How to determine wire cross-section by power online. Conductor cross-section for power and current for electrical wiring in an apartment

When laying electrical wiring, you need to know what cross-section cable you will need to lay. The choice of cable cross-section can be made either by power consumption or current consumption. You also need to take into account the cable length and installation method.

Selecting the cable cross-section according to power

You can select the wire cross-section according to the power of the devices that will be connected. These devices are called load and the method can also be called “by load”. Its essence does not change from this.

Collecting data

First, find the power consumption in the passport data of household appliances and write it down on a piece of paper. If it’s easier, you can look at nameplates - metal plates or stickers attached to the body of equipment and equipment. There is basic information and, more often than not, power. The easiest way to identify it is by its units of measurement. If a product is manufactured in Russia, Belarus, or Ukraine, it is usually designated W or kW; on equipment from Europe, Asia or America, the English designation for watts is usually W, and the power consumption (this is what is needed) is designated by the abbreviation “TOT” or TOT MAX.

If this source is also unavailable (the information has become lost, for example, or you are just planning to purchase equipment, but have not yet decided on the model), you can take the average statistical data. For convenience, they are summarized in a table.

Find the equipment you plan to install and write down the power. Sometimes it is given with a wide spread, so sometimes it is difficult to understand which figure to take. In this case, it is better to take the maximum. As a result, when calculating, you will slightly overestimate the power of the equipment and will need a cable with a larger cross-section. But for calculating the cable cross-section it is good. Only cables with a smaller cross-section than necessary will burn. Routes with a large cross-section work for a long time, as they heat up less.

The essence of the method

To select the wire cross-section for the load, add up the power of the devices that will be connected to this conductor. It is important that all powers are expressed in the same units of measurement - either in watts (W) or in kilowatts (kW). If there are different values, we bring them to a single result. To convert, kilowatts are multiplied by 1000 to get watts. For example, let's convert 1.5 kW into watts. This will be 1.5 kW * 1000 = 1500 W.

If necessary, you can carry out the reverse conversion - convert watts to kilowatts. To do this, divide the figure in watts by 1000 to get kW. For example, 500 W / 1000 = 0.5 kW.

Cable cross-section, mm2	Conductor diameter, mm	Copper wire			Aluminum wire
		Current, A	power, kWt		Current, A	power, kWt
		Current, A	220 V	380 V	Current, A	220 V	380 V
0.5 mm2	0.80 mm	6 A	1.3 kW	2.3 kW
0.75 mm2	0.98 mm	10 A	2.2 kW	3.8 kW
1.0 mm2	1.13 mm	14 A	3.1 kW	5.3 kW
1.5 mm2	1.38 mm	15 A	3.3 kW	5.7 kW	10 A	2.2 kW	3.8 kW
2.0 mm2	1.60 mm	19 A	4.2 kW	7.2 kW	14 A	3.1 kW	5.3 kW
2.5 mm2	1.78 mm	21 A	4.6 kW	8.0 kW	16 A	3.5 kW	6.1 kW
4.0 mm2	2.26 mm	27 A	5.9 kW	10.3 kW	21 A	4.6 kW	8.0 kW
6.0 mm2	2.76 mm	34 A	7.5 kW	12.9 kW	26 A	5.7 kW	9.9 kW
10.0 mm2	3.57 mm	50 A	11.0 kW	19.0 kW	38 A	8.4 kW	14.4 kW
16.0 mm2	4.51 mm	80 A	17.6 kW	30.4 kW	55 A	12.1 kW	20.9 kW
25.0 mm2	5.64 mm	100 A	22.0 kW	38.0 kW	65 A	14.3 kW	24.7 kW

To find the required cable cross-section in the corresponding column - 220 V or 380 V - we find a figure that is equal to or slightly greater than the power we previously calculated. We select the column based on how many phases are in your network. Single-phase - 220 V, three-phase 380 V.

In the found line, look at the value in the first column. This will be the required cable cross-section for a given load (power consumption of devices). You will need to look for a cable with cores of this cross-section.

A little about whether to use copper wire or aluminum. In most cases, when using cables with copper conductors. Such cables are more expensive than aluminum ones, but they are more flexible, have a smaller cross-section, and are easier to work with. But copper cables with a large cross-section are no more flexible than aluminum ones. And under heavy loads - at the entrance to a house or apartment with a large planned power (from 10 kW or more), it is more advisable to use a cable with aluminum conductors - you can save a little.

How to calculate cable cross-section by current

You can select the cable cross-section according to the current. In this case, we carry out the same work - we collect data about the connected load, but we look for the maximum current consumption in the characteristics. Having collected all the values, we summarize them. Then we use the same table. We just look for the nearest higher value in the column labeled “Current”. In the same line we look at the wire cross-section.

For example, we need a peak current consumption of 16 A. We will lay a copper cable, so look in the corresponding column - third from the left. Since there is no value of exactly 16 A, look at line 19 A - this is the nearest greater. A suitable cross-section is 2.0 mm 2 . This will be the minimum cable cross-section for this case.

When connecting powerful household electrical appliances, a separate power supply line is pulled from them. In this case, the choice of cable cross-section is somewhat simpler - only one value of power or current is required

You cannot pay attention to a line with a slightly lower value. In this case, at maximum load, the conductor will become very hot, which can lead to the insulation melting. What could happen next? Might work if it's installed. This is the most favorable option. Household appliances may break down or a fire may start. Therefore, always select the cable cross-section according to the larger value. In this case, it will be possible to later install equipment even slightly larger in power or current consumption without altering the wiring.

Cable calculation by power and length

If the power transmission line is long - several tens or even hundreds of meters - in addition to the load or current consumed, it is necessary to take into account losses in the cable itself. Usually long distances of power lines at . Although all data must be indicated in the project, you can play it safe and check. To do this, you need to know the allocated power per house and the distance from the pole to the house. Next, using the table, you can select the wire cross-section taking into account losses along the length.

In general, when laying electrical wiring, it is always better to take some margin in the cross-section of the wires. Firstly, with a larger cross-section, the conductor will heat up less, and therefore the insulation. Secondly, more and more devices powered by electricity are appearing in our lives. And no one can guarantee that in a few years you won’t need to install a couple more new devices in addition to the old ones. If stock exists, they can simply be included. If it’s not there, you’ll have to get smart—either change the wiring (again) or make sure that powerful electrical appliances don’t turn on at the same time.

Open and closed wiring

As we all know, when current passes through a conductor, it heats up. The higher the current, the more heat generated. But, when the same current passes through conductors with different cross-sections, the amount of heat generated changes: the smaller the cross-section, the more heat is released.

In this regard, when the conductors are laid open, its cross-section may be smaller - it cools down faster, since heat is transferred to the air. In this case, the conductor cools down faster and the insulation does not deteriorate. When the gasket is closed, the situation is worse - heat is removed more slowly. Therefore, for closed installations - in pipes, in the wall - it is recommended to take a cable of a larger cross-section.

The choice of cable cross-section, taking into account the type of installation, can also be made using the table. The principle was described before, nothing changes. There's just one more factor to consider.

And finally, some practical advice. When going to the market to buy cables, take a caliper with you. Too often the stated cross-section does not coincide with reality. The difference can be 30-40%, which is a lot. What does this mean for you? Burnout of wiring with all the ensuing consequences. Therefore, it is better to check right on the spot whether a given cable actually has the required core cross-section (the diameters and corresponding cable cross-sections are in the table above). And more about determining the section The cable by its diameter can be read here.

It is very important to choose the correct wire cross-section. If you take a cable that is too thick, it will cost you a pretty penny, since its price directly depends on the diameter (section) of the conductors. The use of a thin cable leads to its overheating and if the protection does not work, the insulation may melt, a short circuit and, as a result, a fire. The most correct choice would be the wire cross-section depending on the load, which is reflected in the tables below.

The cable cross-section is the cut area of the current-carrying core. If the core section is round (as in most cases) and consists of one wire, then the area/section is determined by the formula for the area of a circle. If there are many wires in the core, then the cross-section will be the sum of the cross-sections of all the wires in this core.

The cross-sectional values are standardized in all countries, and the standards of the former CIS and Europe in this part completely coincide. In our country, the document that regulates this issue is the “Rules for the Construction of Electrical Installations” or briefly - PUE.

The cable cross-section is selected based on the loads using special tables called “Permissible current loads on the cable.” If you have no desire to understand these tables, then it is enough for you to know that it is advisable to use a copper cable with a cross-section of 1.5-2.5 mm² for sockets, and 1.0-1.5 mm² for lighting.

To introduce one phase into an ordinary 2-3 room apartment, 6.0 mm² is quite enough. All the same, your 40-80 m² will not fit larger equipment, even taking into account the electric stove.

Many electricians, in order to “estimate” the required cross-section, believe that 1mm² of copper wire can pass 10A of electric current through itself: accordingly, 2.5 mm² of copper can pass 25A, and 4.0 mm² - 40A, etc. If you analyze the cable cross-section selection table a little, you will see that this method is only suitable for estimation and only for cables with a cross-section no higher than 6.0 mm².

Below is an abbreviated table for selecting cable cross-sections up to 35 mm² depending on current loads. For your convenience, the total power of electrical equipment is given there for 1-phase (220V) and 3-phase (380V) consumption.

When laying the cable in a pipe (i.e. in any closed spaces), the possible current loads on the cable should be less than when laying it openly. This is due to the fact that the cable heats up during operation, and heat transfer in a wall or in the ground is much lower than in open space.

When the load is called in kW, we are talking about the total load. Those. for a single-phase consumer, the load will be indicated for one phase, and for a three-phase consumer - in total for all three. When the load value is named in amperes (A), we are always talking about the load on one core (or phase).

Load table for cable cross-section:

Cable cross-section, mm²	Laid open						Installed in a pipe
	copper			aluminum			copper			aluminum
	current, A	power, kWt		current, A	power, kWt		current, A	power, kWt		current, A	power, kWt
		220V	380V		220V	380V		220V	380V		220V	380V
0.5	11	2.4
0.75	15	3.3
1	17	3.7	6.4				14	3	5.3
1.5	23	5	8.7				15	3.3	5.7
2.5	30	6.6	11	24	5.2	9.1	21	4.6	7.9	16	3.5	6
4	41	9	15	32	7	12	27	5.9	10	21	4.6	7.9
6	50	11	19	39	8.5	14	34	7.4	12	26	5.7	9.8
10	80	17	30	60	13	22	50	11	19	38	8.3	14
16	100	22	38	75	16	28	80	17	30	55	12	20
25	140	30	53	105	23	39	100	22	38	65	14	24
35	170	37	64	130	28	49	135	29	51	75	16	28

To independently calculate the required cable cross-section, for example, for entry into a house, you can use a cable calculator or select the required cross-section from the table.

This table applies to cables and wires with rubber and plastic insulation. These are such widespread brands as: PVS, GDP, VPP, PPV, APPV, VVG. AVVG and a number of others. Paper-insulated cables have their own table, and non-insulated wires and buses have their own.

When calculating the cable cross-section, the specialist must also take into account the methods of laying the cable: in trays, in bundles, etc.

correction factor corresponding to the cable cross-section and its location in the block;
correction factor for ambient temperature;
correction factor for cables laid in the ground;
correction factor for different numbers of operating cables laid nearby.

Calculation of wire cross-section

Let's start not with a table, but with a calculation. That is, each person, without having the Internet at hand, where the PUE with tables is freely available, can independently determine the cable cross-section by current. To do this you will need a caliper and a formula.

If we consider the cross-section of the cable, it is a circle with a certain diameter.
There is a formula for the area of a circle: S= 3.14*D²/4, where 3.14 is the Archimedean number, “D” is the diameter of the measured core. The formula can be simplified: S=0.785*D².

If the wire consists of several cores, then the diameter of each is measured, the area is calculated, then all the indicators are summed up. How to calculate the cross-section of a cable if each core consists of several thin wires?

The process becomes a little more complicated, but not much. To do this, you will have to count the number of wires in one core, measure the diameter of one wire, calculate its area using the described formula and multiply this figure by the number of wires. This will be the cross section of one core. Now you need to multiply this value by the number of cores.

If you don’t want to count the wires and measure their sizes, you just need to measure the diameter of one core, consisting of several wires. You must take measurements carefully so as not to crush the core. Please note that this diameter is not exact because there is space between the wires.

Relation between current and cross section

To understand how an electrical cable works, you need to remember a regular water pipe. The larger its diameter, the more water will pass through it. It's the same with wires.

The larger their area, the greater the current that will pass through them, the greater the load such a wire can withstand. In this case, the cable will not overheat, which is the most important requirement of fire safety rules.

Therefore, the cross-section - current connection is the main criterion that is used in the selection of electrical wires in the wiring. Therefore, you need to first figure out how many household appliances and what total power will be connected to each loop.

Wire core cross-section, mm 2	Copper conductors		Aluminum conductors
	Current, A	Power, W	Current, A	Power, W
0.5	6	1300
0.75	10	2200
1	14	3100
1.5	15	3300	10	2200
2	19	4200	14	3100
2.5	21	4600	16	3500
4	27	5900	21	4600
6	34	7500	26	5700
10	50	11000	38	8400
16	80	17600	55	12100
25	100	22000	65	14300

For example, the kitchen must have a refrigerator, microwave, coffee grinder and coffee maker, an electric kettle and sometimes a dishwasher. That is, all these devices can be turned on simultaneously at the same time. Therefore, the total power of the room is used in the calculations.

You can find out the power consumption of each device from the product passport or on the tag.

Kettle – 1-2 kW.
Microwave and meat grinder 1.5-2.2 kW.
Coffee grinder and coffee maker – 0.5-1.5 kW.
Refrigerator 0.8 kW.

Having found out the power that will act on the wiring, you can select its cross-section from the table. We will not consider all the indicators in this table; we will show those that prevail in everyday life.

Before moving on to the main content, we need to understand what we still want to calculate, the cross-section of a wire or cable, what are the differences between one and the other!? Despite the fact that the average person uses these two words as synonyms, meaning by this something of their own, but if we are meticulous, there is still a difference.

So a wire is one conductive core, be it a single core or a set of conductors, insulated into a dielectric, into a sheath. But a cable is already several such wires combined into a single whole, in its own protective and insulating sheath. In order for you to better understand what's what, take a look at the picture.

So, now we know that we need to calculate exactly the cross-section of the wire, that is, one conductive element, and the second will already move away from the load, back to the power supply.

However, sometimes we ourselves forget ourselves no better than you, so if you catch us by the fact that somewhere you still come across the word cable, then do not consider it ignorance, stereotypes do their job.

Cable selection

It is best to make internal wiring using copper wires. Although aluminum ones are not inferior to them. But there is one nuance here, which is associated with the correct connection of sections in. As practice shows, connections often fail due to oxidation of the aluminum wire.

Another question is which wire to choose: single-core or stranded? Single-core has better current conductivity, so it is recommended for use in household electrical wiring. Multicore has high flexibility, which allows it to be bent in one place several times without compromising quality.

Single or stranded

When installing electrical wiring, wires and cables of the PVS, VVGng, PPV, APPV brands are usually used. This list contains both flexible cables and monocore cables.

Here we would like to tell you one thing. If your wiring will not move, that is, it is not an extension cord, or a bend point that constantly changes its position, then it is preferable to use a monocore.

You will ask why? It's simple! No matter how well the conductors are laid in the protective insulating braid, air containing oxygen will still get under it. Oxidation of the copper surface occurs.

As a result, if there are many conductors, then the oxidation area is much larger, which means the current-carrying cross-section “melts” much more. Yes, this is a long process, but we don’t think that you are going to change the wiring often. The more she works, the better.

This oxidation effect will be especially pronounced at the edges of the cable cut, in rooms with temperature changes and high humidity. So we strongly recommend that you use monocore! The cross-section of a monocore cable or wire will change slightly over time, and this is so important for our further calculations.

Copper or aluminum

In the USSR, most residential buildings were equipped with aluminum wiring; this was a kind of norm, standard, and even dogma. No, this does not mean at all that the country was poor and there was a shortage of copper. Even in some cases it's the other way around.

But apparently the designers of electrical networks decided that they could save a lot economically if they used aluminum rather than copper. Indeed, the pace of construction was enormous; just remember the Khrushchev buildings, in which half of the country still lives, which means the effect of such savings was significant. There is no doubt about this.

However, today the realities are different, and aluminum wiring is not used in new residential premises, only copper. This is based on the rules of the PUE, clause 7.1.34 “Cables and wires with copper conductors should be used in buildings...”.

So, we strongly do not recommend that you experiment and try aluminum. Its disadvantages are obvious. Aluminum strands cannot be soldered and are also very difficult to weld; as a result, the contacts in the junction boxes may break over time. Aluminum is very fragile, two or three bends and the wire falls off.

There will be constant problems connecting it to sockets and switches. Again, if we talk about conducted power, then a copper wire with the same cross-section for aluminum is 2.5 mm2. allows a continuous current of 19A, and for copper 25A. Here the difference is more than 1 kW.

So let’s repeat it again - only copper! Further, we will proceed from the fact that we are calculating the cross-section for a copper wire, but in the tables we will also give values for aluminum. You never know.

Why is the calculation made?

Wires and cables that carry electrical current are the most important part of electrical wiring.

The wire cross-section must be calculated to ensure that the selected wire meets all the requirements for reliability and safe operation of electrical wiring.

Safe operation is that if you choose a cross-section that does not correspond to its current loads, this will lead to excessive overheating of the wire, melting of the insulation, short circuit and fire.

Therefore, the issue of choosing a wire cross-section must be taken very seriously.

What you need to know

The main indicator by which a wire is calculated is its long-term permissible current load. Simply put, this is the amount of current that it is capable of passing for a long time.

To find the rated current value, you need to calculate the power of all connected electrical appliances in the house. Let's consider an example of calculating the wire cross-section for an ordinary two-room apartment.

Table of power/current consumption of household electrical appliances

electrical appliance	Power consumption, W	Current strength, A
Washing machine	2000 – 2500	9,0 – 11,4
Jacuzzi	2000 – 2500	9,0 – 11,4
Electric floor heating	800 – 1400	3,6 – 6,4
Stationary electric stove	4500 – 8500	20,5 – 38,6
microwave	900 – 1300	4,1 – 5,9
Dishwasher	2000 – 2500	9,0 – 11,4
Freezers, refrigerators	140 – 300	0,6 – 1,4
Electric meat grinder	1100 – 1200	5,0 – 5,5
Electric kettle	1850 – 2000	8,4 – 9,0
Electric coffee maker	630 – 1200	3,0 – 5,5
Juicer	240 – 360	1,1 – 1,6
Toaster	640 – 1100	2,9 – 5,0
Mixer	250 – 400	1,1 – 1,8
Hairdryer	400 – 1600	1,8 – 7,3
Iron	900 –1700	4,1 – 7,7
Vacuum cleaner	680 – 1400	3,1 – 6,4
Fan	250 – 400	1,0 – 1,8
TV	125 – 180	0,6 – 0,8
Radio equipment	70 – 100	0,3 – 0,5
Lighting devices	20 – 100	0,1 – 0,4

Once the power is known, the calculation of the cross-section of a wire or cable comes down to determining the current strength based on this power. You can find the current strength using the formula:

1) Formula for calculating current for a single-phase 220 V network:

current calculation for a single-phase network

where P is the total power of all electrical appliances, W;
U—mains voltage, V;
CI = 0.75 - simultaneity coefficient;
cos for household electrical appliances - for household electrical appliances.
2) Formula for calculating the current in a three-phase 380 V network:

current calculation for a three-phase network

Knowing the magnitude of the current, the wire cross-section is found from the table. If it turns out that the calculated and tabulated current values do not coincide, then in this case the nearest larger value is selected. For example, the calculated current value is 23 A, we select the nearest larger one from the table, 27 A - with a cross-section of 2.5 mm2.

Which wire is better to use

Today, for installation of both open and hidden electrical wiring, copper wires are, of course, very popular.

it is stronger, softer and does not break in places of inflection compared to aluminum;
less susceptible to corrosion and oxidation. When connecting aluminum in a junction box, the twist points oxidize over time, which leads to loss of contact;
The conductivity of copper is higher than that of aluminum; with the same cross-section, a copper wire can withstand a higher current load than aluminum.

The disadvantage of copper wires is their high cost. Their cost is 3-4 times higher than aluminum ones. Although copper wires are more expensive, they are still more common and popular in use than aluminum wires.

Calculation of the cross-section of copper wires and cables

Having calculated the load and decided on the material (copper), let’s consider an example of calculating the cross-section of wires for individual groups of consumers, using the example of a two-room apartment.

As you know, the entire load is divided into two groups: power and lighting.

In our case, the main power load will be the socket group installed in the kitchen and bathroom. Since the most powerful equipment is installed there (electric kettle, microwave, refrigerator, boiler, washing machine, etc.).

For this socket group we select a wire with a cross section of 2.5mm2. Provided that the power load will be scattered across different outlets. What does it mean? For example, in the kitchen, to connect all household appliances, you need 3-4 sockets connected with copper wire with a cross-section of 2.5 mm2 each.

If all equipment is connected through one single socket, then a cross-section of 2.5 mm2 will not be enough, in this case you need to use a wire with a cross-section of 4-6 mm2. In living rooms, a wire with a cross section of 1.5 mm2 can be used to power sockets, but the final choice must be made after appropriate calculations.

The entire lighting load is powered by a wire with a cross section of 1.5 mm2.

It is necessary to understand that the power in different sections of the electrical wiring will be different, and accordingly the cross-section of the supply wires will also be different. Its greatest value will be in the introductory section of the apartment, since the entire load passes through it. The cross-section of the input supply wire is selected 4 - 6 mm2.

When installing electrical wiring, wires and cables of the PVS, VVGng, PPV, APPV brands are used.

Selection of cable cross-section by power

Now we get to the essence of our article. However, everything that was above cannot be missed, which means we could not remain silent.

If we try to present the idea logically and simply, then a current of a certain strength can pass through each conventional cross-section of a conductor. This conclusion is quite logical and now all that remains is to find out these ratios and correlate them for different wire diameters, based on its type series.

It also cannot be ignored that here, when calculating the current cross section, temperature also comes into play. Yes, this is a new component – temperature. It is she who can influence the cross section. How and why, let's figure it out.

We all know about Brownian motion. On the constant displacement of ions in a crystal lattice. All this happens in all materials, including conductors. The higher the temperature, the greater these vibrations of ions within the material will be. And we know that current is the directed movement of particles.

So, the directed movement of particles will collide with ions in the crystal lattice, which will lead to an increase in resistance to current.

The higher the temperature, the higher the electrical resistance of the conductor. Therefore, by default, the wire cross-section for a certain current is taken at room temperature, that is, at 18 degrees Celsius. It is at this temperature that all reference values are given in the tables, including ours.

Despite the fact that we do not consider aluminum wires as wires for electrical wiring, at least in an apartment, they are nevertheless used in many places. Let's say for wiring on the street. That is why we will also present the values of the cross-section and current dependencies for aluminum wires.

So, for copper and aluminum there will be the following indicators of the dependence of the cross-section of the wire (cable) on the current (power). See table.

Since 2001, aluminum wires have not been used for wiring in apartments. (PEU)

Yes, here, as our reader noted, we actually did not provide calculations, but only provided reference data, tabulated, based on these calculations. But we dare to tell you that for calculations it is necessary to go through many formulas and indicators. Starting from temperature, resistivity, current density and the like.

Therefore, we will leave such calculations for specialists. It should be noted that they are not final, since they may vary slightly depending on the standard for the material and the current reserve of the wire used in different countries.

But what we would also like to talk about is converting the wire cross-section to diameter. This is necessary when there is a wire, but for some reason there is no marking on it. In this case, the cross-section can be calculated from the diameter of the wire, and vice versa from the diameter of the cross-section.

Common cross-sections for wiring in an apartment

We talked a lot about names, materials, individual characteristics and even temperature, but we lost sight of life circumstances.

So, if you hire an electrician to conduct wiring in the rooms of your apartment or house, then the following values are usually accepted. For lighting, the wire cross-section is taken at 1.5 mm 2, and for sockets at 2.5 mm 2.

If the wiring is intended for connecting boilers, heaters, stoves, then the cross-section of the wire (cable) is already calculated individually.

Selecting the wire cross-section based on the number of consumers

What I also wanted to say is that it is better to use several independent power lines for each room in a room or apartment. Thus, you will not use a wire with a cross-section of 10 mm 2 for the entire apartment, routed to all rooms, from which there are taps.

Such a wire will come to, and then from it, in accordance with the power of the consumed load, selected wire sections will be routed for each of the rooms.

Typical electrical wiring diagram for an apartment or house with an electric stove (indicating the cable cross-section for electrical appliances)

Current loads in DC networks

In networks with direct current, the cross section is calculated somewhat differently. The resistance of a conductor to direct voltage is much higher than to alternating current (with alternating current, resistance at lengths of up to 100 m is generally neglected).

In addition, for DC consumers, as a rule, it is very important that the voltage at the ends is not lower than 0.5V (for AC consumers, as is known, voltage fluctuations within 10% in any direction are acceptable).

There is a formula that determines how much the voltage at the ends will drop compared to the base voltage, depending on the length of the conductor, its resistivity and the current in the circuit:

U = ((p l) / S) I

U—DC voltage, V
p—wire resistivity, Ohm*mm2/m
l — wire length, m
S - cross-sectional area, mm2
I - current strength, A

Knowing the values of these indicators, it is quite easy to calculate the cross section you need: by substitution method, or using simple arithmetic operations on this equation.

If the DC voltage drop at the ends does not matter, then to select the cross-section you can use the table for alternating current, but at the same time adjust the current values by 15% towards a decrease, i.e. with direct current, reference cable cross-sections can carry 15% less current than indicated in the table.

A similar rule also works for choosing circuit breakers for networks with direct current, for example: for circuits with a load of 25A, you need to take a circuit breaker with a 15% lower rating; in our case, the previous standard size of the circuit breaker is suitable - 20A.

The cable that transmits electric current is one of the most important elements of the electrical network. If the cable fails, the operation of the entire system becomes impossible, therefore, to prevent failures, as well as the risk of fire from overheating, an accurate calculation of the cable cross-section for the load should be made.

This calculation gives confidence in the safe and reliable operation of the network and devices, but more importantly, the safety of people.

Choosing a cross-section that is insufficient for the current load leads to overheating, melting and damage to the insulation, and this, in turn, leads to a short circuit and even a fire. So there are many reasons to carry out calculations and carefully select the appropriate cable.

What is needed for load calculations

The main indicator that helps calculate the cross-section and brand of cable is the maximum permissible continuous load (current). To put it simply, this is the amount of current that the cable is capable of passing under the conditions of its installation without overheating for a sufficiently long time.

This requires a simple arithmetic summation of the powers of all electrical appliances that will be connected to the network.

The next important step to achieve safety is to calculate the cable cross-section for the load, for which it is necessary to calculate the current strength using the formula:

For a single-phase 220 V network:

P is the total power for all electrical appliances, W;
U—mains voltage, V;
COSφ - power factor.

For a three-phase network with a voltage of 380 V:

Having received the exact current value, you should refer to tables that allow you to find a cable or wire of the required cross-section and material. But if the obtained current value does not exactly coincide with the table value, then you should not “save”, but rather choose the nearest, but larger value of the cable cross-section.

Example: with a network voltage of 220 V, the resulting current value was 22 amperes, the nearest larger value (27 A) is a copper wire or copper cable with a cross-section of 2.5 mm square. This means that the optimal choice would be just such a cable, and not with a cross-section of 1.5 mm square, which has a permissible continuous current of 19 A.

Current cross-section conductive lived, mm	Copper conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current, A	power, kWt	Current, A	power, kWt
1,5	19	4,1	16	10,5
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	46	10,1	40	26,4
10	70	15,4	50	33
16	85	18,7	75	49,5
25	115	25,3	90	59,4
35	135	29,7	115	75,9
50	175	38,5	145	95,7
70	215	47,3	180	118,8
95	260	57,2	220	145,2
120	300	66	260	171,6

If you choose a cable with aluminum cores, then it is better to take a core cross-section of 4 mm square rather than 2.5.

Current cross-section conductive lived, mm	Aluminum conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current, A	power, kWt	Current, A	power, kWt
2,5	20	4,4	19	12,5
4	28	6,1	23	15,1
6	36	7,9	30	19,8
10	50	11	39	25,7
16	60	13,2	55	36,3
25	85	18,7	70	46,2
35	100	22	85	56,1
50	135	29,7	110	72,6
70	165	36,3	140	92,4
95	200	44	170	112,2
120	230	50,6	200	132

Calculation for premises

The previous calculation made it possible to accurately calculate the material and cross-section of the input cable through which the total maximum load will flow. Now you should make similar calculations for each room and its groups. And here's why: the load on socket groups can vary significantly.

Thus, sockets with a connected washing machine and hair dryer are loaded much more than the socket for a mixer and coffee maker in the kitchen. Therefore, you should not “simplify” the task by laying a wire with a cross-section of 2.5 square meters on the sockets without hesitation, since sometimes this is simply not enough.

It should be remembered that the total load in the room consists of 1) power and 2) lighting. And if everything is clear with the lighting load - it is carried out with a copper wire with a cross-section of 1.5 mm square, then with sockets it is not so simple.

It should be remembered that usually the kitchen and bathroom are the most “loaded” lines, since this is where the refrigerator, electric kettle, boiler, microwave, and sometimes washing machine are located. Therefore, it is best to distribute this load among different outlet groups, rather than using a block of 5-6 outlets.

Sometimes you can hear from “experts” that for sockets in other rooms a “one and a half cable” is enough, but would you highlight those black stripes visible from under the wallpaper that a burnt cable leaves behind after turning on an oil heater or fan heater? !

PPV - flat copper two- or three-core with single insulation for laying hidden or fixed open wiring;
APPV - aluminum flat two- or three-core with single insulation for laying hidden or fixed open wiring;
PVA - round copper, number of cores - up to five, with double insulation for laying open and hidden wiring;
SHVVP – round copper with twisted conductors, double insulation, flexible, for connecting household appliances to power sources;
VVG - round copper cable, up to four cores with double insulation for laying in the ground;
GDP - round single-core copper cable with double PVC (polyvinyl chloride) insulation, P - flat (current-carrying conductors are located in the same plane).

Type of electric current

The type of current depends on the power supply system and the connected equipment.

Select current type: Select Alternating current Direct current

Cable conductor material

The material of the conductors determines the technical and economic indicators of the cable line.

Select conductor material:

Select Copper (Cu) Aluminum (Al)

Total power of connected load

The load power for a cable is defined as the sum of the power consumption of all electrical appliances connected to this cable.

Enter load power: kW

Rated voltage

Enter voltage: IN

AC only

Power supply system: Select Single-phase Three-phase

Power factor cosφ determines the ratio of active energy to total energy. For powerful consumers, the value is indicated in the device passport. For residential consumers cosφ taken equal to 1.

Power factor cosφ:

Cable laying method

The laying method determines the heat dissipation conditions and affects the maximum permissible load on the cable.

Select installation method:

Select Open wiring Hidden wiring

Number of loaded wires in a bundle

For direct current, all wires are considered loaded, for single-phase alternating current - phase and neutral, for three-phase alternating current - only phase ones.

Select number of wires:

Select Two wires in separate insulation Three wires in separate insulation Four wires in separate insulation Two wires in common insulation Three wires in common insulation

Minimum cable cross-section: 0

A cable with a calculated cross-section will not overheat at a given load. To make the final selection of the cable cross-section, it is necessary to check the voltage drop on the current-carrying conductors of the cable line.

Length of cable

Enter cable length: m

Permissible voltage drop across the load

Enter acceptable drop: %

Minimum cable cross-section including length: 0

The calculated value of the cable cross-section is indicative and cannot be used in power supply system projects without professional assessment and justification in accordance with regulatory documents!

Table of cable cross-section by power and current

Section	Copper conductors of wires and cables
Conductors	Voltage 220V		Voltage 380V
mm.sq.		power, kWt		power, kWt












Section	Aluminum conductors, wires and cables
conductors	Voltage, 220V		Voltage, 380V
mm.sq.	current, A	power, kWt	Current, A	power, kWt

Why do you need a section calculation?

Electrical cables and wires are the basis of the energy system; if they are chosen incorrectly, this can lead to a lot of trouble. When making repairs in a house or apartment, and especially when building a new structure, pay due attention to the wiring diagram and choosing the correct cable cross-section to supply power, which may increase during operation.

When installing voltage stabilizers and backup power supply systems, our company’s specialists are faced with the negligent attitude of electricians and builders towards the organization of wiring in private houses, apartments and industrial facilities. Bad wiring can occur not only in those premises where there has been no major repairs for a long time, but also when the house was designed by one owner for a single-phase network, and the new owner decided to “start” a three-phase network, but was no longer able to connect the load evenly to each of them. phases Often, wire of questionable quality and insufficient cross-section occurs in cases where the construction contractor decided to save on the cost of the wire, and any other situations are possible when it is recommended to do an energy audit.

A modern set of household appliances requires an individual approach to calculating the cable cross-section, so our engineers have developed this online calculator for calculating the cable cross-section by power and current. When designing your home or choosing a voltage stabilizer, you can always check what cable cross-section is required for this task. All you have to do is enter the correct values appropriate for your situation.

Please note that an insufficient cable cross-section leads to overheating of the wire, thereby significantly increasing the possibility of a short circuit in the electrical network, failure of the connected equipment and a fire. The quality of power cables and the correct choice of their cross-section guarantees many years of service and safe operation.

Calculation of cable cross-section for direct current

This calculator is also good because it allows you to correctly calculate the cable cross-section for DC networks. This is especially true for backup power systems based on powerful inverters, where high-capacity batteries are used and the direct discharge current can reach 150 Amperes or more. In such situations, it is extremely important to take into account the cross-section of the wire for direct current, since high voltage accuracy is important when charging batteries, and if the cable cross-section is insufficient, significant losses can occur and, accordingly, the battery will receive an insufficient level of DC charging voltage. This situation can be a significant factor in reducing battery life.

You are faced with the question of choosing a wire (cable). It doesn’t matter what you choose it for, for an apartment, house, garage, cottage or for connecting an electric motor, heating device, compressor, electric lamp or any other electrical device, you still need to calculate the cross-section of the conductor that will be used for connection.

Why is the calculation needed? To put it in simple words, any electrical device (equipment) or room has a current consumption, a load. In order for this wire (cable) to withstand the load consumed by the electricity consumer, a calculation is needed.

Naturally, the calculation is carried out after collecting data about the consumer, that is, it is necessary to calculate the load for each electricity consumer separately and the total load, if required.

But first you need to know how the wire cross-section is determined. The calculation is carried out according to the formula:

S = πD² ⁄ 4 = 0.785D²

where: S – wire cross-section; π – 3.14; D – wire diameter.

The diameter of the wire can be easily measured using a caliper or micrometer. If the wire core is multi-wire, then you need to measure one wire, make a calculation and multiply by their number. The cross section of the conductor will be obtained.

Let's take a one-room apartment. What electrical appliances do we use? Below you will see a table showing electrical appliances and tools used in everyday life:

Table 1.

Household electrical appliance	Power, W	Household electrical appliance	Power, W
Bulb	15 – 250	Oven	1000 – 3000
Inkjet printer	30 – 50	microwave	1500 – 3000
Scales	40 – 300	Vacuum cleaner	400 – 2000
Audio system	50 – 250	Meat grinder	1500 – 2200
Computer	300 – 800	Toaster	500 – 1500
Laser printer	200 – 500	Grill	1200 – 2000
Copy machine	300 – 1000	Coffee grinder	500 – 1500
TV	100 – 400	Coffee maker	500 – 1500
Fridge	150 – 2000	Dishwasher	1000 – 2000
Washing machine	1000 – 3000	Iron	1000 – 2000
Electric kettle	1000 –2000	Heater	500 – 3000
Electric stove	1000 – 6000	Air conditioner	1000 – 3000

Let's calculate the total power consumption of electrical appliances used in a one-room apartment. Let's take the minimum:

Energy-saving lamps – 14 pieces, 15 W each;
TV – 200 W;
Audio system – 150 W;
Computer – 500 W;
Laser printer – 300 W;
Refrigerator – 500 W;
Washing machine – 2000 W;
Electric kettle – 2000 W;
Coffee maker – 1000 W;
Microwave oven – 2000 W;
Vacuum cleaner – 1200 W;
Iron – 1000 W;
Air conditioning – 2000 W.

Let's do the calculation:

14 × 15 = 210 W (energy saving lamps);

210 + 200 + 150 + 500 + 300 + 500 + 2000 + 1000 + 2000 + 1200 + 1000 + 2000 = 11,060 W = 11.06 kW

We have calculated the total load that the apartment can consume, but this will never happen. Why? Imagine that you turned on all electrical appliances at the same time. Could this happen to you? Of course not. Why would you turn on, for example, a TV, an audio system, a vacuum cleaner and an air conditioner at the same time in winter, or another combination of household appliances? Of course you won't do this.

Why am I writing all this, but to the fact that there is a so-called simultaneity coefficient, which is equal to ~ 0.75.

11.06 × 0.75 = 8.295 ~ 8.3 kW. You can connect this maximum load with the electrical appliances listed above for a short time. It is for information only.

But to calculate the cross-section of a wire (cable), you still need to take the total load without a coefficient. For this example, 11.06 ~ 11 kW.

We made this calculation for the input wire (cable), which will supply the entire apartment with a voltage of 220 V.

Table for selecting the cross-section of wire (cable) cores by power and current

Table 2.

How to use the table? We look at the table and select “Copper conductors of wires and cables” > “Voltage 220 V” > “Power, kW”, since we have a total power of 11 kW, we always select with a reserve and get 15.4, which corresponds to a cross-section of 10 mm². See below:

I advise you to always take the cross-section of the cable core with a reserve, because the cable cores will not heat up under heavy loads and in the future you may increase your arsenal of household electrical appliances and tools not only in quantity, but also in power.

Looking at this table, you can also determine the cross-section of a copper conductor for a voltage of 380 V, as well as an aluminum conductor for 220 and 380 V.

380 V (3 phases and zero) is used to connect cottages and where it is impossible to do without a three-phase system, for example, connecting 3-phase electric motors, air heaters, refrigeration units, etc.

Let's see what conductor cross-section is needed for each individual 220 V electrical appliance, knowing its power according to the passport:

Table 3.

Cross-section of copper core, mm²	Electrical appliance power, W
0,35	100 – 500
0,5	700
0,75	900
1,0	1200
1,2	1500
1,5	1800 – 2000
2,0	2500
2,5	3000 – 3500
3,0	4000
3,5	4500 – 5000
5,0	6000

Below is a table of the use of copper wires (cables) by cross-section:

Table 4.

Section of copper conductors, mm²	Rated current of the circuit breaker, A	Application example
1,5	19	10	4,1	Lighting
2,5	27	16	5,9	Sockets
4	38	25	8,3	Air conditioners, water heaters
6	46	32	10,1	Electric stoves, cabinets
10	70	50	15,4	Entering the apartment

It is necessary to find out what wire cross-section to use for an electric motor connected to a voltage (U) of 220 V. Its power (P) is not known.

Briefly connect the electric motor to a 220 V network and measure the current (I) using electric clamps. For example, the current is 10 A.

You can use a formula that can quickly calculate everything:

From this formula we find power (P):

P = IU

P = 10 × 220 = 2200 W = 2.2 kW

So, the power of the electric motor is 2.2 kW and the power consumption is 10 A. Using Table 2, we determine the cross-section of the wire, “Copper cores of wires and cables” > “Voltage 220 V” > “Current, A”. The first number starts with 19, and we have 10 A, opposite this number the wire cross-section is 1.5 mm². For our example, 1.5 mm² is more than enough.

In the same table we see that an aluminum wire (cable) with a cross-section of 2.5 mm² is also suitable.

Using simple calculations, we found out the current and wire cross-section, and at the same time the power of the electric motor for a voltage of 220 V. In the same way, you can find out the wire cross-section for other electricity consumers.

Selecting wire cross-section by length

You should be aware that the length of the wire (cable) affects the voltage. The longer the line, the greater the voltage loss. To avoid this, you need to increase the cross-section of the conductor. How to calculate all this?

You have certain consumers of electricity in your home; in total they amount to 5000 W or 5 kW. The length to these consumers from the circuit breaker is 25 m. Since electricity is supplied through one wire and returned through another wire, the length doubles and is equal to 50 m.

I = 5000/220 = 22.72 A

Using current (A) or power (P) in Table 2, we determine the cross-section of the wire. According to the table, this is 1.5 mm² of copper wire.

Since the wire has its own resistance ® we make the calculation taking into account the following data using the formula:

R – conductor resistance, Ohm;

p – resistivity, Ohm mm²/m;

L – wire length, m;

S – cross-sectional area, mm².

From the formula: value (p) is always a constant value. For copper it is 0.0175, and for aluminum it is 0.0281.

We calculate:

R = 0.0175 × 50/1.5 = 0.583 Ohm

dU – voltage loss, V;

I – current strength, A;

R – conductor resistance, OM.

dU = 22.72 × 0.583 = 13.24 V

After this calculation, you need to find out the percentage of voltage loss. If it is higher than 5%, then the conductor should be selected one position higher, referring to Table 2.

13.24 V / 220 V × 100% = 6.01%

Since the percentage of voltage losses is higher than 5%, the cross-section of the wire (cable) instead of 1.5 mm² we choose 2.5 mm².

That's the whole calculation. Difficult? No.

Conclusion

You learned how to choose the right wire (cable) cross-section for household (and not only) use. As you can see, it is not so difficult to do all this. You just have to count it once and that’s it. After such a calculation, you will be completely confident that the wires or cables you have selected will not let you down and will last for many years.

With you, Alexey Darensky.

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

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

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

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

"Traveled" paths of computing

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

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

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

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

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

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

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

Calculation of section size based on load

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

The calculation algorithm is as follows:

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

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

How to calculate the current cross section?

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

Allowable and operating current density

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

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

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

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

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

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

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

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

Studying the calculation scheme

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

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

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

Video guide for accurate calculations

Which cable is better to buy?

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

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

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