Cross-section of cable diameters according to GOST. Determining the wire cross-section by diameter

It often happens that wire sellers involuntarily overestimate the real value of the cross section of the wire core, and in fact it turns out that the 2.5 squares indicated on the price tag turn out to be, for example, 2.1 squares. This is not at all surprising, since copper savings on an industrial scale are enormous, and the seller is not to blame for the manufacturer's desire to save.

Under these conditions, the buyer himself should not lose vigilance. Well, imagine: you want to lay wiring, say, in a house, figured out the typical load that the wiring must be guaranteed to withstand, calculated the required wire cross-section, bought it, believing the factory markings, and one fine day the wiring suddenly starts to melt unexpectedly, a short circuit occurs, and it’s not far from the fire, it’s good if the machine works when it closes.

Often the reason that comes to the mind of the unfortunate installer seems to be an incorrectly calculated wire section. However, when recalculating, it turns out that everything was calculated correctly, besides, the load did not exceed the current limit, but for some reason it overheated and the insulation melted. Taking a closer look at the problem, armed with a caliper, a person finds that the diameter is 0.15 millimeters less, and for current this is already a critical difference of 2 amperes.

How to be? First of all, you need to be able to independently calculate the actual cross-section of the wire (core) before buying it. Next, consider a simple way to calculate the cross section of the core.

First of all, armed with a caliper, measure the diameter of the conductor core in millimeters. Divide the resulting value by 2 to get the radius. The next step is to square the value of the radius (multiply its value by itself), and multiply the result by the number Pi, equal to 3.1416. You will get the cross section value of the round conductor in square millimeters.

I have a copper wire, the cross section of which I want to know. I measure the diameter with a caliper, it turns out 1.2 mm, this is the diameter of the core. So the core radius is 0.6 mm. I square it, and I get 0.36, then I multiply 0.36 by pi, which is 3.1416, I get 1.13 square millimeters. I conclude: this wire will definitely withstand 3 kilowatts at 220 volts.

But what to do if there was no caliper at hand? It is enough to expose larger wires, and wind several turns tightly, say on a screwdriver shaft, and then measure the length of the winding in millimeters with a ruler, and divide it by the number of turns.

All the same wire, with the same core. We wound 10 turns of this core tightly on a screwdriver, we measure it with a ruler: they occupy 12 millimeters, which means that the core has a diameter of 1.2 millimeters. Therefore, the radius is 0.6 mm, and the cross-sectional area is 0.6 * 0.6 * 3.1416 = 1.13 square millimeters.

Of course, it is not always convenient to wind a thick wire on a rod, it is much more convenient to use a caliper, but if there is no choice, then a ruler, a screwdriver (or another cylindrical object, or at least a piece of plywood) and a calculator is enough, well, plus knowledge of the formula.

In general, there are tables by which you can easily determine the cross-sectional area of ​​\u200b\u200bthe core of a single-core wire knowing its diameter, and vice versa. These tables also apply to flexible single-core wires, then the diameter of the conductive part of the wire, consisting of many strands, is taken into account, and the total cross-sectional area of ​​the conductive stranded part is determined.

We hope that this brief article was useful for you, and now you can easily determine the actual wire cross-section, regardless of what is written on the label. Usually, knowing the actual cross section of the conductor and the maximum current allowed for this cross section, you can easily calculate what diameter the wire will be most suitable for your purposes so that the operation of power circuits is safe.

Cable is the basis of any electrical network. When laying wiring and repair work, it becomes necessary to install electrical wiring. The cable cross-section by cable diameter must be determined according to the relevant parameters in order to prevent further problems with the use of household electrical appliances.

The price of the cable is quite high, this is another reason to carefully consider the choice of products. When buying a product, many are guided by the cost, and not by the manufacturer. Therefore, in order to carry out the work correctly, it is important to learn how to determine and check the diameter of the cable yourself.

• Method 1
• Method 2
• Method 3
• • Convert watts to kilowatts
• • Choosing a material
  • Choosing a brand of cable

Method 1

If it is not possible to use a special device. You can use improvised means. To do this, you need an object that has a round oblong shape, it can be any writing utensil - a pen or pencil, a ruler. We clean the wire to a length of at least 30 cm. Then we wind it tightly around the handle with a spiral. There should be no gaps between the turns.

We count the number of turns and the length of the wire used for them. Then we divide the length by the quantity.

For example, a wire has 21 turns with a length of 40 millimeters. To calculate the diameter, divide the length by the quantity. That is, 40 divided by 21, it turns out 1.904 millimeters.

Formula: S \u003d πr 2, where π is 3.14, S is the area of ​​the circle, r is the radius of the circle.

Since the calculated number is the diameter, not the radius. Then we change the formula for this measurement: S \u003d (πd 2) / 4, where d is the diameter.

The resulting number is substituted into the formula. The result will be the diameter.

For example, d = 3.635. 3.14 × 3.635 ÷ 4 = 2.84

Method 2

This method requires a mechanical or electronic caliper and a micrometer.

Measure with a micrometer. The device has two main parts - handles and recesses in a semicircle for measurement. The wire is inserted into the micrometer connector, the handle is twisted until it stops. When the screws converge on the sides, twist the ratchet on the handle of the device until it starts to scroll. The measurement is made, it is shown by the scale on the micrometer drum.

An electronic micrometer shows exact numbers, which eliminates the calculation error by a person.

Calculation of the section with a caliper. For correct use, it is necessary to know the structure of the instrument. It consists of a scale with a marking of 1 mm, the length of a standard ruler is 15 cm, a sponge for measuring, a ruler for depth, a screw for clamping an object.

Cut the cable, separate the cores. Clear one of them. Spread the jaws, insert the core so that the jaws fit snugly around it. Fix with a screw. Now you can see the length of the item. Further, we consider according to the already known formula.

Method 3

You can also find out the cross section of the cores using the finished table.

To determine the required copper cable KG, it is proposed to use the table.

To determine the desired aluminum cable, it is proposed to use the following table.

Why is it important to determine the cable cross section?

The ability of a cable to conduct current depends on its cross section.

When using the wrong wire, the voltage drops. With a thin layer of insulation and insufficient wire cross-section, in an emergency, a short circuit may occur, and the insulation will melt. This may cause a fire. Not only the wire can melt, but also the socket to which it leads, as well as the plug of the device and its wire.

Convert watts to kilowatts

For electrical appliances that use more electric current - an iron, a stove, a heater, for weak products, such as an incandescent lamp, the power is indicated in watts. There is a need to convert watts to kilowatts or vice versa. One kW contains 1 thousand W.

Definition of wire for power 380V

When using appliances that require a large amount of electrical power, it is necessary to connect to the mains from three phases. Electricity comes in three lines, instead of two, as usual, thus a smaller wire size is required.

Each core uses less voltage by 1.75 per phase. This must be taken into account in the calculations according to the table.

Calculate the cross section of a three-core wire

The stranded wire consists of three single-core veins. The principle of counting is the same as that of a single-core. You can use a high-tech device, or you can use ordinary items. The diameter of each core is considered separately. First, fluff the vein, count how many veins. And calculate the diameter using one of three methods.

Then multiply the resulting number by the number of wires. This will be the cross section of the entire cable.

For example, the diameter of one core of the KG is 2.52. According to the formula: S = πr 2

2.52×2.52×3.14= 19.94

In this case, we divided the finished result of the KG cable into four, given that this is not the radius, but the diameter of one core. We get the cross section of one wire KG.

Then we calculate the total cross section of the wire KG = 4.98 × 3 = 14.95

For an approximate calculation, you can calculate the total value without dividing into individual wires. But the air gap must be taken into account. Therefore, the resulting value is multiplied by 0.91.

According to this principle, the cross section of multi-core cables is calculated.

An important point is the connection of the wires. When connecting several cores, a voltage loss occurs. Losses especially increase with a large number of connections.

Choosing a material

Copper is considered the best material, as it has greater conductivity and strength. Aluminum breaks easily when bent, oxidizes when combined with air. If aluminum comes into contact with copper, it undergoes electrocorrosion and breaks down. Contacts deteriorate, the wire heats up, sparks. This may cause a fire.

Choosing a brand of cable

The brand of wire is a literal value, it means the characteristics of the material, the degree of flexibility, insulation. In domestic cables, the following markings:

1 letter - core material (A - aluminum). Copper has no letter.

2nd letter - wire.

3rd letter - insulation composition (rubber (R), kapron (K), polyethylene (P)).

Some wires have a letter indicating the type of rubber insulation. It can be nayrite (H) or polyvinyl chloride (B).

4th letter - asphalted structure (A), armored with tapes (B), protected by a braid (O).

For example - APP, TRP, PVS, APPV.

Determining the cable cross section is a necessary step for the safe installation of electrical wires and their further operation. It becomes significant due to the use of numerous devices. The cross section of the cable must match the voltage required by the electrical appliances.

Determining what section of wire you need is only half the battle. We still need to find the required section. The fact is that some manufacturers, in order to increase profits, produce cables with wires of a much smaller cross section than stated in the accompanying documents. For example, veins of 4 mm 2 are declared, and in real life - 3.6 mm 2 or even less. That's a big difference. If it is not noticed at the time, the wiring can heat up and this, in turn, can lead to a fire. Therefore, we will continue to talk about how to find out the wire cross-section by diameter, because the diameter can always be measured. Further, according to the measurement results, we find out the actual parameters of the core.

When buying an electrical cable or wire to check the cross section of the core, it is necessary to measure its diameter. There are several ways to do this. You can use measuring instruments such as calipers or micrometers. They measure the size of the bare part of the conductor. The device is simply attached to the core, clamped between the jaws, and the result is displayed on the scale.

How to measure the diameter of the core - take a caliper or micrometer

For private use, the measurements are quite accurate, with a small error. Especially if the devices are electronic.

For the second method, you only need a ruler and some kind of even rod. But in this case, you still have to deal with calculations, however, very simple ones. About this method - further.

Ruler + rod

If there are no measuring instruments on the farm, you can get by with a regular ruler and any rod of the same diameter. This method has a high error, but if you try it will be accurate enough.

We take a piece of wire about 10-20 cm long, remove the insulation. We wind the bare copper or aluminum wire onto a rod of the same diameter (any screwdriver, pencil, pen, etc. will do). We lay the coils neatly, close to one another. The number of turns is 5-10-15. We count the number of full turns, take a ruler and measure the distance that the wound wire occupies on the rod. Then divide this distance by the number of turns. The result is the diameter of the conductor.

As you can see, there is an error here. First, you can loosely lay the wire. Secondly, it is not enough to accurately measure. But if you do everything carefully, the discrepancies with the real sizes will not be so big.

How to measure the diameter of stranded wire

If you need to find out the diameter of a stranded wire, measurements are taken with one of the wires that make it up. The process is the same: remove the insulation, remove the braid (if any), fluff the wires, selecting one, take measurements in any way (using a micrometer or winding it on a rod).

Multiply the found size by the number of wires in one conductor (fluff and count). That's all, you have found the diameter of the stranded conductor. It remains to find out how to find out the cross-section of the wire by diameter, because when planning the wiring, it is the cross-sectional area of ​​\u200b\u200bthe wires that is used.

How to calculate by formula

Since the cross section of the wire is a circle, we will use the circle area formula (pictured). As you can see, you can calculate the cross section of the wire using the measured diameter or calculate the radius (divide the diameter by 2). For clarity, let's take an example. Let the measured wire size be 3.8 mm. We substitute this figure into the formula and get: 3.14 / 4 * 3.8 2 \u003d 11.3354 mm 2. You can round the result - it will be 11.3 mm 2. Impressive cable.

The second part of the formula uses the radius. This is half the diameter. That is, to find the radius, divide the diameter by 2, we get 3.8 / 2 = 1.9 mm 2. Next, we substitute into the formula and get: 3.14 * 1.9 2 \u003d 11.3354 mm 2.

The numbers are the same as they should be. So, with a wire diameter of 3.8 mm, its cross-sectional area is 11.34 mm 2. You know how to find out the cross section of a wire using the formula. But it is not always possible to do the calculations. This is where tables can help.

Determination of the wire cross-section by diameter according to the tables

For cable and wire products, there is a certain set of sections that are prescribed in the regulations. Knowing what section you need, according to the table we find the diameter of the conductor. Next, you just need to find products with the right parameters.

Now a little about how to work with this table. You go for products with certain parameters. For example, you know that you need a 4 mm2 cable. Having found the corresponding value in the table, we are looking for the required parameters in cable products. In this case, it will be necessary to find wires with a diameter of 2.26 mm. If we find similar parameters in a store or on the market, this is already good. But more often on cables with 4 squares declared on the tags, there are much thinner wires and you have to look for a cable with the required data.

There are two ways to find what you need. The first is to look for products that match the declared parameters. Perhaps, after spending some time, you will be able to find it. But the search will take a lot of time. There are too few responsible producers. There is, by the way, a sign by which you can navigate. This is the price. It is well above average. This is because more copper or aluminum has been spent. If you use this sign, it will take less time.

The second option is to look at products with a declared high denomination. In our case, we argue like this: we need a wire of 4 squares. The next one is 6 mm 2. It is very likely that the parameters of this cable in real life will be close to the required 4 squares. Perhaps the cross section of the conductors will be larger, but this is good - the wiring will definitely not heat up. The disadvantage of this option is that you will spend more money, since such cables cost more.

In general, you know not only how to find out the wire cross-section by diameter, but also how to choose the right one. Even if the declared characteristics do not match the real ones.

They say that repairing a house is like a fire. And to some extent this is true. After all, even if you start doing only small cosmetics, one work begins to pull another along with it, and it’s not far from a complete repair.

And, of course, rarely repair takes place without replacing the wiring. After all, somewhere it is necessary to put an additional outlet, and somewhere the wire itself is already becoming unusable (this is especially true for aluminum products). And then you have to think about what thickness of wire to choose, so that it is not too complicated in installation, and not overpay for extra, unnecessary square centimeters, but, at the same time, and so that it is enough for all electrical appliances, which every year becomes in apartments more and more.

Of course, the question of the characteristics of the wire is not only very important, but also complex. It requires a serious approach, calculations and care.

Now we will try to understand how to correctly determine the wire cross-section by diameter, power, current strength, and also how to get the correct thickness (measured in mm 2). Indeed, sometimes the marking may not coincide with the actual diameter.

Cable marking

To begin with, it makes sense to deal with the cross section of conductive products, which is indicated on the marking, on the outside. For example, the wire is marked as AVVG 3x2.5. From this designation, you can find out that this is an aluminum conductor with PVC core insulation, with a general insulation of the same material, without armor, in the language of electricians, “naked”. But this information, which can be learned from the letter designation, although important, is not as important as the numerical marking. And by the numbers you can find out that the cable is three-core, and the cross-sectional area of ​​\u200b\u200bthe conductor, that is, the core, is 2.5 mm.

But it often happens that the marking is not entirely accurate, the error can be up to 40%, and this is a considerable value (for example, KG is written 3x16, but in reality no more than 12 mm 2). Well, the consequences of such an inaccuracy, of course, are burned-out cables (well, if not a burned-out apartment), and possibly damaged household appliances.

But, about the methods by which you can measure the cable cross section when buying a little lower, but now it’s worth considering the materials from which the wires are made. It must be remembered that for the same load, the cross section of an aluminum cable is required more than a copper one. In addition, copper gives less loss of electrical conductivity, and is also much more durable. Of course, the cost of copper wires is higher, but this is compensated during operation, and therefore, such cables are preferable.

Calculation of the wire cross-section by diameter

The first thing to do before going to the store for a wire is to calculate the required cable cross-section for a particular room. To do this, you need to understand which devices will “load” the room. Summing up the power of all household appliances, take the total, and already on it, according to the table, select the desired characteristics of the cable.

Similarly, calculations are made for the current strength. The main thing in this case is not to miss anything. A cable with a thickness of 15–20% more than the required load will be optimal. Then, if necessary, you can connect some more devices that may eventually appear in the room.

All tables for selecting the wire cross-section by power or current strength are given in this article. But how to determine the cable cross-section without looking at the marking, because it may not correspond to reality? Calculating the cross-sectional area of ​​the wire is easy.

How to calculate the cross section when buying

When purchasing a cable, you must make sure that its cross section corresponds to the declared marking. To do this, you can purchase a test sample. Usually the minimum length on sale is 0.5 meters - this length will be enough.

To measure, find and take with you a caliper (mechanical or electronic, which is preferable) or a micrometer. Electronic devices, of course, more precisely, but not everyone has them, but almost everyone has a mechanical one.

But even if it is not there, a simple screwdriver and a ruler can help out. Now let's try to figure out how to calculate the parameters of the section according to the calculated radius.

Measurements with a micrometer or caliper

In order to calculate the cross-sectional area of ​​\u200b\u200bthe conductor, first you need to strip one of the strands of the wire, the diameter of which we need. A sufficient length for measuring in this way is 1 cm. Further, using a caliper or micrometer, the thickness of the core is measured - this, as you might guess, will be the diameter of the cable. But to calculate the ratio of the section to the diameter according to the formula, we need such a value as the radius, and therefore we divide the resulting value by 2. After such a transfer, the diameter is no longer used, everyone counts with the radius data.

After the measurements, a formula is used by which the cable cross-section is calculated, that is, the cable cross-sectional area - S \u003d π * r2, where π is a constant value equal to 3.14.

Thus, if the core diameter was 3.6 mm, then the calculations would be as follows:

3.6:2 = 1.8; after 3.14 x (1.8 x 1.8) = 3.14 x 3.24 = 10.17. It follows that the cross-sectional area of ​​the cable being determined, the core diameter of which was 3.6 mm. equal to 10.17 sq. mm.

Similarly, you can calculate the thickness of a multi-wire flexible conductive product, but with such calculations, you need to measure the diameter of one wire from the core, then multiply the resulting figure by the number of wires that make up the core, and then calculate the cable thickness using the above formula.

As it becomes clear, it is not so difficult to calculate the thickness of the conductor by diameter, and, even at the project stage, you can convert the cross section into diameter, then you will not need to calculate the data while standing at the counter, which is the plus of this action.

Cable measurements with a ruler

In the absence of high-precision devices for measuring the thickness of the wire, you can use a regular ruler and a screwdriver. For measurement, you will need to strip at least 10 cm of the core (the more it is stripped, the more accurately you can calculate the diameter).

After removing the insulation, the bare core is wound on a screwdriver so that there are no gaps between the turns, and the spiral formed on the tip of the screwdriver is measured with a ruler. For convenience, it is desirable to take an integer in millimeters. For example, from the initial edge of the wire to the edge of the 10th turn, it turned out 23 mm. Then it is necessary to divide 23 mm by the number of turns, which will be equal to 23:10 = 2.3 mm. This will be the required value in order to calculate the thickness of the cable core. Well, then again according to the same formula - 2.3:2 = 1.15x1.15 = 1.3225x3.14 = 4.15. So we converted the diameter to the cross section of the conductor.

Similarly, calculations are made for flexible stranded wires.

Determining the wire cross section from the tables

How to determine the transverse parameters of the cable, if you do not want to make calculations near the counter? For such cases, there is a table for determining the cross section and diameter of the wire, which is also presented in this article. But at the same time, it is necessary to be prepared for the fact that the required core diameter will not be in them. In this case, it is better to take the nearest smaller value as necessary. At least in this case, a small margin of power is formed.

Also, even at the design stage of the electrical installation, it is necessary to determine, using the tables, the cable section that will be needed. It must be understood that this wire parameter is influenced by many factors.

Of course, it is mainly necessary to take into account the power consumption or current consumption of all household electrical appliances. But, besides this, the length of the cable is also taken into account, that is, the distance from switchboard to the appliance or to a junction box, from which cables of smaller diameter can go. The ambient temperature also affects the thickness of the wire. If the wiring is mounted in a room with an elevated temperature, then you can safely add 15–20%.

Again, if the wiring is carried out outdoors, a smaller diameter cable may be used, since the surrounding air will cool the wire strands better.

Wire material

As you know, copper and aluminum wires have different resistances, as well as different service lives, from which we can conclude that calculations for the power or current of their cross section must be made separately.

Copper wire, as already mentioned, requires less thickness than aluminum, with the same load on the cable, and here's why. The specific resistance of aluminum is higher than that of copper, and therefore the current losses are greater. And it is precisely due to this that the cable is heated, since household electrical appliances do not understand through what material the voltage was applied to them. They take exactly what they need.

But copper, which has a resistance equal to 0.017 Ohm * kV mm / m. consumes less electricity for heating than aluminum with its resistivity of 0.028 ohm*sq. mmm. As a result, the heating of copper is less, the wire is thinner, and the efficiency of the copper cable is higher.

That is why, despite the high cost compared to aluminum, copper wires are more in demand in the electrical engineering market.

Features of the wire cross section for 380 volts

When choosing a cross-section or diameter of a wire that will operate with a voltage of 380 volts, it must be borne in mind that the phase through such a cable is supplied not through one, but through three cores. Therefore, the load will be distributed across all three. How to find out the cross section of a wire with three cores? Yes, very simple. It is also necessary to determine the diameter of one of the cores, then, knowing how to find the cross section of a two-core wire, translate into this parameter.

And after that, the resulting figure can be safely multiplied by three. Or initially divide the maximum load by the same.

In general, such cables are used mainly in industry, since in an ordinary residential apartment there is no equipment that operates on such a voltage, and therefore this issue should not be considered too deeply.

Instead of an afterword

Now the question of determining the wire cross-section by diameter does not seem so difficult.

When choosing the required cable diameter for installing electrical wiring in an apartment, you should not rely too much on the integrity of the manufacturer, in any case, most of them do not care about our safety, but about their financial well-being. Many of them increase the thickness of the insulation, while reducing the actual parameters. As a result, the product looks outwardly as it should, but the power for which it should be designed no longer withstands. Therefore, it makes sense to always recalculate the thickness in the manner described above, even if this is a product from a trusted manufacturer.

As the saying goes, trust but verify. After all, it is not for the manufacturer to use the mounted wiring, and it is not for him to redo it in case of a burnout. Therefore, everyone should take care of their own convenience and comfort of living.