Section by diameter calculator. Cross-section of multi-core cable. Why do you need to calculate the cable load?

In the modern technological world, electricity has almost become on the same level of importance as water and air. It is used in almost any area of ​​human activity. The concept of electricity appeared back in 1600; before that, we knew about electricity no more than the ancient Greeks. But over time, it began to spread more widely, and only in 1920 did it begin to displace kerosene lamps from street lighting. Since then, electric current began to spread rapidly, and now it is available even in the most remote village, at least illuminating the house and for telephone communications.

Electricity itself is a stream of directed charges moving along a conductor. A conductor is a substance capable of passing these electric charges through itself, but each conductor there is resistance(except for the so-called superconductors, the resistance of superconductors is zero, this state is achievable by lowering the temperature to -273.4 degrees Celsius).

But, of course, there are no superconductors in everyday life, and it is still a long time before they appear on an industrial scale. In everyday life, as a rule, current is passed through wires, and is mainly used as a conductor. copper or aluminum wires. Copper and aluminum are popular primarily due to their conductivity properties, which is the inverse of electrical resistance, and also because they are cheap compared to, for example, gold or silver.

How to understand the cross-sections of copper and aluminum cables for wiring?

This article is intended to teach you how to calculate the cross-section of a wire. It's like the more water you want to supply, the larger the diameter of the pipe you need. So here, the greater the electrical current consumption, the larger the cross-section of cables and wires should be. I will briefly describe what it is: if you bite through a cable or wire and look at it from the end, you will see its cross-section, that is, the thickness of the wire, which determines the power that this wire is capable of transmitting when heated to the permissible temperature.

In order to select the correct cross-section of the power wire, we it is necessary to take into account the maximum value of the current load consumed. The current values ​​can be determined by knowing the rated power of the consumer, which is determined by the following formula: I=P/220, where P is the power of the current consumer, and 220 is the number of volts in your outlet. Accordingly, if the outlet is 110 or 380 volts, then we substitute this value.

It is important to know that the calculation of the value for single-phase and three-phase networks is different. In order to find out how many phases of the network you need, you need to calculate the total amount of current consumption in your home. Let's give an example of the average set of equipment that you may have at home.

A simple example of calculating cable cross-section based on current consumption, now we will calculate the sum of the powers of connected electrical appliances. The main consumers in an average apartment are the following devices:

• TV - 160 W
• Refrigerator - 300 W
• Lighting - 500 W
• Personal computer - 550 W
• Vacuum cleaner - 600 W
• Microwave oven - 700 W
• Electric kettle - 1150 W
• Iron - 1750 W
• Boiler (water heater) - 1950 W
• Washing machine - 2650 W
• Total 10310 W = 10.3 kW.

Once we know the total electricity consumption, we can use the formula to calculate the cross-section of the wire for the normal functioning of the wiring. It's important to remember that for single-phase and three-phase networks the formulas will be different.

Calculation of wire cross-section for a network with one phase (single-phase)

The wire cross-section is calculated using the following formula:

I = (P × K u) / (U × cos(φ))

I- current strength;

• P- power of all energy consumers in total
• K and- simultaneity coefficient, as a rule, the generally accepted value for calculations is 0.75
• U- phase voltage, which is 220V but can range from 210V to 240V.
• cos(φ)- for household single-phase appliances this value is fixed and equals 1.

When we have found the current consumption according to the formula, we can start choosing a cable, which suits us in terms of power. Or rather, its cross-sectional area. Below is a special table that provides data that compares the current value, cable cross-section and power consumption.

Data may vary for wires made of different metals. Today, for residential applications, copper, rigid cable is typically used. Aluminum cable is practically not used. But still, in many older houses, aluminum cable is still present.

Table of estimated cable current capacity. The choice of copper cable cross-section is made according to the following parameters:

We also provide a table for calculating the current consumption of an aluminum cable:

If the power value turns out to be an average between two indicators, then you need to select a larger wire cross-section value. Since there must be a power reserve.

Calculation of the wire cross-section of a network with three phases (three-phase)

Now let’s look at the formula for calculating the wire cross-section for three-phase networks.

To calculate the cross-section of the supply cable, we use the following formula:

I = P / (√3 × U × cos(φ))

• I- current strength by which the cross-sectional area of ​​the cable is selected
• U- phase voltage, 220V
• Cosφ - phase angle
• P- shows the total consumption of all electrical appliances

Cosφ- in the above formula is extremely important, since it personally affects the current strength. It varies for different equipment; this parameter can most often be found in the technical documentation, or the corresponding marking on the case.

The total power is found very simply, we sum up the value of all power indicators and use the resulting number in the calculations.

A distinctive feature in a three-phase network is that a thinner wire can withstand a larger load. We select the required wire cross-section according to the table below.

Calculation of wire cross-section by current consumption used in a three-phase network is used using such a value as √3 . This value is needed to simplify the appearance of the formula itself:

U linear = √3 × U phase

In this way, if the need arises, the product of the root and phase voltage is replaced by the linear voltage. This value is equal to 380V (U linear = 380V).

Concept of continuous current

Also, one equally important point when choosing a cable for a three-phase and single-phase network is that it is necessary to take into account a concept that sounds like permissible long-term current. This parameter shows us the current strength in the cable that the wire can withstand for an unlimited amount of time. You can define the ego in a special table. They also differ significantly for aluminum and copper conductors.

When this parameter exceeds the permissible values, the conductor begins to overheat. The heating temperature is inversely proportional to the current strength.

Temperatures may increase in some areas not only due to incorrectly selected wire cross-section, and also with poor contact. For example, in the place where wires are twisted. This quite often happens at the point of contact between copper cables and aluminum cables. In this regard, the surface of the metals undergoes oxidation, becoming covered with an oxide film, which greatly impairs the contact. In such a place the cable will heat up above the permissible temperature.

When we have carried out all the calculations and checked the data from the tables, you can safely go to a specialized store and buy the cables you need for laying a network at home or in the country. Your main advantage over, for example, your neighbor will be that you have fully understood this issue with the help of our article, and you will save a lot of money without overpaying for what the store wanted to sell you. Yes, and knowing how to calculate the current cross-section for copper or aluminum wires will never be superfluous, and we are sure that the knowledge gained from us will come in handy many times on your life’s journey.

Wires are widely used in the field of electrical networks for various purposes. At first glance, energy transportation through cables and wires seems simple and understandable.

However, to ensure safe operation of electrical wiring, it is necessary to take into account a number of important nuances when designing and arranging electrical networks. One of these details is the ability to correctly calculate the cross-section of a wire by diameter, because the limit of the permissible current flowing through the conductor depends on the accuracy of the determination.

How to determine the cross-section or diameter, is there a difference between these parameters? Let's try to figure it out in the article. In addition, we have prepared summary tables that will help you choose a conductor depending on the installation conditions of the electrical network, the material of the cable core and the power characteristics of the connected units.

Electric current powers a wide variety of equipment with varying power levels. And the power range is very wide.

Each individual electrical device represents a load, depending on the magnitude of which a current supply of a certain strength is required.

By “default” or simple ignorance of the basics of electrical engineering, it is easy to connect conductors, ignoring all existing requirements for diameters and cross-sections. Another question is what can come out of this practice during operation.

The required amount of current for the required load can be passed through wires of different diameters (sections).

But when the cross-section of the conductor is insufficient to pass a given amount of current, the effect of increased resistance occurs. As a result, heating of the wire (cable) is noted.

If you ignore this phenomenon and continue to pass current, there is a real danger of heating up to the point of fire. This situation threatens a serious emergency. That is why increased attention must be paid to calculations and selection of current transmission circuits to the load.

The consequences of inaccurate calculations of electrical conductors by cross-section (diameter) can be accompanied by phenomena ranging from minor deformation of the insulating material to a real fire and a major fire

Correct calculation and proper selection also have a positive effect on the operation of equipment acting as a load.

So, in addition to the safety factor, calculating the cross-sections of the electrical cable by diameter or vice versa is a mandatory action from the point of view of ensuring the efficient operation of electrical machines.

Determining the diameter of the conductor core

Actually, this operation can be performed with a simple linear measurement. For accurate measurements, it is recommended to use a point tool, such as a caliper, or even better, a micrometer.

A relatively low accuracy result, but quite acceptable for many applications of wires, is obtained by measuring the diameter with a regular ruler.

By the way, the insulating coating of, for example, a copper wire is also considered to be a thin layer of sprayed varnish, which also needs to be removed when a very precise calculation is required.

There is a “household” method of measuring diameter, suitable in cases where point measuring instruments are not available. To use this method, you will need an electrician's screwdriver and a school ruler.

The conductor for measurement is first stripped of insulation, after which it is wound tightly turn to turn on the screwdriver rod. Usually ten turns are wound - a convenient number for mathematical calculations.

In fact, it turns out that one sheet of paper or a picture loaded into a smartphone contains voluminous technical information that allows you to do without the above-mentioned mathematical (linear) calculations.

Moreover, many manufacturers of cable products, in order to make it easier for the buyer to choose the right conductor, for example, for installing sockets, offer a table in which all the necessary values ​​are entered.

All that remains is to determine what load is planned for a specific electrical point and how the installation will be performed, and based on this information, select the correct wire with copper or aluminum conductors.

Examples of such options for calculating the cross-sectional diameter of a wire are given in the table, which discusses options for copper and aluminum conductors, as well as methods for laying wiring - open or hidden type. From the first table you can determine the indicator.

Table of cross-sectional diameters of copper and aluminum conductors depending on installation conditions

In addition, there is a standard for cross-sections and diameters that applies to round (shaped) unsealed and sealed conductive conductors of cables, wires, and cords. These parameters are regulated GOST 22483-2012.

The standard covers cables made of copper (tinned copper), aluminum wire without metal coating or with metal coating.

Copper and aluminum conductors of cables and wires for stationary installation are divided into classes 1 and 2. Wires, cords, cables for non-stationary and stationary installation, where an increased degree of flexibility in installation is required, are divided into classes from 3 to 6.

Conformity table by class for cable (wire) copper conductors

For aluminum conductors and cables, GOST 22483-2012 also provides parameters for the nominal cross-section of the core, which correspond to the corresponding diameter, depending on the class of the core.

Moreover, according to the same GOST, the indicated diameters can be used for class 1 copper conductor if you need to calculate its minimum diameter.

Conformity table by class for cable (wire) aluminum conductors

Working with electrical wires always requires a responsible attitude from a calculation point of view.

Therefore, an electrician of any rank must know the calculation methodology and be able to use existing technical tables. This achieves not only significant cost savings on installation due to accurate calculations, but most importantly, the safety of operation of the introduced line is guaranteed.

Do you have anything to add or have questions about determining the wire cross-section? You can leave comments on the publication, participate in discussions and share your own experience in selecting wires for installing an electrical network in a house or apartment. The contact form is located in the lower block.

When purchasing, you should always pay attention to its actual cross-section, since you can often find cable products in stores with a cross-section that does not correspond to its marking, and significantly so. And this, as you understand, can lead to overheating of the cable and ultimately to a short circuit.

To independently calculate the actual wire cross-section, several simple methods will help us. The most convenient way is to calculate the cross-section of the wire based on its diameter. To do this you will need a micrometer or caliper.

Having measured the diameter of the core, we recall the formula for the area of ​​a circle:

For example, let’s take a wire whose insulation is marked VVGng 3×2.5. We measure the diameter of the core with a caliper - we get 1.7 mm. Next, we substitute this value into the formula:

Skr = 0.785 x 1.7 x 1.7 = 2.27 mm2.

It turns out that the actual cross-section of the wire is 2.27 mm2 instead of the stated 2.5.

Everything is clear with a single-core wire, but what about multi-core?

Everything is about the same here. We take one core from a stranded wire and measure it with a caliper. For example, the diameter turned out to be 0.4 mm.

Skr = 0.785 x 0.4 x 0.4 = 0.125 mm2.

Then we count the total number of veins in the wire, suppose 12.

Now we find out the total cross-section of the wire by multiplying the value of one core 0.125 mm2 by the number of cores - 12.

S = 0.125 x 12 = 1.5mm2- this is the actual cross-section of the wire.

Of course, not everyone has a caliper, much less a micrometer, in which case you will have to go another way.

To do this, we will need a ruler and a pencil, or some kind of round rod, from available means. We remove the insulation from the wire and wind about 10 turns around the rod. The main thing is that the turns fit tightly to each other, without gaps.

Using a ruler, measure the length of the winding and divide by the number of turns. We get the diameter of the core. And then, using the same formula, we find the cross-section of the core. The method is quite accurate, but not very convenient - and you can’t measure it in a store this way and you can’t wind thick wires.

In order not to calculate the cross-section each time on a calculator, below I will post a table of the correspondence of diameters and cross-sections of wires, which contains the most common sizes. You can rewrite it or print it out and take it with you to the store. All that remains is to measure the diameter of the core and compare it with the value from the table. If the measured value differs significantly from the table, then it is better not to buy such a cable.

Proper selection of cables for restoration or installation of electrical wiring guarantees flawless operation of the system. The devices will receive full power. There will be no overheating of the insulation with subsequent destructive consequences. A reasonable calculation of the wire cross-section according to power will eliminate both the threat of ignition and the unnecessary costs of purchasing expensive wire. Let's look at the calculation algorithm.

In simple terms, a cable can be compared to a pipeline transporting gas or water. In the same way, a flow moves along its core, the parameters of which are limited by the size of a given current-carrying channel. The consequence of incorrect selection of its cross-section are two common erroneous options:

• The current-carrying channel is too narrow, due to which the current density increases significantly. An increase in current density entails overheating of the insulation, then its melting. As a result of melting, “weak” places for regular leaks will appear at a minimum, and at a maximum there will be a fire.
• The vein is too wide, which is actually not bad at all. Moreover, the presence of space for transporting electric current has a very positive effect on the functionality and operational life of the wiring. However, the owner’s pocket will be lightened by an amount approximately twice the amount actually required.

The first of the erroneous options is downright dangerous; at best, it will lead to an increase in electricity bills. The second option is not dangerous, but extremely undesirable.

"Traveled" paths of computing

All existing calculation methods are based on Ohm's law, according to which current multiplied by voltage equals power. Household voltage is a constant value, equal to standard 220 V in a single-phase network. This means that only two variables remain in the legendary formula: current and power. You can and should “dance” in calculations from one of them. Using the calculated values ​​of current and expected load in the PUE tables, we will find the required cross-sectional size.

Please note that the cable cross-section is calculated for power lines, i.e. for wires to sockets. Lighting lines are a priori laid with a cable with a traditional cross-sectional area of ​​1.5 mm².

If the room being equipped does not have a powerful disco spotlight or chandelier that requires a power supply of 3.3 kW or more, then it makes no sense to increase the cross-sectional area of ​​the lighting cable core. But the rosette issue is a purely individual matter, because... Such unequal tandems as a hair dryer with a water heater or an electric kettle with a microwave can be connected to the same line.

For those who plan to load the power line with an electric hob, boiler, washing machine and similar “gluttonous” equipment, it is advisable to distribute the entire load over several outlet groups.

If it is not technically possible to divide the load into groups, experienced electricians recommend laying a cable with a copper core cross-section of 4-6 mm² without any fuss. Why with a copper current-carrying core? Because the strict PUE code prohibits laying cables with aluminum “filling” in housing and in actively used domestic premises. Electrical copper has much less resistance, it passes more current and does not heat up like aluminum. Aluminum wires are used in the construction of external overhead networks; in some places they still remain in old houses.

Note! The cross-sectional area and diameter of the cable core are two different things. The first is indicated in square mm, the second simply in mm. The main thing is not to confuse!

To search for tabular values ​​of power and permissible current, you can use both indicators. If the table shows the size of the cross-sectional area in mm², and we only know the diameter in mm, the area must be found using the following formula:

Calculation of section size based on load

The simplest way to select a cable with the required size is to calculate the wire cross-section based on the total power of all units connected to the line.

The calculation algorithm is as follows:

• First, let's decide on the units that we can presumably use at the same time. For example, while the boiler is operating, we suddenly want to turn on the coffee grinder, hair dryer and washing machine;
• then, according to the technical data sheets or according to approximate information from the table below, we simply sum up the power of household units simultaneously operating according to our plans;
• Let's assume that in total we have 9.2 kW, but this specific value is not in the PUE tables. This means that you will have to round up to a safe higher side - i.e. take the closest value with some excess power. This will be 10.1 kW and the corresponding cross-sectional value is 6 mm².

We direct all roundings upward. In principle, it is possible to sum up the current strength indicated in the data sheets. Calculations and rounding for current are carried out in a similar way.

How to calculate the current cross section?

Table values ​​cannot take into account the individual characteristics of the device and network operation. The specificity of the tables is average. They do not list the parameters of the maximum permissible currents for a particular cable, but they differ for products of different brands. The type of gasket is touched upon very superficially in the tables. For meticulous craftsmen who reject the easy way of searching through tables, it is better to use the method of calculating the size of the wire cross-section by current. More precisely, by its density.

Allowable and operating current density

Let's start with mastering the basics: remember in practice the derived interval 6 - 10. These are the values ​​​​obtained by electricians over many years of “experimental testing”. The strength of the current flowing through 1 mm² of copper core varies within the specified limits. Those. a cable with a copper core with a cross-section of 1 mm² without overheating and melting of the insulation allows a current of 6 to 10 A to easily reach the waiting consumer unit. Let's figure out where it came from and what the designated interval fork means.

According to the code of electrical laws PUE, 40% is allocated to the cable for overheating that is not dangerous for its sheath, which means:

• 6 A distributed per 1 mm² of current-carrying core is the normal operating current density. Under these conditions, the conductor can work indefinitely without any time restrictions;
• 10 A distributed per 1 mm² of copper core can flow through the conductor for a short time. For example, when you turn on the device.

An energy flow of 12 A in a copper millimeter channel will initially be “crowded”. Due to the crowding and crowding of electrons, the current density will increase. The temperature of the copper component will then increase, which will invariably affect the condition of the insulating shell.

Please note that for a cable with aluminum current-carrying conductor, the current density displays an interval of 4 - 6 Amperes per 1 mm² of conductor.

We found out that the maximum current density for a conductor made of electrical copper is 10 A per cross-sectional area of ​​1 mm², and normal is 6 A. Therefore:

• a cable with a conductor cross-section of 2.5 mm² will be able to transport a current of 25 A in just a few tenths of a second when the equipment is turned on;
• it will be able to transmit a current of 15A indefinitely.

The above current densities are valid for open wiring. If the cable is laid in a wall, in a metal sleeve or, the specified current density value must be multiplied by a correction factor of 0.8. Remember one more subtlety in organizing open wiring. For reasons of mechanical strength, cables with a cross-section of less than 4 mm² are not used in open circuits.

Studying the calculation scheme

There will be no super complex calculations again; calculating the wire for the upcoming load is extremely simple.

• First, let's find the maximum permissible load. To do this, we summarize the power of the devices that we plan to simultaneously connect to the line. Let's add up, for example, the power of a washing machine 2000 W, a hair dryer 1000 W and an arbitrary heater 1500 W. We received 4500 W or 4.5 kW.
• Then we divide our result by the standard voltage of a household network of 220 V. We got 20.45 ... A, round up to a whole number, as expected.
• Next, we introduce a correction factor, if necessary. The value with the coefficient will be equal to 16.8, rounded 17 A, without the coefficient 21 A.
• We remember that we calculated the operating power parameters, but we also need to take into account the maximum permissible value. To do this, we multiply the current strength we calculated by 1.4, because the correction for thermal effects is 40%. We got: 23.8 A and 29.4 A, respectively.
• This means that in our example, for safe operation of open wiring, a cable with a cross-section of more than 3 mm² will be required, and for a hidden version, 2.5 mm².

Let's not forget that, due to various circumstances, we sometimes turn on more units at the same time than we expected. That there are also light bulbs and other devices that consume little energy. Let's stock up on some reserve section in case of increasing the fleet of household appliances and, with the calculations, go for an important purchase.

Video guide for accurate calculations

Which cable is better to buy?

Following the strict recommendations of the PUE, for the arrangement of personal property we will buy cable products with the “letter groups” NYM and VVG in the marking. They are the ones who do not cause any complaints or quibbles from electricians and firefighters. Option NYM is an analogue of domestic VVG products.

It is best if the domestic cable is accompanied by the NG index, this means that the wiring will be fire resistant. If you intend to lay the line behind a partition, between joists or above a suspended ceiling, buy products with low smoke emission. They will have the LS index.

This is a simple way to calculate the cross-section of the cable conductor. Information about the principles of calculations will help you rationally select this important element of the electrical network. The necessary and sufficient size of the current-carrying core will provide power to home appliances and will not cause a fire in the wiring.

We'll tell you how to calculate the cable cross-section and power by diameter - our tables and formulas will help you carry out the calculations yourself. In order to understand which wire you will need in different situations, you should distinguish the diameter of the cable cross-section. The table of values ​​can tell amateur electricians how to choose the right cable depending on its purpose in the future - connecting powerful, large equipment or carrying electrical wiring into the house.

To carry out the measurement procedure yourself, it will be easiest to use special instruments: for example, using a micrometer you can get the most accurate result, which cannot be achieved with a regular ruler, although it can be used for such purposes. It should be remembered that the use of improvised means requires great precision and knowledge of calculation formulas.

General information about cable and wire

When working with conductors, it is necessary to understand their designation. There are wires and cables that differ from each other in their internal structure and technical characteristics. However, many people often confuse these concepts.

By wire is a conductor that has in its design one wire or a group of wires woven together and a thin common insulating layer.

Cable also called a core or a group of cores that have both their own insulation and a common insulating layer (sheath).

Each type of conductor will have its own methods for determining cross sections, which are almost similar.

Conductor materials

The amount of energy that a conductor transmits depends on a number of factors, the main one of which is the material of the current-carrying conductors.

The following non-ferrous metals can be used as the core material of wires and cables:
1. Aluminum. Cheap and lightweight conductors, which is their advantage. They are characterized by such negative qualities as low electrical conductivity, a tendency to mechanical damage, high transient electrical resistance of oxidized surfaces;
2. Copper. The most popular conductors, which have a high cost compared to other options. However, they are characterized by low electrical and transition resistance at the contacts, fairly high elasticity and strength, and ease of soldering and welding;
3. Aluminum copper. Cable products with aluminum cores coated with copper. They are characterized by slightly lower electrical conductivity than their copper counterparts. They are also characterized by lightness, average resistance and relative cheapness.

How and with what to measure the diameter of a wire (wire)

To measure the diameter of the wire, a caliper or micrometer of any type (mechanical or electronic) is suitable. It’s easier to work with electronic ones, but not everyone has them. You need to measure the core itself without insulation, so first move it aside or remove a small piece. This can be done if the seller allows it. If not, buy a small piece to test and take measurements on it.

On a conductor stripped of insulation, measure the diameter, after which you can determine the actual cross-section of the wire from the found dimensions. Which measuring device is better in this case? If we talk about mechanical models, then a micrometer. Its measurement accuracy is higher. If we talk about electronic options, then for our purposes they both give quite reliable results.

If you don't have a caliper or micrometer, take a screwdriver and a ruler with you. You'll have to strip a fairly decent piece of conductor, so you'll hardly be able to do without buying a test sample this time. So, remove the insulation from a 5-10 cm piece of wire.

Wind the wire around the cylindrical part of the screwdriver. Lay the coils close to each other, without a gap. All turns must be complete, that is, the “tails” of the wire must stick out in one direction - up or down, for example.

The number of turns is not important - about 10. You can have more or less, it’s just easier to divide by 10. Count the turns, then apply the resulting winding to the ruler, aligning the beginning of the first turn with the zero mark (as in the photo). Measure the length of the section occupied by the wire, then divide it by the number of turns. You get the diameter of the wire. It's that simple.

For example, let's calculate the size of the wire shown in the photo above. The number of turns in this case is 11, they occupy 7.5 mm. Divide 7.5 by 11, we get 0.68 mm. This will be the diameter of this wire. Next, you can look for the cross section of this conductor.

Methods for measuring conductor diameter

When selecting 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 exposed part of the conductor.

The device is simply attached to the core, clamped between the jaws, and the result is displayed on the scale. 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 do calculations, albeit very simple ones. More on this method later.

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 quite accurate.
Take a piece of wire about 10-20 cm long and 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 carefully, 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. Firstly, you can lay the wire loosely. Secondly, it is not enough to take accurate measurements. But if you do everything carefully, the discrepancies with the actual sizes will not be so large.

Application of measuring instruments

To determine the diameter of the cores of wires and cables, various measuring instruments are widely used, showing the most accurate results. Basically, the use of micrometers and calipers is practiced for these purposes. Despite their high efficiency, a significant drawback of these devices is their high cost, which is of great importance if the tool is planned to be used only 1-2 times.

As a rule, professional electricians who are constantly engaged in electrical installation work use special devices. With the right approach, it becomes possible to measure the diameter of wire cores even on working lines.

About choosing a cable brand for home wiring

Making apartment electrical wiring from aluminum wires at first glance seems cheaper, but operating costs due to low reliability of contacts over time will be many times higher than the costs of electrical wiring made from copper.

Which wire is better to use when installing electrical wiring, single-core or stranded? From the point of view of the ability to conduct current per unit of cross-section and installation, single-core is better. So for home wiring you only need to use solid wire.

Stranded allows multiple bends, and the thinner the conductors in it, the more flexible and durable it is. Therefore, stranded wire is used to connect non-stationary electrical appliances to the electrical network, such as an electric hair dryer, an electric razor, an electric iron and all the others.

After deciding on the cross-section of the wire, the question arises about the brand of cable for electrical wiring. The choice here is not great and is represented by only a few brands of cables: PUNP, VVGng and NYM.

PUNP cable since 1990, in accordance with the decision of Glavgosenergonadzor “On the ban on the use of wires such as APVN, PPBN, PEN, PUNP, etc., produced according to TU 16-505. 610-74 instead of APV, APPV, PV and PPV wires according to GOST 6323-79*" is prohibited for use.

Cable VVG and VVGng - copper wires in double polyvinyl chloride insulation, flat shape. Designed for operation at ambient temperatures from −50°С to +50°С, for wiring inside buildings, outdoors, in the ground when laid in tubes. Service life up to 30 years.

The letters “ng” in the brand designation indicate the non-flammability of the wire insulation. Two-, three- and four-core wires are available with core cross-sections from 1.5 to 35.0 mm 2 . If in the cable designation there is a letter A (AVVG) before VVG, then the conductors in the wire are aluminum.

The NYM cable (its Russian analogue is the VVG cable) with round copper cores with non-flammable insulation, complies with the German standard VDE 0250. Technical characteristics and scope of application are almost the same as the VVG cable. Two-, three- and four-core wires are available with core cross-sections from 1.5 to 4.0 mm 2 .

As you can see, the choice for laying electrical wiring is not large and is determined depending on what shape the cable is more suitable for installation, round or flat. A round-shaped cable is more convenient to lay through walls, especially if the connection is made from the street into the room. You will need to drill a hole slightly larger than the diameter of the cable, and with a larger wall thickness this becomes relevant. It is more convenient to use a VVG flat cable.

Dependence of current, power and core cross-section

It is not enough to measure and calculate the cross-sectional area of ​​the cable based on the diameter of the core. Before installing wiring or other types of electrical networks, it is also necessary to know the capacity of the cable products.

When choosing a cable, you must be guided by several criteria:
• the strength of the electric current that the cable will pass;
• consumer power;

Power

The most important parameter during electrical installation work (in particular, cable laying) is throughput. The maximum power of electricity transmitted through it depends on the cross-section of the conductor. Therefore, it is extremely important to know the total power of the energy consumption sources that will be connected to the wire.

Typically, manufacturers of household appliances, appliances and other electrical products indicate on the label and in the documentation accompanying them the maximum and average power consumption.

For example, a washing machine can consume electricity ranging from tens of W/h during rinsing mode to 2.7 kW/h when heating water.

Accordingly, a wire with a cross-section that is sufficient to transmit electricity of maximum power must be connected to it. If two or more consumers are connected to the cable, then the total power is determined by adding the limit values ​​of each of them.

The average power of all electrical appliances and lighting devices in an apartment rarely exceeds 7500 W for a single-phase network. Accordingly, the cable cross-sections in the electrical wiring must be selected to this value.

In individual residential buildings, a three-phase power supply system of 380 V is often used. However, most equipment is not designed for such electrical voltage. A voltage of 220 V is created by connecting them to the network through a neutral cable with an even distribution of the current load across all phases.

Electric current

Often the power of electrical equipment and equipment may not be known to the owner due to the absence of this characteristic in the documentation or completely lost documents and labels. There is only one way out in such a situation - to calculate using the formula yourself.

Power is determined by the formula:

P = U*I

Where:
• P – power, measured in watts (W);
• I – electric current strength, measured in amperes (A);
• U is the applied electrical voltage, measured in volts (V).

When the strength of the electric current is unknown, it can be measured using instrumentation:
• ammeter;
• multimeter;
• current clamps.

After determining the power consumption and electric current, you can use the table below to find out the required cable cross-section.

Calculation of the cross-section of cable products based on current load must be carried out to further protect them from overheating. When too much electric current passes through conductors for their cross-section, destruction and melting of the insulating layer can occur.

The maximum permissible long-term current load is the quantitative value of the electric current that can pass the cable for a long time without overheating. To determine this indicator, it is initially necessary to sum up the powers of all energy consumers.

After this, calculate the current load using the formulas:

single-phase network: I = P ∑ *Ki/U

three-phase network: I = P ∑ *Ki/(√3*U)

Where:
• P ∑ – total power of energy consumers;
• Ki – coefficient equal to 0.75;
• U – electrical voltage in the network.

Stranded wire

The PVS cable for connecting power tools and electrical appliances is made flexible, since all the cores are stranded. Measuring the diameter of the harness at the same time will give an incorrect result, since there are air gaps inside. The correct calculation principle is the same as for cable.

The core should be fluffed up, count how many wires are in it, and then measure the diameter of one of them. Knowing their total number in the vein, you can calculate the total cross-section using the previous formula. It’s best to take measurements using a micrometer. It is more convenient to use, since the caliper easily presses through thin wires.

Segment cable

A cable with a cross-section of up to 10 mm 2 is always made round. They can always provide the household needs of an apartment or private house. With a larger cable cross-section, the input cores from the external power supply are made segmental, which is difficult to calculate. It is convenient to determine the cross-sectional area when there is a ready-made calculation table. To do this, you must first measure the height and width of the segment.

How to calculate the cross-section of a stranded wire

Stranded wire, or as it is also called stranded or flexible, is a single-core wire twisted together. To calculate the cross-section of a stranded wire, you must first calculate the cross-section of one wire, and then multiply the resulting result by their number.

Let's look at an example. There is a multi-core flexible wire, in which there are 15 cores with a diameter of 0.5 mm. The cross-section of one core is 0.5 mm × 0.5 mm × 0.785 = 0.19625 mm 2, after rounding we get 0.2 mm 2. Since we have 15 wires in the wire, to determine the cable cross-section we need to multiply these numbers. 0.2 mm2×15=3 mm2. It remains to determine from the table that such a stranded wire will withstand a current of 20 A.

You can estimate the load capacity of a stranded wire without measuring the diameter of an individual conductor by measuring the total diameter of all twisted wires. But since the wires are round, there are air gaps between them. To eliminate the gap area, you need to multiply the result of the wire cross-section obtained from the formula by a factor of 0.91. When measuring the diameter, you need to make sure that the stranded wire does not flatten.

Let's look at an example. As a result of measurements, the stranded wire has a diameter of 2.0 mm. Let's calculate its cross-section: 2.0 mm × 2.0 mm × 0.785 × 0.91 = 2.9 mm 2. Using the table (see below), we determine that this stranded wire will withstand a current of up to 20 A.

Undersized wire cross-section - what is the danger?

So, let's consider the dangers that await us when using low-quality wires in everyday life. It is clear that the current characteristics of current-carrying conductors decrease in direct proportion to the decrease in their cross-section. The load capacity of the wire decreases due to the reduced cross-section. According to the standards, the current that the wire can pass through is calculated. It will not collapse if less current passes through it.

The resistance between the cores decreases if the insulation layer is thinner than required. Then, in an emergency situation, when the supply voltage increases, a breakdown may occur in the insulation. If, along with this, the core itself has a reduced cross-section, that is, it cannot pass the current that, according to standards, it should pass, the thin insulation begins to gradually melt.

All these factors will inevitably lead to a short circuit and then to a fire. A fire occurs from sparks that appear during a short circuit. Let me give you an example: a three-core copper wire (for example, with a cross-section of 2.5 2), according to regulatory documentation, can pass 27 A for a long time, usually 25 A is considered.

But the wires that come into my hands, produced in accordance with the specifications, actually have a cross-section from 1.8 mm 2 to 2 mm 2 (this is with the declared 2.5 mm 2). Based on the regulatory documentation, a wire with a cross-section of 2 mm2 can carry a current of 19 A for a long time.

Therefore, if a situation occurs when a current designed for such a cross-section flows through the wire you have chosen, which supposedly has a cross-section of 2.5 mm 2, the wire will overheat. And with prolonged exposure, the insulation will melt, followed by a short circuit.

Now imagine the consequences of all this! It’s especially disappointing when a beautiful renovation has been made, new appliances have been installed, for example, an air conditioner, an electric oven, a hob, a washing machine, an electric kettle, a microwave oven. And so you put the buns in the oven to bake, started the washing machine, turned on the kettle, and even the air conditioner, since it became hot.

These switched on devices are enough to cause smoke to come out of junction boxes and sockets. Then you will hear a pop, which is accompanied by a flash. And after that the electricity will disappear. Everything will still end well if you have .

What if they are of low quality? Then you won't get away with a bang and a flash. A fire will start, accompanied by sparks from the wiring burning in the wall. The wiring will burn in any case, even if it is tightly walled under the tile.

The picture I described makes it clear how responsibly you need to choose wires. After all, you will use them in your home. This is what it means to follow not GOSTs, but TUs.

Calculation of the cross-section of electrical wiring according to the power of connected electrical appliances

To select the cross-section of the cable wires in your home or home, you need to analyze the fleet of existing electrical household appliances from the point of view of their simultaneous use. The table provides a list of popular household electrical appliances indicating the current consumption depending on the power.

You can find out the power consumption of your models yourself from the labels on the products themselves or data sheets; often the parameters are indicated on the packaging. If the current consumed by an electrical appliance is not known, it can be measured using an ammeter.

Table of power consumption and current for household electrical appliances at a supply voltage of 220 V

Typically, the power consumption of electrical appliances is indicated on the housing in watts (W or VA) or kilowatts (kW or kVA). 1 kW=1000 W.

Current is also consumed by the refrigerator, radiotelephone, chargers, and TV in standby mode. But in total this power is no more than 100 W and can be ignored in calculations.

If you turn on all the electrical appliances in the house at the same time, you will need to select a wire cross-section capable of passing a current of 160 A. You will need a finger-thick wire! But such a case is unlikely. It’s hard to imagine that someone is capable of grinding meat, ironing, vacuuming and drying hair at the same time.

Calculation example. You got up in the morning, turned on the electric kettle, microwave, toaster and coffee maker. The current consumption will accordingly be:

7 A + 8 A + 3 A + 4 A = 22 A

Taking into account the switched on lighting, refrigerator and, in addition, for example, a TV, the current consumption can reach 25 A.

Selecting a wire cross-section for connecting electrical appliances to a three-phase 380 V network

When operating electrical appliances, for example, an electric motor, connected to a three-phase network, the consumed current no longer flows through two wires, but through three and, therefore, the amount of current flowing in each individual wire is somewhat less. This allows you to use a smaller cross-section wire to connect electrical appliances to a three-phase network.

To connect electrical appliances to a three-phase network with a voltage of 380 V, for example an electric motor, the wire cross-section for each phase is taken 1.75 times smaller than for connecting to a single-phase 220 V network.
Attention, when choosing a wire cross-section for connecting an electric motor based on power, you should take into account that the nameplate of the electric motor indicates the maximum mechanical power that the motor can create on the shaft, and not the electrical power consumed.

The electrical power consumed by the electric motor, taking into account efficiency and cos φ, is approximately two times greater than that created on the shaft, which must be taken into account when choosing the wire cross-section based on the motor power indicated on the plate.

For example, you need to connect an electric motor that consumes power from a 2.0 kW network. The total current consumption of an electric motor of such power in three phases is 5.2 A. According to the table, it turns out that a wire with a cross-section of 1.0 mm 2 is needed, taking into account the above 1.0 / 1.75 = 0.5 mm 2. Therefore, to connect a 2.0 kW electric motor to a three-phase 380 V network, you will need a three-core copper cable with a cross-section of each core of 0.5 mm 2.

It is much easier to choose the wire cross-section for connecting a three-phase motor based on the current consumption, which is always indicated on the nameplate. For example, the current consumption of a 0.25 kW motor for each phase at a supply voltage of 220 V (the motor windings are connected in a delta configuration) is 1.2 A, and at a voltage of 380 V (the motor windings are connected in a star configuration) it is only 0.7 A.

Taking the current strength indicated on the nameplate, according to the table for selecting the wire cross-section for apartment electrical wiring, we select a wire with a cross-section of 0.35 mm 2 when connecting the electric motor windings in a “triangle” pattern or 0.15 mm 2 when connecting in a “star” pattern.

Knowing the diameter of the wire, you can determine its cross-section using a ready-made dependence table. The table for calculating the cable cross-section by core diameter looks like this:

Wire cross-section and power table

When the cross-section is known, it is possible to determine the permissible power and current values ​​for copper or aluminum wire. In this way, it will be possible to find out what load parameters the current-carrying core is designed for. To do this, you will need a table of the dependence of the cross section on the maximum current and power.

As we can see from the table, the cross-section of the cores depends, in addition to the load, on the material from which the wire is made.

Parallel connection of electrical wiring wires

There are hopeless situations when you urgently need to lay wiring, but there is no wire of the required cross-section available. In this case, if there is a wire with a smaller cross-section than necessary, then the wiring can be made from two or more wires, connecting them in parallel. The main thing is that the sum of the sections of each of them is not less than the calculated one.

For example, there are three wires with a cross section of 2, 3 and 5 mm 2, but according to calculations, 10 mm 2 is needed. Connect them all in parallel and the wiring will handle up to 50 amps. Yes, you yourself have repeatedly seen the parallel connection of a large number of thin conductors to transmit large currents.

And when installing and removing the battery, it is necessary to move the wires to the side, that is, the wire must be flexible enough. The method of increasing the cross-section of an electrical wire by connecting several wires of different diameters in parallel can be used only as a last resort. When laying home electrical wiring, it is permissible to connect in parallel only wires of the same cross-section taken from the same reel.