Calculation method for selecting fuse current size

In electrical equipment and circuit design, fuses are an important overcurrent protection component that can effectively prevent circuit damage due to overload or short circuit. Correctly selecting the current size of the fuse is the key to ensuring the safe operation of the equipment and extending its service life. This article will introduce in detail the selection and calculation method of fuse current size to help engineers and technicians determine fuse parameters scientifically and reasonably.

The first step in selecting the current size of a fuse is to determine the current rating of the circuit. Rated current refers to the maximum current value of the circuit under normal operating conditions. Usually obtained based on the nameplate parameters or design requirements of the equipment. Accurate rated current data is the basis for fuse selection to ensure that the fuse will not accidentally open during normal operation.

Some motors or electrical equipment will have a starting current or inrush current that is much higher than the rated current at the moment of starting. This factor must be considered when selecting a fuse to avoid frequent fuse blowing due to excessive starting current. Generally, the rated current of the fuse can be selected to be 1.5 to 2 times the starting current. The specific ratio needs to be determined based on the characteristics of the equipment.

In order to ensure that the fuse does not blow under normal operating conditions, the rated current is usually multiplied by a safety factor. Commonly used safety factors range from 1.25 to 1.5. That is, the rated current of the fuse = rated current × safety factor. This coefficient can effectively prevent malfunctions caused by short-term current fluctuations.

The maximum allowable current is the maximum continuous current that the fuse can withstand. When selecting a fuse, ensure that its rated current is greater than or equal to the maximum allowable current of the circuit. If the fuse current is too small, it will easily blow; if it is too large, the protection will fail.

Ambient temperature has a great impact on fuse performance. High temperature environment will reduce the rated current capacity of the fuse, causing the fuse to blow prematurely. Therefore, when selecting the fuse current size, the rated current should be adjusted according to the actual ambient temperature, and if necessary, refer to the temperature correction curve provided by the manufacturer.

Different types of fuses (fast-acting, time-delay, etc.) respond to current at different speeds. The fast type is suitable for protecting sensitive components, and the delay type is suitable for motor starting and other circuits with large starting current. Selecting the appropriate type of fuse based on circuit characteristics and protection needs will help control the protection current more accurately.

The selection of fuses should comply with relevant national or industry standards, such as GB, IEC and other specifications. These standards have clear requirements for the rated current and fusing characteristics of fuses. Complying with standards not only ensures safety, but also facilitates later maintenance and replacement.

After theoretical calculation and selection, it is best to verify the protective effect of the fuse through actual testing. The test includes simulating working conditions such as short circuit and overload, and observing whether the fuse can be blown in time and protect the circuit. Through verification, the fuse parameters can be further optimized to ensure safety and reliability.

The selection and calculation method of fuse current size covers many aspects such as circuit rated current confirmation, starting current consideration, safety factor application, ambient temperature adjustment and type selection. Scientifically and reasonably determining the rated current of the fuse can not only effectively protect the safety of circuits and equipment, but also avoid unnecessary shutdowns and losses. During the design and maintenance process, engineers should combine the actual working conditions and standard specifications and comprehensively use the above methods to ensure that the fuse plays the best protective role.