Electrical table for power and cable cross-section. Calculation of cross-section by current or power. Open and closed method of laying wires

Comfort and safety in the home depends on the correct choice of electrical wiring cross-section. When overloaded, the conductor overheats and the insulation may melt, causing a fire or short circuit. But it is not profitable to take a cross-section larger than necessary, since the price of the cable increases.

In general, it is calculated depending on the number of consumers, for which they first determine the total power used by the apartment, and then multiply the result by 0.75. The PUE uses a table of loads along the cable cross-section. From it you can easily determine the diameter of the cores, which depends on the material and the passing current. As a rule, copper conductors are used.

The cross-section of the cable core must correspond exactly to the calculated one - in the direction of increasing the standard size range. It is most dangerous when it is underestimated. Then the conductor constantly overheats, and the insulation quickly fails. And if you install the appropriate one, it will trigger frequently.

If the wire cross-section is increased, it will cost more. Although a certain reserve is necessary, since in the future, as a rule, it is necessary to connect new equipment. It is advisable to use a safety factor of about 1.5.

Calculation of total power

The total power consumed by the apartment falls on the main input, which enters the distribution board, and after it branches into the lines:

• lighting;
• groups of sockets;
• individual powerful electrical appliances.

Therefore, the largest cross-section of the power cable is at the input. On outlet lines it decreases, depending on the load. First of all, the total power of all loads is determined. This is not difficult, since it is indicated on the housings of all household appliances and in their passports.

All powers add up. Calculations are made similarly for each circuit. Experts suggest multiplying the amount by 0.75. This is explained by the fact that all devices are not connected to the network at the same time. Others suggest choosing a larger section. Due to this, a reserve is created for the subsequent commissioning of additional electrical devices that may be purchased in the future. It should be noted that this cable calculation option is more reliable.

How to determine the wire cross-section?

All calculations include the cable cross-section. It is easier to determine it by diameter if you use the formulas:

• S=π D²/4;
• D= √(4×S/π).

Where π = 3.14.

S = N×D²/1.27.

Stranded wires are used where flexibility is required. Cheaper solid conductors are used for permanent installations.

How to choose a cable based on power?

In order to select wiring, use the load table for the cable cross-section:

• If the open type line is energized at 220 V, and the total power is 4 kW, a copper conductor with a cross section of 1.5 mm² is taken. This size is usually used for lighting wiring.
• With a power of 6 kW, conductors of a larger cross-section are required - 2.5 mm². The wire is used for sockets to which household appliances are connected.
• A power of 10 kW requires the use of 6 mm² wiring. It is usually intended for the kitchen, where an electric stove is connected. The supply to such a load is made through a separate line.

Which cables are better?

Electricians are well aware of the cable of the German brand NUM for office and residential premises. In Russia they produce brands of cables that have lower characteristics, although they may have the same name. They can be distinguished by compound leaks in the space between the cores or by its absence.

The wire is produced monolithic and multi-wire. Each core, as well as the entire twist, is insulated on the outside with PVC, and the filler between them is non-flammable:

• Thus, the NUM cable is used indoors, since the insulation outdoors is destroyed by sunlight.
• And as an internal cable, VVG brand cable is widely used. It is cheap and quite reliable. It is not recommended to use it for laying in the ground.
• VVG brand wire is made flat and round. No filler is used between the cores.
• made with an outer shell that does not support combustion. The cores are manufactured round up to a cross-section of 16 mm², and above - sector.
• The PVS and ShVVP cable brands are made multi-wire and are used primarily for connecting household appliances. It is often used as home electrical wiring. It is not recommended to use multi-wire conductors outdoors due to corrosion. In addition, flexural insulation cracks at low temperatures.
• On the street, armored and moisture-resistant cables AVBShv and VBShv are laid underground. The armor is made of two steel strips, which increases the reliability of the cable and makes it resistant to mechanical stress.

Determination of current load

A more accurate result is obtained by calculating the cable cross-section by power and current, where the geometric parameters are related to the electrical ones.

For home wiring, not only the active load must be taken into account, but also the reactive load. The current strength is determined by the formula:

I = P/(U∙cosφ).

The reactive load is created by fluorescent lamps and motors of electrical appliances (refrigerator, vacuum cleaner, power tools, etc.).

Current example

Let's find out what to do if it is necessary to determine the cross-section of a copper cable for connecting household appliances with a total power of 25 kW and three-phase machines with a capacity of 10 kW. This connection is made with a five-core cable laid in the ground. The food at home comes from

Taking into account the reactive component, the power of household appliances and equipment will be:

• P everyday life = 25/0.7 = 35.7 kW;
• P rev. = 10/0.7 = 14.3 kW.

The input currents are determined:

• I life = 35.7×1000/220 = 162 A;
• I rev. = 14.3×1000/380 = 38 A.

If you distribute single-phase loads evenly across three phases, one will carry the current:

I f = 162/3 = 54 A.

I f = 54 + 38 = 92 A.

All equipment will not work at the same time. Taking into account the reserve, each phase accounts for the current:

I f = 92×0.75×1.5 = 103.5 A.

In a five-core cable, only the phase conductors are taken into account. For a cable laid in the ground, you can determine a core cross-section of 16 mm² for a current of 103.5 A (table of loads by cable cross-section).

Refined calculation of current allows you to save money, since a smaller cross-section is required. With a rougher calculation of cable power, the core cross-section will be 25 mm², which will cost more.

Cable voltage drop

Conductors have resistance that must be taken into account. This is especially important for long cable lengths or small cross-sections. PES standards have been established, according to which the voltage drop on the cable should not exceed 5%. The calculation is done as follows.

1. The conductor resistance is determined: R = 2×(ρ×L)/S.
2. Voltage drop is found: U pad. = I×R. In relation to the linear percentage, it will be: U % = (U falling / U linear) × 100.

The following notations are used in the formulas:

• ρ - resistivity, Ohm×mm²/m;
• S - cross-sectional area, mm².

Coefficient 2 shows that current flows through two wires.

Example of cable calculation based on voltage drop

• The wire resistance is: R = 2(0.0175×20)/2.5 = 0.28 Ohm.
• Current strength in the conductor: I = 7000/220 =31.8 A.
• Voltage drop across carrier: U pad. = 31.8×0.28 = 8.9 V.
• Voltage drop percentage: U% = (8.9/220)×100 = 4.1 %.

The carrier is suitable for the welding machine in accordance with the requirements of the operating rules for electrical installations, since the percentage of voltage drop across it is within the normal range. However, its value on the supply wire remains large, which can negatively affect the welding process. Here it is necessary to check the lower permissible limit of the supply voltage for the welding machine.

Conclusion

In order to reliably protect electrical wiring from overheating when the rated current is exceeded for a long time, cable cross-sections are calculated based on long-term permissible currents. The calculation is simplified if a load table for the cable cross-section is used. A more accurate result is obtained if the calculation is made based on the maximum current load. And for stable and long-term operation, an automatic switch is installed in the electrical wiring circuit.

So, the known power of each electrical appliance in the house, the known number of lighting fixtures and lighting points allow us to calculate the total power consumed. This is not an exact sum, since most values ​​for the powers of various devices are averages. Therefore, you should immediately add 5% of its value to this figure.

Average power readings for common electrical appliances

And many believe that this is enough to select almost standard copper cable options:

• cross section 0.5 mm2 for wires for lighting spotlights;
• cross section 1.5 mm2 for lighting wires for chandeliers;
• cross-section 2.5 mm2 for all sockets.

At the level of household use of electricity, such a scheme looks quite acceptable. Until the refrigerator and electric kettle decided to turn on in the kitchen at the same time, while you were watching TV there. The same unpleasant surprise overtakes you when you plug in a coffee maker, washing machine and microwave into one outlet.

Thermal calculation using correction factors

For several lines in one cable channel, the tabulated values ​​of the maximum current should be multiplied by the appropriate coefficient:

• 0.68 — for the number of conductors from 2 to 5 pcs.
• 0.63 — for conductors from 7 to 9 pcs.
• 0.6 — for conductors from 10 to 12 pcs.

The coefficient refers specifically to the wires (cores), and not to the number of passing lines. When calculating the number of laid wires, the neutral working wire or grounding wire is not taken into account. According to PUE and GOST 16442-80, they do not affect the heating of wires during the passage of normal currents.

Summarizing the above, it turns out that in order to correctly and accurately select the wire cross-section, you need to know:

1. The sum of all maximum powers of electrical appliances.
2. Network characteristics: number of phases and voltage.
3. Characteristics of cable material.
4. Tabular data and coefficients.

At the same time, power is not the main indicator for an individual cable line or the entire internal power supply system. When selecting a cross-section, be sure to calculate the maximum load current, and then check it with the rated current of the home circuit breaker.

This article will tell you how to calculate the wire cross-section based on power consumption yourself. You need to know this not only when working in the house, but also when carrying out work on cars, for example. If the wire cross-section is insufficient, it will begin to heat up very much, which will lead to a significant loss of safety level. Taking into account all the recommendations that will be outlined below, you will be able to independently calculate the parameters of the wires for installing electrical power 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 based on power consumption (12V and 220V) is carried out in the same way.

Calculating the length of electrical wiring

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

1. Measuring the distance from panels to sockets and switches according to the installation diagram. Moreover, this can be done with a ruler on a pre-prepared electrical wiring plan - just 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, you need to take into account that the wires must somehow be connected, so there should 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 wiring load

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

Current consumption of electrical installations

Now let’s talk about how to calculate the current consumption of an electrical appliance. You can do this in your head, or you can do it on a calculator. See the instructions for the device to see what power consumption it has. Of course, an alternating current with a voltage of 220 volts flows in a household electrical network. Therefore, using a simple formula (power consumption divided by supply voltage), the current can be calculated. For example, an electric kettle has a power of 1000 W. This means that 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, it is necessary to install a circuit breaker of a higher rating). But note that this is not always the exact value. For example, if the design of an electrical appliance has a motor, you can increase the obtained value by approximately 25% - the current consumption of the motor in the starting mode is much greater than during idling.

But you can use a set of rules and standards. There is such a document as the Electrical Installation Rules, which regulates all the rules for installing wiring not only in private property, but also in factories, factories, etc. According to these rules, the standard for electrical wiring is the ability to withstand a load of 25 amperes for a long time. Therefore, in apartments, all electrical wiring should be done only using copper wire, its cross-section is at least 5 square meters. mm. Each core must have a cross-section of over 2.5 square meters. mm. The conductor diameter should be 1.8 mm.

To ensure that all electrical wiring operates as safely as possible, a circuit breaker is installed at the input. It will protect the apartment from short circuits. Also, recently, most homeowners have been installing residual current devices, which instantly change the resistance in the circuit. In other words, if you accidentally touch a live one, they will immediately de-energize and you won't get hit. it is necessary to calculate the current, and be sure to choose with a reserve so that it is always possible to install any electrical appliance in the house. Proper calculation of the wire cross-section according to power consumption (you will learn how to make the right choice of wires from this material) is the key to ensuring that the power supply will function correctly and efficiently.

Materials for making wires

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

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

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

Wire brands

For electrical wiring, it is best to use two brands of wires - VVGng and VVG. The first one 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. Operates stably in the temperature range -50... +50. Guaranteed service life - at least 30 years. The cable can have two, three or four cores, each with a cross-section in the range of 1.5... 35 sq. mm. Please also note that it is necessary to calculate the wire cross-section based on power consumption and length (in the case of a long overhead line).

Make sure 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, meets 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 it is necessary to install through the wall. But for wiring indoors, flat domestic ones turn out to be more convenient.

Aluminum wires

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

Table for calculating power cross-section

It should also be mentioned that the maximum permissible current load is much less than for copper ones. The table below will help you calculate the core cross-section

Wire cross-section depending on the type of wiring

There are two types of installation of electrical wiring in houses - open and closed. As you understand, you need to take this nuance into account when making calculations. Hidden wiring is installed 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, when exposed to a heavy load for a long time, heats up very much. Therefore, when calculating the wire cross-section based on power consumption, be sure to take into account the effect on heating. The following parameters must also be taken into account:

1. Long-term 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 and can be neglected. But if a long line is being calculated, there is no escape from this. After all, the calculation of the wire cross-section based on power consumption (the influence of length is very large) depends on such a parameter as the length of the line.

Wire power calculation

So, you will need to know the following characteristics:

1. The material from 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 the total power that is dissipated on a piece of electrical wiring. If you choose the wrong cross-section, excessive heating will occur, and the result can be disastrous - ignition of the electrical wiring and fire. Therefore, it is worthwhile to accurately calculate the wire cross-section based on power consumption. The risk factors are too great and too many.

Optimal parameters

Optimal sections:

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

Please note 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 a wire based on power consumption (you now know the definition of important characteristics and other small factors). Based on all the above data, you can independently, without resorting to the help of professionals, draw up a correct power supply plan for your home or apartment.

How to calculate a cable by current, voltage and length. , as you know, come in different sections, materials and with different numbers of cores. Which one should you choose 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, it is necessary to calculate the cable. The cross section is calculated by knowing the power of the devices powered from the network and the current that will flow through the cable. You also need to know a few other wiring parameters.

Basic Rules

When laying electrical networks in residential buildings, garages, and apartments, rubber or PVC insulated cables designed for a voltage of no more than 1 kV are most often used. There are brands that can be used outdoors, indoors, in walls (grooves) and pipes. Usually this is a VVG or AVVG cable with different cross-sectional areas and number of cores.
PVA wires and SHVVP cords are also used to connect electrical appliances.

After calculation, the maximum permissible cross-section value is selected from a number of cable grades.

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

For violation of the rules, administrative fines are provided. But the most important thing is that violation of the rules can lead to failure of electrical appliances, fire of wiring and serious fires. Fire damage 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, you need to remember your school physics lessons.

Current flows through the wires and heats them. The stronger the power, the greater the heating. Active current power is calculated using the formula:

P=U*I* cos φ=I²*R

R– active resistance.

As you can see, power depends on current and resistance. The greater the resistance, the more heat is generated, that is, the more the wires heat up. Same 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– length of the conductor;

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, do not forget that the area is calculated using the formula:

S=π*d²/4

d– diameter.

Don't forget resistivity either. It depends on the material from which the wires are made. The resistivity of aluminum is greater than that of copper. This means that with the same area, aluminum will heat up more strongly. It immediately becomes clear why it is recommended to use aluminum wires with a larger cross-section than copper wires.

In order not to go into a long calculation of the cable cross-section each time, standards for selecting the cross-section of wires in tables were developed.

Calculation of wire cross-section by 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 average characteristics.

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

Knowing the power, the rated current is determined using the formula:

I=(P*K)/(U*cos φ)

P– power in watts

U=220 Volt

K=0.75 – simultaneous switching factor;

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=380 Volt

Having calculated the current, you need to use the tables that are presented in the PUE and determine the cross-section of the wire. The tables indicate the permissible continuous current for copper and aluminum wires with various types of insulation. Rounding is always done upward to allow for margin.

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

Special calculators have been developed that can be used to determine the cross-section, knowing the power consumption, the phase number of the network and the length of the cable line. You should pay attention to the installation conditions (in a pipe or outdoors).

Influence of wiring length on cable selection

If the cable is very long, then additional restrictions arise on the choice of cross-section, since voltage losses occur over an extended section, which in turn lead to additional heating. To calculate voltage losses, the concept of “load torque” 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 consumption is 2 kW and the cable length is 40 m, then the torque is 80 kW*m. For copper cable with a cross-section of 2.5 mm². this means that the voltage loss is 2-3%.

If the losses exceed 5%, then it is necessary to take a cross section with a margin greater than that 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, since the load power is distributed over three phases. Consequently, losses are reduced and the effect of 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 be almost halved. 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 everyday conditions:

ΔU=I*R

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

I– current strength, found from Ohm’s law;

Let's say we get that I=4000 W/220 IN=18.2 A.

The resistance of one strand of copper wire with a length of 20 m and an area of ​​1.5 mm2. amounted to R=0.23 Ohm. The total resistance of the two wires is 0.46 Ohms.

Then ΔU=18.2*0.46=8.37 V

Percentage

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

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

Every master wants to know... how to calculate the cable cross-section for a particular load. You have to deal with this when wiring in a house or garage, even when connecting machines - you need to be sure that the selected power cord will not smoke when you turn on the machine...

I decided to create a calculator for calculating cable cross-section by power, i.e. The calculator calculates the current consumed, and then determines the required wire cross-section, and also recommends the closest circuit breaker.

Power cables GOST 31996-2012

Calculation of the cable cross-section by power is carried out in accordance with the tables of the normative document GOST 31996-2012 “Power cables with plastic insulation”. In this case, the cross-section is indicated with a current reserve to avoid heating and fire of the wire operating at the maximum current. I also introduced a coefficient of 10%, i.e. another 10% is added to the maximum current for smooth operation of the cable :)

For example, we take a load power of 7000 W at a voltage of 250 Volts, we get a current of 30.8 Amps (adding 10% in reserve), we will use a single-core copper wire laid through the air, as a result we get a cross-section: 4 sq. mm., i.e. cable with a maximum current of 39 Amps. Cable with a cross section of 2.5 sq. mm. It is not recommended to use it for a current of 30 Amps, because the wire will be operated at the maximum permissible current values, which can lead to heating of the wire with subsequent destruction of the electrical insulation.

Table of cable cross-section by current and power for copper wire

Also check out these articles

The data in the tables is given for OPEN wiring!!!

Table of aluminum wire cross-section by power consumption and current

Cable cross section calculator

The online calculator is designed to calculate the cable cross-section by power.

You can select the required electrical appliances by ticking them to automatically determine their power, or enter the power in watts (not kilowatts!) in the field below, then select the remaining data: network voltage, conductor metal, cable type, where it is laid and the calculator will calculate the wire cross-section by power and tell you which circuit breaker to install.

I hope my calculator will help many craftsmen.

Calculation of cable cross-section by power: