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How to select the fuse
Date:01/22/2013   Click:1015
1. The rated current - In 
Rated current of the fuse is to point to its nominal rated current, usually the maximum current value of the circuit can long-term work. 
Correct selection of rated current of the fuse should be paid attention to the following several aspects. 
(1) want to consider the reduction rate of the fuse. Set working current of the circuit = 1.5 A, for example, for IEC specifications of the fuse, not consider reduction requirements, have rated current In = Ir = 1.5 A; For UL specification fuse f0, reduction rate must be considered In Ir/f0 = = 1.5/0.75 = 2 a, f0 take 0.75 here. 
(2) if the guest rated current is not universal, should choose the higher value of the nearby. 
(3) the rated current of the fuse is only a nominal value of it, and the actual operation of select it must take a closer look at it when time and speed of action of fusing features, and then can be correctly chosen the rated current of fuse. 
(4) directly will require selected fuse fusing current value as the method to select the rated current value is wrong. 
2. The rated voltage, the U 
Fuse rated voltage refers to the nominal voltage, it is often a fuse disconnect after can withstand maximum voltage value. 
Fuse energized the both ends of the voltage is less than the rated voltage greatly, so the extra burden on voltage basically irrelevant. At the right choose fuse rated voltage, should consider the following several aspects. 
(1) rated voltage should be equal to or greater than the circuit voltage. For example, the 250 v fuse can be used 125 v circuit. 
(2) in low voltage in electronic circuits, communication can be used for dc fuse. 
(3) about the fuse rated voltage should be considered: when the circuit voltage is less than the fuse product rated voltage fuse is capable of breaking the maximum current is given. 
3. The environmental temperature 
The working temperature of known or environmental temperature movements has a direct effect of the fuse. The higher the temperature, fuse the heat at work, life will be shorter. Both UL specifications and IEC specifications, the fuse of the technical requirements are in the room 
Temperature of 25 oC conditions. Such as environment or working temperature is higher, want to consider the temperature reduction rate of the fuse. 
4. The voltage drop/cold resistance - Ud/R 
In general, the fuse is inversely proportional to the resistance to its rated current value. Requirements in the protection circuit fuse resistance as small as possible, so its power loss is small. So in fuse parameter specifies the maximum voltage drop. 
The voltage drop is connected to a dc rated current of the fuse, the fuse after reaching heat balance of the proceeds of the voltage readings. 
Fuse the cold resistance is under the condition of less than 10% rated current measured resistance readings. 
The fuse of the voltage drop and cold resistance conversion to each other. 
Method of work output current. 
5. The time - current feature - I - T or Ann - second properties 
Fuse when the current exceeds the rated current, the melt crossing rise gradually, and finally fusing, this is the consequences arising out of the state of overload. 
The fuse should have certain overload ability, specific as follows: 
UL specification fuse is 110% In the biggest fusing current; 
The biggest not fuse current IEC standard fuse is 150% or 120% In In. 
Has also asked the fuse when exceed the set limit to overload current can burn out in a timely manner, including: 
UL standard minimum fuse current of fuse In around 130%. 
IEC standard minimum fuse current of fuse in around 180 in %. 
Time/current characteristic is the fuse of the main performance index, it shows that the fuse fusing the time range under different overload current load. 
Time/current characteristic of overload fuse performance very well. Each kind of type specification fuse fusing feature can be expressed in a continuous curve, every point on the curve can be corresponding to the load current value on the abscissa and ordinate the melting time. This is the most important when choosing a fuse. 
Usually rules using the curve of several key points to examine the fuse of the overload performance. In most of the fuse in the samples of the products have the fusing characteristics, specific provisions for the fuse in some electrical test flow range of melting time, this is the most main basis for acceptance of the fuse. UL fuse norms by 110%, In 135 In % and 200% In test points; IEC fuse norms of 150% (150%, 210% (200%) In, In 275%, 400% and 1000% In In In test points, etc. 
According to IEC 127, to provide direct current (dc) to determine the melting time of the fuse, which can be concluded that the time - current curve. If you provide the exchange and melting time will have change, especially when the fuse fuse in a very short time, it will be as closed circuit of ac sine wave phase Angle change and change. 
Different types of fuse characteristic curves with different shapes, the same type of fuse with similar shape characteristic curve. 
According to different fusing characteristics, can be divided into fast and delay until the fuse. Fast fuse are commonly used in the impedance circuit, protect some particularly sensitive to changes in current components; Time delay fuse used in circuit state changes from time to tome a big wave surge current sense/capacitive circuit, it can withstand the pounding of switch machine surge pulse, the real failure can quickly disconnect circuit. 
6. Breaking capacity - Ir 
Fuse when the current is quite large even when short circuit, still can fuse safety breaking circuit, and do not bring any destructive. 
Breaking capacity is one of the main fuse safety indicators. It table under the specified voltage fuse safety, cutting off one of the biggest current. Breaking capacity, also known as the biggest breaking capacity, short circuit breaking capacity or maximum breaking current. 
The fuse breaking capacity depends on the structure and material used in the fuse. In general, most of the low ability to fuse are glass shell; High ability to fuse usually have ceramic shell, many of which are still filled with pure granular quartz material. 
When overload current shall not exceed the maximum breaking current, the fuse can't appear broken, explosion, splash, as well as the peripheral person coal and other components, such as damage caused by unsafe phenomenon. 
The rated breaking capacity () in the UL file related to fuse rated current and load voltage directly. The greater the rated current, the greater the breaking ability also; Higher load voltage, breaking capacity will decline. 
UL 198 - G specifications of breaking capacity: under the condition of ac 125 v, the fuse must be able to cut off the current of 10000 a, 
Small size fuse greatly influenced by the voltage drop of low voltage circuit, it is important to note! In extreme cases, it can make the circuit without 
Method of work output current. 
5. The time - current feature - I - T or Ann - second properties 
Fuse when the current exceeds the rated current, the melt crossing rise gradually, and finally fusing, this is the consequences arising out of the state of overload. 
The fuse should have certain overload ability, specific as follows: 
UL specification fuse is 110% In the biggest fusing current; 
The biggest not fuse current IEC standard fuse is 150% or 120% In In. 
Has also asked the fuse when exceed the set limit to overload current can burn out in a timely manner, including: 
UL standard minimum fuse current of fuse In around 130%. 
IEC standard minimum fuse current of fuse in around 180 in %. 
Time/current characteristic is the fuse of the main performance index, it shows that the fuse fusing the time range under different overload current load. 
Time/current characteristic of overload fuse performance very well. Each kind of type specification fuse fusing feature can be expressed in a continuous curve, every point on the curve can be corresponding to the load current value on the abscissa and ordinate the melting time. This is the most important when choosing a fuse. 
Usually rules using the curve of several key points to examine the fuse of the overload performance. In most of the fuse in the samples of the products have the fusing characteristics, specific provisions for the fuse in some electrical test flow range of melting time, this is the most main basis for acceptance of the fuse. UL fuse norms by 110%, In 135 In % and 200% In test points; IEC fuse norms of 150% (150%, 210% (200%) In, In 275%, 400% and 1000% In In In test points, etc. 
According to IEC 127, to provide direct current (dc) to determine the melting time of the fuse, which can be concluded that the time - current curve. If you provide the exchange and melting time will have change, especially when the fuse fuse in a very short time, it will be as closed circuit of ac sine wave phase Angle change and change. 
Different types of fuse characteristic curves with different shapes, the same type of fuse with similar shape characteristic curve. 
According to different fusing characteristics, can be divided into fast and delay until the fuse. Fast fuse are commonly used in the impedance circuit, protect some particularly sensitive to changes in current components; Time delay fuse used in circuit state changes from time to tome a big wave surge current sense/capacitive circuit, it can withstand the pounding of switch machine surge pulse, the real failure can quickly disconnect circuit. 
6. Breaking capacity - Ir 
Fuse when the current is quite large even when short circuit, still can fuse safety breaking circuit, and do not bring any destructive. 
Breaking capacity is one of the main fuse safety indicators. It table under the specified voltage fuse safety, cutting off one of the biggest current. Breaking capacity, also known as the biggest breaking capacity, short circuit breaking capacity or maximum breaking current. 
The fuse breaking capacity depends on the structure and material used in the fuse. In general, most of the low ability to fuse are glass shell; High ability to fuse usually have ceramic shell, many of which are still filled with pure granular quartz material. 
When overload current shall not exceed the maximum breaking current, the fuse can't appear broken, explosion, splash, as well as the peripheral person coal and other components, such as damage caused by unsafe phenomenon. 
The rated breaking capacity () in the UL file related to fuse rated current and load voltage directly. The greater the rated current, the greater the breaking ability also; Higher load voltage, breaking capacity will decline. 
UL 198 - G specifications of breaking capacity: under the condition of ac 125 v, the fuse must be able to cut off the current of 10000 a, 
Under the condition of ac 250 v, the fuse must be able to cut off the current shown in the following table. 
Under the condition of 250 v rated breaking capacity of the fuse 
The rated current of fuse 
The rated breaking capacity 
0 A ~ 1 A 
35 A 
1.1 A to 1.1 A 
100 A 
3.6 A ~ 19 A 
200 A 
10.1 A ~ 15 A 
750 A 
15.1 A ~ 30 A 
1500 A 
IEC 127 specifies in ac 250 V breaking capacity: under the condition of low ability to fuse (LBC) must be 35 A or 10 in the largest; High ability to fuse (HBC) must pass 1500 A; Enhance the ability to fuse (MBC) must pass 150 A. 
According to routine, when the protected system is directly connected to the power input circuit and the fuse is in the power input part, be sure to use high ability to fuse. In the part of the secondary circuit, especially when the voltage is lower than the power supply voltage, choose low enough ability to fuse. 
7. Value - I2t melting heat 
1) the instantaneous current and pulse 
Transient current is derived from the internal protection circuit of the capacitive and inductive energy storage device switch operation. External transient current is derived from external injection system like a surge into the current, the duration is very short. 
Duration of less than 10 ms instantaneous current is known as the pulse current, pulse can be harmful, it might damage the fuse and fuse failure. 
In most cases, the time delay fuse are best suited for circuit protection with a pulse. 
2) the I2t value 
I2t value is the energy needed for the direct determination of blow out the fuse, and there are 
Total I2t (removal of I2t) = melting fly solitary I2t I2t + 
Here, remove I2t refers to fuse all heat energy in the process of completely disconnect; The preflight melting I2t (equivalent to the IEC standard solitary I2t) refers to the starting from the melt melts to fly alone the energy needed to power a moment; Fly, solitary time refers to the solitary moment to fly alone finally extinguished time to start. For low voltage fuse, fly alone time is very short, usually be ignored. 
8. Durability -- -- life 
Fuse is a long life, in the case of a trouble-free almost with the life of the equipment can be synchronized. 
IEC specifications of small fuse life test method: under the condition of dc power supply, to 1.20 (or 1.05) In electricity flow conductivity In 1 h, the opening 15 min, 100 cycles In a row, and then to 1.5 (or 1.05) In electricity flow In 1 h, cannot have a fuse or during other anomaly phenomenon. 
Under normal conditions the fuse the shelf life of not less than two years, expire after re-inspection qualified can store all right again. 
9. The structure features and installation form 
1) structural features 
(1) tubular glass tube, low ability, ceramic tube, high breaking capacity; Filling fine quartz sand, used for solitary, glass tube color - fusing instructions; And welded inside and outside welding type; Add lead for cap - welding (sometimes need first 
Will lead to shape)... 
(2) the micro resistance type, transistor type, diaphragm... 
(3) other inserting disk, bolt type, sealed, alarm type... 
(4) the melt structure round wire, flat wire, single, double wire, composite wire, straight, wavy, serrated; Flake melt (with one or more of the bottleneck part)... 
(5) the composite melt Tin ball, fuse, sheet metal, resistance, etc. 
2) the type of installation 
(1) panel installation fuse box, fuse plug sitting... 
(2) the floor installation fuse, the fuse clip to sit... 
(3) printed circuit board plug-in installation (wave soldering) : axial and radial lead, lead... The surface installation (infrared welding) : traditional, wafer type... Sometimes need to outside of tube heat shrink sleeve, to insulate the fuse with the surrounding components. 
(4) hanging installation fuse.