December 05, 2023

It takes three minutes to learn how to evaluate current resistance of wires, which is very easy to use!

ForewordHi everyone, I'm Mr. Lin, and today I will take you three minutes to learn how to evaluate withstand current of a power line. Don't waste time, let's start directly. Text

It takes three minutes to learn how to evaluate current resistance of wires, which is very easy to use!

Operating temperature 30℃, long-time continuous load capacity 90%

1.5 square millimeters - 14A 

2.5 square millimeters——26A  

4 square millimeters——32A  

6 square millimeters - 47A   

16 square millimeters — — 92A  

25 square millimeters - 120 A  

30 square millimeters - 150 A

It takes three minutes to learn how to evaluate current resistance of wires, which is very easy to use!

Current Conversion Power

1 A \u003d 220 W, 10 A \u003d 2 200 W, etc. If bandwidth of copper wire is 14A, that is: 220W × 14 \u003d 3080W, then power of copper wire with a cross section of 1.5 square meters is 3, 08 kW.

Copper core wire provides continuous current

2.5 square millimeters (16-25A)

4 square millimeters (25A~32A)

6 square millimeters (32A~40A)

Aluminum core wire carries current for a long time

2.5 square millimeters (13-20A)

4 square millimeters (20-25A)

6 square millimeters (25A~32A)

It takes three minutes to learn how to evaluate current resistance of wires, which is very easy to use!

Give an example

1. The power consumption of each computer is about 200-300W (about 1-1.5A), so a 2.5 square millimeter copper wire is required to power 10 computers, otherwise a fire may occur.

2. Power consumption of a large 3 HP air conditioner is about 3000 W (about 14 A), so a separate wire with a copper core of 2.5 square millimeters is required to power one air conditioner.

3.Incoming house wires are mainly 4 square millimeter copper wires. Therefore, household appliances turned on should not exceed 25A (that is, 5500 W). Some people replace house wires with 6 square millimeter copper wires .Useless because wires going into meter are 4mm².

4. In early housing (15 years ago), incoming wires were generally 2.5 square millimeters of aluminum wires, so household appliances turned on should not exceed 13A (that is, 2800 W).

International allowable long-term current

4 squares - 25~32A

6 squares - 32-40 A

These are theoretical safety values ​​and limits should be higher than these values.

The maximum power allowed for copper wires with a cross section of 2.5 sq. – 5,500, 4 sq. – 8,000 W, 6 sq. - 9,000 watts, no problem. There are no problems with a conventional 9000W digital meter at 40A, and a mechanical 12000W will not burn out.

Cable load capacity Standard load capacity of copper core cable and cable:

Rating formula:

Multiply 2.5 by 9, then subtract 1 from up direction.

Thirty-five times three point five, minus five points in pairs. Change of conditions plus refurbishment, high temperature 10% discount on copper refurbishment. The number of passing pipes is two, three or four, and full load current is between 87 and 60 percent.

The formula in this section does not directly indicate current carrying capacity (safe current) of various insulated wires (rubber and plastic insulated wires), but expresses it by "multiplying section by a certain multiple", which is obtained by mental calculation.

"Multiply by 2.5, multiply by nine, minus one and increase" refers to aluminum-core insulated wires with various cross-sections of 2.5 mm² or less, and their current carrying capacity is about 9 times number of cross-sections. sections. For example, 2.5mm² wire, load capacity is 2.5×9=22.5(A).

The ratio between current and multiple of a wire with a cross section of 4 mm² and above is located according to wire number, and multiple is successively reduced by l, that is, 4×8, 6×7, 10×6, 16×5, 25×4. “Thirty-five times 3.5, minus 5 points in pairs” means that throughput of a wire with a cross section of 35 mm² is 3.5 times number of segments, that is, 35×3.5=122.5(A).

For wires of 50 mm² and above, multiple of ratio between allowable load and number of cross sections becomes a group of two wire numbers, and multiples are successively reduced by 0.5.

That is, current strength of 50 and 70 mm wires is three times cross-sectional area, current strength of 95 and 120 mm² wires is 2.5 times cross-sectional area, and so on.

Changing conditions plus transformation, high temperature 10% copper upgrade." The above formula is based on condition of insulated aluminum core wire and exposed gasket at an ambient temperature of 25°C. If aluminum core insulated wire is exposed to high ambient temperature for a long time around 25℃, current carrying capacity of wire can be calculated from above formula, and then a 10% discount is sufficient; when copper core insulated aluminum wire is used instead, its current carrying capacity is slightly greater than that of aluminum wire of same specification. 16 mm² copper wire can be calculated as 25 mm² aluminum wire.

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