Everyone has encountered the problem of wire selection in professional audio and lighting engineering. The correct choice will make your construction easier. If you choose the wrong one, then there will be certain troubles. For example, if the cross-sectional area of the wire is selected smaller, the electrical load is likely to cause the consequences of electrical fires; if the cross-sectional area is selected larger, it will cause high costs and waste of materials. Audio.com introduces you the formula for selecting the wire.
"Multiply three and five times by nine, and go up and minus one shun. Thirty-five times three and five, two and two groups minus five. The conditions are changed and the conversion is added, the high temperature is increased by the copper upgrade, and the number of piercing pipes is two or three. Four, eight, seven, and six percent full load current." This formula does not directly point out the various insulation carrying capacity (safe current), but "the cross section is multiplied by a certain multiple to express it, and it is obtained through calculation." That is: the multiple decreases with the increase of the cross section.
Multiply three and five times by nine, and go up minus one. "It means that various cross-sectional area aluminum core insulated wires below 3.5mm2 have a current carrying capacity of about 9 times the number of cross-sections. For example, a 2.5mm2 wire has a current carrying capacity. It is 2.5x9=22.5(A). The multiple relationship of the cross-sectional area of the wire of 4mm2 and above is arranged along the line number, and the multiple is gradually reduced by 1, namely 4×8, 6×7, 10×6, 16×5 , 25×4, 35×3.
"Thirty-five times 3.5, doubles in groups minus five" means that the current carrying capacity of a 35mm2 wire is 3.5 times the cross section, that is, 35×3.5=122.2(A). From the wire above 50mm2, the relationship between the current carrying capacity and the number of faces becomes a group of two wire numbers, and the multiples are successively reduced by 0.5. That is, the current-carrying capacity of a 50～70mm2 wire is 3 times the number of sections; a 95～120mm2 wire’s flow is 2.5 times its cross-sectional area, and so on.
"Conditions are changed and converted, high temperature 10% copper upgrade." It means that if the aluminum core insulation is exposed to the area where the ambient temperature is higher than 25℃ for a long time, the current carrying capacity of the wire can be calculated according to the above formula, and then discounted. If it is a copper core wire, its current-carrying capacity is larger than that of an aluminum core. For example, a 16mm2 copper wire can be calculated as a 25mm2 aluminum wire.