# Practical wire and cable square number calculation method and how to determine whether the cable is up to standard.

Published on:

2022-09-29

A few squares is a nominal value specified in the national standard, a few squares is the user to choose the wire and cable according to the load of the wire and cable. Wire square number is a verbal term in the renovation of plumbing construction, often said a few square wire is not added to the unit, that is, square millimeters.

Conversion method:

Knowing the square of the wire, calculate the radius of the wire using the formula for finding the area of the circle:

Square number of wires (square millimeters) = circumference (3.14) × the radius of the wire (mm) square

Knowing the square of the wire, calculate the wire diameter as well, e.g:

2.5 square wire diameter of the wire is: 2.5 ÷ 3.14 = 0.8, and then open the square to get 0.9 mm, so 2.5 square wire diameter of the wire is: 2 × 0.9 mm = 1.8 mm.

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

The square of the wire = circumference of the circle (3.14) × the square of the wire diameter / 4

Cable size is also used square nominal, multi-stranded line is the sum of the cross-sectional area of each wire.

The formula for calculating the cross-sectional area of the cable: 0.7854 × wire diameter (mm) square × number of shares such as 48 (0.2 mm per wire diameter) 1.5 square line: 0.7854 × (0.2 × 0.2) × 48 = 1.5 square

Wire square number and current conversion relationship

The safe current carrying capacity of 2.5 square millimeter copper power cord - 28A.

The safe load capacity of 4 square mm copper power cord - 35A.

Safe load capacity of 6 square mm copper power cord - 48A.

Safe load capacity of 10 square mm copper power cord - 65A.

Safe load capacity of 16 square mm copper power cord - 91A.

25 square millimeters of copper power cord safety load capacity - 120A.

If the aluminum wire, the wire diameter to take 1.5-2 times the copper wire.

If the copper wire current is less than 28A, 10A per square millimeter to take sure safe.

If the copper wire current is greater than 120A, according to 5A per square millimeter to take.

General copper wire capacity wire safety capacity is based on the maximum allowable core temperature, cooling conditions, laying conditions to determine the.

General copper wire safety load capacity of 5 ~ 8A / mm2, aluminum wire safety load capacity of 3 ~ 5A / mm2.

[Key point]

The general safety load capacity of copper conductor is 5~8A/mm2, and the safety load capacity of aluminum conductor is 3~5A/mm2.

Such as:

2.5mm2BVV copper conductor safe load capacity of the recommended value of 2.5 × 8A/mm2 = 20A4mm2BVV

The recommended value of copper conductor safe load capacity 4 × 8A/mm2 = 32A.

Second, calculate the cross-sectional area of the copper conductor using the recommended value of the safe load capacity of copper conductors 5 ~ 8A/mm2.

Calculate the selected cross-sectional area of copper conductors S up and down the range of:

S = [I / (5 ~ 8)] = 0.125I ~ 0.2I (mm2)

S - copper conductor cross-sectional area (mm2)

I - load current (A)

Third, the power calculation general load (can also become appliances, such as lighting, refrigerators, etc.) is divided into two types, a type of resistive load, an inductive load.

For resistive load calculation formula: P = UI

For fluorescent lamp load formula: P=UIcosф, where the power factor of fluorescent lamp load cosф=0.5.

Different inductive loads have different power factors, and the power factor cosф can be taken as 0.8 when calculating household appliances in a uniform way.

That is to say, if a family all appliances plus the total power of 6000 watts, the maximum current is I = P/Ucosф = 6000/220 * 0.8 = 34 (A)

However, in general, the home appliances are not likely to be used at the same time, so a common factor is added, and the common factor is generally 0.5.

So, the above calculation should be rewritten as

I=P*Common factor/Ucosф=6000*0.5/220*0.8=17(A)

In other words, the total current value of this family is 17A. then the main gate air switch can not use 16A, should use greater than 17A.

How to see the square number of electric wire?

A few squares is a nominal value specified by the national standard, a few squares is the user to choose the wire and cable according to the load of the wire and cable. Wire square number is a verbal term in the renovation of plumbing construction, often said a few square wire is not added to the unit, that is, square millimeters.

The square of the wire is actually marked by the cross-sectional area of the wire, that is, the area of the circular cross-section of the wire, in square millimeters.

1, the whole bundle of new wire, the packaging surface will be wired label, clearly marked line brand, model, wire diameter (square number of wires).

2, some large brands of wire in the insulation layer printed with the brand, model, wire diameter (square number of wires).

3, for the unmarked wire, experienced electricians can visually inspect, see the square number of wires.

4, inexperienced people, if you want to determine the thickness of the wire (square), available vernier tape measure the diameter of the wire, and then find the cross-section.

If you want to judge the thickness of the wire (square), the available vernier scale to measure the diameter of the wire, and then find the cross-section.

The formula for calculating the cross-section: S = radius of the square R × π (R is the radius of the wire)

For example, the diameter of 1.76 wire, is 1.76 ÷ 2 × 3.14 = 2.76 square ≈ 2.5 square, (to take the approximation).

If you are to choose the size of the wire, generally based on the size of the power of appliances to calculate the current, and then according to the current in the electrician's manual can be, so more accurate.

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

You can know the cross-sectional area of the wire, and some lines are twisted together by a combination of multiple cores, so you can not use the single-core method to calculate, only one of the multiple lines in this wire to connect the single-core line, and then multiply by the number of strands of the line can be.

The formula is S = radius * radius * 3.14 * N.

Where N is the number of wires twisted into this one!

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