The mnemonic for current carrying capacity of wires: how to calculate the size of wires to be used in engineering construction

For wires of 1.5, 2.5, 4, 6, and 10mm2, their cross-sectional area can be multiplied by 5 times.

For wires of 16 and 25mm2, their cross-sectional area can be multiplied by 4 times.

For wires of 35 and 50mm2, their cross-sectional area can be multiplied by three times.

For wires of 70 and 95mm2, their cross-sectional area can be multiplied by 2.5 times.

For wires of 120, 150, and 185mm2, their cross-sectional area can be multiplied by 2 times

The operating temperature is 30 ℃, and the current carrying capacity under long-term continuous 90% load is as follows:

1.5 square millimeters -18A

2.5 square millimeters -26A)

4 square millimeters -26A*

6 square millimeters -47A3

10 square millimeters -66A

16 square millimeters -92A

25 square millimeters -120A

Square millimeter -150A

Power P=Voltage U × Current I=220V × 18A=3960W

Load current values for wires specified in GB4706.1-1992/1998 (partial)

Copper core wire: Copper core wire cross-sectional area Allow long-term current 2.5 square millimeters (16A~25A)

4 square millimeters (25A~32A). 6 square millimeters (32A~40A)

Aluminum core wire: cross-sectional area of aluminum core wire Allow long-term current 2.5 square millimeters (13A-20A)

4 square millimeters (20A~25A). 6 square millimeters (25A~32A)

[Example] 1. Each computer consumes about 200-300W (about 1-1.5A) of electricity, so 10 computers need a 2.5mm ² copper core wire to supply power, otherwise a fire may occur.

2. The power consumption of a 3-horsepower air conditioner is about 3000W (about 14A), so one air conditioner requires a separate 2.5mm square copper core wire for power supply.

3. The current housing inlet wire is generally a 4 square millimeter copper wire, therefore, household appliances that are turned on at the same time must not exceed 25A (5500 watts). It is useless for someone to replace the wires in the house with 6 square millimeter copper wire because the wires entering the electricity meter are 4 square millimeters.

4. In the early days of housing (15 years ago), the incoming line was generally 2.5 square millimeters of aluminum wire, so household appliances that were turned on at the same time should not exceed 13A (2800 watts).

5. The household appliances with relatively high power consumption are: air conditioner 5A (1.2 horsepower), electric water heater 10A, microwave oven 4A, rice cooker 4A, dishwasher 8A, washing machine with drying function 10A, and electric water heater. 90% of fires caused by power supply are due to joint heating, so all joints must be welded. Contactors that cannot be welded must be replaced after 5-10 years (such as sockets, air switches, etc.).

Long term current allowed by national standards

4 square meters is 25-32A

The square is 32-40A

In fact, these are theoretical safety values, and the limit values are even greater than these,

The maximum power allowed for a 2.5 square copper wire is 5500W. 8000W for a 4 square wire and 9000W for a 6 square wire is not a problem

A 40A digital meter with 9000W output is definitely not a problem The mechanical 12000W won't burn out either

Copper core wire and cable current carrying capacity standard cable current carrying capacity port decision:

Estimation mnemonic:

Multiply 2.5 by 9 and subtract one from the top to follow the order.

Thirty five times three and a half, in pairs, subtract five points.

Conditions are subject to change and conversion, with high temperature copper upgraded at a 10% discount.

The number of pipes passing through is 2-34, with a full load flow of 876.

Explanation:

The mnemonic in this section does not directly indicate the current carrying capacity (safe current) of various insulated wires (rubber and plastic insulated wires), but rather represents it by multiplying the cross-section by a certain multiple, obtained through mental calculation. The phrase 'Multiply 2.5 by 9 and subtract one from the top in order' refers to aluminum core insulated wires with various cross-sections of 2.5mm 'and below, whose current carrying capacity is approximately 9 times the number of cross-sections. For a 2.5mm 'wire, 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 wires with a diameter of 4mm 'and above is arranged in ascending order according to the wire number, and the multiple is gradually reduced by l, that is, 4 × 8, 6 × 7, 10 × 6, 16 × 5, and 25 × 4. The current carrying capacity of a 35mm conductor is 3.5 times the number of cross-sections, that is, 35 × 3.5=122.5 (A). The multiple relationship between the current carrying capacity and the number of cross-sections of wires with a diameter of 50mm 'and above is changed to two wire numbers grouped together, and the multiples are sequentially reduced by 0.5. The current carrying capacity of 50 and 70mm 'wires is three times the number of cross-sections; The current carrying capacity of wires 95 and 120mm is 2.5 times their cross-sectional area, and so on. Conditions are subject to change and conversion, with high temperature copper upgraded at a 10% discount. The above mnemonic is determined for aluminum core insulated wire and exposed to an ambient temperature of 25 ℃. If the aluminum core insulated wire is laid openly 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 discounted by 10%; 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 current carrying capacity that is one wire size larger than aluminum wire can be calculated using the above formula. The current carrying capacity of 16mm 'copper wire can be calculated based on 25mm2 aluminum wire.