This formula is "ten times five hundred up to two, two times five hundred up to three, seven times five and a half times seven hundred and ninety-five, the threading temperature is 10% off, the copper wire is upgraded, and the bare wire is half".
The specific meaning of the whole article is: 10 down to 5 refers to the wiring of current 5A per square meter below 10, and 100 up to 2 refers to the wiring of current 2A per square meter and 253543 boundaries above 100, and refers to the wiring of 3~4A per square meter of 25 and 35 square meters. The current carrying capacity of the section between 70 and 95 is 2.5 times of the number of sections (for example, 2.5a * 70 = 175a). According to the cross-section arrangement order, the cross-section of copper conductor is increased by one level, and then it is calculated according to the corresponding aluminum wire conditions (for example, 35 square millimeter copper wire at 25℃. Upgrade to 50 mm2, and press 50 mm2 for aluminum wire, which is 225 A at 25℃). That is, add half (multiplied by 1.5) after calculating the current as above. This means that the current-carrying capacity of aluminum core insulated conductor with the same cross section can be increased by half compared with that of aluminum wire (for example, 16 square millimeter aluminum wire, 96 A).
To be clear, this formula is based on the bare condition of aluminum core insulated conductor at ambient temperature of 25℃. This is an electrician's quick calculation skill, which is suitable for the majority of electrician teachers to learn and apply, and can also be used as a reference for electrician technicians and related professional teaching staff.