Correspondence table of wire section and current. How to choose the right cable section

This article will talk about how to calculate the wire cross-section for power consumption yourself. You need to know this not only when in the house, but also when working in cars, for example. If the wire section is insufficient, it will start to heat up very much, which will lead to a significant loss of safety level. Given all the recommendations that will be outlined below, you will be able to independently calculate the parameters of the wires for installing the power supply in the house. But if you are not confident in your abilities, it is better to contact specialists in this field. Moreover, it should be noted that the calculation of the wire cross-section for power consumption (12V and 220V) is carried out similarly.

Carrying out the calculation of the length of the wiring

For any type of electronic system, the most important condition for stable and trouble-free operation is the competent calculation of the cross sections of all wires for current and power. The first step is to calculate the maximum length of the entire wiring. There are several ways to do this:

1. Measuring the distance from shields to sockets, switches according to the installation diagram. Moreover, this can be done with a ruler on a pre-prepared wiring plan - it is enough to multiply the obtained length values ​​​​by the scale.
2. And the second, more accurate way is to arm yourself with a ruler and walk through all the rooms, taking measurements. Moreover, it must be borne in mind that the wires must somehow be connected, so there must always be a margin - at least one or two centimeters from each edge of the wiring.

Now you can proceed to the next step.

Calculation of the load on the wiring

To calculate the total load, you need to add up all the minimum power consumers in the house. Let's say you are doing a calculation for the kitchen, it has lamps, a microwave oven, an electric kettle and stove, a dishwasher, and so on. All powers must be summed up (see the power consumption on the back covers, but you will have to calculate the current yourself from this parameter). Then multiply by a correction factor of 0.75. It is also called the simultaneity factor. Its essence is clear from the name itself. This figure, which will be obtained as a result of calculations, you will need in the future to calculate the parameters of the wires. Please note that the entire power supply system must be safe, reliable and durable. These are the basic requirements that must be taken into account when calculating the wire cross-section for power consumption of 12V and 220V.

Current consumption of electrical installations

Now about how to calculate the current consumption of an electrical device. You can do this in your mind, or you can use a calculator. See the instructions for the device, what is the value of the power consumption of it. Of course, in the household electrical network flows alternating current with a voltage of 220 volts. Therefore, using a simple formula (power consumption divided by supply voltage), you can calculate the current. For example, an electric kettle has a power of 1000 watts. So, if we divide 1000 by 220, we get a value approximately equal to 4.55 amperes. It is produced very simply in terms of power consumption. How to do this is described in the article. In operating mode, the kettle consumes 4.55 amperes from the network (for protection, you must install a circuit breaker of a larger rating). But note that this is not always the exact value. For example, if there is a motor in the design of an electrical appliance, the value obtained can be increased by about 25% - the current consumption of the motor in the start mode is much greater than during idling.

But you can use a set of rules and standards. There is such a document as the Rules for the Installation of Electrical Installations, it is he who regulates all the standards for wiring not only in private estates, but also in factories, factories, etc. According to these rules, the wiring standard is the ability to withstand a load of 25 amperes for a long time. Therefore, in apartments, all electrical wiring should be carried out only using copper wire, its cross section is not less than 5 square meters. mm. Each core must have a cross section of more than 2.5 square meters. mm. The conductor diameter must be 1.8 mm.

In order for all electrical wiring to work as safely as possible, an automatic switch is installed at the input. It will protect the apartment from short circuits. Also, recently, most homeowners have been installing residual current devices that instantly act on a change in resistance in the circuit. In other words, if you accidentally touch them while energized, they will instantly de-energize and you won't get hit. it is necessary to calculate by current, and be sure to choose with a margin, so that it is always possible to install any electrical appliance in the house. A competent calculation of the wire cross-section according to the power consumption (how to make the right choice of wires, you will learn from this material) is a guarantee that the power supply will function correctly and efficiently.

Materials for the manufacture of wires

As a rule, wiring in a private house or apartment is done using three-core wires. Moreover, each core has a separate insulation, they all have different colors - brown, blue, yellow-green (standard). The core is the part of the wire through which the current flows. It can be both single-wire and multi-wire. Some brands of wire use a cotton braid over the strands. Materials for the manufacture of wire cores:

1. Steel.
2. Copper.
3. Aluminum.

Sometimes you can find combined ones, for example, a stranded copper wire with several steel conductors. But these were used for field telephone communications - a signal was transmitted over copper, and steel was used for the most part for fastening to supports. Therefore, in this article we will not talk about such wires. For apartments and private houses, copper wire is ideal. It is durable, reliable, the characteristics are much higher than that of cheap aluminum. Of course, the price of copper wire bites, but it is worth mentioning that its service life (guaranteed) is 50 years.

Wire Marks

For laying electrical wiring, it is best to use two brands of wires - VVGng and VVG. The first has the ending "-ng", which indicates that the insulation does not burn. It is used for electrical wiring inside structures and buildings, as well as in the ground, in the open air. Works stably in the temperature range -50 ... +50. Guaranteed service life - not less than 30 years. The cable can be with two, three or four cores, the cross section of each is in the range of 1.5 ... 35 square meters. mm. Please also note that it is necessary to calculate the wire cross-section according to the power consumption and length (in the case of an overhead long line).

Pay attention to the fact that there is no letter “A” before the name of the wire (for example, АВВГ). This suggests that the cores inside are made of aluminum. There are also foreign analogues - the NYM brand cable, which has a round shape, complies with the standards adopted in Germany (VDE0250). The conductors are copper, the insulation is not subject to combustion. The round shape of the wire is much more convenient if you need to install through the wall. But for wiring indoors, it turns out to be more convenient than a flat domestic one.

aluminum wires

They are lightweight and, most importantly, low cost. Therefore, they are useful for those cases when you need to lay long lines through the air. If all work is carried out correctly and correctly, you will get an ideal air line, since aluminum has one huge advantage - it is not subject to oxidation (unlike copper). But often aluminum wiring was also used in houses (usually in old ones). The wire used to be easier to get, and it cost a penny. It should be noted that the calculation of the wire cross-section according to the power consumption (the features of this process are known to every electrician) is the main step in creating a house power supply project. But you need to pay attention to one feature - the cross section of the aluminum wire must be larger than the copper wire in order to withstand the same load.

Table for calculating the power section

It is also necessary to mention that the maximum permissible current load is much less than for copper ones. The table below will help calculate the cross section of the cores

Cross section of wires depending on the type of wiring

There are two types of electrical wiring in homes - open and closed. As you understand, this nuance must be taken into account when making calculations. Hidden is mounted inside ceilings, as well as in grooves and channels, in pipes, etc. Closed wiring has higher requirements, since it has less cooling capacity. And any wire with prolonged exposure to a large load heats up very much. Therefore, in the case when you calculate the cross section of the wire according to the power consumption, be sure to take into account the effect on heating. The following parameters must also be taken into account:

1. continuous current load.
2. Loss of voltage.

As the wire length increases, the voltage decreases. Therefore, in order to reduce voltage losses, it is necessary to increase the cross section of the wire cores. If we are talking about a small house or even a room, then the loss value is extremely low, they can be neglected. But if a long line is calculated, this cannot be avoided. After all, the calculation of the wire cross-section according to the power consumption (the influence of the length is very large) depends on such a parameter as the length of the line.

Calculation of the wire by power

So, you need to know the following characteristics:

1. The material of which the cable cores are made.
2. Maximum power consumption.
3. Supply voltage.

Please note that when any current flows, the temperature rises and some heat is released. Moreover, the amount of heat is proportional to all the power that is dissipated on a piece of electrical wiring. If you choose the wrong section, then excessive heating will occur, and the result can be disastrous - ignition of the electrical wiring and fire. Therefore, it is worth making an accurate calculation of the wire cross-section according to the power consumption. The risk factors are too big, and there are many of them.

Optimal parameters

Optimal sections:

1. For wiring sockets - 2.5 square meters. mm.
2. Lighting group - 1.5 sq. mm.
3. High power electrical appliances (electric stove) - 4-6 sq. mm.

At the same time, pay attention to the fact that copper wires can withstand the following loads:

1. Wire 1.5 sq. mm - up to 4.1 kW (current load - 19 amperes).
2. 2.5 sq. mm - up to 5.9 kW (current - up to 27 amperes).
3. 4-6 sq. mm - more than 8-10 kW.

Therefore, when the load increases, you will always have a fairly large reserve.

Conclusion

Now you know how to calculate the cross section of the wire according to the power consumption (the definition of important characteristics and other small factors is now known to you). Based on all of the above data, you can independently, without resorting to the help of professionals, draw up the correct power supply plan for your house or apartment.

How to calculate the cable by current, voltage and length. , as you know, there are different sections, materials and with a different number of cores. Which one should be chosen so as not to overpay, and at the same time ensure the safe stable operation of all electrical appliances in the house. To do this, you need to calculate the cable. The calculation of the cross section is carried out knowing the power of the devices powered by the network and the current that will pass through the cable. You also need to know a few other wiring parameters.

Basic Rules

When laying electrical networks in residential buildings, garages, apartments, most often they use a cable with rubber or PVC insulation, designed for a voltage of not more than 1 kV. There are brands that can be used outdoors, indoors, in walls (strobes) and pipes. Usually this is a VVG or AVVG cable with a different cross-sectional area and number of cores.
PVA wires and ShVVP cords are also used for connecting electrical appliances.

After the calculation, the maximum allowable cross-sectional value is selected from a number of cable brands.

The main recommendations for choosing a section are in the Electrical Installation Rules (PUE). The 6th and 7th editions have been released, detailing how to lay cables and wires, install protection, distribution devices, and other important points.

Administrative fines are provided for violation of the rules. But the most important thing is that violation of the rules can lead to failure of electrical appliances, ignition of wiring and serious fires. Damage from a fire is sometimes measured not in monetary terms, but in human casualties.

The importance of choosing the right section

Why is cable sizing so important? To answer, we must remember the school lessons of physics.

Current flows through the wires and heats them up. The more power, the more heat. Active current power is calculated by the formula:

P=U*I* cos φ=I²*R

R- active resistance.

As you can see, the power depends on the current strength and resistance. The greater the resistance, the more heat is generated, that is, the more the wires heat up. Likewise for current. The larger it is, the more the conductor heats up.

Resistance, in turn, depends on the material of the conductor, its length and cross-sectional area.

R=ρ*l/S

ρ - resistivity;

l- conductor length;

S- cross-sectional area.

It can be seen that the smaller the area, the greater the resistance. And the greater the resistance, the more the conductor heats up.

If you buy a wire and measure its diameter, then do not forget that the area is calculated by the formula:

S=π*d²/4

d– diameter.

Don't forget the resistivity as well. It depends on the material from which the wires are made. The specific resistance of aluminum is greater than that of copper. So, with the same area, aluminum will heat up more. It immediately becomes clear why it is recommended to take aluminum wires with a larger cross section than copper ones.

In order not to go into a long calculation of the cable cross-section each time, the rules for choosing the wire cross-section in the tables have been developed.

Calculation of the wire cross section for power and current

The calculation of the wire cross section depends on the total power consumed by electrical appliances in the apartment. It can be calculated individually, or use the average characteristics.

For the accuracy of calculations, a block diagram is drawn up, which shows the devices. You can find out the power of each from the instructions or read on the label. Electric stoves, boilers, air conditioners have the highest power. The total figure should be in the range of approximately 5-15 kW.

Knowing the power, the formula determines the rated current:

I=(P*K)/(U*cos φ)

P- power in watts

U\u003d 220 Volts

K\u003d 0.75 - coefficient of simultaneous inclusion;

cos φ=1 for household electrical appliances;

If the network is three-phase, then a different formula is used:

I=P/(U*√3*cos φ)

U\u003d 380 Volts

Having calculated the current, it is necessary to use the tables that are presented in the PUE, and determine the cross section of the wire. The tables show the permissible continuous current for copper and aluminum wires with various types of insulation. Rounding is always done up, so that there is a margin.

You can also refer to the tables in which it is recommended to determine the cross section only by power.

Special calculators have been developed by which the cross section is determined, knowing the power consumption, the phase of the network and the length of the cable line. Pay attention to the laying conditions (in a pipe or outdoors).

Influence of wire length on cable selection

If the cable is very long, then there are additional restrictions on the choice of section, since voltage losses occur on an extended section, which in turn lead to additional heating. To calculate voltage losses, the concept of "load moment" is used. It is defined as the product of power in kilowatts and length in meters. Next, look at the value of losses in the tables. For example, if the power input is 2 kW and the cable length is 40 m, then the torque is 80 kW*m. For 2.5 mm² copper cable. this means that the voltage loss is 2-3%.

If the losses exceed 5%, then it is necessary to take a section with a margin, more than recommended for use at a given current.

Calculation tables are provided separately for single-phase and three-phase networks. For a three-phase load torque increases as the load power is distributed over the three phases. Therefore, the losses are reduced and the influence of the length is reduced.

Voltage losses are important for low voltage devices, in particular gas discharge lamps. If the supply voltage is 12 V, then with a loss of 3% for a 220 V network, the drop will be little noticeable, and for a low-voltage lamp it will almost halve. Therefore, it is important to place ballasts as close as possible to such lamps.

Calculation of voltage losses is performed as follows:

∆U = (P∙r0+Q∙x0)∙L/ Un

P— active power, W.

Q— reactive power, W.

r0— active resistance of the line, Ohm/m.

x0— line reactance, Ohm/m.

Un- rated voltage, V. (it is indicated in the characteristics of electrical appliances).

L- line length, m.

Well, if it’s simpler for domestic conditions:

∆U=I*R

R- cable resistance, calculated by the well-known formula R=ρ*l/S;

I- current strength, found from Ohm's law;

Let's assume that we have I=4000W/220 IN\u003d 18.2 A.

The resistance of one strand of copper wire 20 m long and 1.5 mm square. amounted to R\u003d 0.23 Ohm. The total resistance of the two wires is 0.46 ohms.

Then ΔU\u003d 18.2 * 0.46 \u003d 8.37 V

Percentage

8,37*100/220=3,8%

On long lines from overloads and short circuits, they are installed with thermal and electromagnetic releases.

Find out the cable cross-sections by power and wire length. We use an effective online wire diameter calculator. Cables are the main elements in the process of transmission and distribution of current. They play an important role in connecting electricity, which is why it is necessary to accurately and accurately calculate the cable cross-section along the length and load power in order to create favorable conditions for the uninterrupted passage of electricity and avoid negative emergency consequences.

If the wrong wire diameter is chosen during the design and development of the electrical network, overheating and failure of various electrical equipment are possible. And also the cable insulation will be broken, which will lead to a short circuit and fire. There will be significant costs for the restoration of not only electrical wiring, but also all electrical appliances in the room. To avoid this, you need to correctly select the cable cross-section for power and length.

Online calculator for cable selection by power

Attention! If the data is entered incorrectly, the calculator may give inaccurate values, for clarity, use the table of values ​​​​below.

On our website, you can freely make the necessary calculation of the wire diameter in a few seconds, using a ready-made program for obtaining data on the cross section of the cable core.
To do this, you need to enter several individual parameters into the finished table:

• the power of the proposed facility (total load indicators of all used electrical appliances);
• choose the nominal voltage (most often single-phase, 220 V, but sometimes three-phase - 380 V);
• specify the number of phases;
• core material (technical characteristics of the wire, there are two compositions - copper and aluminum);
• line length and type.

Be sure to include all values. After that, click on the "calculate" button and get the finished result.

This value ensures that when calculating the cable cross-section for power online, the wire will not overheat under the working load. Ultimately, it is important to take into account the factor of the voltage drop on the conductors of the wire, while selecting the parameters for a particular line.

Table for the selection of the wire section depending on the power (W)

How to make your own calculation of the cable cross-section along the length?

In domestic conditions, such data is necessary in the manufacture of extension cords for a long distance. However, even with accurately obtained results, it is necessary to leave 10-15 cm in stock for switching wires and (by welding, soldering or crimping).

In industry, the formula for calculating the cable cross-section by power and length is used at the design stage of networks. It is important to accurately determine such data if the cable will have additional and significant loads.

An example of calculation in everyday life: I = P / U cosφ, where

I - current strength, (A);

P – power, (W);

U - voltage in the network, (V);

cosφ is a coefficient equal to 1.

Using such a calculation formula, you can find the correct length of the wiring, and the cable section indicators can be obtained using an online calculator, or manually. To convert Watts to Amps -.

Program for calculating the cable cross-section by power

To find out the power of the equipment or device, you need to look at the tag, which indicates their main characteristics. After adding up the data, for example, 20,000 W, this is 20 kW. This indicator indicates how much energy all electrical appliances consume. If their percentage is used at a time about 80%, then the coefficient will be equal to 0.8. Calculation of the cable cross-section by power: 20 x 0.8 = 16 kW. This is the cross section of the core for a copper wire measuring 10 mm. For a three-phase circuit - 2.5 mm at a voltage of 380 V.

It is better to choose the wire of the largest cross section in advance, in case of connecting unplanned equipment or devices. It is better to add money today and do everything qualitatively than to change the cable and buy a new kettle tomorrow.

A more detailed calculator that takes into account different coefficients.

Standard residential wiring is designed for a maximum current consumption during continuous load - 25 amperes (copper wire with a cross section of 5 mm and a diameter of 2.5 mm is used). The more the current consumption is planned, the more cores should be in the cable. If the wire is 2 mm in diameter, then its cross section can be easily determined by the following formula: 2 mm × 2 mm × 0.785 = 3.14 mm 2. If you round the value, it turns out - 3 mm squared.

To make a choice of cable cross-section by power, you need to independently determine the total current of all electrical appliances, add up the result and divide by 220.

The choice for laying the cable depends on its shape, it is better to lay round wiring through walls, and for interior work, flat cable is better suited, which is easy to install and does not create obstacles in operation. Their specifications are the same.

In the modern technological world, electricity has practically become on the same level in importance as water and air. It is applied in almost any sphere of human activity. There was such a thing as electricity 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, the electric current began to spread rapidly, and now it is 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 still no superconductors in everyday life, and it will not be soon to appear on an industrial scale. In everyday life, as a rule, current is passed through wires, and it is mainly used as a core copper or aluminum wires. Copper and aluminum are popular primarily due to their conductive properties, which are inverse to electrical resistance, and also because they are cheap compared to, for example, gold or silver.

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

This article is intended to teach you how to calculate wire size. It's like the more water you want to supply, the larger diameter pipe you need. So here, the greater the consumption of electric current, the greater should be the cross section of cables and wires. I will briefly describe what it is: if you bite a cable or wire and look at it from the end, then you will just see its cross section, that is, the thickness of the wire, which determines the power that this wire is able to pass, warming up to an acceptable temperature.

In order to correctly select the cross section of the power wire, we the maximum load current must be taken into account. You can determine the values ​​\u200b\u200bof currents, knowing the nameplate power of the consumer, it is determined by the following formula: I \u003d 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. Here is an example of an average set of equipment that you might have at home.

A simple example of calculating the cable cross-section for current consumption, now we will calculate the sum of the power of connected electrical appliances. The main consumers in the 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.

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

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

The calculation of the wire cross section is carried out using the following formula:

I = (P × K and) / (U × cos(φ))

I- current strength;

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

When we have found the current consumption power 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 in which data is provided, which compares the amount of current, cable cross-section and power consumption.

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

Table of estimated cable power by current. The choice of the copper cable section is made according to the following parameters:

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

If the power value turned out to be the average between the two indicators, then it is necessary to select the value of the wire cross section in the larger direction. Since the power reserve must be present.

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

And now we will analyze 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, according to which the cross-sectional area of ​​\u200b\u200bthe cable is selected
• U- phase voltage, 220V
• Cos φ - phase angle
• P- shows the total consumption of all electrical appliances

Cos φ- in the above formula is extremely important, since it personally affects the current strength. It differs 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 very simple, 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 is able to withstand a greater load. The wire section we need is selected according to the table below.

The calculation of the wire cross section for the current consumed, 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 necessary, the product of the root and the phase voltage is replaced by a linear voltage. This value is equal to 380V (U linear = 380V).

The concept of continuous current

Also, one no less important point when choosing a cable for a three-phase and single-phase network is that it is necessary to take into account such a concept that sounds like a permissible continuous current. This parameter shows us the amount of current in the cable that the wire can withstand for an unlimited amount of time. You can determine the ego in a special table. Also for aluminum and copper conductors, they differ significantly.

In the case when this parameter exceeds the permissible values, the conductor overheats. The heating temperature is inversely proportional to the current strength.

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

When we have done all the calculations and checked the data from the tables, you can safely go to a specialized store and buy the cables you need to lay the network at home or in the country. Your main advantage over, for example, your neighbor will be that you have completely figured out this issue with the help of our article, and 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 be useful many times on your life path.

In this article, I will tell you how choose the right cable section for a house or apartment. If- this is the "heart" of our power supply system, then the cables connected to the automatic switches of the electrical panel are"blood vessels" that feedelectricity from our household appliances.

When installing electrical wiring in a house or apartment, all stages, from designing the power supply of a private house, apartment, to the final installation of sockets or switches, must be approached with full responsibility, because your personal electrical safety depends on it, as well as the fire safety of your house or apartment . Therefore, we approach the choice of cable cross-section with all seriousness, because another way of transmitting electricity in a private house or apartment has not yet been invented.

It is important to choose the right cable cross-section, specifically for a specific line (group) of power receivers. Otherwise, if we choose an underestimated section cable is will lead to its overheating, destruction of insulation and further to a fire If you touch a cable with damaged insulation, you will receive an electric shock. If you choose an oversized cable cross-section for a house or apartment, this will lead to an increase in costs, as well as difficulties in wiring cable lines, because the larger the cable cross-section, the more difficult it is to work with it, not every socket will fit a cable with a cross section of 4 sq. mm .

I bring common universal table, which I myself use to select the rated current of automatic machines for protecting cable lblue.

I will not fill your head with abstruse formulas for calculating the cable cross-section from books on electrical engineering, so that you can choose the correct cable cross-section. Everything has long been calculated and tabulated.

Please note that with different wiring methods(hidden or open) , cables with the same cross section have different continuous currents.

Those. at open way wiring, the cable heats up less due to better cooling. At h indoor way installation of electrical wiring (in strobes, pipes, etc.), vice versa - it heats up more. This is an important point, because if you choose the wrong automatic machine for protecting the cable, the nominal value of the automatic machine may turn out to be too high relative to the long-term permissible current of the cable, due to which the cable can get very hot, and the machine will not turn off.

I will bring example, for example, we have a cable cross section of 6 sq. mm.:

• with the open method, its long-term permissible current is 50A, therefore the machine must be set to 40A;
• with a hidden method, its long-term permissible current is 34A, in this case the machine is 32A.

Suppose we chose a cable section for an apartment, which are laid in strobes or under plaster (in a closed way). If we confuse and put 50A circuit breakers for protection, then the cable will overheat, because. with a closed method of laying it In = 34 A, which will lead to the destruction of its insulation, then a short circuit and a fire.

TABLES ARE OUT OF DATE. WHEN SELECTING A CABLE BREAKER, REFER TO THE TABLE ABOVE.

Cable cross section for hidden electrical wiring

Cable cross section for open electrical wiring

In order to use the tables and choose the right cable cross-section for a house or apartment, we need to know the current strength, or know the power of all household electrical receivers.

The current is calculated using the following formulas:

— for a single-phase network with a voltage of 220 Volts:

where P is the sum of all the powers of household electrical receivers, W;

U - voltage of a single-phase network 220 V;

Cos (phi) - power factor, for residential buildings it is 1, for production it will be 0.8, and on average 0.9.

— for a three-phase network with a voltage of 380 Volts:

in this formula, everything is the same as for a single-phase network, only in the denominator, because the network is three-phase, add root 3 and the voltage will be 380 V.

To select the cable cross-section for a house or apartment, according to the above tables, it is enough to know the sum of the capacities of the electrical receivers of a given cable line (group). We will still need to calculate the current when designing an electrical panel (selection of automatic devices, RCDs or differential automatic devices).

Below are the average power values ​​of the most common household electrical receivers:

Knowing the power of electrical receivers, you can accurately select the cable cross-section for a specific cable line (group) in a house or apartment, and therefore an automatic machine (difavtomat) to protect this line, in which the rated current must be lower than the long-term permissible cable current, a certain section. If we choose a copper cable section of 2.5 sq. mm., which conducts current up to 21 A for an arbitrarily long time ( hidden laying method), then the automatic (difavtomat) in the electrical panel for this cable must be with a rated current of 20 A so that the automatic machine turns off before the cable starts to overheat.

Typical sections of cables for electrical installation in everyday life:

• In apartments, cottages or private houses, for socket groups lay copper cable 2.5 sq.mm.;
• For lighting group- copper cable section 1.5 sq.mm;
• For single phase hob(electric stoves) - cable section 3x6 sq. mm., for a three-phase electric stove - 5x2.5 sq. mm. or 5x4 sq. mm. depending on power;
• For other groups (ovens, boilers, etc.) - by their power. And also on the connection method, through a socket or through terminals. For example, if the oven power is more than 3.5 kW, then a 3x4 cable is laid and the oven is connected through the terminals, if the oven power is less than 3.5 kW, then a 3x2.5 cable and connection through a household outlet are sufficient.

To choose the correct cable section and denominations of machines for the electrical panel of a private house, apartment, you need to know important points, ignorance of which can lead to sad consequences.

For example:

• For socket groups choose a cable cross section of 2.5 sq. Mm, but the machine is chosen at the same time, with a rated current not 20A, but 16A, because household sockets are designed for a current of not more than 16 A.
• For lighting I use a 1.5 sq. mm cable, but machine no more than 10A, because switches are designed for current not more than 10A.
• You need to know that the machine passes current up to 1.13 times its nominal value, for as long as you like, and if the nominal value is exceeded up to 1.45 times, it can turn off only after 1 hour. And all this time the cable will be heated.
• The cable cross-section should be correctly chosen according to the hidden laying method so that there is a necessary margin of safety.
• PUE p.7.1.34. prohibits the use aluminum wiring inside buildings.

Thank you for your attention.