Cable area by diameter. Multi-core cable cross-section

One of the important and basic parts of electrical wiring is the cables that conduct current. In order for everything to work as it should, without short circuits and melted wires, it is important to select the wiring so that it can withstand the voltage. You can make sure that the wire is reliable, safe and meets operating requirements by calculating the wire cross-section. If the wire is of insufficient cross-section, it can lead to a short circuit and fire in the house. Let's figure out how to determine the wire cross-section to avoid such consequences.

Serious question

If you plan to replace electrical wiring, then first of all you need to decide what cross-section of wire is needed. When you calculate the planned current load on the wire, it will immediately become clear what cross-section is needed for normal operation. For this purpose, use the table below.

Let's say, having calculated everything, you have determined the current strength to be 27 A. It turns out that you need a two-core wire with a cross-section of 2.5 mm 2. You went to the store and bought good wire, with a cross-section of 2.5 mm 2 declared by the manufacturer and installed the electrical wires. After the time has passed when the system was up and running, the machine on your dashboard turns off. This may indicate a damaged line.

After you inspect the wiring, you may find that there was a short circuit. The reason is simple - the insulation on the wire melted due to strong heating. But how can this be? You did everything right, calculated, purchased the right wire. And the whole point is not in the calculations and your error with the connection. The whole reason lies in deception. Yes, precisely in deception, since very often manufacturers producing wires supply goods that do not correspond to the declared cross-section. For example, you bought a cable with a wire area of ​​2.5 mm 2, but when you checked it yourself, it turned out that the cable cross-section is only 2.1 mm 2, which is less than what you need in terms of power. So it turns out that the wire heats up, and the risk of a short circuit increases.

But why would cable companies do this? It's all about greed, since by lowering the cross-section of the wire, the manufacturing company saves quite a significant amount of money. Judge for yourself: to make 1000 m of wires with a cross-section of 2.5 mm 2, you will need approximately 22.3 kg of copper. But if you make them with a smaller cross-section, 2.1 mm 2, then their production will require 18.8 kg. It turns out that the savings in favor of the manufacturer are 3.5 kg of copper. And when large volumes of products are produced, this figure increases significantly.

So it turns out that determining the wire cross-section is an important and serious step that must be performed when installing wiring. This way you can avoid insulation melting, short circuits and, as a result, fire.

How can you determine the cable cross-section

So, you bought a wire, let's find out how you can measure its cross-section. For this purpose you will need:

• calipers;
• calculator;
• the cable itself;
• utility knife or stripper for removing insulation.

The cross section is determined by the diameter of the wire. Let's look at how to do this step by step.

1. Take the wire and remove the insulation from it using a stripper or a utility knife.
2. Using a caliper, measure the diameter of the wire.
3. Now, you will have to remember your geometry lessons at school. In order to determine the area of ​​a circle, there is a certain formula:

S cr = π r 2,

where the number π = 3.14, and r is the radius of the wire.

But here we have a problem: using a caliper it is impossible to measure the radius - only the diameter. Therefore, the formula needs to be slightly modified to suit the diameter. As we know, the radius is half the diameter. In order for our data to fit, the formula needs to be redone like this:

S cr = (π d 2)/4,

where d is the core diameter.

In this case, the formula can be shortened by dividing the number π by four. As a result, we arrive at the standard formula for calculating the cross-section of the core by diameter:

All that remains is to substitute the numbers into the formula and get the area of ​​the circle, which will be its cross section. For example, the diameter of your copper wire is 1.68 mm. This number squared is 2.8224. Multiply 2.8224 by 0.785. If we round, then in the end the desired cross-section is 2.2 mm 2.

That's all, as you can see, this procedure will not take much time and effort, but it is a very important part of the electrical installation work. After all, even a deviation of a few tenths of a millimeter can play a cruel joke. But what if you are not an electrician and you don’t have a caliper at hand? Don’t rush to run to the store; there is a simple method for calculating the diameter using available tools.

A simple method for determining diameter

Everyone has everything they need at their fingertips. For this method you only need a pencil or pen and a ruler.

1. First of all, take the wire whose cross-section you need to find out and remove 300–400 mm of insulation along its length.
2. Take a pencil, pen, felt-tip pen, or whatever you have on hand, and wrap a wire around it. In order to achieve the most accurate result, the turns must be fitted closely one to one.
   The more turns you make, the more accurate the result will be. The recommended quantity is 10 or more turns.
3. Then count the number of turns you wound around the pencil and write that number down or remember it.
4. Using a ruler, measure the total length of the counted turns. For example, you got 19 turns that are 32 mm long.
5. To determine the diameter of the wire, all that remains is to divide the length by the number of turns. It turns out like this: 32/19 = 1.68 mm.

That's all, now all that remains is to substitute the diameter of the wire into the formula and you will get a wire cross-section of 2.2 mm 2. This result can be considered accurate under two conditions: the turns were wound closely, and their number exceeds 10 pieces - the more, the better. As a result, you won't have to spend extra money.

The only disadvantage of this method: if the core has a large cross-section, you won’t be able to wrap it around a pencil.

How to measure the cross-section if the wire is stranded

Well, you say, if there is only one wire, it’s easy to calculate the cross-section. But what if it is multi-core? There are a lot of such individual wires, how can you recognize it in this case? Define cross section stranded wire not as hard as it seems. All you need to do is determine the cross-section of one of the cores.

1. First, take the wire and strip the insulation from it.
2. Now all the wiring needs to be disconnected and their number recalculated.
3. Take one of the wires and measure its diameter.
4. Using the formula presented above, determine the area of ​​one core.
5. Having the cross-section of one core, you can find out the total cross-section. To do this, multiply the area of ​​one wire by their total number. For example, you have a wire consisting of 15 cores. You learned that the cross-section of one wire is 0.2 mm 2. In order to find out their total cross-section, 0.2 must be multiplied by 15. We get: 0.2 × 15 = 3 mm 2.

But it should be taken into account that all the wires in the wire cannot be connected closely. Because they are round, there is an air gap between them. It needs to be taken into account. To do this, multiply the resulting result by 0.91. Let’s say if the wire cross-section is 3 mm 2, then multiplying it by a factor of 0.91, we get a cross-section of 2.7 mm 2. That's all. There is nothing complicated, you just need to follow the instructions.

As you can see, anyone who knows how to use formulas can determine the wire cross-section. But, despite the simplicity of such work, it is one of the most important stages, which must be done before wiring throughout the house.

The main and most common method of transmitting electricity to the consumer is an electrical wire and electrical cable. An electrical wire and electrical cable is an electrical product consisting of a metal conductor or several conductors. Each core is electrically insulated. All insulated conductors of a wire or electrical cable are placed in general insulation.

Currently, the industry produces a wide variety of electric wires and electrical cables. Cables and wires are mainly copper and aluminum, i.e. the composition of the cable or wire cores is copper or aluminum.

Electrical cables and wires can be single-core or multi-core. The core of a cable or wire can be either single-wire (monolithic) or multi-wire. The cores are made mainly in round shape, however, often for electrical cables with a large cross-section, the shape of the stranded core can be made in the form of a triangle. Today we will tell you how to calculate the cross-section of a wire by diameter.

Marking of electrical cable (wire)

There is a standard range of wire and electrical cable cross-sections that are used. This is 1mm 2; 1.5mm 2; 2.5mm 2; 4mm 2; 6mm 2; 8mm 2; 10mm 2 etc. The type, cross-section and number of cores are indicated either on the tag that comes with the cable or wire, or on the product itself. For example, markings are often applied to the general insulation of cables and wires. Also, technical data of electrical conductors are indicated in the product passport.

Let's say there is a VVGng 3x2.5 cable available. This marking is deciphered quite simply: a copper cable with PVC insulation, in a PVC sheath, non-flammable, the number of cores is three, the cross-section of each core is 2.5 mm 2. If the letter “A” appears at the beginning of the marking, i.e. The cable type will be AVVG, which means that the cable has aluminum cores.

By marking the wire, you can also find out not only the type of wire itself, but also the number and cross-section of current-carrying wires. For example, PVS wire 3x1.5. The decoding is as follows: wire with PVC insulation and PVC sheath, connecting. The number of cores is also three, and the cross-section of each wire is 1.5 mm 2 .

Conductor cross-section

Each wire and cable core has its own cross-section. It can be either very small (1mm 2 or less) or very large (95mm 2 or more). The cross-section of the conductor affects the ability to withstand long-term and short-term electricity a certain size. The larger the cross-section of the core, the greater the current it can withstand for an almost unlimited time.

An incorrectly selected cross-section during design may subsequently cause overheating of the conductor, damage (destruction) of its insulation during the process of high heating, which may result in a short circuit and, as a result, fire and fire.

Section mismatch

The cause of overheating of a cable or wire during operation may not always be an incorrect calculation of the cross-section. As often happens in practice, the reason is very simple. Not all manufacturers of cable and wire products are conscientious about the quality of their products. The fact is that very often the cross-section of manufactured cables and wires is actually underestimated, i.e. does not correspond to the declared value.

To avoid purchasing an electrical cable or wire with an undersized cross-section, you must first visually assess its actual cross-section. Almost any electrical specialist is able to “by eye” determine the cross-section of a conductor. But when this is not enough, a professional can independently calculate the area cross section electrical conductor. The cross section is calculated using the usual mathematical formula:

S = π*D 2 /4– formula No. 1

S=π* R 2 – formula No. 2

where: π is a mathematical constant, which is always equal to approximately 3.14;

R – wire radius;

D – wire diameter.

The radius is equal to half the diameter:

R=D/2– formula No. 3

Calculation of the actual cross-section of the electrical conductor

Knowing the formula for calculating the cross-section of a conductor, you can calculate its actual value and find out how much the manufacturer’s declared cross-section value is underestimated or overestimated (which happens rarely).

Single-wire (monolithic core)

First, you need to remove the insulation layer from a wire core or an electrical cable core to expose the core itself. Then the diameter of the core is measured with a caliper. Because the vein is monolithic, then there will be only one measurement. After measuring the diameter of the core, you need to substitute the value of the diameter (radius) into one of the above formulas.

Example No. 1

Let’s say that a cable or wire has a declared core cross-section of 2.5 mm 2 . When measured, the core diameter turned out to be 1.7 mm. Substituting the value into formula No. 1, we get:

S = 3.14*1.7 2 /4 = 2.26865 ≈ 2.3mm 2

Calculation using formula No. 1 showed that the cross-section of the core is underestimated by 0.2 mm 2 from the standard value.

Now let’s calculate the actual value of the cross-section using formula No. 2, but first, let’s determine the radius using formula No. 3:

R = 1.7/2 = 0.85mm

We substitute the radius value into formula No. 2 and get:

S = 3.14*0.85 2 = 2.26865 ≈ 2.3mm

The calculation using the second formula turned out to be similar to the calculation using the first. Those. The cross-section of the cable core turned out to be underestimated by 0.2 mm 2.

Example No. 2

Let’s say the core diameter, when measured with a caliper, turns out to be 1.8 mm. Substituting given value into formula No. 1, we get:

S = 3.14*1.8 2 /4 = 2.5434 ≈ 2.5 mm 2

Those. the actual cross-section was 2.5 mm 2, which in principle corresponds to the standard value.

Stranded core

If you determine the cross-section of a stranded conductor, then you cannot measure the diameter using the monolithic conductor method, because the calculation will have a large error. To determine the cross-section of a stranded core, it is necessary to measure the diameter of each individual wire in the core.

If the total cross-section of the core is large enough, then measuring each wire is quite possible, because You can actually measure the diameter with a caliper. But if the stranded core has a small cross-section, then determining the diameter of each wire is very problematic due to the thinness of the conductor.

Instructions

To determine the cross-section of a round, measure its diameter using a micrometer or caliper. If you don't have a micrometer at hand, the diameter of the wire can be approximately determined using a regular ruler. To use this method, strip the wire of insulation to a length of half a meter to one meter. Wind 10 turns of wire around the ruler. The winding should be tight, turn to turn. Determine the length of the winding using the ruler scale and divide by ten. The resulting value is the desired wire diameter. To increase the accuracy of diameter determination, increase the number of winding turns.

Square the diameter of the wire, expressed in . Multiply the resulting value by the number PI, and then divide by four. The result of all actions will be the cross-section of the wire, in square millimeters. To obtain satisfactory accuracy, it is enough to take the value of the PI number equal to 3.14. The number of mathematical operations can be reduced if you divide the number PI by four in advance. In this case, the squared diameter is multiplied by 0.785.

It is somewhat more difficult to calculate the cross-section of a stranded wire. To find it, count the number of individual veins. Select one core and measure its diameter. Calculate the cross section of this core. Find the required cross-section of a stranded wire by multiplying the number of cores by the cross-section of one core.

If rectangular wire is used, determine its width and height using one of the above measuring instruments. The resulting values ​​should have a dimension of millimeters. Multiply the length by the width. The result of the multiplication is the cross-sectional area of ​​the rectangular wire.

Video on the topic

note

Attention: the geometric characteristics of the wire are determined in the absence of insulation on it. Neglecting this rule may lead to an overload of the electrical circuit or incorrect parameters of its operation.

Helpful advice

When purchasing, you can find out the wire cross-section by the marking. The first number following letter designation wire type, displays its cross-section.

Sources:

• how to calculate wire diameter

Tip 2: How to find the cross-sectional area of ​​a conductor

The maximum amount of current that can be safely passed through a conductor depends on factors such as the material of the conductor, its cross-sectional area, type of insulation, temperature conditions, etc. Cross-sectional area is the main of these factors. To determine it, it is necessary to carry out measurements and then calculations.

You will need

- voltmeter;

- caliper or micrometer;

- ruler;

- calculator.

Instructions

Completely de-energize the conductor in which you want to determine the cross-sectional area. Make sure that all capacitors in the device where it is located are discharged. If necessary, discharge them not with a short circuit, but with a load, and then check with a voltmeter that the capacitors are really discharged.

During all these actions, do not touch live parts; use insulated wires and probes. Measure the geometric parameters of the conductor in the place where there is no insulation on the conductor. What exactly to measure depends on what cross-sectional shape the conductor has. If it is round, you need to find out the diameter, if it is square - one of the sides, if it is rectangular - two perpendicular sides.

Do not apply voltage to the conductor until you remove the caliper or micrometer. The measurement result, if it is not in millimeters, is converted into these units, and then the value of the cross-sectional area will be obtained in square millimeters.

The diameter of any conductor must match the parameters specified in the documentation that comes with it. But in our time this is, unfortunately, rare. For example, if the marking says that the cable is 3 X 2.5, then its cross-section must be at least 2.5 mm2. But do not be surprised if, after checking, it turns out that the wire is 20-30% less than the declared figure. Therefore, it is better not to be lazy and check the size of the conductor before purchasing, otherwise it can lead to disastrous consequences.

Determination of wire cross-section by diameter

It is best to use a micrometer or caliper to measure the thickness (diameter) of the wire. Micrometers, whether mechanical or electronic, will show the most accurate result, but the results given by a caliper are also quite suitable. To take measurements, you should clean the wire from the plastic insulation, but not every seller will allow you to do this with the end of the wire on a coil put up for sale. Therefore, it is best to buy a meter of cable and then take measurements. Once data on the diameter of the core has been obtained, you can begin to calculate the cross-section.

Video:

You can measure the width of the conductor without resorting to precision instruments. Often, a person simply does not have them, and buying such a tool just to measure the wire diameter once is a waste of money. Therefore, you can resort to another method.

In this case, you will need a screwdriver and a regular ruler to measure. To carry out such a test, the wire will have to be stripped thoroughly, by 15 - 20 centimeters. Then the cleaned end of the core is wound around a flat, rounded metal part of a screwdriver in the manner of a spring, and each subsequent turn must be complete and fit tightly to the previous one. The number of turns is not critical, but it would be better to increase them to 10. This will make it easier to count. The width of tight 10 turns is measured with a ruler, the result is divided by 10 and, as a result, the diameter of one turn is obtained. You can see an example in the photo below.

At the top there is a photo in which such a “spring” is measured. It is clearly seen that the width of 11 tightly packed turns is 7.5 mm. We take a calculator and divide 7.5 mm by 11. It turns out that the diameter of the core being tested is 0.68 mm. Knowing it, you can calculate the cross-section of the wire.

We determine the cross-section of the wire by its diameter using the formula.

It doesn’t matter whether it’s a wire or a wire, its shape is invariably round, which means that in cross-section any cable core has the shape of a circle. The cross-section is nothing more than the circumference area of ​​the wire when cut. And the area of ​​any circle, knowing its diameter (and therefore its radius), can be easily found using a simple formula, familiar to everyone from school: S = πR2. “π” is a constant number and is always equal to 3.14, “R2” is the radius squared. We substitute the values ​​into the formula, first dividing the diameter by two to find out the radius, since in this formula the area is found out precisely with its help. It turns out: S = 3.14 X 0.342. Solving a simple example, we get the figure 0.36. That is, the cross-section of the wire being tested is 0.36 mm2. But it is better not to use such a “weak” wire in the power network.

Also, to determine the cross-section, the formula for finding the area of ​​a circle by diameter is also suitable. She looks different: S = π/4 X D2. It is more labor-intensive, but, one way or another, by substituting the numbers and solving the example, we get the same result.

Determination of wire cross-section according to the table.

When going to the store, it would be a good idea to take this table with you:

Conductor diameter	Conductor cross-section
0.8 mm	0.5 mm2
0.98 mm	0.75 mm2
1.13 mm	1 mm2
1.38 mm	1.5 mm2
1.6 mm	2.0 mm2
1.78 mm	2.5 mm2
2.26 mm	4.0 mm2
2.76 mm	6.0 mm2
3.57 mm	10.0 mm2
4.51 mm	16.0 mm2
5.64 mm	25.0 mm2

This will eliminate the need to make unnecessary calculations. Despite the fact that each cable coil has a tag that indicates its marking and all its parameters, you should not trust what is written. It would be better to play it safe and measure the diameter of the conductor, and then use the table to estimate approximately what its cross-section is.

In particular, the following will be written on the tag: “ VVNG 2x4" It follows that the cable has 2 cores, each with a cross-section of 4 mm2. To confirm or refute the stated parameters, we measure the diameter of the cable core without insulation using one of the methods. We carry out calculations.

If the cross-section coincides with that indicated on the tag, you can take it. If the resulting result is significantly less, you should opt for a more powerful cable that has the following parameters, or look in other stores for a higher quality conductor that meets GOST, which is a difficult task in our time. Stores prefer to buy something cheaper so that they can sell it at a higher price later. But a high-quality cable will never be cheap. Hence the conclusion.

Before you finally decide to purchase, you need to inspect the insulation very carefully. The plastic shell of the core must be continuous, have an impressive thickness, and be uniform along the entire length. If, in addition to discrepancies in diameter, negative nuances with the braid are also revealed, it is better to look not only for another cable, but also for another store, since, often, all types of cable sold in one place are purchased from the same manufacturer. Therefore, there is no guarantee that even if you take a cable with a more powerful parameter, its insulation will be better. It's not worth taking risks with electricity.

Still, it is better to overpay, spend more time searching, but buy a high-quality GOST conductor than one produced according to specifications. Only in such a case can it be guaranteed that the cable will serve the time stated in the documents without any problems, and, most likely, much longer. You should not risk the building just to reduce the search time or save extra pennies. Negligence when choosing a cable can cost disproportionately more.

Determination of the cross-section of a stranded wire.

Very often, the cores consist of many thin wires. What to do in this case? Some “clever guys” twist all the wires into one tight twist, measure it with a caliper and calculate the cross-section using the found diameter.

Table for determining the cross-section of stranded wire:

This is the wrong approach. To measure the cross-section of a stranded conductor, you need to measure the diameter of one small wire. Here only a micrometer will do. Having found out the cross-section of one wire, you should count the number of others, and multiply the cross-section of one by total number postings. Only in this case will the cross-section of the stranded wire have the correct parameters.

Imagine that you find an old electrical cable in your bins that you want to use. But you are faced with the problem of determining its cross section. It’s impossible to tell by eye; of course, there are no tags left on it. What to do? There are several methods based on the diameter of the core. That is, the wire diameter and cross-section are directly dependent on each other, which is confirmed by the circle formula, because the cross-sectional shape of the core is a circle. Here is the formula:

S=3.14d²/4=0.785d².

Therefore, it is necessary to first determine the diameter of the core.

Method No. 1

For this you will need a caliper. You just need to strip the core of insulation and measure the diameter. After which the resulting value is substituted into the circle formula. So much for the cross-sectional area of ​​the wire.

Let's just say that this option is the simplest and most accurate. Therefore, it is worth keeping this measuring tool in the electrician’s arsenal.

Method No. 2

It can be used in case you don’t have a caliper at hand. This determination process is not easy and requires a certain accuracy in carrying out all its stages. So, here you will need either a pencil, or a pen, or a screwdriver, or any tube made of dense material (preferably metal). Here is the algorithm of actions:

• Twenty to thirty centimeters of insulation is removed.
• Now we wind the wire around a pencil or other object described above. The more turns are made, the more accurate the indicator. In this case, the turns must be wound so that they are pressed tightly against each other.
• The number of turns is counted.
• The length of the twisted turns is measured using a regular ruler, that is, using a pencil from the first to the last.
• Now you need to carry out one mathematical operation - divide the length of the turns by their number. This will be the diameter of the wire.

Of course, it is not the most accurate, because everything will depend on how the cable core was wound. Here, as mentioned above, the density of turns is of primary importance. Now you can substitute the value of the wire diameter into the formula for the area of ​​a circle.

Method No. 3

This method concerns determining the cross-section of a wire based on the diameter of a stranded core. In fact, all of the above methods are suitable for this option, with only one condition. It is necessary to fluff up the vein, so to speak. Select one wire and measure its diameter with a caliper or use a pencil. Then the resulting value must be multiplied by the number of delays, which will not be difficult to calculate. This is the diameter of the core, which is substituted into the section formula.

Method No. 4

This is the so-called tabular method, that is, to determine the cable area you will need a table that shows the main parameters of the product. Such a table is also available on the Internet, so you shouldn’t have any problems finding it. You can refer to the PUE tables, which also describe the parameters and indicators of electrical cables.

Why do you need to know the wire cross-section?

Everyone knows that the thicker the wire, the more current loads it can withstand, the more power household appliances can be connected to it. Therefore, the cable cross-section is the main characteristic that will help avoid unpleasant moments associated with overheating of the electrical wiring, and, accordingly, the occurrence of fires.

There are certain standards that stipulate what cross-section (diameter) of the wire should be installed for the required current loads. These standards are determined by the electrical installation control rules (EPR), which contain tables. They clearly define positions related to area, material from which the wires are made, and current load or power consumption.

But there is one very subtle point that the buyer should know. There are electrical wires that are made according to technical specifications(TU), there are manufactured according to state standards (GOST). Their differences lie in the fact that products manufactured according to specifications sometimes have a smaller core diameter (ten to thirty percent), and, accordingly, a reduced cross-section. And this is the reason for the decrease current load, which the cable can pass through itself. Plus, the insulation is made in a thinner layer. You can probably guess what this could lead to.

Therefore, the recommendation: if you choose electrical wiring, manufactured according to technical specifications, it is recommended to choose its cross-section an order of magnitude higher. For example, according to your calculations, you need a 1.5 mm² cable, then it is better to choose 2.5 mm². In reality, this figure will be an area of ​​1.8-2.0 mm².

How can I find out what standards the wire was made to?

• Firstly, this must be indicated in the product quality certificate.
• Secondly, you can check the insulation. If it is soft and quickly removed from the core, then this is definitely a material made according to specifications.
• Third, measure the diameter of the wire with a caliper. And then, using the circle formula, calculate the area of ​​the core. In principle, this can be done on a cell phone calculator, that is, right in the store. If the calculated value corresponds to the nominal value, then this is a GOST material. If the value is lower, then this is a wire manufactured according to specifications.

Conclusion on the topic

As you can see, there are several ways to find out and determine the cross-section of a wire based on the diameter of the core. The simplest one is number one. But in this case you will need a caliper. If you have the Internet at hand, you can use the World Wide Web. That is, everyone chooses what is convenient for them at a certain point in time.