Whether in daily life or in industrial settings, accidents such as fires and electric shocks caused by cable overload and insulation failure are frequent. Therefore, in the electrical control systems of machinery, the correct selection of wires and cables is undoubtedly a crucial link in ensuring the safe use of mechanical equipment. In this issue, we will elaborate on the general requirements for the selection of wires and cables given in GB/T5226.1 : 2019 standard, as well as the specific requirements for flexible cables, busbars, and busbar systems.
General requirements
The selection of conductors and cables should be suitable for the working conditions (such as rated voltage, current, cable grouping, etc.) and possible external environmental influences (such as ambient temperature, presence of water and possible mechanical stress).
Generally, the conductor should be made of copper, and its cross-sectional area should not be less than the value specified in the table below:
The current-carrying capacity during normal operation depends on several factors, including the insulation material, the number of conductors in the cable, and the installation method. Typical examples of current-carrying capacity applicable to PVC-insulated circuits under steady-state conditions can be found in the table below:
Under normal operating conditions, the voltage drop of any power circuit cable from the power source to the load should not exceed 5% of the rated voltage . To meet this requirement, it may be necessary to use conductors with a cross-sectional area larger than that specified in the table above.
Specific requirements for flexible cables
If the cable is dragged across a rough surface during mechanical movement, it may be scratched, or it may be damaged due to winding or rewinding by the guide wheels. To mitigate such hazards, the cable transport system should be designed to minimize stress, meaning that the tensile stress on the conductors should be minimized during mechanical operation.
When using copper wire, the tensile stress of the copper conductor should not exceed 15 N/mm² . When the tensile stress exceeds 15 N/mm² , a cable with special structural characteristics should be selected.
If the cable is wound on a cable reel, the cross-sectional area of its conductor should be taken into account, and the maximum current-carrying capacity in air should be deducted according to the following table:
Specific requirements for busbars, busways and bus loops
If busbars, busbars, and bus rings are used, measures should be taken to provide them with basic protection, including insulation protection for live parts and enclosure protection or shielding that meets at least IP2X or IPXXB standards. Busbars, busbars, and bus rings used to protect lines should not carry current during normal operation, and the protective conductor ( PE ) and neutral conductor ( N ) should each use separate busbars, busbars, and bus rings.
Busbars, busbars, and bus rings used in power circuits should be able to withstand mechanical forces and the thermal effects of short-circuit currents.
