1： The pithy formula in this section does not directly point out the current carrying capacity (safety current) of various insulated wires (rubber and plastic insulated wires), but is expressed by "multiplying the section by a certain multiple", which is obtained by mental calculation. It can be seen from Table 53 that the multiple decreases with the increase of the section.

2： "Two point five times nine, minus one from the top" refers to aluminum core insulated wires with various sections of 2.5mm 'and below, and their current carrying capacity is about 9 times of the number of sections. If 2.5mm 'conductor, the current carrying capacity is 2.5 × 9＝22．5(A)。 The multiple relationship between the current carrying capacity and the number of cross sections of conductors 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。 The current carrying capacity of 35mm conductor is 3.5 times the number of sections, i.e. 35 × 3．5＝122．5(A)。 From the multiple relationship between the current carrying capacity and the number of cross sections of the conductor of 50mm 'and above, it changes to two wire numbers in a group, and the multiple is reduced by 0.5 in turn. That is, the current carrying capacity of 50 and 70 mm 'conductor is 3 times of the number of sections; The current carrying capacity of 95 and 120 mm conductor is 2.5 times of its sectional area, and so on.

3： "Conditions are subject to change and conversion, and high-temperature copper is upgraded at a discount of 10%". The above pithy formula is determined by the aluminum core insulated wire and exposed laying at the ambient temperature of 25 ℃. If the aluminum core insulated wire is laid in an 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 it can be discounted by 10%; When copper core insulated wire is used instead of aluminum wire, its current carrying capacity is slightly larger than that of aluminum wire of the same specification. The current carrying capacity of one wire larger than that of aluminum wire can be calculated according to the above formula method. For example, the current carrying capacity of 16mm 'copper wire can be calculated as 25mm2 aluminum wire.