# What is the calculation method for cable size?

How to calculate the cable size (mm²)?

The wire size is a standard value specified by the standard. The wire size is actually the cross-sectional area of the wire, that is, the area of the circular cross-section of the wire, in units of mm². It is the user who selects the wire and cable according to the load of the wire and cable.

There are three standards commonly used internationally for wire sizes and dimensions: American (AWG), Imperial (SWG) China (CWG), and Imperial (SWG).

## How do you see the size of the wire and cable?

### What does size mean?

The size is a nominal value specified by international standards, and the size is the user selects the wire and cable according to the load of the wire and cable.

Cable size is a verbal term in construction. It is often said that the cable is mm, but actually refers to mm².

The wire size is actually the cross-sectional area of ​​the wire, which is the area of ​​the circular cross-section of the wire, in mm².

### 4 ways to get the cable size

#### The label on the package

The whole bundle of new lines, the label on the surface of the package will be wired, clearly mark the brand, model and size of the line (the square of the wire).

#### Printing on the cable

The wires of the big brand are printed with the brand, model and size (square of the wire) on the insulation layer. SanHeng Cable Co., Ltd. has brands, models and sizes (squares of wires).

#### Visual inspection

For unmarked wires, experienced electricians can visually check the size of the wires. However, it is generally more difficult and requires a certain degree of professionalism.

#### Measure the diameter and calculate the size

If you want to measure the size (square) of the wire, measure the diameter of the wire with a vernier caliper or a micrometer, and then find the section.

To determine the size (square) of the wire, use a vernier to measure the diameter of the wire and then find the section

The calculation formula for the section:

S=R²×π (R is the radius of the wire)

The wire with a diameter of 1.76 is 1.76 ÷ 2 × 3.14 = 2.76 square ≈ 2.5 square, (approximate value).

If you want to choose the size of the cable, generally calculate the current according to the power of the electrical appliance, and then according to the current in the electrician manual, this is more accurate.

If it is a single-core, you can measure its diameter and then get the radius.
Formula according to area S = radius * radius * 3.14

It is possible to know the cross-sectional area of ​​the cable, and some cables are twisted together by a plurality of cable cores so that it cannot be calculated by a single-core method, and only a plurality of cables in the cable can be used. One can count the single-core cable, and then multiply the number of strands of the cable.

The formula is S = radius * radius * 3.14 * N, where N is the number of twisted cables!

## Wire and cable size calculation method

Generally speaking, the empirical load is when the grid voltage is 220V, and the empirical load per square wire is about one kilowatt.

Each square of copper wire can carry 1-1.5KW, and the aluminum wire can carry 0.6-1KW per square. Therefore, it is sufficient to use only one square copper wire for an electric appliance with a power of 1 KW.

Specific to the current, when the short-distance power transmission, the general copper wire can carry 3A to 5A per square. The heat dissipation condition is good to take 5A/mm², and it is not good to take 3A/mm².

### Conversion method:

Knowing the square of the wire, calculating the radius of the wire is calculated using the formula for the area of ​​the circle:

mm²=π×R²

### The square of the wire, calculate the wire diameter

The same is true, such as:
The wire diameter of the 2.5 square wire is 2.5 ÷ 3.14 = 0.8, and the square root is 0.9 mm, so the wire diameter of the 2.5 square wire is 2 × 0.9 mm = 1.8 mm.

Knowing the diameter of the wire, calculating the square of the wire is also calculated using the formula for the area of ​​the circle:

Square of wire = π (3.14) × square of wire diameter / 4
The cable size is also nominally squared, and the multiple strands are the sum of the cross-sectional areas of each conductor.

### The calculation formula for cable cross-sectional area:

0.7854 × cable diameter (mm)² × number of shares

For example, 48 strands (wire diameter 0.2 mm per strand) 1.5 square line:
0.7854 × (0.2 × 0.2) × 48 = 1.5²

### Conversion relationship between wire size and current

• The safe current carrying capacity of the 2.5mm² copper power cord –28A.
• The safe current carrying capacity of the 4mm² copper power cord — 35A.
• The safe current carrying capacity of the 6mm² copper power cord –48A.
• The safe current carrying capacity of the 10mm² copper power cord — 65A.
• The safe current carrying capacity of the 16mm² copper power cord — 91A.
• The safe current carrying capacity of the 25mm² copper power cord — 120A.

If it is aluminum wire, the wire diameter should be 1.5-2 times that of the copper wire.
If the copper current is less than 28A, it is 10A per square millimeter.
If the copper current is greater than 120A, it is 5A per square millimeter.

### Cable diameter and current calculation method

How much current can be used for a 1mm² power cord? How much power does it have?

For example, how many wires are used in the construction of 2.5mm² wires?

1. For 1.5mm², 2.5 mm², 4 mm², 6 mm², 10 mm² wires, the number of cross-sectional areas can be multiplied by 5 times.
2. For a 16 mm², 25 mm² wire, multiply the cross-sectional area by a factor of four.
3. For 35 mm², 50 mm² wire, multiply the cross-sectional area by 3 times.
4. For a 70 mm², 95 mm² wire, the cross-sectional area can be multiplied by 2.5 times.
5. For 120 mm², 150 mm², 185 mm² wires, the number of cross-sectional areas can be multiplied by 2 times.

The voltage drop of the copper core wire is related to its resistance, and its resistance calculation formula:
20 ° C: 17.5 ÷ cross-sectional area (square mm) = resistance per kilometer (Ω)
At 75 ° C: 21.7 ÷ cross-sectional area (square mm) = resistance per kilometer (Ω)
Its pressure drop calculation formula (according to Ohm’s law): V = R × A
Line loss is related to the voltage drop and currently used.
Its line loss calculation formula: P=V×A
P-line loss power (watts) V-pressure drop value (volts) A-line current (amperes)

### Copper core power line current calculation method

• The safe current carrying capacity of the 1mm² copper power cord – -17A.
• The safe current carrying capacity of the 1.5 mm² copper power cord – 21A.
• The safe current carrying capacity of the 2.5 mm² copper power cord –28A.
• Safe Current Carrying Capacity of 4 mm² Copper Power Cord–35A
• Safe Current Carrying Capacity of 6 mm² Copper Power Cord–48A
• The safe current carrying capacity of the 10 mm² copper power cord – 65A.
• Safe Current Carrying Capacity of 16 mm² Copper Power Cord–91A
• Safe Current Carrying Capacity of 25 mm² Copper Power Cord–120A

The single-phase load is 4.5A per kilowatt (COS&=1), and the current is calculated and the conductor is selected.

### Current comparison method between the copper core wire and aluminum core wire

• 2.5mm² copper core wire is equal to 4mm² aluminum core wire
• 4mm² copper core wire is equal to 6mm² aluminum core wire
• 6mm² copper core wire is equal to 10mm² aluminum core wire

lower than 10mm: ×5
2.5 mm² copper core cable = (4 mm² aluminum core cable × 5) 20A = 4400KW;
4 mm² copper core cable=(6 mm² aluminum core cable×5)30A=6600KW;
6 mm² copper core cable = (10 mm² aluminum core cable × 5 ) 50A = 11000KW;

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