1: The mantra in this section does not directly indicate the current carrying current (safety current) of various insulating wires (rubber and plastic insulated wires), but is expressed as "cross-section multiplied by a certain multiple", which is obtained through mental arithmetic. It can be seen from Table 5 3 that the multiple decreases with the increase of the cross-section.
Second: "2.5 times nine, minus one order up" refers to aluminum core insulation wires of various sections of 2.5mm' and below, and its current carrying capacity is about 9 times the number of sections. For example, 2.5mm' wire, the current carrying capacity is 2．5×9＝22．5(A)。 The multiple relationship between the ampacity carrying capacity and the number of cross-sections of wires from 4mm' and above is arranged upwards along the wire number, and the multiples are subtracted by l, that is, 4×8, 6×7, 10×6, 16×5, 25×4。 "Thirty-five times three points, double group minus five", it is said that the current carrying capacity of the wire of "35mm" is 3.5 times the number of cross-sections, that is, 35×3.5 = 122.5 (A). From 50mm' and to The multiple relationship between the current carrying capacity and the number of cross-sections becomes two two wire numbers in a group, and the multiples are subtracted by 0.5 in turn. That is, the ampacity carrying capacity of 50 and 70 mm' wires is 3 times the number of cross-sections; 95. The ampacity carrying capacity of the 120mm" wire is 2.5 times its cross-sectional area, and so on.
Three: "Conditions change and conversion, high temperature 90% copper upgrade". The above mantra is determined by the aluminum core insulation wire and the application under the condition of ambient temperature of 25 °C. If the aluminum core insulation wire is laid on a place where the ambient temperature is higher than 25°C for a long time The ampacity of the wire can be calculated according to the above formula calculation method, and then it can be discounted by 90%; When using not aluminum wire but copper core insulation wire, its ampacity is slightly larger than that of aluminum wire of the same specification, which can be calculated according to the above mantra The ampacity of one wire number is increased than that of aluminum wire. For example, the ampacity of 16mm' copper wire can be calculated as 25mm2 aluminum wire.