The concept of fuse holder and matters needing attention in selection | HINEW

Fuse holder manufacturer

Are you unfamiliar with the fuse holder? Then the next and xiaobian together to understand the concept of the fuse holder and the matters for attention when selecting it.

The concept of a fuse holder

Fuse holder is a protective measure installed in the circuit to provide insulation protection for the fuse and ensure the safe operation of the circuit. The fuse holder when circuit failure or abnormal, such as wet water, short circuit and damage, etc., will lead to the current in the circuit rising and generate a lot of heat, and the rise in current is likely to damage to some of the important components in the circuit or precious device, when heat up to a certain degree, even a fire, burning circuit, serious when still can fire. If the circuit is correctly placed in the fuse sheath fuse seat, then the fuse will be in the current abnormal rise to a certain height and a certain time, their own fusing, at this time the fuse seat pray isolated from the outside world, so as to protect the safe operation of the circuit.

Some factors affecting the service life of a fuse

(1) Working environment temperature: high ambient temperature is harmful to the life of the fuse holder. Ordinary fuse holder, tin begins to spread into the wire at a temperature of about 160 degrees; The temperature at which the melt begins to oxidize more vigorously is about 200 degrees. With the oxidation of the fuse from outside to inside, multiple diffusion, thermal stress fatigue, etc., the life of the fuse will be gradually shortened. Therefore, it is recommended that the delay fuse holder should not work above 150℃ for a long time, and the normal fuse holder should not work above 175~225℃ for a long time.

Pulse current: pulse impact, will produce thermal cycle, resulting in the diffusion of the fuse, oxidation, thermal stress, and even accelerate. The fuse holder will gradually age with the increase in pulse power and frequency. The impact life of the fuse holder depends on the percentage of I2t of the pulse to I2t of the fuse itself. Normally, it should be less than 20%, so that the fuse can withstand more than 100,000 shocks.

(3) Contact: fuse holder contact tube clamp, and the length and cross-sectional area of the connecting wire, etc. The contact resistance between the fuse holder and the tube clamp is large, which may impair the service life. The UL standard stipulates that the contact resistance between the fuse holder and the tube clamp is less than 3m ω. When the contact resistance is high, the clamp does not dissipate heat but generates heat and transmits it to the fuse.

Matters needing attention in fuse selection

1. Rated current:

Pay attention to the current derating according to different certification standards. The derating according to the UL standard is 0.75, that is, the actual steady-state operating current should not exceed 75% of In. According to the IEC standard, the actual steady-state operating current can be equal to In. For UL fuses: operating at 25℃, the operating current should not exceed 75% of the rated current of the fuse to avoid harmful fuses. Generally speaking, the available current specifications provided by the supplier are less than the standard recommended tap. It is recommended to select from the existing current specifications of the supplier, and it is not recommended to require the supplier to conduct additional design.

2. Rated voltage:

The fuse rating shall be equal to or greater than the effective circuit voltage.

3. Working environment temperature:

fuse current carrying capacity test is carried out at 25℃ environment temperature, this test is affected by the change of environment temperature. The higher the ambient temperature, the higher the operating temperature of the fuse, the shorter its life. Conversely, operating at lower temperatures will extend the life of the fuse. Therefore, the rated current of the fuse should be adjusted according to the actual working environment temperature of the fuse.

4. Electric step-down and cold resistance:

in general, the resistance of the fuse is inversely proportional to the rated current. The resistance that chooses fuse is smaller had better, the loss power of such fuse is smaller also. The voltage drop of the fuse is tested in the dc rated current, because the fuse with the small rated current has a relatively large resistance, so the impact on the low-voltage power is also relatively large, in the process of selecting small specifications of the fuse, we should pay attention to the influence of resistance.

5. Time - current characteristic curve:

it is one of the most important basis to choose fuse. This determines whether the fuse can effectively protect the circuit and fuse correctly in the event of a fault current. Each type of fuse has its own time current curve for fusing characteristics. The abscissa of the curve is the current, and the ordinate is the time of the fusing. Generally, in the selection process, this curve is used as a reference, and the key points in the curve are selected as the basis. The selection of key points is different according to the type of fuse certification. When selecting a fuse, it is necessary to determine the time when the protected fault current can safely exist in the circuit.

6. Segmented ability grade:

the breaking ability of fuses in different certification standards is different. The rated breaking ability of fuses must meet or exceed the maximum fault current in the circuit. When the protected system is directly connected to the power input circuit and the fuse is placed in the power input section, always use high break capacity fuse. In most secondary circuits, especially when the voltage is below the supply voltage, a low-breaking fuse will suffice.

7. Nominal melting heat energy:

in the case of fuse must withstand high current, the current large and short duration pulse, such as the impact current and starting current, flood current, and other similar "pulse" type of circuit transient value, the fuse should be able to withstand such high current energy, abnormal circuit should not occur. The nominal melting heat rating of a fuse is determined in a laboratory and there is only one nominal melting heat rating for each size of fuse.

8 durability (life) :

the life of the fuse is relatively long, in the case of the correct selection, generally do not consider the replacement for life reasons, but need to pay attention to the change and failure of the fuse material may occur due to environmental conditions.

9. Structural features :

According to the actual working conditions of the fuse, choose different shapes/sizes. There are usually the following options

Tubular: glass tube - low breaking capacity, ceramic tube - high breaking capacity, etc.

Micro: resistance type, surface stick type, film type, etc.

Melt structure: round wire, flat wire, straight line, wave type, etc.

Combined melt: add tin ball - slow melting delay

10. Certification requirements:

Fuse mainly adopts UL certification standards, IEC standards, due to the fuse of the IEC standards and UL standard in terms of content and specification content difference is bigger, so by the two kinds of standard authentication fuse cannot replace each other, at the same time in respect of the same kind of fuse and no way to get these two standard certification.

11. Identification:

According to the requirements of safety specifications, the following identification of the fuse (fuse holder) should be provided next to the circuit board: rated current, rated voltage, fusing characteristics, explosion-proof characteristics, etc., and there is a safety warning label for replacing the fuse. For example, we choose a rated current of 2A, rated voltage of 125V, fusing characteristics of fast fusing, explosion-proof characteristics of low explosion-proof fuse, then the silk screen identification of the fuse holder on the circuit board is: F2AL,125V; For internally mounted fuses (e.g. wire mounted fuses, panel mounted fuses), an explicit cross-reference table containing relevant instructions is allowed in the maintenance documentation.

12. Fuse holder:

Select appropriate fuse holder components and mounting methods, such as fuse clip, mounting box, panel mounting, shielding mounting, etc. Be careful not to use a silver plated fuse holder.

13. Selection of welding and soft cover:

The welding fuse and fuse holder can not be used in the welding process of silver plated heat absorption device is recommended. The soft fuse sleeve can insulate exposed parts of the fuse, protect it during live work and prevent the danger of fuse explosion. Therefore, when the glass tube fuse with low breaking ability is used in ac system, it is recommended to use the soft fuse sleeve.

After reading so much, we must have some understanding of the concept of the fuse seat and the matters for attention in selection. As a professional fuse seat manufacturer, we have the confidence and ability to provide you with the best service. Looking forward to your friendly cooperation.

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Post time: Jul-04-2022