Determine the cross section of the conductor. How to calculate the cross section of the wire and its diameter. Wire area selection rule for maximum current

One of the main characteristics of both household and industrial wiring is the cross-sectional area of ​​the conductor, which is directly related to the diameter of the conductive wires. The useful power transmitted by the conductor, the degree of heating of the conductor and the overall safety of the power supply system depend on this indicator. If the cross-sectional area is insufficient, the fire hazard increases significantly electrical system due to overheating of the conductors.

The cross section of the wire and the diameter of the table reflecting the relationship between these parameters will be given below, form the main parameters of any power lines. The use of properly selected wires significantly increases the service life of power lines and increases the reliability of operation.

There are several common methods for correctly determining the cross-sectional area of ​​a conductor. First of all, it is necessary to measure the diameter of the wire with a sufficient degree of accuracy.

How to measure the diameter of wires by cross section

Currently, the parameters of the wires declared in the technical specifications do not always correspond to reality. Such an important parameter as the diameter of the conductive core can be underestimated, which leads to a sharp increase in current density and, as a result, to overheating and failure of the insulation, and sometimes to a fire.

In order to avoid such unpleasant situations, it will not be superfluous to measure the diameter of the core yourself before purchasing the wire and make sure that the declared characteristics correspond to the actual ones.

The use of a micrometer is the most exact method measuring the diameter, however, in domestic conditions, such a tool is rarely used, so it can be replaced with a sufficient degree of accuracy with a caliper.

In the absence of these measuring instruments, with a sufficient degree of accuracy, you can measure the diameter of the wire using an ordinary ruler. To do this, it is necessary to remove the insulating material at a distance of about 10-15 cm. After that, tightly pressing the turns to each other, wind 10 turns of wire on the rod and measure the linear size of the resulting winding. The resulting size is divided by the number of turns and thus the diameter of the conductive core is calculated.

In itself, the determination of the diameter of the wire is a fundamental point and serves to determine such an important parameter as the cross-sectional area of ​​\u200b\u200bthe conductor, but the importance of this measurement should not be underestimated.

Determining the cross section of wires by diameter

To determine the cross section of the conductor with a known diameter, the formula known from the school geometry course is used:

S \u003d π * R 2, or S \u003d π / 4 * D 2

In this formula:

S - desired area, mm 2;

D - measured diameter of the conductive core, mm;

R - radius, mm; R=D/2;

In the case of multi-core cables, the area is determined as the sum of the areas of the individual conductors.

After calculating the cross section of the wire in this way, it is possible to carry out calculations of the load and operational parameters of the electrical wiring with a sufficient degree of accuracy.

Diameter and section of wires in the table

When buying electrical wires, it is not always convenient to calculate the cross section of the wires, although it is not difficult to determine the diameter of the conductive core. For this case, special tables have been developed that reflect the relationship between the diameter of the conductor and its cross-sectional area. The use of such tables is extremely convenient for determining the parameters of an unfamiliar wire.

At first glance, the use of such tables is not advisable, since the conductor's tag indicates its main parameters, however, there were certain subtleties here as well. The fact is that the parameters declared by the manufacturer do not always correspond to reality, but the parameters given in the table are absolutely objective.

If, when measuring the diameter, the result given in the table does not differ significantly from the declared one, then you are dealing with a high-quality wire, but there are times when the cross-sectional area does not correspond to the measured wire diameter, in this case, using the table will avoid buying low-quality cable.

The most important thing when installing electrical wiring is to choose a high-quality cable, because you can always easily replace a socket or a switch, and it will be difficult to replace a burned-out cable, not to mention what the consequences of this may be. Very often, the cable section differs from that declared by the manufacturer, because a decrease in the section allows unscrupulous manufacturers to save on the most expensive component - copper. In order not to become a victim of fraud, it is advisable to measure its cross section yourself before buying a cable, but how to determine the cable cross section by diameter in three simple ways we will tell in this article.

Method number 1 - using a caliper or micrometer

With the help of a caliper or micrometer, the diameter of the conductor of the cable stripped of insulation is measured. It is desirable to make a measurement on several sections of the core, as well as on all cable cores, and record the lowest values. If you take measurements with a micrometer, then the measurement must be made on a flat section of the core, so the indicators will be more accurate.

As is known from the school mathematics course, the area of ​​​​a circle (and in our case it will be the area of ​​\u200b\u200bthe cable section) is calculated by the formula S \u003d πR² and if this formula is simplified by dividing the number π by 4, then as a result we get a formula by which we can determine the cable cross-section by diameter:

Method number 2 - using a ruler

What to do if there is no caliper at hand, or even more than a micrometer, how to determine the cable cross-section by diameter without these tools? The old and proven method of measuring with a ruler and a pencil will come to the rescue.

The principle of measurement using this method is as follows: the cleaned core is wound on a pencil, as shown in the figure below. The minimum number of turns should be 15-20, but here you also need to proceed from the thickness of the conductor, if it is too thin, then it is advisable to wind more turns.

To reduce the measurement error, the turns must be wound as tightly as possible. Next, using a ruler, we measure the length of the wound wire and divide by the number of turns, we get the diameter of the core, everything is simple.

Using the formula already known to us, we determine the cable cross-section by diameter. For clarity, let's give an example: let's say we wound 20 turns of wire, and got a result of 19.6 mm, we divide this number by the number of turns of 20, and we get a diameter of 0.98 mm. Using the formula, we calculate: 0.785 * 0.98 * 0.98 \u003d 0.753914 mm², round up, and get 0.75 squares.

The disadvantage of this method for determining the cable cross-section by diameter is that it will be difficult to wind a wire with a large cross-section with it, but for small cross-sections this method, on the contrary, will give a more accurate result. In addition, you will probably need to buy a piece of wire to check, because no seller will allow such experiments to be carried out.

Method number 3 - using a table

The easiest way to determine the cable cross-section is by diameter, but you still need a measuring tool, a caliper, or a micrometer. We measure the thickness of the core diameter, and using the table we determine the cross section.

In conclusion, it must be said that it is also important to pay attention to the composition of the conductive core, most often they fake wires and cables with a copper core. Buy cable products from a trusted seller. Our store sells only high-quality, certified products of proven domestic manufacturers. If you want to ask a question related to the choice of cable products, then you can always consult with our consultants, you just need to contact us via

The correct calculation of the cable in terms of power and length avoids problems with electrical loads. As a result, it is possible to avoid the appearance of a short circuit and overheating of the line. An electrical cable varies in its thickness and the number of strands inside the wire. An incorrectly selected element can cause premature failure of a household appliance or a fire in wiring in a living space.

How to correctly calculate consumables? What should you pay special attention to in the selection process? We bring to your attention detailed instructions for calculating the cable cross section. Here are detailed formulas that make the task easier.

The main rules for correct calculation

In the process of laying the wiring, a special cable with a rubber type of insulation is used. As a rule, it is able to withstand a voltage that does not exceed a power of 1kV. On sale are different models of wire that can be used inside the space, for street circuits and wall planes.

Quite often, these products are of the VVg or AVVG brand. They differ in cross-sectional area and the number of metal cores inside the cable. To connect the power supply to household appliances, another type with PVC marking is used.

Before making a purchase, it is recommended to carry out an accurate calculation of the cable cross-section by load and area in relation to the electrical appliance. Information about the power of the current that will be distributed through this cable will help you make the right choice.

The main recommendations for the correct calculation are contained in the manual of the Rules for the Arrangement of Electrical Installations. Abbreviated name of the material (PUE). Here are seven publications that describe in detail all the techniques for laying electrical wires.

Improper installation is accompanied by administrative fines. In addition, an incorrect calculation leads to a failure of the electrical circuit and a fire in household appliances. The damage from fire is a large financial cost and serious harm to human health.

Basic calculation formula

Many novice electricians often ask themselves: “Why is it important to correctly calculate the cross-sectional area of ​​\u200b\u200bthe electrical cable?”. In fact, everything is quite simple. To do this, remember the laws of physics.

Electric current moving along the wire begins to heat it. In this case, the higher the power, the more its surface heats up. The active power of electricity can be calculated using the following formula:

P=UI cos y=I2*R.

R - acts as active resistance. According to this formula for calculating the cable cross section, it can be seen that the power directly depends on the transverse resistance and current intensity. In simple terms, the greater the power, the faster the surface of the cable heats up.

The resistance of conductors directly depends on the material from which they are made, as well as its length. Calculations are carried out according to the formula:

p is an indicator of resistivity;

I is a value that measures the length of the conductor;

S - acts as a cross-sectional area.

According to these calculations, it is obvious that with a smaller conductor area, its resistance is greater.

When buying a cable, it is important to consider its diameter and area. This can be calculated using the following formula:

Here d is the diameter. In addition, it is not recommended to forget about the resistivity of the product. Aluminum wires have a higher resistance than copper wires. That is why, it is better to choose a larger parameter for aluminum products.

Special tables help to facilitate the selection process for the correct calculation of wire cross-sections.

Calculation by power and current strength

The calculation of the cross section directly depends on the total amount of energy consumed. If the total power is known, the strength of the eclectic current can be determined.

To do this, we use the following formula:

• P is the electrical power measured in W;
• U = 220 W;
• K is the coefficient with the simultaneous inclusion of all devices;
• cos - coefficient for one electrical appliance.

To date, special calculators have been developed that greatly facilitate the calculation of the value. In the process of laying, you must be very careful. Some types of cable are designed for enclosed spaces, while others are suitable for outdoor power lines.

How does the length of the electrical wiring affect the choice of a suitable cable?

Too long electrical circuit is accompanied by high losses. As a rule, they provoke heating of the cable during operation.

The formula helps to calculate this coefficient:

U= (P*ro +Q*xo)*L /Uh

• P is the active power of the device;
• Q is the reactive power. It is measured in W;
• ro is the coefficient of active resistance;
• ho - acts as a reactance;
• Uh is an indicator of the rated voltage. It shows the maximum consumption of the household appliance.
• L is the length of the electrical circuit.

For a long chain, automatic devices are additionally used to prevent premature overheating of the conductors. They are equipped with a thermal and electromagnetic splitter. In addition, these devices reduce the risk of a short circuit.

Online calculation of the cable section

Photo of a different cable section

People who are just getting to know electricity better need to know how to determine cable cross-sections by diameter. This parameter can be considered one of the most important and therefore every electrician should have information regarding it. But still, it is a little difficult for novice electricians or students to determine the cable cross-section by the diameter of the core, and therefore this issue should be discussed in more detail.

You need to understand that any cable consists of a certain number of cores, which in cross section have the shape of a circle. It is from what area a particular cable will have in cross section that the parameters of its conductivity will be determined. The thicker the cable, the more electricity it can carry.

What is a cable?

A cable is a long wire, inside of which there are several cores that interact with each other. Several metal cores are required in order to increase the power of the cable. If there are not enough cores, then during voltage drops in the network, this wire will overheat greatly and may burn out.

If you need to determine the cable cross-section, it is enough to pay attention to just one parameter - its diameter. How exactly to use it to carry out the necessary calculations and what tools are suitable for this, it is worth considering in more detail.

What is needed for calculations?

To understand what the wire cross section is and correctly calculate it according to the cable diameter, the user will need to stock up on the following things:

• one cable having an unknown section;
• micrometer or caliper;
• a table that shows the parameters of the resistivity of substances.

Armed with everything you need, you can proceed to the moment of determining the section of a particular cable, which will be performed according to its diameter.

Detailed instructions for taking measurements

The whole process of calculating the cable section parameters can be divided into 6 stages, each of which has its own specifics and must obey specific rules.

Stage 1

You need to take a cable for which a person is going to determine the section parameter. Most often, wires consisting of 2 or 4 cores are used for this purpose. The cores must be insulated from each other with special materials.

As a rule, the cores inside the cable have the same diameter indicators, but you can also find such wire options where one of the cores is much thinner than the other options. If the cable has one thin core, then it is intended for grounding.

Stage 2

The cores must be very carefully cleaned of wire insulation - for this purpose, you need to use a small but very sharp knife.

Then take a caliper or micrometer and, using the tool, calculate the diameter of the core. The value obtained in millimeters should be written down somewhere. Using this parameter, you will need to calculate such an indicator as the cross-sectional area. To do this, a person will have to multiply the coefficient 0.25 by the number P, which equals 3.14, as well as the resulting value of the diameter squared. The general formula for this calculation is as follows − S=0,25 xPxDsquared. The resulting value must be multiplied by the number of cores that are present in a particular cable.

Additionally, you need to calculate the resistance of the wire, for which you will need the following indicators:

• wire length;
• cable section;
• the material from which the cable is made.

With these parameters, you can easily calculate the resistance index.

Stage 3

To understand how measurements are made in practice and find out the necessary information, you need to consider the moment of calculation using a specific example. If the user has a copper cable in his hands, which consists of 4 cores, and its diameter parameter is 2 mm, then you can search for its cross-sectional area.

Advice! For measurements, it is better to use a micrometer, which will allow you to get more accurate readings, which means that the whole calculation will be as accurate and correct as possible.

To determine this parameter, it is worth taking up the moment of calculating the cross-sectional area for one of the cores. The following formula allows you to do this:

S\u003d 0.25x3.14x2 squared \u003d 3.14mm squared

The principle of calculation is very simple and understandable. By determining the cross-sectional parameter of one of the wires, you can find this indicator for the whole cable. To determine it, it is enough to multiply the indicator obtained by the formula above by the total number of cables.

Stage 4

By determining the cross-sectional parameter, a person can find out what maximum current can flow exactly through the selected cable. Also, having the above indicator on hand, a person can determine the resistance. For example, the maximum current for a copper cable can be calculated using the ratio of 8A per 1mm squared. Based on this, the current limit value will be 8x12.56=100.5A. for aluminum cable, slightly different parameters are used, which are 5A per 1mm square.

Stage 5

Knowing the value of the cable length, you can easily get ahead of its resistance. To understand how this is done, you need to consider everything with a specific example. For example, if the length of a particular cable is 200m, then to determine the resistance index, you need to multiply the resistivity of the material by the length of the cable and divide by its cross-sectional area. Having made these calculations, you can easily determine the desired parameter.

Having made the necessary measurements, you can determine the cable cross-section using the indicators of a special table. By measuring the thickness of the core diameter using a special table, you can determine the cross section.

The cable section calculation table is as follows:

Thanks to this table, you can find out the necessary information very quickly and without unnecessary problems. The table shows the cross-sectional area of ​​\u200b\u200bdifferent cables and makes it possible to significantly simplify the calculation process, because for some novice electricians, using only the formula, it is not easy to determine this indicator.

If you put a low-quality cable at home, then it can simply burn out from the slightest fluctuations in the network. To prevent this from happening, the craftsmen, before installing the wiring, measure the cross section of the cable by its diameter. This helps to understand how much voltage a particular wire can withstand and whether it is worth installing it. If the calculation of the section is carried out and the parameter turned out to be underestimated, then the user runs the risk of facing the following danger:

• the load capacity of the wire decreases;
• if a smaller or larger current is blown through the wire, then it will completely collapse;
• ignition can occur in any zone of the cable and start a fire.

Statistics show that now there are a lot of fires due to the fact that the electrical wire system works poorly. Therefore, in order to avoid fatal consequences, it is worthwhile to calculate the cable cross-section according to its diameter.

Advice! When choosing a cable in a store, you should not always trust the information that is indicated on it. Often, manufacturers put better technical data than they actually are in order to sell their products and make good money on it.

It is possible to measure the cross section of the cable by using a simple ruler. This is a very old way of taking measurements, but it is no less effective than carrying out the same actions using special devices. To measure using a regular ruler, follow the instructions below:

• carefully strip the core from insulation;
• tightly wind the core on a regular pencil;
• measure the total winding length with a ruler;
• divide the winding length by the total number of strands present in the cable.

When winding a core on a pencil, you need to make sure that at least 15 turns are obtained. The coils should be pressed very tightly against each other, so that there is no free space between them. It is necessary to take measurements not once, but several times, so that the result is as accurate as possible.

It is important! This method is only suitable for determining the diameter of thin wires. If the cable is thick, then it will be very difficult to wind it up, which will not allow you to do everything efficiently and make an accurate measurement.

Experienced electricians already know how to determine the cable cross-section correctly, even by eye. For those who do not understand this matter very well or take measurements for the first time, professionals are ready to give some useful tips. And so, experts advise people who want to take cross-sectional measurements to follow these rules:

• you need to pay attention to the quality of the metal from which the core is made (aluminum or copper core should have a rich color, otherwise a low-quality metal alloy was used, and this can be dangerous to use);
• the section should be performed exclusively along the core, because the insulating material should not be taken into account;
• doubting the size of the conductor, you need to take a thicker cable, because then there is definitely a guarantee that it will withstand a certain load.

Using these tips, everyone will be able to independently cope with electrical cables and calculate the desired value.

Measuring the section of a flexible cable

For a multi-wire flexible cable, its own method of measuring the cross section is used. This method is concluded in the following points:

• wind one vein from the bundle on a pencil;
• measure the length of all turns;
• divide the length by the number of turns and multiply the result by the total number of wires.

The method is quite simple and understandable, so absolutely everyone can use it. To take measurements correctly, you need to perform all the steps as accurately as possible.

This procedure is not difficult for professional electricians, but it will not be so easy for beginners to cope with this task. In such a responsible process, the main thing is to do everything carefully and then you can get the most accurate result.

Conclusion

You can quickly determine the cable cross-section by diameter. In order to visualize this parameter, a person can use one of several available methods. The main thing, when performing the measurement process, is to carry out all actions carefully and accurately. To quickly calculate the desired indicator, you can use a special table that contains all the data. If a person does not use the table, then he will be able to perform all the calculations using a special formula.

In favor of whatever method a person chooses, all actions should be carried out carefully and carefully. Everyone can take measurements of this nature, taking into account the advice given by professional electricians. Measurements can be taken using special instruments or a regular ruler.

You can measure the cross section of the cable in just a couple of minutes, finding out if it can be used for specific purposes. When choosing a cable, you must always remember that. That the markings on them do not always correspond to reality. That is why it is worth checking the necessary parameters yourself in order to know what quality products are used. By calculating the desired parameter, a person can verify the quality of the cable and use it to replace the wiring. The main thing is to take all the measurements correctly and then the wire used will be as safe as possible for home use, there will actually be no risk of any short circuits or other troubles.

Often found in the supermarket electrical products without tags and identification marks. Among it can easily be a coil of wire or cable. How do you know if the wire size is right for your particular situation? The answer is simple - measure it or consult the seller.

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

Problems of quality of produced wires

Many manufacturers of cable and wire products, trying to earn more, artificially underestimate the thickness of the insulation and overestimate the diameter of the cable. By specifying a larger wire cross-section than in reality, the manufacturer saves a very large amount. For example, the production of a thousand meters of copper wire with a cross section of 2.5 mm2 requires 22.3 kg of copper, and in the manufacture of a wire of 2.1 mm2, only 18.8 kg are required. So it turns out a saving of 3.5 kg of copper.

Another way to reduce the cost of products is the manufacture of a conductive core from low-quality raw materials. When cheap impurities are added, the conductance decreases, therefore, cable length calculations must be changed.

Why do you need to calculate the cable load?

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

As a result of the operation of the new wiring, the machine on the electrical panel first “knocks out”, and then damage to the wire is detected. Moreover, it often turns out to be completely melted, as a result of which a short circuit occurred. It turns out that incorrect calculations were made, and how to find out the minimum allowable 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 at the same time. Among the most powerful household appliances that are commonly used at home for cooking and creating our comfort, we can distinguish:

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

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

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

How to calculate?

Experienced electricians can "by eye" with great accuracy determine the cross section of the wire. It is much more difficult for an ordinary person to do this. Therefore, it is best to calculate the cable cross-section by diameter right in the store. At the very least, it will come out much cheaper than eliminating the consequences of a short circuit due to an overload in the power grid.

Let's try to do this on specific examples using the arithmetic formulas of school mathematics.

Everyone roughly understands what the cross section of the wire is. If you bite it across with wire cutters, you can see a round cross-section of a copper or aluminum core. It is measured according to the 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 Skr = 0.785d2, it can be seen that in order to calculate the cross-sectional area, you need to know the exact diameter of the wire. To do this, it is necessary to clean the core from insulation.

Stranded wire calculation

Stranded wire (stranded) is a single-core wire twisted together. Anyone who is at least a little friendly with mathematics understands perfectly well that it is necessary to count the number of these wires in a stranded wire. After that, the cross section of one thin wire is measured and multiplied by their total number. Consider the following options.

Calculation with a caliper

The measurement is carried out with a vernier caliper with a conventional scale (or micrometer). Experienced craftsmen always have this tool at hand, but not everyone is professionally engaged in electrics.

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

Then choose one core and clean it with a knife or scissors. Next, measure this core. Should be 1.8mm. Refer to the calculations as proof of correct measurement.

The resulting figure of 2.54 mm2 is the actual cross section of the core.

Measuring with a pen or pencil

If you don’t have a caliper handy, you can use the methods at hand, using a pencil and a 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, it turned out 10 turns with a total winding length of 18 mm. It is easy to calculate the diameter of one turn, for this we divide the total length by the number of turns.

As a result of all the calculations made according to the formula, get the desired core diameter. 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 are the same.

Using tables

How can you find out and measure the cable cross-section if there was no caliper, no ruler, no micrometer at hand. Instead of racking your brains over complex mathematical formulas, it is enough to remember that there are already ready-made tables of values ​​​​for measuring the cable section. There are, of course, very complex tables with many parameters, but, in principle, it is enough to start with the simplest of the two columns. In the first column, the diameter of the conductor is entered, and in the second column, the finished values ​​\u200b\u200bof the wire section are given.

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.