Calculation method of current carrying capacity of electric wires and cables

(1) Estimation formula:  Multiply two point five by nine, and go up minus one in order.  Thirty five times three point five, double pairs minus five.  The conditions are changed and converted, and the high temperature copper is upgraded with a 90% discount.  The number of pipes threaded is 234, and 876% is full flow.  Note: The pithy formula in this section does not directly indicate the current carrying capacity (safety current) of various insulated wires (rubber and plastic insulated wires), but rather represents it by multiplying the cross section by a certain multiple, which is obtained through mental calculation. As can be seen from Table 53, the multiple decreases with the increase of the cross section.  (2) Multiply it by nine at 2:5 and go up minus one in order.  "Multiplying two point five by nine and going up by subtracting one sequential number" refers to various cross-section aluminum core insulated wires of 2.5mm 'and below, with a current carrying capacity of about 9 times the number of cross sections. For example, a 2.5mm 'conductor has a current carrying capacity of 2.5 × 9=22．5(A）。 The multiple relationship between the current carrying capacity and the number of cross sections of conductors from 4mm 'and above is arranged upward along the wire number, and the multiple is gradually reduced by 1, that is, 4 × 8、6 × 7、10 × 6、16 × 5、25 × 4.  (3) Thirty five times three point five, double pairs minus five.  "Thirty five times three point five, double pairs subtract point five," which means 35 mm. The current carrying capacity of a conductor is 3.5 times the number of cross sections, that is, 35 × 3．5=122．5(A）。 From the multiple relationship between the current carrying capacity and the number of cross sections of conductors with a diameter of 50mm 'and above to a group of two wire numbers, the multiple is reduced by 0.5 in turn.  That is, the current carrying capacity of 50 and 70mm 'conductors is 3 times the number of cross sections; The current carrying capacity of "95, 120mm" conductors is 2.5 times its cross-sectional area, and so on.  (4) The conditions are changed and converted, and the high temperature copper is upgraded with a 90% discount.  "Conditions are subject to change and conversion, and high-temperature copper is upgraded with a 10% discount.". The above formula is based on aluminum core insulated wire exposed to an ambient temperature of 25 ℃.  If the aluminum core insulated wire is exposed to an area where the ambient temperature is above 25 ℃ for a long time, the current carrying capacity of the wire can be calculated according to the above formula calculation method, and then a 10% discount can be given; When using copper core insulated wire instead of aluminum wire, its current carrying capacity is slightly larger than that of aluminum wire of the same specification. The above formula can be used to calculate the current carrying capacity by one wire number larger than that of aluminum wire. For example, the current carrying capacity of 16mm 'copper wire can be calculated as 25mm2 aluminum wire.  (5) The number of pipes threaded is 234, and 876% is full flow.  "When two, three, or four wires are laid through the pipe, the current carrying capacity is 80%, 70%, and 60% of the calculated current carrying capacity of the electrician (laying a single wire).".