How is the national standard cable calculated?

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This post was last edited by yuchenchf on 2017-5-16 08:37 "National Standard" is* * standards, "national standard cable" means compliance with * * Standard wire and cable. So * * How do standards stipulate wires and cables? 　　Generally, the standard we usually use is the conductor cross-sectional area of ​​wires and cables, for example, 1 square meter cable, 2.5 square meter cable, 4 square meter cable, etc. Commonly used wire and cable types and specifications range from 0.2 and 0.3 square meters to 300 and 400 square meters. After years of use, many people inside and outside the industry now use the cross-street area as a criterion for assessing whether wires and cables are national standard cables. However, wires and cables * * The standard wire and cable testing index is resistance, which is generally the conductor resistance at 20°C (≤Ω/㎞). This resistance value determines the conductive performance of wires and cables, that is, the usage characteristics, and the matching * * The standard provides a reference value for conductor construction. 　　For example, the reference value of BV line 227IEC01 (BV) 450/750V general-purpose single-core hard conductor unsheathed cable BV2.5mm? under this standard GB5023-1997 is: 　　The conductor structure is 1/1.78, and the conductor resistance (≤Ω/㎞) at 20℃ is 7.41. 　　This value means that the reference data of BV2.5 (2.5 square wire) is a single core, a single wire diameter is 1.78mm, and the conductor resistance is ≤7.41Ω/㎞ at 20℃. 　　Through the calculation formula of the circle area (πr?), it can be concluded that the conductor cross-sectional area of ​​BV2.5 is: π * (1.78/2)?=2.488455…≈2.5mm?. In other words, BV2.5 does not necessarily have to reach 2.5 square meters, but when the resistance reaches the standard * * The reference value calculation result provided by the standard is approximately 2.5 square meters. However, it is very troublesome to use resistors to name and calculate wires and cables in daily use. Therefore, they are all agreed on the approximate conductor cross-sectional area in integers, which is what we usually call 1 square meter, 1.5 square meters, 2.5 square meters, etc. 　　The above data standards are just reference values. What we call national standard cables are strictly * * The standard value is the resistance value, and the conductor cross-sectional area is for reference only. When purchasing, you can refer to the cross-sectional area standards of wires and cables, and of course, the resistance value. This is the most basic element to ensure the safety of wires and cables.