What is a square wire? Cross-section of multi-core cable. Ways to find out the real diameter of the wire

The smaller cross-section of the copper wire allows higher currents to pass and, accordingly, is designed for increased power or load.

This feature is due to low resistance values, which makes it possible to use a copper core in the home in the presence of a voltage of not only 220 V, but also 380 Volts.

Electrical cable products differ in the type of insulation, cross-sectional diameter and material of the conductor.

These parameters determine not only the area of ​​use, but also the basic operating conditions.

The working element of any copper cable product is represented by a conductive core made from electrical copper.

In this case, several insulated cores are enclosed in one common shell. The outer covering is represented by the so-called “armor”, or a special protective screen.

The undeniable advantages of copper cable products are presented:

• high thermal conductivity;
• good current conductivity;
• plasticity and flexibility;
• resistance to kinking or twisting;
• ease of self-installation;
• duration of operation;
• stability to corrosive changes;
• minimal risk of fire.

Copper core

When choosing a cable product, you should pay attention to the markings. Laying in tunnels, in the open air and in the ground, is carried out with armored copper cable having durable double insulation. The mark “ng-LS” indicates the high fire safety ratings of the product.

It should be noted that single-core copper products are most often used when installing stationary wiring, and a multi-core conductor is in demand when it is necessary to use increased flexibility and elasticity, as well as resistance to vibration.

The cross-section of the copper wire is marked with the first number following the letter designation of the conductor type.

Wiring with copper conductors is used for internal and external installation in residential premises and office buildings, in industrial and production complexes, due to its high technical and quality characteristics.

Selection of wire cross-section

Copper is a reliable material with sufficient resistance to bending, a high level of electrical conductivity, and low susceptibility to corrosive changes. It is for this reason that, under conditions of the same level, a smaller cross-section of the copper core is provided compared to aluminum cable products.

The purchase of a copper-type electrical wire is carried out with a certain reserve cross-section, which reduces the risk of overheating as a result of an increase in load when connecting new volatile devices.

Cable VVGng 4x4 0.66 kV

It is important that the cross-section fully corresponds to the maximum load, as well as the current value for which automatic protective devices are designed.

The current value is one of the main indicators that influences the calculation of the wire cross-sectional area in copper cable products. A certain area determines the throughput of current over a long period of time. This parameter is called long-term permissible load. In this case, the cross-section of the copper core is the total cut area of ​​the central part conducting current to consumers.

Determined by the main dimensions measured using a caliper:

• for a circle - S = πd 2 / 4;
• for a square - S = a 2;
• for a rectangle - S = a × b;
• for a triangle - πr 2 / 3.

Power 16-core cable

Standard design symbols: radius (r), diameter (d), width (b) and length (a) of the section, as well as π = 3.14. As a rule, the standard cross-section of the input cable is 4-6 mm 2, the wiring for connecting the socket group is 2.5 mm 2, and the cross-sectional area for connecting the main lighting system is about 1.5 mm 2.

Before installing a copper conductor, it is necessary to take into account the specific operating conditions and the expected maximum current load that will flow through the electrical wiring for a long time.

Calculation of wire cross-section

To independently determine the rated current value, you need to calculate the maximum power of all connected volatile devices.

Given the already known indicators of the power consumed by the devices, the current strength is calculated.

Standard calculation formula for a single-phase 220 V network:

I = P × K and / U × cos φ

• P - total power indicators consumed by all connected electrical appliances (W);
• U - power supply voltage indicators (V);
• K and - simultaneity coefficient equal to 0.75;
• cos φ - indicator for connected household energy-dependent appliances.

Standard calculation formula for a 380 V electrical network:

I = P / √3 × U × cos φ

After calculating the current value, you can easily determine the cross-section of the copper wire using tabular data for this purpose.

You need to select the cable cross-sectional area taking into account the current value and the required power indicators, using the table and rounding the obtained values ​​up with the addition of 15-20% margin.

Cross-section of copper wire by power: table

Tabular data is the most convenient to use and most accurate, therefore experts recommend determining the cross-section of a copper cable product in accordance with the power indicators in the table.

How to determine the cross-section for a stranded wire?

Stranded copper wires are conductors whose cross-section is represented by several cores, which in some brands of cable products are intertwined with each other. any stranded wire is calculated using the standard formula S = π × d²/4.

In this case, the total cross-sectional area of ​​a copper cable product will be the sum of the cross-sectional area of ​​all its cores.

An assessment of the load capacity of a stranded wire can be made without measuring the diameter of each individual conductor.

In this case, you need to measure the overall diameter of the multi-core cable product, and then use the standard increase factor of 0.91 in the formula.

The diameter of copper wires can be measured using a caliper or a micrometer.

Maximum flexibility and a high level of elasticity are observed in copper conductors, the cores of which are woven into a dense thread.

As a result of the use of special terminals, the connection of multi-core conductors acquires high reliability and lower current resistance, but in high-frequency electrical circuits the use of such cable products is limited.

Very often, before purchasing a wire, it becomes necessary to independently determine its cross-section, so as not to become a victim of deception. In addition, you have to measure the diameter of the cores when adding a new electrical point if there are no letter markings on the old wiring. Next, we will tell you how to take measurements correctly and what determination methods can be used for this.

The important point is that even if you correctly carry out all the calculations and select the appropriate product, such a nuisance as an accident may still occur. This is due to the fact that the cross-section of the cores indicated on does not always correspond to the actual values. This is only the fault of the manufacturer, because undoubtedly the characteristics do not match due to some economic “tricks” in the company. Sometimes there are no markings on the shelves at all, which also casts doubt on their quality.

You ask: “Why does a company need to spoil its reputation?”, to which you can immediately find several logical answers:

1. The plant decided to save on the quality of the product. For example, if you make a 2.5 mm core thinner by 0.2 mm2, you can win several kilograms of metal per 1 linear kilometer. With mass production, the savings are quite significant.
2. In the struggle for a “place in the sun,” electrical wiring companies are trying to lure consumers to them by making the price lower than that of their competitors. Accordingly, the low price is set due to a slight reduction in diameter (not noticeable to the eye).

As you can see, both answers are quite reasonable, so it’s better to be careful and do a few simple calculations, which we’ll talk about next.

Determination methods

There are several ways to determine cable cross-section. They all boil down to first calculating the diameter of the core, and then using small calculations to find out the final value.

Method No. 1 – Devices to help!

Today, there are engineering instruments with which you can easily determine the diameter of a wire or cable core. Such instruments include a caliper and a micrometer (click on the photo to view all the tools).

This method of determination is the most accurate, but the “other side of the coin” is the cost of the caliper/micrometer itself. The price, of course, is not astronomical, but for one-time use there is no point in purchasing this tool.

Most often, this option is chosen by professional electricians whose lives are directly related to. Having a caliper, you can most accurately determine the cross-section of the wire on your own. The advantage of this technique is that you can measure the diameter of the cores even on a section of a working line (for example, in a socket).

After the measurement, you must use the following formula:

Don't forget that Pi is 3.14. To simplify the formula as much as possible, you can divide 3.14 by 4, after which the calculations will be reduced to multiplying 0.785 by the diameter squared!

Method number 2 - Using a ruler

If you do not want to spend money (and you are doing the right thing!), then we recommend using a simple “old-fashioned” method to determine the cross-section of the wire by its diameter. If you have a wire, a simple pencil and a ruler, you can find the answer in a matter of minutes. All you need is to strip the core of insulation, then tightly wind it onto a pencil (as shown in the picture) and use a ruler to measure the total length of the winding.

The essence of the method is that it is necessary to measure the total length of the wound conductor and divide it by the number of cores. The resulting value is the diameter that you need to determine.

Despite its simplicity, the calculations have their own peculiarity:

• the more cores are wound around the pencil, the more accurate the result will be, the minimum number of turns is 15;
• the turns must be pressed tightly against each other so that there is no free space, which will significantly increase the error;
• the determination must be carried out several times (changing the initial side of the measurement, turning the ruler over, etc.). Again, the more calculations, the smaller the error.

We draw your attention to the significant disadvantages of this method. Firstly, only thin conductors are suitable for measurement (due to the fact that a thick cable will be difficult to wind). Secondly, in the store before purchasing for this technique, you need to separately purchase a small piece of the product.

After all the measurements, you must use the same formula that we indicated above. The video shows an example of determining the cross-section of a conductor using a ruler:

Using rulers and formulas

Method #3 – Using tables

Instead of determining the cable cross-section using a formula, you can simply use ready-made tables that will reduce your time and make the result more accurate.

The table is quite simple: one column shows the diameters of the cores, the second shows their cross sections in squares.

We've provided existing methods, but that's not all.

1. In addition to the cross-section of the product, pay attention to the metal of the core. The copper or aluminum core must have a characteristic rich color. If the color is questionable, then most likely it is an alloy of metals, which allows the manufacturer to save money. Such an alloy is extremely dangerous for... its current conductivity and rated loads are several times less than that of the original product.
2. The cross-section needs to be determined only by the core. Even if the product appears to be of normal thickness, it is possible that the reduced dimensions of the core were compensated by an increased layer of insulation.
3. If you are in doubt about the size of the conductor, purchase a larger gauge wire. The power reserve will definitely not damage your electrical wiring!
4. If you are dealing with a cable, the calculation will be slightly different (due to the fact that the cable may consist of n number of wires). To correctly carry out the calculations, you must first determine the diameter of each individual wire, then sum up all the values ​​and select products according to the final number.

You can often find electrical products in supermarkets without tags or identification marks. Among it there could easily be a coil of wire or cable. How do you know if the wire size is appropriate for your specific situation? The answer is simple - measure it or consult the seller.

Anyone who sells cables and wires can tell you what load they can withstand. In addition, inscriptions (numbers) are stamped on the wires, characterizing the cross-section and number of cores. But in real practice, not everything is as simple as it seems. The quality of cable products has recently deteriorated noticeably.

Problems with the quality of manufactured wires

Many manufacturers of cable and wire products, trying to make more money, artificially reduce the thickness of the insulation and increase the diameter of the cable. By specifying a larger wire cross-section than in reality, the manufacturer saves a very large amount. For example, to produce thousands of meters of copper wire with a cross-section of 2.5 mm2, 22.3 kg of copper is required, and to produce a wire of 2.1 mm2, only 18.8 kg is required. This results in a saving of 3.5 kg of copper.

Another way to reduce the cost of products is to manufacture a conductor from low-quality raw materials. When adding cheap impurities, the current conductivity decreases, therefore, cable length calculations must be changed.

Why do you need to calculate the cable load?

This question often arises when installing wiring in an apartment or home. First, all planned loads are considered, and then the required wire cross-section is determined. Then the necessary material is purchased from the store and electrical wiring is installed in the house.

As a result of using new wiring, the circuit breaker on the electrical panel first “knocks out”, and then damage to the wire is discovered. Moreover, it often turns out to be completely melted, as a result of which a short circuit occurs. It turns out that the calculations were made incorrectly, and how can you find out the minimum permissible value of the wire cross-section in this case?

To avoid serious overloads, it is necessary to calculate how many electrical appliances in the apartment will be used simultaneously. Among the most powerful household appliances that are usually used at home when preparing food and creating our comfort are:

• electric stove;
• air conditioner;
• microwave;
• electric kettle;
• iron;
• washing machine and dishwasher;
• coffee grinder;
• vacuum cleaner.

The power consumption of these household appliances ranges from 1 to 2 kilowatts (with the exception of electric stoves).

Important! If the cross-section of the wire is indicated incorrectly (underestimated), then when using it, it is natural for large overloads to occur, which lead to a fire in the wiring.

How to calculate?

Experienced electricians can “by eye” determine the wire cross-section with great accuracy. This is much more difficult for an ordinary person to do. Therefore, it is best to calculate the cable cross-section by diameter right in the store. At least it will be much cheaper than eliminating the consequences of a short circuit due to an overload in the electrical network.

Let's try to do this with specific examples using arithmetic formulas in school mathematics.

Everyone roughly understands what a wire cross-section is. If you bite it across with wire cutters, you can see the round cross-section of a copper or aluminum core. It is measured using a standard mathematical formula: as the area of ​​a circle. Where r is the radius of the circle, squared and multiplied by the constant “pi” (π=3.14).

The larger the diameter of the cable/wire, the more current can pass in a certain amount of time. And, accordingly, the more energy consumed by electrical appliances, the larger the cross-section of the wire should be.

From the simplified formula Scr = 0.785d2 it is clear that to calculate the cross-sectional area you need to know the exact diameter of the wire. To do this, it is necessary to remove the insulation from the core.

Calculation for stranded wire

Stranded wire (stranded) consists of single-core wires twisted together. Anyone who is even a little familiar with mathematics understands perfectly well that it is necessary to count the number of these wires in a stranded wire. After this, the cross-section of one thin wire is measured and multiplied by their total number. Let's consider the following options.

Calculation using a caliper

The measurement is carried out with a caliper with a conventional scale (or micrometer). Experienced craftsmen always have this tool at hand, but not everyone is a professional electrician.

To do this, using the VVGng cable as an example, cut the thick sheath with a knife and spread the wires in different directions.

Then select one core and strip it with a knife or scissors. Next, measure this core. The size should be 1.8 mm. Please refer to the calculations to prove the measurement is correct.

The figure 2.54 mm2 obtained as a result of the calculation is the actual cross-section of the core.

Measuring with a pen or pencil

If you don’t have a caliper at hand, you can use improvised methods using a pencil and ruler. First, take the wire to be measured, strip it and wind it around a pencil or pen so that the turns lie close to each other. The more turns, the better. Now let's count the number of wound turns and measure their total length.

For example, we got 10 turns with a total winding length of 18 mm. It is easy to calculate the diameter of one turn; to do this, divide the total length by the number of turns.

As a result of all the calculations made using the formula, you will obtain the required diameter of the core. In this case it is 1.8 mm. Since the diameter of one core is known, it is not difficult to calculate the cross-section of the entire VVGng wire using the already known formula.

You can see that the results were equal.

Using tables

How can you find out and measure the cable cross-section if you don’t have a caliper, a ruler, or a micrometer at hand? Instead of racking your brains over complex mathematical formulas, just remember that there are ready-made tables of values ​​for measuring cable cross-section. There are, of course, very complex tables with many parameters, but, in principle, to begin with it is enough to use the simplest of the two columns. The diameter of the conductor is entered in the first column, and the ready-made values ​​​​of the wire cross-section are given in the second column.

There is another “approximate” method that does not require measuring the thickness of individual wires. You can simply measure the cross-section (diameter) of the entire thick scroll. This method is usually used by experienced electricians. They can find out the cable cross-section both “by eye” and with the help of tools.

In order to successfully buy a wire, before purchasing it is necessary measure wire diameter, otherwise you may become a victim of deception. You will also have to measure the cross-section of the wire if you add a new electrical point on the old wiring, since there may not be a letter marking on it. The information below will help you choose the right technique wire diameter measurements and use it effectively in practice.

At the same time, the question will immediately arise: “What is the point of a company spoiling its reputation?” There may be several explanations for this: But the whole point is that even after making the correct calculations of the wire cross-section, you may still encounter a problem, despite the fact that you buy wire with suitable diameter. An accident may occur due to the fact that the marking of the wires will indicate a cross-section of conductors that does not correspond to the actual one. This may happen as a result of the fact that the manufacturing plant saved on the material, or the company producing this product did not comply with all the characteristics of the product. You can also find wires on the shelves that have no markings at all, which initially casts doubt on their quality.

1. In order to save money. For example, the plant made wire diameter less by only 2 mm. sq. with a 2.5 mm core, which made it possible to win several kilograms of metal per linear meter, not to mention the profit in mass production.

2. As a result of great competition, the company reduces the price of electrical wiring, trying to lure most of the consumers. Naturally, this happens due to reducing wire diameter, which cannot be determined with the naked eye.

Both the first and second options take place in the sales market, so you better play it safe and make your own accurate calculations, which will be discussed further.

Three main ways to determine wire diameter.

There are several ways, but each of them is based on determination of diameters cores with subsequent calculations of the final results.

Method one. Using instruments. Today there are a number of devices that help measure wire diameter or wire strands. This is a micrometer and caliper, which come in both mechanical and electronic (see below).

This option is primarily suitable for professional electricians who are constantly installing electrical wiring. The most accurate results can be obtained using a caliper. This technique has the advantage that it is possible measure wire diameter even on a section of a working line, for example, in a socket.

After you have measured wire diameter, it is necessary to carry out calculations using the following formula:

It must be remembered that the number “Pi” is 3.14, so if we divide the number “Pi” by 4, we can simplify the formula and reduce the calculation to multiplying 0.785 by the diameter squared.

Method two. We use a ruler. If you decide not to spend money on a device, which is logical in this situation, then you can use a simple proven method for measuring the cross-section of a wire or wire?. You will need a simple pencil, ruler and wire. Strip the core of insulation, wind it tightly onto a pencil, and then use a ruler to measure the total length of the winding (as shown in the figure).

Then divide the length of the wound wire by the number of cores. The resulting value will be wire cross-section diameter.

But the following must be taken into account:

• the more cores you wind on a pencil, the more accurate the result will be; the number of turns should be at least 15;
• press the coils tightly against each other so that there is no free space between them, this will significantly reduce the error;
• take measurements several times (change the measuring side, the direction of the ruler, etc.). Several results obtained will again help you avoid a large error.

Please note the disadvantages of this measurement method:

1. You can only measure the cross-section of thin wires, since it will be difficult for you to wind a thick wire around a pencil.

2. To begin with, you will need to purchase a small piece of the product before making the main purchase.

The formula discussed above is suitable for all measurements.

Method three. We use the table. In order not to carry out calculations using the formula, you can use a special table in which wire diameter is indicated? (in millimeters) and conductor cross-section (in square millimeters). Ready-made tables will give you more accurate results and will significantly save your time, which you will not have to spend on calculations.

Which does not correspond to the declared characteristics, is not manufactured in accordance with GOST, undesirable consequences may occur. Moreover, you can find cables on sale whose labeling and packaging contain unreliable indicators. The declared cross-section may not correspond to the true figure. It turns out that the core of the cable, purchased taking into account a specific load, cannot cope with the current that it should pass. As a result, the insulation melts. The risk of an emergency, including a short circuit, increases significantly. To prevent this from happening, you need to know how to determine the cross-section of a multi-core cable.

Features of calculating the cross-section of a single-wire (monolithic) core

So, you purchased a cable with a single-wire core and decided to measure its cross-section. To make this possible, you first need to acquire a caliper, a calculator, an insulation stripper and a utility knife. Set the cross-section to the cable diameter. To do this, do the following:

Remove the insulation from the cable.
. Measure the diameter of the core (using a caliper).
. Remember school geometry, namely the formula that allows you to calculate the area of ​​a circle (circular conductive core):

S = π r2, where π = 3.14 and r is the radius of the core.

Thanks to a caliper, you can only find out the diameter, but what is required is the radius. The formula should be modified. It is known that the radius is half the diameter. The formula will look like this:

S = (π d2)/4, where d is the diameter of the core.

To shorten the formula, you can divide the number π by 4. You will get a standard formula for calculating the cross-section of the core by diameter:

Let us carry out the calculation using the example of a cable whose core diameter, when measured with a caliper, is 1.35 mm. Substitute the value into the formula:

S = 0.785*1.352 = 1.43 mm²

From the calculations it is clear that the actual cross-section of the core is 4.7% less than the declared one, which is an acceptable underestimation.

As practice shows, it is not difficult to calculate a single-wire conductor. The main thing is to be careful and not confuse the diameter with the radius and vice versa.

Subtleties of calculating the cross-section of a stranded conductor

Not all cables have solid cores, and in such cases the question arises: how to determine the cross-section of a multi-core cable with stranded cores?

Awareness of how to measure the cross-section of a multi-core cable will allow you to be confident in the safety and reliability of using the product. Here, too, everything is extremely clear. The cross-sectional area of ​​a multi-core cable with stranded cores must be measured based on the area of ​​one wire of the cores. Proceed in the following order:

1. Take the cable and remove the sheath and insulation from one of the cores.
2. Fluff the core and count all the wires.
3. Measure the diameter of one of the wires that makes up the core.
4. Use the above formula to calculate the single-wire conductor. This will allow you to find out the area of ​​one wire.
5. Multiply the resulting value by the total number of cores.

For example, you have a cable. Having stripped, fluffed the core, measured one of the wires with a micrometer, and also counted the number of wires, we obtain the following data:

Number of wires - 28 pcs.
. Diameter of one wire - 0.26 mm

First, let's calculate the cross-section of one wire:

S = 0.785*0.262 = 0.053 mm²

Now the obtained value must be multiplied by the number of wires in the core - and we get a cross-section of 1.378 mm²

However, when calculating the cross-section of stranded conductors, it is also necessary to take into account the wire twist factor, which will be equal to 1.053 for cables with stranded conductors of class 5. As a result, we obtain a conductor cross-section equal to 1.45 mm² - the actual cross-section of the conductor is also less than the declared one by 3.3%, which is acceptable.

Anyone can calculate the cross-section and multi-core cable. To do this, you just need to use the above formulas. Knowing how to measure the cross-section of a multi-core cable, you will be able to choose the right product, and in the end there will be no problems. Therefore, before carrying out any manipulations related to the use of a cable, be sure to make this calculation.

The company "Kable.RF ®" is one of the leaders in the sale of cable products and has warehouses located in almost all regions of the Russian Federation. By consulting with the company’s specialists, you can purchase the brand you need at competitive prices.