Introduction to the parameters and terminology of current fuses

1. Rated current:

Also known as the nominal working current of the fuse, the code is In. The rated current of the fuse is determined by the manufacturing department under laboratory conditions. The rated current values ​​are usually 100mA, 200mA, 315mA, 400mA, 500mA, 630mA, 800mA, 1A, 1.6A, 2A, 2.5A, 3.15A, 4A, 5A, 6.3A, etc., but our company generally provides the rated current values ​​of various fuses according to customer needs and actual uses.

2. Rated voltage:

The nominal working voltage of the fuse, the code is Un. The standard voltage rating of general fuses is 32V, 60V, 125V, 250V, 300V, 500V, 600V. Fuses can be used at voltages not greater than their rated voltages, but they are generally not allowed to be used in circuits where the circuit voltage is greater than the rated voltage of the fuse.

3. Voltage drop:

The voltage across the fuse measured when the rated current is passed and the fuse reaches thermal equilibrium, that is, the temperature stabilizes. The code is Ud. Since the voltage drop across the fuse will have a certain impact on the circuit, there are clear regulations on voltage drop in the European regulations.

4. Fuse resistance:

It is usually divided into cold resistance and hot resistance. The cold resistance is the resistance value measured by the test current less than 10% of the rated current under the condition of 25°C. The hot resistance is converted from the voltage drop measured by the test current with the full rated current value. The calculation formula is Rhot=Ud/In. Usually, the hot resistance is larger than the cold resistance. The fuse resistance value provided by our company is the cold resistance value and is only for reference.

5. Overload current:

Overload current refers to the current flowing through the circuit that is higher than the normal working current. If the overload current cannot be cut off in time, it may cause damage to other equipment in the circuit. Short-circuit current refers to the current generated by a partial or complete short circuit in the circuit. The short-circuit current is usually large and larger than the overload current.

6. Fusing characteristics:

that is, time/current characteristics (also called ampere-second characteristics). There are usually two ways of expression, namely IT diagram and test report. The IT diagram is a curve formed by connecting the average fusing time coordinate points of the fuse under different current loads in a coordinate system consisting of load current as x coordinate and fusing time as y coordinate. Each type and specification of fuse has a corresponding curve to represent its fusing characteristics. This curve can be used as a reference when selecting a fuse. The test report is a record of test data of the test items tested in accordance with the standard requirements. Our IT diagram and test report are based on the data measured under experimental conditions. Under actual use conditions, the curve diagram or test report will be different, so the test report and IT diagram provided by our company are only for reference.

7. Breaking capacity:

also known as rated short-circuit capacity, that is, the maximum current value (AC is the effective value) that the fuse can safely break under rated voltage. It is an important safety indicator of the fuse. The code for breaking capacity is Ir.

8. Melting heat value:

the energy value required for the fuse to melt, its code is It, read as A2Sec. It is the product of the square of the current corresponding to the fuse when it is disconnected in 8ms or less and the melting time. The time is limited to within 8ms so that all the heat generated by the fuse is used for melting and there is no time for heat dissipation. It is a constant for each different fuse component. It is a parameter of the fuse itself and is determined by the design of the fuse.

9. Temperature rise:

Temperature rise refers to the difference between the temperature value when the fuse reaches a stable state under the condition of passing the specified current value (100%In in UL and 115%In in Japanese regulations) and the temperature before power is turned on.