Talking about the current carrying capacity standard of copper core wire and cable

    After the reform and opening up, the economy has developed rapidly, public utilities and housing construction have developed rapidly, and household electrical equipment and other electrical equipment have been increasing day by day. However, it cannot be ignored that in the fires that occur every year, electrical fires are also on the rise. In just a few years, the proportion of electrical fires has more than doubled, and a considerable part of it is caused by faults such as damage to the insulation of cables and wires, overheating and spontaneous combustion, poor contact, single-phase grounding of cables, and short-circuits between phases.

Derivatives/new products of wire and cable are mainly due to different application occasions, different application requirements, convenience of equipment and requirements for reducing equipment costs, etc., and the use of new materials, special materials, or changing product structures, or improving process requirements, or different Varieties of products are combined. Use different materials such as flame-retardant cables, low-smoke zero-halogen/low-smoke and low-halogen cables, anti-termite, anti-mouse cables, oil/cold/temperature resistant cables, etc.; change product structure such as fire-resistant cables, etc.; improve technology Requirements such as: medical cables, etc.; combined products such as: OPGW, etc.; convenient installation and reducing equipment costs, such as: prefabricated branch cables.

The Standardization Technical Committee of Building Electrical Installations, together with the International Copper Association, has now drafted the IEC 60364-5-523 standard related to the current carrying capacity of copper core cables and wires to provide references for design, production, construction and installation, quality inspection, operation and management. . The International Electrotechnical Commission began to revise the 1983 ampacity standard in 1995 and has now entered the final approval stage. After a detailed comparison of the two, the readers will be informed of the following situations and changes:

　　 1. The applicable voltage range is changed to AC 1KV and DC 1.5KV.

　　2. The current carrying capacity of cables with copper core 1.0mm2 and aluminum core 1.0mm2, 1.5mm2 has been deleted.

　　3. There is basically no change in current-carrying capacity, and individual changes do not exceed 7%.

　　 4. The types of cables and wires and the temperature rise limit have not changed.

　　 5. Added the correction coefficient when the soil thermal resistivity is not 2.5K.m/W.

　　 6. The part of the cable and wire laying method in the table that was originally described in words is changed to the diagram.

　　7. Cancel the current-carrying capacity data of non-perforated trays in Table 52-E4 and E5.

　　 8. The following amendments were made to Article 523.5:

  (1). When only three-phase conductors have load current and are balanced, 4-core and 5-core cables can have a larger current carrying capacity;

  (2). When the three-phase load is unbalanced, the temperature rise caused by the neutral line current will be offset by the heat generated by the line current reduction. In this case, the conductor cross-section should be selected according to the maximum phase wire current;

　　 (3). When the neutral line has a load current and the phase line current is not reduced accordingly, the neutral line harmonic current is greater than 10%, and the neutral line section should not be less than the phase line section. See Appendix C for larger harmonic current correction coefficients.