Even if it can be regarded as the wire cross-sectional area, the more conductive the current is, the more current the fuse is. The same fuse has a resistance of 0.023 ohms and has the same current and voltage in front of the wire with the same cross-sectional area. The temperature is higher than the wire with the same cross-sectional area and the same voltage, the current fuse has the same voltage, the current is lower than the wire, the voltage is ignored, and the current is only 2.3% of the fuse's endurance limit. The fuse is equivalent to the wire. The 20mA fuse is similar to the wire and the fuse is connected in parallel with the bulb: the current is lower than the rated current of the fuse, the bulb has only a weak voltage, and the current (similar to a short circuit) current exceeds the rated current of the fuse. The bulb is on and the fuse is blown.
2. Does the fuse have a resistance value?
The fuse has a resistance value. In fact, even the wire has resistance, but the resistance of the wire is very small (the nature of the conductor). In general circuit calculations, we usually do not count it, but the resistance of the fuse is obviously larger than that of the wire of equal length. So that it can play the role of protection circuit.
The fuse is marked with "5A 250V", indicating that the maximum current allowed by the fuse is 5A, which is called the rated current; the maximum voltage allowed to pass is 250V, which is called the rated voltage. If the current or voltage exceeds the rated value, the fuse will blow, breaking the circuit, thus protecting the appliance (if there is no fuse, the appliance may burn out).
The fuse blows and the principle is Joule's law. Joule's Law: The heat generated by a current passing through a conductor is proportional to the square of the current, proportional to the resistance of the conductor, and proportional to the time it is energized. The mathematical expression of Joule's law: Q=I²Rt, and the derived formulas are Q=UIt and Q=U²2/R×t. All the work done by the current in the fuse generates heat, that is, all electrical energy is converted into internal energy, at this time Q=W. Therefore, when I or U is greater than the rated value, Q becomes larger, so that the fuse cannot dissipate heat in time and overheat, and eventually fuse.
In general, when the circuit current or voltage exceeds the rated value, the fuse will not blow immediately, because the fuse allows a larger current or voltage value to pass, allowing a short-term excess working state. That is to say, if you find that the current or voltage of the circuit is abnormal, you still have the opportunity to correct the error, but for accidental mistakes (such as short circuit of the main line), the insurance may not have time to fuse the wire and cause the wire to catch fire. Take precautions, there is no chance of regret.
The above is the introduction of "Why the fuse has high resistivity". If you need to know more details about the fuse holder, please contact our manufacturer.