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What is the Main Function of Current Fuses?

Article Source:Thermal protectorAuthor:YaxunPopularity:Published time:2019-05-31 11:32

The earliest fuse was invented by Edison more than a hundred years ago. Because of the underdeveloped industrial technology at that time, incandescent lamps were very valuable, so it was originally used to protect expensive incandescent lamps with fuses. The fuse protects the electronic device from overcurrent damage and also prevents serious damage to the electronic device due to internal faults. Therefore, each fuse has a rated specification, and the fuse will blow when the current exceeds the rated specification. When the current between the conventional non-fusing current and the rated breaking capacity (current) specified in the relevant standards acts on the fuse, the fuse should be able to work satisfactorily without endangering the surrounding environment.

The expected fault current of the circuit in which the fuse is placed must be less than the rated breaking capacity current specified in the standard. Otherwise, when the fuse breaks down, there will be some phenomena such as continuous arc, ignition, fuse burning, fuse melting together with the contact parts, and fuse marking can not be identified. Of course, the breaking capacity of inferior fuses does not meet the requirements of the standard, and the hazard also occurs when used.

In addition to the fuse resistors, the protective components used in electronic equipment include ordinary fuses, thermal fuses, and self-recovery fuses. The protection component is generally connected in series in the circuit. When an abnormal phenomenon such as overcurrent, overvoltage or overheating occurs in the circuit, it will immediately fuse and protect it, preventing the fault from further expanding.

Fuse structure

(1) Ordinary current fuse
commonly known as fuses, are fuse-unrecoverable fuses that can only be replaced with new ones after fuses. It is represented by "F" or "FU" in the circuit, and Figure 17-5 is its circuit graphic symbol.
Fuse circuit graphic symbol

1. Structural Features of Common Fuses Common fuses are usually composed of glass tubes, metal caps and fuses.

Two metal caps are placed on both ends of the glass tube, and a fuse (made of a low-melting metal material) is placed in the glass tube, and the two ends are respectively welded to the central holes of the two metal caps.
When in use, the fuse is placed in the fuse holder and connected in series with the circuit.

Most of the fuses of the fuses are linear, and only the delay fuses used in color televisions and computer monitors are spiral fuses.

2. The main parameters of ordinary fuses are rated current, rated voltage, ambient temperature and reaction speed.
The rated current, also called the breaking capacity, refers to the current value at which the fuse can be blown at the rated voltage.
The normal operating current of the fuse is less than 30% of the rated current.
The rated current of the domestic fuse is usually marked on the metal cap, and the imported fuse is marked on the glass tube with a color ring, as shown in Figure 17-6. Table 17-1 shows the meaning of the various colors on the color ring fuse.

Rated voltage: refers to the most regulated voltage of the fuse, which is divided into four specifications: 32V, 125V, 250V and 600V. The actual operating voltage of the fuse should be lower than or equal to the rated voltage. If the operating voltage of the fuse exceeds the rated voltage, it will blow quickly.

The experiment of the current carrying capacity of the fuse was carried out at an ambient temperature of 25 °C. The life of the fuse is inversely proportional to the operating ambient temperature. The higher the ambient temperature, the higher the operating temperature of the fuse and the shorter its life.
The reaction rate refers to the rapid degree of response of the fuse to various electrical loads.
Fuse can be divided into normal response type, time delay type, fast action type and current limit type according to reaction speed and performance.