Current fuse, small fuse, tubular fuse application selection guide 3 parts

Four. Test conditions for small tubular fuses
The test results of small tubular fuses have a great relationship with the test conditions, the most important of which are the following three aspects:
1. The use of constant current power supply
It is more accurate to use a constant current power supply when evaluating a fuse than to use a stabilized power supply. If a stabilized power supply is used, the current flowing through the fuse will be changed due to the increase in temperature after the load. The result of this current change makes the measured fusing time inaccurate .
A DC constant current power supply must be used when testing the fusing characteristics of the fuse
When testing the voltage drop of the fuse, AC power should be used, load the rated current and obtain the thermal balance before reading
When testing the rated breaking capacity of the fuse, AC power should be used, and it should be equipped with a phase selection switch and safety protection device. When testing the durability of the fuse, AC power should be used, and only one interruption is allowed during the entire test.
2. Use of standard test equipment
The fusing characteristics of small tubular fuses must be tested using specific test equipment, including the fuse fixture, the diameter and length of the connecting wire, and the accuracy of the test instrument.
The test fixtures of IEC and UL are different. The IEC test fixture is shown in Figure 1.
UL's test fixture is shown in Figure 2.


The ambient temperature and other conditions of the laboratory are in accordance with the requirements specified in the safety standards.



3. Voltage drop and cold resistance

Generally speaking: the cold resistance of the fuse is basically a fixed value, and the voltage drop (thermal resistance) will change with the rise and fall of the temperature, so in the application, the voltage drop at the rated current is important.
A fuse with a lower rated current has a higher resistance. In low-voltage application conditions, the voltage drop will play a decisive role. In some extreme cases, it may cause the required test (application) current to be unable to be output.
The voltage drop of the fuse and the cold resistance can generally be converted to each other.
The voltage drop of the fuse should be tested with alternating current, and the cold resistance of the fuse can be tested with direct current.
4. Breaking capacity
The breaking capacity test of the fuse requires a large power supply, and the general manufacturer does not have the corresponding conditions. Littelfuse has a very large testing organization that is capable of performing all tests on various fuses.
The AC sine wave has different current values in different phases, and the energy it carries is also very different. The breaking capacity of the fuse is carried out under the AC rated voltage, so it has a large closing phase with the load circuit. The IEC test requirements stipulate that the test circuit must be closed at the phase of 300C after the voltage crosses zero.
5. Durability
The IEC standard stipulates that the endurance test of the fuse should be connected in series with six samples. During the entire test process, only one interruption caused by an accident is allowed. After the interruption, the entire test will continue to be performed continuously.
6. Melting heat value and power
The melting heat value and power of the fuse are a reference basis for the selection of the fuse, and there is no requirement for testing.
Most fuse suppliers cannot provide this parameter. Only Littelfuse’s product catalog has marked the melting heat value parameter for almost every type of fuse, which provides complete reference data for users to select accurately.
7. Tension and torque
Tubular fuses are required to withstand a tensile force of 0.5Kg without torque requirements.
The method of tensile test is to use the specified special tools.


The IEC standard stipulates that the fuse needs to be immersed in 150C-350C warm water for 2 hours and then the lint test is carried out. For convenience, it can also be carried out under normal temperature conditions.
8. Collimation
The end cap of the fuse and the tube body must be kept on the same axis to ensure good contact during connection. The collimation of the fuse must be inspected using the specified special collimation gauge.
9. Sign
The logo of small tubular fuse is generally hard printed on the copper caps at both ends, and its contents include:
The first end: the manufacturer’s trademark, such as Littelfuse’s LF or LF OVS;
Various safety certification marks, such as:
The second end: fusing characteristic symbol: F--represents fast fusing,
T--represents slow fusing,
M--represents medium-speed fusing,
FF-stands for very fast fusing,
TT-stands for very slow fusing;
Rated current value: 1 A or more is expressed by XX A,
Below 1 A, it is expressed by XX mA;
Breaking capacity type: L--represents low breaking class,
H--represents high breaking class;
Rated voltage value: 250 V or 125 V
Some fuses also have a color ring mark on the tube case or a label inside the tube to facilitate identification when installed in a circuit.
six. Safety certification of fuses
The fuse is a safety element, and its quality is directly related to the safety of people and property. As a safety element, it must be certified by the relevant organization before it can be produced, sold and used. Many countries (regions) have their own certification requirements for fuses, and only certified fuses with corresponding marks will be allowed to enter the country (region) market.
The codes of safety certification agencies in various countries:
Australia DVE UK BSI
Finland FI Denmark DEMKO
Ireland IE Germany VDE
Switzerland SEV Norway NEMKO
Belgium CEB Sweden SEMKO
France UTE Italy IMQ
China CCC Austria OVE
Canada CSA Spain AEE
Greece ELOT Israel SII
Japan PSE South Korea KC
Netherlands KEMA India BIS
Singapore SISIR Hungary MEEI
U.S. UL
Underwriters Laboratories
MET Laboratories
ETL Testing Laboratories Inc
Major safety certification marks:
BSI VDE
SEMKO MITI
CCC CSA
UL UR
The safety certification of a fuse is different from other components. It not only requires safety tests in terms of structure and materials, but also requires various performance tests including electrical and mechanical properties.
From the foregoing, we know that there are differences in different regions for fuses, so their safety certifications are correspondingly divided into two categories: Europe and North America.
The main standard for European certification is the standard of the International Electrotechnical Commission of IEC. The IEC organization does not directly certify products, but each country is responsible for certification, and the certification mark is used for issuing certificates and using certification.
The national standards of European industrial countries are basically the same as IEC, with only small differences. The standards of China and many other countries (regions) are also based on IEC, and there is great interchangeability between them.
The main standard for North American certification is the UL Underwriters Laboratories standard. The American UL organization directly certifies products, and issues certificates and uses certification marks. The Canadian CSA organization belongs to the North American system, and its certification and standards are similar to UL. UL and CSA can also certify products of other types of fuses, and make some differences in the certification marks.
Mark for certification made by UL standard by UL organization
Non-UL standard certification mark;
CSA organization CSA standard certification mark
Non-CSA standard certification mark.
There are two types of fuse products in Japan: Class A and Class B. Among them, the standard of Class A is equivalent to UL, and the standard of Class B is Japan's own specifications, and its certification mark is: MITI—
The Certification Body Committee (CCB) of the International Electrotechnical Commission for the Safety Certification of Electrotechnical Products (IECEE) has uniformly developed a certificate that can be exchanged between members-the CB test certificate, issued by a certification and accredited national certification body The document, together with the attached test report, is used to notify other national certification bodies that a sample of a certain electrical product has been tested in accordance with a certain standard adopted by IECEE, and it proves that the sample(s) comply with the
Item standards. Products that have obtained the CB test certificate can easily enter the market of other countries (regions) with the same standard system, and can also be easily converted into the safety certification of these countries.
There are more than 30 member states of the CB system, most of the industrial countries in North America and Europe are its member states, and China is also one of its members. The 617 and 618 series products of Suzhou Liteoweisi Fuse Co., Ltd. are the only fuse products in China that have obtained the CB test certificate.
In order to facilitate inquiries and reading, I have sorted out some of the main standards related to fuses as follows:
The main standards of electronic fuses:
International Electrotechnical Commission Standard
IEC 127 general rules for miniature fuses
IEC 127-1 Part 1: Definition and general requirements for miniature fuses
IEC 127-2 Part 2: Tubular Fuse Link
IEC 127-3 Part 3: Subminiature Fuse Link
IEC 127-4 Part 4: General Modular Fuse Links (Technical Trend Document)
IEC 127-5 Part 5: Guidelines for the quality assessment of small fuse-links
IEC 127-6 Part 6: Fuse Box
IEC 127-7 Part 7: (leave blank for future documents)
IEC 127-8 Part 8: (leave blank for future documents)
IEC 127-9 Part Nine: Test Block and Test Circuit
IEC 127-10 Part 10: User Guide
The standards of most European countries are based on IEC 127.
Underwriters Laboratories Standards:
UL-198G various miscellaneous fuses-equivalent to IEC 127-2
(UL 248-1) Miniature fuse ---- equivalent to a part of IEC 127-3
Ultra-miniature fuse-equivalent to a part of IEC 127-3
And part of IEC 127-4
The performance of Class A fuses in North American countries such as the United States, Canada and Japan have adopted
Requirements of UL standards.
Other advanced standards

DIN 41567, etc.: Fuse for instrument
BSI 1362: General fuse for household and similar purposes ......
my country's current standards
GB 9364 miniature fuse (equivalent to IEC127)
GB 9364. 1 Part One Definition of Small Fuses and General Requirements for Small Fuses
GB 9364. 2 Part II Tubular fuse-link
GB 9364. 3 Part III Ultra-small fuse-links
GB 9364. 4 Part IV General-purpose modular fuses
GB 9364. 6 Part VI Fuse holders for tubular fuse-links
Notice:
There are two types of fuse certification by UL certification body:
UL----Using the UL standard text to test and confirm the fuse,
UR----Using non-UL standard text to test the fuse
The IEC does not directly certify the fuse, but each participating country conducts its own certification
The fuse that has obtained the CB test certificate can be converted into the safety certification of its member country!
IEC and UL standard fuses cannot be used interchangeably!
It is impossible for IEC and UL standard fuses to obtain IEC and UL certification at the same time!
The main standard of strong current fuse
International Electrotechnical Commission Standard
IEC 269 low voltage fuse
IEC 269-1 Part One General Requirements for Low-Voltage Fuses
IEC 269-2 Part II Supplementary requirements for fuses used by designated personnel
IEC 269-3 Part 3 Supplementary requirements for fuses used by unskilled personnel
IEC 269-4 Part 4 Partial charging requirements for fuses used to protect semiconductor devices
IEC 282 high voltage fuse
IEC 282-1 Part 1 Current-limiting fuses
IEC 282-2 Part 2 Jet and similar fuses
The third part of IEC 282-3 is to test the current-limiting fuse, the determination of the short-circuit power factor of jet fuse
IEC 291 fuse definition
IEC 549 high voltage fuse for external protection of parallel power capacitors
IEC 644 Specification for High Voltage Fuses Used in Motor Circuits
Guidelines for Selection of High Voltage Fuse Links for IEC 787 High Voltage Circuits
Underwriters Laboratories Standards:
UL 248 low voltage fuse
UL 248-1 Part One General Requirements
UL 248-2 Part II Class C Fuse
UL 248-3 Part III Class CA and CB Fuses
UL 248-4 Part 4 Class CC Fuse
UL 248-5 Part 5 Class G Fuse
UL 248-6 Part VI Class H Fuse Non-recoverable
UL 248-7 Part 7 Class H Fuse Recoverable
UL 248-8 Part VIII Class J Fuse
UL 248-9 Part 9 Class K Fuse
UL 248-10 Part 10 Class L Fuse
UL 248-11 Part 11 Plug-in fuses
UL 248-12 Part 12 Class R Fuse
UL 248-13 Part 13 Semiconductor Fuses
UL 248-14 Part 14 Supplementary Fuse
UL 248-15 Part 15 Class T Fuse
UL 248-16 Part 16 Test Limits
UL 198B-Class H fuse
UL 198C----High breaking capacity, current-limiting fuse
UL 198D-Class K fuse
UL 198E-Class R fuse
UL 198F----Plug-in fuse
UL 198H-Class T fuse
UL 198L----Industrial DC Fuses
UL 198M----Mining Fuse
Other advanced standards
DIN VDE 0636 low voltage fuse
DIN VDE 0820 instrument fuse
BS 88 tubular fuse (low voltage)
BS 2692 high voltage fuse
BS 5907 high voltage fuse for motor circuit
my country's current standards
GB 13539 low voltage fuse (equivalent to IEC269)
GB 13539. 1 Part 1 Basic requirements for low-voltage fuses
GB 13539. 4 Part 4 Supplementary requirements for fuses for the protection of semiconductor devices
GB/T 9815 Household and similar fuses (equivalent to IEC241)