Which cable is better to use for wiring in an apartment: brands, sections, choice. Calculation of cable cross-section by current, power, length Select conductor cross-section

Cable products are now presented on the market in a wide range, the cross-section of the cores ranges from 0.35 mm2. and above, this article will give an example cable cross-section calculation.

To calculate the conductor resistance, you can use the conductor resistance calculator.

Wrong selection of cable cross-section for household wiring, can lead to the following results:

1. A linear meter of too thick core will cost more, which will cause a significant “blow” to the budget.

2. The conductors will soon begin to heat up and will melt the insulation if the wrong conductor diameter is selected (smaller than necessary) and this can soon lead to a short circuit or spontaneous combustion of the electrical wiring.

In order not to waste money, it is necessary to carry out the correct installation before installing electrical wiring in an apartment or house. cable cross-section calculation depending on current, power and line length.

Calculation of cable cross-section based on the power of electrical appliances.

Each cable has a rated power that it can withstand when operating electrical appliances. When the power of all electrical appliances in the apartment exceeds the calculated rating of the conductor, an accident will soon be inevitable.

You can calculate the power of electrical appliances in an apartment or house yourself; to do this, you need to write down the characteristics of each appliance separately (TV, vacuum cleaner, stove, lamps) on a sheet of paper. Then all the obtained values ​​are summed up, and the finished number is used to select the optimal diameter.

The power calculation formula looks like this:

Ptotal = (P1+P2+P3+…+Pn)*0.8, where: P1..Pn is the power of each electrical appliance, kW

It is worth paying attention to the fact that the resulting number must be multiplied by a correction factor - 0.8. This coefficient means that only 80% of all electrical appliances will work at the same time. This calculation will be more logical, because a vacuum cleaner or hair dryer will definitely not be used for a long time without a break.

An example of calculating cable cross-section by power is shown in the tables:

For conductor with aluminum conductors.

For conductor with copper conductors.

As can be seen from the tables, their data has meanings for each specific type of cable, you just need to find the closest power value and look at the corresponding cross-section of the cores.

For example calculation of cable cross-section by power looks like that:

Let's say that in the apartment the total power of all devices is 13 kW. It is necessary to multiply the obtained value by a factor of 0.8, as a result this will give 10.4 kW of actual load. Then the appropriate value must be found in the table column. The nearest figure is 10.1 for a single-phase network (220V voltage) and for a three-phase network the figure is 10.5. This means we choose the cross-section for a single-phase network on a 6 mm conductor or for a three-phase network on a 1.5 mm conductor.

Calculation of cable cross-section based on current load.

More accurate calculation of cable cross-section for current, so it is best to use it. The essence of the calculation is similar, but in this case it is only necessary to determine what the current load on the electrical wiring will be. First you need to calculate the current strength for each of the electrical appliances using formulas.

Average power of household electrical appliances

An example of displaying the power of an electrical appliance (in this case, an LCD TV)

To calculate, you need to use this formula if the apartment has a single-phase network:

I=P/(U×cosφ)

When the network is three-phase, the formula will look like this:

I=P/(1.73×U×cosφ) , where P is the electrical power of the load, W;

• U - actual voltage in the network, V;
• cosφ - power factor.

It should be noted that the values ​​of the table values ​​will depend on the conditions for laying the conductor. The power and current loads will be significantly greater when installing open electrical wiring than if the wiring is laid in a pipe.

It is recommended to multiply the resulting total value of currents for the reserve by 1.5 times, because over time more powerful electrical appliances can be purchased for the apartment.

Calculation of cable cross-section along the length.

You can also Calculate cable cross-section based on length. The essence of such calculations is that each of the conductors has its own resistance, which contributes to current loss as the length of the line increases. It is necessary to choose a conductor with larger cores if the loss value exceeds 5%.

Calculations proceed as follows:

• The total power of all electrical appliances and current strength are calculated.
• Then the electrical wiring resistance is calculated using the formula: conductor resistivity (p) * length (in meters).
• It is necessary to divide the resulting value by the selected cable cross-section:

R=(p*L)/S, where p is the tabular value

You should pay attention to the fact that the length of current passage must be multiplied by 2 times, since initially the current flows through one core and returns back through the other.

• The voltage loss is calculated: the current is multiplied by the calculated resistance.
• Next, the amount of losses is determined: voltage losses are divided by the network voltage and multiplied by 100%.
• The final number is analyzed. If the obtained value is less than 5%, then the selected core cross-section can be left, but if it is more, then it is necessary to select a thicker conductor.

Resistivity table.

It is imperative to make calculations taking into account losses along the length if the line is stretched over a fairly long distance, otherwise there is a high probability select cable section wrong.

The cable through which electricity enters the apartment is a very important section of electrical wiring. It is this cable that bears the load from all electrical appliances operating indoors. The parameters of the input cable determine how many devices and what power the wiring in the room can serve. Let's consider a key parameter - the cable cross-section and the method of selecting it.

Section diameter is an indicator of cable power

Physical laws say that the maximum amount of current that this conductor can conduct through itself without heating depends on the cross-sectional diameter of the conductor. If you try to conduct a current more than the limit figure, this will lead to heating of the conductor, and the greater the current and the duration of the “session”, the higher the temperature.

For a residential subscriber, the above is interpreted as follows.

The diameter of the cable cross-section means the maximum permissible number of kilowatts (kW) that can be consumed in the apartment. That is, which and how many electrical appliances can operate simultaneously. The larger the diameter, the more devices can be used simultaneously without any fear for life and health. Theoretically, it is possible to “hang” more power on the cable than its diameter allows. But in this case, heating of the current-carrying conductor, damage to the insulation, followed by the effects of burnout, combustion... ignition, is inevitable.

Therefore, the choice of the cross-section of the input cable must be approached with all seriousness: after all, both the safety and ease of use of household electrical appliances depend on it.

Section calculation algorithm

There is a proven diagram for calculating the cross-section of the input cable, which is used in design. It is based on the postulate that the cross-sectional diameter of the input cable is selected depending on the expected power of all devices operating in the apartment.

Stage 1: Inventory

At the first stage, a list of electrical appliances that are present in the apartment is compiled. It is assumed what equipment will be purchased in the future and the list is expanded. Assumptions, of course, are best made with a reasonable margin for the long-term future. Each device is assigned an approximate power consumption.

You can use a table that roughly shows a list of typical household electrical appliances and their approximate power consumption.

Stage 2: Simple Arithmetic

Next, the total cardinality of our list is calculated. The approximate power required for lighting is added, depending on the size of the apartment, the expected lighting intensity, and the expected type of lighting fixtures.

The resulting figure is an estimate of the power consumption in the apartment for the case if all devices are turned on at the same time. However, such a situation is very unlikely, and therefore in electrical engineering it is generally accepted that a maximum of 75% of the available equipment is turned on at the same time. And the resulting total power is multiplied by a factor of 0.75, and the resulting figure is taken as the basis for calculating the cross-section of the input cable.

Stage 3: Logic and Physics

Currently, electrical cable cores are made of copper and aluminum. There are formula relations that connect the maximum permissible current (and, accordingly, power) for a copper cable with the diameter of its cross-section. For standard copper cable sizes, there are calculated current and maximum power ratings for 220V and 380V AC. The following table provides these figures in a "usable" form.

Let us assume that the calculated power of all devices is 12 kW, and with a coefficient of 0.75 - 9 kW. It turns out that you need to choose a cable for which the maximum permissible power will be at least 9 kW. For a voltage of 220 V, a section with a diameter of 6 mm is required - it is capable of passing a current of 46 A and a power of 10.1 kW. For the smaller cross-section from the table - 4 mm - the maximum permissible current is 38 A, and the power is 8.3 kW. This is less than necessary, so a cable of this cross-section will not work and you should stop at a 6-mm cross-section.

If you choose a cable with a larger cross-section than necessary, this will provide a good reserve for the future (for example, the emergence of new powerful household appliances) and a reserve for wear. However, you should also not exceed the rated power too much: this will affect the cost of the input cable, and the input cable may turn out to be more powerful than the internal electrical wiring, which is not reasonable and safe.

What else is needed

A machine must be installed on the input cable, which will be tasked with turning off the power supply if the current approaches the maximum permissible level. The rating of the machine is selected slightly less than the maximum permissible current through the input cable: in this way an additional degree of protection is provided. In this example, you should install a 40 A machine.

So, the parameters of the input cable require careful selection. Errors threaten, for example, a “bottleneck” situation - when all the home electrical wiring is powerful enough, but the input cable is not able to provide the required power. The cross-sectional diameter of the input cable is selected taking into account the total power of electrical appliances that will be used in the room. In order for all the nuances to be taken into account and the input cable to serve for many years without any emergencies, it is better to entrust the reconstruction of the electrical wiring to professional electricians.

Standard apartment wiring is calculated for a maximum current consumption at a continuous load of 25 amperes (the circuit breaker that is installed at the entrance of wires into the apartment is also selected for this current strength) and is carried out with copper wire with a cross-section of 4.0 mm 2, which corresponds to a wire diameter of 2.26 mm and load power up to 6 kW.

According to the requirements of clause 7.1.35 of the PUE the cross-section of the copper core for residential electrical wiring must be at least 2.5 mm 2, which corresponds to a conductor diameter of 1.8 mm and a load current of 16 A. Electrical appliances with a total power of up to 3.5 kW can be connected to such electrical wiring.

What is wire cross-section and how to determine it

To see the cross-section of the wire, just cut it across and look at the cut from the end. The cut area is the cross-section of the wire. The larger it is, the more current the wire can transmit.

As can be seen from the formula, the cross-section of the wire is light according to its diameter. It is enough to multiply the diameter of the wire core by itself and by 0.785. For the cross-section of a stranded wire, you need to calculate the cross-section of one core and multiply by their number.

The diameter of the conductor can be determined using a caliper with an accuracy of 0.1 mm or a micrometer with an accuracy of 0.01 mm. If there are no instruments at hand, then an ordinary ruler will help out.

Section selection
copper wire electrical wiring by current strength

The magnitude of the electric current is indicated by the letter “ A" and is measured in Amperes. When choosing, a simple rule applies: The larger the cross-section of the wire, the better, so the result is rounded up.

The data I have provided in the table is based on personal experience and guarantees reliable operation of electrical wiring under the most unfavorable conditions of its installation and operation. When choosing a wire cross-section based on the current value, it does not matter whether it is alternating current or direct current. The magnitude and frequency of the voltage in the electrical wiring also does not matter; it can be the on-board network of a DC car at 12 V or 24 V, an aircraft at 115 V with a frequency of 400 Hz, electrical wiring 220 V or 380 V with a frequency of 50 Hz, a high-voltage power line at 10,000 IN.

If the current consumption of an electrical appliance is unknown, but the supply voltage and power are known, then the current can be calculated using the online calculator below.

It should be noted that at frequencies above 100 Hz, a skin effect begins to appear in wires when electric current flows, which means that with increasing frequency, the current begins to “press” against the outer surface of the wire and the actual cross-section of the wire decreases. Therefore, the choice of wire cross-section for high-frequency circuits is carried out according to different laws.

Determining the load capacity of 220 V electrical wiring
made of aluminum wire

In houses built a long time ago, electrical wiring is usually made of aluminum wires. If connections in junction boxes are made correctly, the service life of aluminum wiring can be one hundred years. After all, aluminum practically does not oxidize, and the service life of electrical wiring will be determined only by the service life of the plastic insulation and the reliability of the contacts at the connection points.

In the case of connecting additional energy-intensive electrical appliances in an apartment with aluminum wiring, it is necessary to determine by the cross-section or diameter of the wire cores its ability to withstand additional power. Using the table below, this is easy to do.

If your apartment wiring is made of aluminum wires and there is a need to connect a newly installed socket in a junction box with copper wires, then such a connection is made in accordance with the recommendations of the article Connecting aluminum wires.

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

To select the cross-section of cable wire cores when laying electrical wiring in an apartment or house, 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 unknown, it can be measured using an ammeter.

Table of power consumption and current for household electrical appliances
at supply voltage 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, lighting fixtures, 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.

for 220 V network

You can select the wire cross-section not only by the current strength, but also by the amount of power consumed. To do this, you need to make a list of all electrical appliances planned to be connected to a given section of electrical wiring, and determine how much power each of them consumes separately. Next, add up the data obtained and use the table below.

If there are several electrical appliances and for some the current consumption is known, and for others the power, then you need to determine the wire cross-section for each of them from the tables, and then add up the results.

Selecting the cross-section of copper wire according to power
for the car's on-board network 12 V

If, when connecting additional equipment to the vehicle’s on-board network, only its power consumption is known, then the cross-section of the additional electrical wiring can be determined using the table below.

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

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, it should be taken 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 in 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, in the nameplate shown in the photograph, the current consumption of a motor with a power of 0.25 kW for each phase at a supply voltage of 220 V (the motor windings are connected in a delta pattern) is 1.2 A, and at a voltage of 380 V (the motor windings are connected in a delta pattern) "star" circuit) is only 0.7 A. Taking the current indicated on the nameplate, using the table for selecting the wire cross-section for apartment wiring, select a wire with a cross-section of 0.35 mm 2 when connecting the electric motor windings according to the "triangle" or 0.15 mm pattern 2 when connected in a star configuration.

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. I recommend making the wiring exclusively from copper wires! Aluminum wires are indispensable when laying overhead electrical wiring, as they are light and cheap and, when properly connected, serve reliably for a long time.

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 copper cores, round in shape, 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. For internal wiring, it is more convenient to use a VVG flat cable.

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. For example, welding uses a current of up to 150 A and in order for the welder to control the electrode, a flexible wire is needed. It is made from hundreds of thin copper wires connected in parallel. In a car, the battery is also connected to the on-board network using the same flexible stranded wire, since when starting the engine, the starter consumes current from the battery up to 100 A. And when installing and removing the battery, the wires must be taken 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.

Online calculators for calculating the cross-section and diameter of a wire

Using the online calculator presented below, you can solve the inverse problem - determine the diameter of the conductor by cross-section.

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 mm 2 ×15=3 mm 2. 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.

Electrical cable cross-section.

Electrical cable cross-section- This is one of the fundamental components of proper electrical wiring in the apartment. This means comfortable operation of electrical appliances and equipment, as well as the safety of consumers, i.e. all of us. The purpose of this article is to explain, for an apartment electrical network, based on the power of the electrical appliances used. And also tell us which wire is needed for this or that section of home electrical wiring.

Before starting a conversation on the main topic of the article, let me remind you of some terms.
● Vein- this, in the general sense, is a separate conductor (copper or aluminum), which can be either a solid conductor or consist of several individual wires twisted together into a bundle or wrapped in a common braid.
● Wire- this is a product that consists of one single-wire or multi-wire core, clad in a light protective sheath.
● Installation wire is a wire that is used for electrical wiring intended for lighting or power networks. It can be one, two or three wires.
- this is a wire with a core cross-section of up to 1.5 mm2. Cords are used to power light mobile (portable) electrical appliances and equipment. It is made of a multi-wire core, due to which it has increased ductility.
● Electrical cable- this is a product consisting of several insulated wires, on top of which there is from one to several protective sheaths.

To select a cable (wire) of the required cross-section for indoor wiring, you need to use the table given above, and to determine the current load on the cable, you can use the formula used earlier:
I race = P/U nom.

Where:

I race – calculated continuous current load;
P– power of connected equipment;
U nom. – network voltage;

Let's say you need to select a cable to connect an electric boiler with a power of 3 kW. Substituting the original values ​​into the formula, we get:

Iras. = 3000 W/220 V = 13.63 A,

rounding this value up, we get 14 A.

For a more accurate calculation of the current load, there are various coefficients depending on environmental conditions and cable laying methods. There is also a coefficient of repeated-short-term mode. But they all, to a greater extent, relate to a three-phase 380 V network, so they are not required for our calculations. But to increase the safety margin of the conductor, we apply the average value of 5 A. And we get:

14 A + 5 A = 19 A

In the column of table 1. 3. 4. “Three-core wires” we look for the value of 19 A. If it is not there, you need to select the largest one closest to it. This is the value of 21 A. A cable with a core cross-section of 2.5 mm² can withstand such a long-term permissible current load. We conclude that to connect an electric boiler (or other electrical equipment) having (consuming) a power of 3 kW, you need a three-core copper cable with a conductor cross-section of 2.5 mm².

In the case when it is necessary to connect a socket (or block of sockets) from which several electrical appliances will be powered, you can use the above formula, in which the value of “P” will be equal to the sum of the powers of the devices or equipment simultaneously connected to the socket (block of sockets).
Since all electrical appliances with a power exceeding 2 kW are recommended to be connected to the power supply through a separate supply (a separate branch from the apartment electrical panel), we can conclude that the socket group of apartment electrical wiring requires a copper (preferably) cable with a core cross-section of 2.5 mm². Due to the fact that lighting devices do not have much power, the wire for the electrical wiring supplying them with electricity must have a core cross-section of at least 1.5 mm².

This is what concerns electrical wiring with copper conductors. But what about wiring that has aluminum conductors? There is a simple way to calculate the cross-section of an aluminum wire core.

Due to the fact that the electrical conductivity of aluminum is 65.9% of the electrical conductivity of copper, when connecting devices with the same power consumption to them (wires or cables), the cross-section of the aluminum core must be larger than the copper one. For example. Referring to the calculations made above in the text, it was determined that the cross-section of the copper core in the wire for connecting a 3 kW boiler should be 2.5 mm². When using a cable with an aluminum conductor, according to table. 1.3.4, the cross-section of the core must be selected by a factor higher, i.e. - 4 mm².
Turning to the PUE Ch. 1. item 3. table. 1. 3. 5 can confirm this assumption.

Table 1. 3. 5.

When choosing a cable for electrical wiring, it is necessary to use not only the principles of economy, but also take into account the mechanical strength of the wire, as well as be guided by the Electrical Installation Rules. Which state that for wiring inside residential premises it is necessary to use a cable with a core cross-section of at least 1.5 mm 2 (PUE Chapter 7; Section 7.1; Table 7.1.1). Thus, if, according to your calculations, a cable with a cross-section of less than 1.5 mm 2 is sufficient for electrical wiring, then, guided by the Safety Rules and Standards, choose the recommended wiring.

All necessary norms and rules, as well as tables can be viewed, and, if necessary, downloaded in the file "Rules for Electrical Installations" .

There is another, simplest way to select the cross-section of the wire for electrical wiring. All electricians probably use it. Its essence is that the cross-section is calculated based on a current strength of 6 - 10 A per 1 mm 2 of cross-sectional area for wires with copper conductors and 4 - 6 A per 1 mm 2 for an aluminum conductor. Thus, we can say that the operation of electrical wiring with a copper conductor at a current strength of 6 A per 1 mm 2 section is the most comfortable and safe. Whereas with a current density of 10 A per 1 mm 2, it can only be used in short-term mode. The same can be said about aluminum conductors.

Let's try using this method to select a wire for connecting equipment with a power of 3 kW, as in the example discussed above. After making calculations, a value of 14 A was obtained (3000 W / 220 V = 14 A). To select a cable with a copper conductor, we take the smallest (for a greater margin of safety) value (from the “plug” 6 - 10 A per 1 mm 2) - 6 A. From here it can be seen that for a current of 14 A you need a wire with a core cross-section

14 A / 6 A = 2.3 mm 2 ≈ 2.5 mm 2.

Which confirms our previous calculations.

As additional information, I can add: if you do not have a conductor of the required cross-section, it can be replaced with several wires with a smaller cross-section connected in parallel. So, for example, you need a cable with a cross-section of 4 mm². You have at your disposal wires of the required length, but with a cross-section of 1 mm², 1.5 mm² and 2.5 mm². It is enough to take wires whose total cross-section is not less than the required one (one wire 1.5 mm² and one wire 2.5 mm² or two wires 1.5 mm² and one wire 1 mm²) and connect them in parallel (lay them lengthwise next to each other and , “twist” the ends). An example of this would be stranded wire for extension cords. As you probably noticed, each of its conductors consists of many thin wires. And connected in parallel, into one “harness” they provide a conductor (core) of the required cross-section. This achieves its elasticity while maintaining the required throughput. But this is only suitable for wiring that connects low-power electrical appliances or is subject to short-term peak loads. For other types of wiring, a wire (cable) is recommended whose cores consist of a solid (single, single-wire or multi-wire) conductor.

Having learned how to determine the cross-section of a wire that has a core made of one (solid) wire, the question remains open: “How to calculate the cross-section of a wire whose core consists of many wires?”

Section of a stranded conductor.

Following the logic, you need to find out the cross-section of one individual wire and multiply it by the number of them in the core. This is absolutely correct, but the hairs may be too thin and therefore it is not always possible to measure them. You can, of course, measure the diameter of the entire “harness” of wiring and, using the formula indicated in the photo “Calculation of the cross-section of a wire strand relative to its diameter,” determine the cross-section of the entire strand. This, in principle, is sufficient for very rough calculations. But here you need to take into account that the wires that make up the core are round in cross section and, therefore, there is space between them when twisted. To make a more accurate calculation, you need to multiply the value obtained after calculating using the formula in the photo by 0.91. It is this coefficient that eliminates the area of ​​the gaps between the hairs in the stranded core. For example, there is a wire with a stranded core with a diameter of 2.5 mm. Substitute the values ​​into the formula and get:

S = 3.14 × D² / 4 = 3.14 × 2.5² / 4 = 4.90625 mm² ≈ 4.9 mm².
4.9 × 0.91 = 4.459 ≈ 4.5 mm².

Thus, the cross-section of a stranded core with a diameter of 2.5 mm is 4.5 mm². (this is just an example, so no need to link it to actual sizes).

That's probably all I wanted to say about how to calculate cable cross-section. Armed with the information received, you can independently select an electrical wire or cable that will meet safety requirements.

Remember: incorrectly selected electrical wires can cause a fire!

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When installing electrical wiring in a new house or replacing an old one during renovation, every home craftsman asks the question: what cross-section of wire is needed? And this question is of great importance, since not only the reliable operation of electrical appliances, but also the safety of all family members largely depends on the correct choice of cable cross-section, as well as the material for its manufacture.

Which wire to choose - the material of manufacture comes first

The most common types of wiring in our homes are aluminum and copper. Which one is better is a question that still haunts users of numerous forums. For some, copper is a priority, while others say that there is no need to overpay and aluminum will do for a home network. In order not to be unfounded, let's do a little analysis of these options and then everyone can choose an option for themselves.

Aluminum wiring is lightweight, due to which it is widely used in the electrical power industry. It is used for laying power lines, since in this way the load on the supports can be minimized. In addition, it has gained popularity due to its low cost. Aluminum cable costs several times less than its copper counterpart. During the Soviet Union, aluminum wiring was very common; it can still be found in houses built some 15-20 years ago.

However, aluminum cable also has its downsides. One of these points that is definitely worth mentioning is the short service life. After two decades, aluminum wiring becomes highly susceptible to oxidation and overheating, which often leads to fires. Therefore, if you still have such cables in your home, think about replacing them. In addition, the oxidation to which aluminum is susceptible reduces the useful cross-section of the cable with a simultaneous increase in resistance, and this leads to overheating. Another significant disadvantage of aluminum is its fragility. It breaks quickly if the cable is bent several times.

Important! PUE prohibits the use of aluminum cable for installation in electrical networks if its cross-section is less than 16 mm.

Copper cable bends well and does not break

As for copper wire, its advantages include a long service life - more than half a century, excellent conductivity and mechanical strength. It is much easier to work with copper cable, because it bends without breaking and can withstand repeated twisting. The disadvantage of copper cable wiring is the cost. To replace the power cable in the entire apartment you will need a significant amount of money. To save money, some craftsmen combine the laying of aluminum wires with copper ones. The entire lighting part is mounted from aluminum, and the socket part is made from copper, since lighting does not require such a large load as electrical appliances powered into the network.

Choosing a section - what you need to know and what to pay attention to

If previously the equipment in an apartment was limited to a refrigerator and a TV, then nowadays you won’t find anything in an apartment: vacuum cleaners, computers, hair dryers, microwave ovens, etc. All this requires power, and depending on the time of day, the load from devices connected to the network can vary greatly. And in order to choose the right cable for each point to which the device is powered, you need to know:

• current strength;
• voltage;
• power consumption of the device in watts or kilowatts.

For single-phase networks that are present in our apartments, there is a certain formula that allows you to determine the current strength of the devices:

I = (P × K u) / (U × cos(φ)), where

I – current strength;

P – power consumption of all electrical appliances (it is necessary to add their nominal value):

K and is the simultaneity coefficient (often, for simplicity, a value of 0.75 is used);

U – phase voltage, it is 220 (V), but can range from 210 to 240 (V);

Cos (φ) – for household appliances the value is unchanged and equals 1.

For simplicity, you can use the formula: I = P / U.

When the current is determined, the wire cross-section can be determined using the following table:

Table of power, current and cross-section of cable and conductor materials

If during the calculations it turns out that the value does not coincide with any one given in the table, then the next larger number should be taken as a basis. For example, if your value is 30 A, then when using aluminum wiring you should choose a wire cross-section of 6 mm 2, and 4 mm 2 will be enough for copper.

Typically a modern apartment consumes approximately 10 kW.

We determine the cross-section of the wire by diameter and by the method of wiring

When buying a wire, it would be useful to check its cross-section, since many manufacturers work according to specifications. Because of this, not all products meet the declared characteristics. Therefore, it is necessary to stock up on calipers and measure the diameter of the core, which will help us determine the real value of the wire cross-section. To simplify the work, we present the simplest formula, so you will not need to make additional calculations: S = 0.785d 2, where S is the desired section; d – core diameter. The final value must be rounded to 0.5. So, if you get a value of 2.4, then you should choose a cable with a cross-section of 2.5 mm 2.

In most of our houses, the cable is laid in the walls. This is called closed wiring. Wires can run through cable ducts, pipes, or simply be walled into the wall. In some houses, and this applies to wooden buildings and old housing stock, you can find open wiring. It is noteworthy that for open installation you can use a cable of a smaller cross-section, since such a wire heats up less than the one that is walled into the wall. For this reason, when laying wires in grooves, it is recommended to choose a cable with a larger cross-section. This way the cable will heat up less, which means it will wear out more slowly. In the table below you can find out how many squares of cable you need to take for devices of different power, be it 1 or 6 kW: