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

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

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

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

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

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

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

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

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

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

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

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

I = (P × K u) / (U × cos(φ))

I- current strength;

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

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

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

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

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

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

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

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

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

I = P / (√3 × U × cos(φ))

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

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

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

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

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

U linear = √3 × U phase

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

Concept of continuous current

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

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

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

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

During the repair process, replacement is usually always carried out. old electrical wiring. This is due to the fact that recently many useful household appliances have appeared that make the life of housewives easier. Moreover, they consume a lot of energy, which old wiring, it just may not stand it. Such electrical appliances include washing machines, electric ovens, electric kettles, microwaves etc.

When laying electrical wires, you should know what cross-section of wire needs to be laid in order to power a particular electrical appliance or group of electrical appliances. As a rule, the choice is made both by power consumption and by the current strength consumed by electrical appliances. In this case, you need to take into account both the laying method and the length of the wire.

It is quite simple to select the cross-section of the cable to be laid according to the load power. This can be a single load or a collection of loads.

Each household appliance, especially a new one, is accompanied by a document (passport), which indicates its basic technical data. In addition, the same data is available on special plates attached to the product body. This plate, which is located on the side or back of the device, indicates the country of manufacture, its serial number and, of course, its power consumption in watts (W) and the current that the device consumes in amperes (A). On products from domestic manufacturers, power may be indicated in watts (W) or kilowatts (kW). On imported models there is the letter W. In addition, the power consumption is designated as “TOT” or “TOT MAX”.

An example of such a plate showing basic information about the device. Such a plate can be found on any technical device.

If it is not possible to find out the necessary information (the inscription on the plate is worn out or household appliances not yet) you can find out approximately what power the most common household appliances have. All this data can actually be found in the table. Basically, electrical appliances are standardized in terms of power consumption and there is no particular variation in the data.

In the table, exactly those electrical appliances that you plan to purchase are selected, and their current consumption and power are recorded. From the list it is better to choose indicators that have maximum values. In this case, it will not be possible to miscalculate and the wiring will be more reliable. The fact is that the thicker the cable, the better, since the wiring heats up much less.

How the choice is made

When choosing a wire, you should sum up all the loads that will be connected to this wire. At the same time, you should ensure that all indicators are written out either in watts or kilowatts. To convert the indicators to one value, you should either divide the numbers or multiply by 1000. For example, to convert to watts, you should multiply all the numbers (if they are in kilowatts) by 1000: 1.5 kW = 1.5x1000 = 1500 W. When transferring back, actions are performed in reverse order: 1500 W = 1500/1000 = 1.5 kW. Usually, all calculations are made in watts. After such calculations, a cable is selected using the appropriate table.

You can use the table as follows: find the corresponding column where the supply voltage is indicated (220 or 380 volts). This column contains a number that corresponds to the power consumption (you need to take a slightly higher value). In the line that corresponds to power consumption, the first column indicates the wire cross-section that can be used. When going to the store to buy a cable, you should look for a wire whose cross-section matches the records.

Which wire to use - aluminum or copper?

IN in this case it all depends on the power consumption. In addition, copper wire can withstand twice the load than aluminum wire. If the loads are large, then it is better to give preference to copper wire, as it will be thinner and easier to lay. In addition, it is easier to connect it to electrical equipment, including sockets and switches. Unfortunately, copper wire has a significant disadvantage: it costs much more than aluminum wire. Despite this, it will last much longer.

How to calculate cable cross-section by current

Most craftsmen calculate wire diameters based on current consumption. Sometimes this simplifies the task, especially if you know what current a wire of a particular thickness can withstand. To do this, you need to write down all the indicators of current consumption and sum them up. The wire cross-section can be selected using the same table, only now you need to look for the column where the current is indicated. As a rule, a larger value is always selected for reliability.

For example, to connect hob, which can consume a maximum current of up to 16A, a copper wire must be selected. If you turn to the table for help, the desired result can be found in the third column on the left. Since there is no value 16A, we choose the nearest, larger one - 19A. A cable cross-section of 2.0 mm square is suitable for this current.

As a rule, when connecting powerful household appliances, they are powered by separate wires, with the installation of separate automatic switches. This greatly simplifies the process of selecting wires. Besides, this is part modern requirements to electrical wiring. Plus, it's practical. In an emergency, you do not have to turn off the electricity completely in your entire home.

It is not recommended to select wires with a lower value. If the cable is constantly running at maximum loads, then this can lead to emergency situations in electrical network. The result can be a fire if the circuit breakers are incorrectly selected. At the same time, you should know that they do not protect the wire sheath from fire, and it will not be possible to select the exact current so that it can protect the wires from overload. The fact is that they are not regulated and are issued at a fixed current value. For example, 6A, 10A, 16A, etc.

Choosing a wire with a reserve will allow you to install another electrical appliance or even several on this line in the future, if this corresponds to the current consumption rate.

Cable calculation by power and length

If we take into account the average apartment, the length of the wires does not reach such values ​​as to take this factor into account. Despite this, there are cases when when choosing wires, their length should be taken into account. For example, you need to connect a private house from the nearest pole, which may be located at a considerable distance from the house.

With significant current consumption, a long wire can affect the quality of power transmission. This is due to losses in the wire itself. The longer the wire, the greater the losses in the wire itself. In other words, the longer the wire, the greater the voltage drop across this area. In our time, when the quality of power supplies leaves much to be desired, this factor plays a significant role.

To know this, you will again have to refer to the table, where you can determine the cross-section of the wire, depending on the distance to the power point.

Table for determining wire thickness, depending on power and distance.

Open and closed method of laying wires

Current passing through a conductor causes it to heat up, since it has a certain resistance. So, the greater the current, the more heat stands out on it, under conditions of the same cross-section. At the same current consumption, more heat is generated on conductors of smaller diameter than on conductors with a larger thickness.

Depending on the laying conditions, the amount of heat generated on the conductor also changes. When laying open, when the wire is actively cooled by air, you can give preference to a thinner wire, and when the wire is laid closed and its cooling is minimized, it is better to choose thicker wires.

Similar information can also be found in the table. The principle of selection is the same, but taking into account one more factor.

And finally, the most important thing. The fact is that nowadays the manufacturer is trying to save on everything, including the material for the wires. Very often, the declared cross-section does not correspond to reality. If the seller does not inform the buyer, then it is better to measure the wire thickness on the spot if this is critical. To do this, just take a caliper with you and measure the thickness of the wire in millimeters, and then calculate its cross-section using the simple formula 2*Pi*D or Pi*R squared. Where Pi is a constant number equal to 3.14, and D is the diameter of the wire. In another formula - respectively, Pi = 3.14, and R squared is the radius squared. The radius is very easy to calculate; just divide the diameter by 2.

Some sellers directly point out the discrepancy between the declared cross-section and the actual one. If the wire is chosen with a large margin, then this is not at all significant. The main problem is that the price of the wire, compared to its cross-section, is not underestimated.

In this article I will tell you how to choose the right cable cross-section for your home or apartment. If- this is the “heart” of our power supply system, then the cables connected to the electrical panel circuit breakers are"blood vessels" that supplyelectricity from our household electrical receivers.

When installing electrical wiring in a house or apartment, all stages, starting from designing the electrical supply of a private house or apartment, and ending with the final installation of sockets or switches, must be approached with full responsibility, because your personal electrical safety, as well as the fire safety of your house or apartment, depends on this . Therefore, we approach the choice of cable cross-section with all seriousness, because no other method of transmitting electricity in a private house or apartment has yet been invented.

It is important to choose the correct cable cross-section, specifically for a specific line (group) of electrical receivers. Otherwise, if we choose a lower section cable is will lead to 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 a cable cross-section that is too high for a house or apartment, this will lead to increased costs, and difficulties will arise during the electrical installation of 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 .

Update 06/01/2017. I provide a general universal table, which I myself use to select the rated current of circuit breakers for cable protection. blue

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

Please note that when in different ways installation of electrical wiring(hidden or open) , cables with the same cross-section have different continuous-permissible currents.

Those. at open way installation of electrical wiring, the cable heats up less due to better cooling. At h covered way installation of electrical wiring (in grooves, pipes, etc.), on the contrary, it heats up more. This is an important point, because if you choose the wrong machine to protect the cable, the rating of the machine may be overestimated relative to the long-term permissible current of the cable, which is why the cable can get very hot, but the machine will not turn off.

I'll bring you example, for example, we have a cable cross-section of 6 sq. mm:

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

Suppose we chose a cable cross-section for an apartment, which are laid in grooves or under plaster (in a closed way). If we mix it up and install 50A circuit breakers for protection, the cable will overheat, because... at closed method its gasket In = 34 A, which will lead to destruction of its insulation, then a short circuit and fire.

TABLES ARE NOT CURRENT. WHEN SELECTING A MACHINE FOR CABLES, USE THE TABLE ABOVE.

Cable cross-section for hidden electrical wiring

Cable cross-section for open electrical wiring

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 powers of household electrical receivers, W;

U - single-phase network voltage 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 powers of electrical receivers for a given cable line(groups). We will still need current calculations when designing an electrical panel (choosing automatic machines, RCDs or differential circuit breakers).

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

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 device (difavtomatic) to protect this line, whose rated current must be lower than the continuous-permissible current of the cable of a certain cross-section. If we choose a copper cable cross-section of 2.5 sq. mm, which conducts current up to 21 A for as long as desired ( hidden installation method), then the automatic circuit breaker (difavtomat) in the electrical panel for this cable must have a rated current of 20 A so that the circuit breaker turns off before the cable begins to overheat.

Typical cable sections for household electrical installations:

• In apartments, cottages or private houses, for socket groups laying copper cable 2.5 sq.mm.;
• For lighting group- copper cable cross-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 power oven more than 3.5 kW, then lay a 3x4 cable and connect the oven through the terminals; if the oven power is less than 3.5 kW, then a 3x2.5 cable and connection through a household outlet is sufficient.

To select the correct cable cross-section and ratings of circuit breakers for the electrical panel of a private house, apartment, you need to know important points , not knowing which can lead to dire consequences.

For example:

• For socket groups, select a cable cross-section of 2.5 sq. mm, but the machine is chosen with a rated current of not 20A, but 16A, because household sockets designed for a current of no more than 16 A.
• For lighting I use a 1.5 sq. mm cable, but automatic machine no more than 10A, because switches are designed for a current of no 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 by up to 1.45 times, it can turn off only after 1 hour. And all this time the cable will heat up.
• Select the correct cable cross-section according to in a hidden way gaskets so that there is the necessary margin of safety.
• PUE clause 7.1.34. prohibits the use aluminum wiring inside buildings.

Thank you for your attention.

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 doing calculations for a kitchen; it has lamps, a microwave oven, an electric kettle and a stove, 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 about how to calculate current consumption 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 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. Automatic switches must be calculated based on current, and they must be chosen with a reserve so that it is always possible to install any electrical appliance in the house. Correct calculation of wire cross-section based on power consumption (how to right choice wires, you will learn from this material) is a guarantee 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 communication - 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 have little weight, 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 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 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.

The article discusses the main criteria for choosing a cable cross-section and provides examples of calculations.

In markets you can often see handwritten signs indicating which one the buyer needs to purchase depending on the expected load current. Do not believe these signs, as they are misleading. The cable cross-section is selected not only by the operating current, but also by several other parameters.

First of all, it is necessary to take into account that when using a cable at the limit of its capabilities, the cable cores heat up by several tens of degrees. The current values ​​shown in Figure 1 assume heating of the cable cores to 65 degrees at a temperature environment 25 degrees. If several cables are laid in one pipe or tray, then due to their mutual heating (each cable heats all other cables), the maximum permissible current is reduced by 10 - 30 percent.

Also, the maximum possible current decreases when elevated temperature environment. Therefore, in a group network (a network from panels to lamps, plug sockets and other electrical receivers), as a rule, cables are used with currents not exceeding 0.6 - 0.7 of the values ​​​​shown in Figure 1.

Rice. 1. Permissible long-term current of cables with copper conductors

Based on this, the widespread use of circuit breakers with a rated current of 25A to protect socket networks laid with cables with copper conductors with a cross-section of 2.5 mm2 is dangerous. Tables of reduction coefficients depending on temperature and the number of cables in one tray can be found in the Electrical Installation Rules (PUE).

Additional restrictions arise when the cable is longer. In this case, voltage losses in the cable can reach unacceptable values. As a rule, when calculating cables, the maximum loss in the line is no more than 5%. Losses are not difficult to calculate if you know the resistance value of the cable cores and the calculated load current. But usually, to calculate losses, they use tables of the dependence of losses on the load torque. The load moment is calculated as the product of the cable length in meters and the power in kilowatts.

Data for calculating losses at a single-phase voltage of 220 V are shown in Table 1. For example, for a cable with copper conductors with a cross-section of 2.5 mm2, with a cable length of 30 meters and a load power of 3 kW, the load moment is 30x3 = 90, and the losses will be 3%. If the calculated loss value exceeds 5%, then it is necessary to select a cable with a larger cross-section.

Table 1. Load moment, kW x m, for copper conductors in a two-wire line for a voltage of 220 V at a given conductor cross-section

Using Table 2, you can determine the losses in a three-phase line. Comparing tables 1 and 2, you can see that in a three-phase line with copper conductors with a cross-section of 2.5 mm2, losses of 3% correspond to six times the load torque.

A triple increase in the load torque occurs due to the distribution of load power across three phases, and a double increase due to the fact that in a three-phase network when symmetrical load(identical currents in phase conductors) the current in the neutral conductor is zero. With an asymmetrical load, cable losses increase, which must be taken into account when choosing the cable cross-section.

Table 2. Load moment, kW x m, for copper conductors in a three-phase four-wire line with zero for a voltage of 380/220 V at a given conductor cross-section (to enlarge the table, click on the figure)

Cable losses have a significant impact when using low-voltage lamps, such as halogen lamps. This is understandable: if 3 Volts drop on the phase and neutral conductors, then at a voltage of 220 V we most likely will not notice this, and at a voltage of 12 V, the voltage on the lamp will drop by half to 6 V. That is why transformers for powering halogen lamps need to be maximally bring it closer to the lamps. For example, with a cable length of 4.5 meters with a cross-section of 2.5 mm2 and a load of 0.1 kW (two 50 W lamps), the load torque is 0.45, which corresponds to a loss of 5% (Table 3).

Table 3. Load moment, kW x m, for copper conductors in a two-wire line for a voltage of 12 V at a given conductor cross-section

The tables above do not take into account the increase in resistance of conductors due to heating due to current flowing through them. Therefore, if the cable is used at currents of 0.5 or more of the maximum permissible current of the cable of a given cross-section, then a correction must be introduced. In the simplest case, if you expect losses of no more than 5%, then calculate the cross section based on losses of 4%. Also, losses may increase if there is large quantity connections of cable cores.

Cables with aluminum conductors have a resistance 1.7 times greater than cables with copper conductors, and accordingly their losses are 1.7 times greater.

The second limiting factor for long cable lengths is exceeding the permissible resistance value of the phase-zero circuit. To protect cables from overloads and short circuits, as a rule, circuit breakers with a combined release are used. Such switches have thermal and electromagnetic releases.

The electromagnetic release provides instantaneous (tenths and even hundredths of a second) shutdown of the emergency section of the network in the event of a short circuit. For example, a circuit breaker designated C25 has a 25 A thermal release and a 250 A electromagnetic release. Automatic circuit breakers of group “C” have a multiplicity of the breaking current of the electromagnetic release to the thermal one from 5 to 10. But the maximum value is taken.

The total resistance of the phase-zero circuit includes: the resistance of the step-down transformer of the transformer substation, the resistance of the cable from the substation to the input switchgear of the building, the resistance of the cable laid from the ASU to switchgear(RU) and the cable resistance of the group line itself, the cross-section of which must be determined.

If the line has a large number of connections of cable cores, for example, a group line of a large number of lamps connected by a cable, then the resistance of the contact connections must also be taken into account. Very accurate calculations take into account the arc resistance at the fault point.

Circuit impedance phase - zero for four-core cables are given in Table 4. The table takes into account the resistance of both the phase and neutral conductors. Resistance values ​​are given at a cable core temperature of 65 degrees. The table is also valid for two-wire lines.

Table 4. Circuit impedance phase - zero for 4-core cables, Ohm/km at core temperature 65 o C

In urban transformer substations, as a rule, transformers with a capacity of 630 kV or more are installed. A and more, having an output resistance Rtp less than 0.1 Ohm. In rural areas, transformers of 160 - 250 kV can be used. And having an output resistance of about 0.15 Ohm, and even transformers for 40 - 100 kV. A, having an output impedance of 0.65 - 0.25 Ohm.

Supply network cables from city transformer substations to ASUs of houses are usually used with aluminum conductors with a phase conductor cross-section of at least 70 - 120 mm2. If the length of these lines is less than 200 meters, the resistance of the phase-neutral circuit of the supply cable (Rpc) can be taken equal to 0.3 Ohm. For a more accurate calculation, you need to know the length and cross-section of the cable, or measure this resistance. One of the devices for such measurements (Vector device) is shown in Fig. 2.

Rice. 2. Device for measuring the resistance of the phase-zero circuit "Vector"

The line resistance must be such that in the event of a short circuit, the current in the circuit is guaranteed to exceed the operating current of the electromagnetic release. Accordingly, for the C25 circuit breaker the current short circuit in the line must exceed the value of 1.15x10x25=287 A, here 1.15 is the safety factor. Therefore, the resistance of the phase-zero circuit for the C25 circuit breaker should be no more than 220V/287A=0.76 Ohm. Accordingly, for the C16 circuit breaker the circuit resistance should not exceed 220V/1.15x160A=1.19 Ohms and for the C10 circuit breaker - no more than 220V/1.15x100=1.91 Ohms.

Thus, for urban apartment building, taking Rtp=0.1 Ohm; Rpc=0.3 Ohm when using a cable with copper conductors with a cross section of 2.5 mm2, protected in the socket network circuit breaker C16, cable resistance Rgr (phase and neutral conductors) should not exceed Rgr = 1.19 Ohm - Rtp - Rpk = 1.19 - 0.1 - 0.3 = 0.79 Ohm. From Table 4 we find its length - 0.79/17.46 = 0.045 km, or 45 meters. For most apartments, this length is sufficient.

When using a C25 circuit breaker to protect a cable with a cross-section of 2.5 mm2, the circuit resistance must be less than 0.76 - 0.4 = 0.36 Ohm, which corresponds to a maximum cable length of 0.36/17.46 = 0.02 km, or 20 meters.

When using a C10 circuit breaker to protect a group lighting line made with a cable with copper conductors with a cross-section of 1.5 mm2, we obtain the maximum permissible cable resistance of 1.91 - 0.4 = 1.51 Ohm, which corresponds to a maximum cable length of 1.51/29, 1 = 0.052 km, or 52 meters. If such a line is protected by a C16 circuit breaker, then the maximum line length will be 0.79/29.1 = 0.027 km, or 27 meters.