All wire sections. How to calculate the cable cross-section for a household electrical network

Right choice cable or wire for electrical wiring in a private house or apartment - the basis safe operation electrical internal networks. The choice is based on the cable cross-section, which can be independently calculated using the formula: S=π*D², where π is the Archimedean number (3.14), and D is the diameter of the cable cores. To clarify the topic of this article, we will answer the question, what wire cross-section is needed for a 5 kW load?

So, let's start with the fact that there is a regulatory document according to which you can choose a wire or cable for a load of 5 kW. This document is “Rules for Electrical Installations” or abbreviated as “PUE”. So, these rules indicate that there are three parameters that form the basis for choosing a section:

• the material from which the wire is made;
• supply voltage;
• current load in amperes or power in kilowatts.

If you choose the wrong wire cross-section based on current load or power consumption, it will definitely heat up, its insulation will melt, and there will be a high probability of a short circuit, often accompanied by fires. Therefore, you should not save on electrical wiring.

True, you shouldn’t overplay your hand by choosing a cross-section much larger than necessary. This will primarily affect your wallet, because wires with a larger cross-section are more expensive. Although it is possible to calculate the possible increase in load with the appearance of new ones in the future household appliances definitely necessary. But this must be done competently.

Criterias of choice

The PUE has tables from which you can select the wire cross-section. There are several of them. It's all about what exists a large number of the wires themselves, which are used in the electrical wiring of an apartment or house. Each wire has its own characteristics and specifications, for example, a sheath insulating bare conductors. It can be made of PVC, rubber, with a protective sheath of lead and so on. Plus, there are two installation methods, which also determines what cross-section of wire to choose. The gasket can be open or closed.

Therefore, in order not to look at all the tables and search for the required cable parameter, we have created a summary table that takes into account all the above technical conditions with the addition of the material from which the wire is made. Here is the table:

Since our task in this article is to select the wire cross-section for a load of 5 kW, it becomes clear from the table that:

• firstly, there is no such load, which means you will have to choose the nearest larger one, which is 5.5 kW;
• secondly, the voltage is selected: 220 or 380 volts;
• thirdly, the method of laying: by air or in the ground;
• Fourth, the raw material of the wire: copper or aluminum.

Since 5.5 kW for a small private house or standard apartment- this is a normal load, then bring them to better wire copper. And since most often this is laying through the air, it becomes clear from the table that for such an electrical supply you will need a wire with a cross-section of 2.5 mm². At the same time, it will withstand a current load of 25A.

But there is one point that concerns the nominal value of the input machine. It should be noted that this indicator is established by the project and approved by the energy supply organization. So the rating of the input circuit breaker with a load of 5.5 kW, that is, 25 amperes, should correspond to them. That is, at the entrance to the room, a 25 A circuit breaker is installed in the distribution board.

The rules stipulate that the wire supplied to the house or apartment must have a current rating higher than that of the machine. We look at the table, in which the next higher current load indicator is 35 amperes. We will take it as the actual value. Hence the other characteristics of the electrical wire:

• cross section – 4 mm²;
• withstand power – 7.7 kW.

For such installation conditions, you will need a VVGng wire, which will be laid in an open way.

There is one more indicator that should be taken into account when selecting the wire cross-section. This is the so-called conditional breaking current. It will also depend on the circuit breaker installed in the distribution panel. This device has one characteristic, its name is time-current characteristic. So, for a machine with a rating of 25 amperes, the conditional shutdown current will be:

1.45x25=36.25 amperes.

In a cold state, the circuit breaker at a given load will turn off only after an hour. As the temperature rises, this parameter decreases. Since the example we are considering indicated a wire cross-section of 4 mm², then it corresponds to a long permissible current, equal to 35 amperes. Let's compare it with the same indicator of the machine. The difference is insignificant, so you can leave everything as is. But under these conditions, experts recommend installing a wire with a cross-section of 6 mm², which corresponds to a long-term permissible current of 42 amperes.

Attention! The current load on the wires that power household appliances operating from a 220-volt network is greater than those operating from a 380-volt network.

You can calculate the current load manually, without resorting to tables. For example, if a cable is being calculated for connecting an electric stove or water heater with heating elements with a power of 3 kW. To do this, you will have to use Ohm’s law, or rather, its formula:

I=P/U, where P is power equal to 3 kW, U is voltage (380 V).

We substitute our values ​​into the formula and get: I = 3000:380 = 7.89 A. Round up to 8 amperes. Now you can select a wire from the same table. In some cases, correction factors are used when calculating the current load, but in living conditions operation of electric stoves and other equipment where there are no high starting loads, they have a negligible value, so they are not used in these calculations. It is recommended to simply increase the current indicator by a small amount: 3-5 amperes, which is added to the calculated value.

From the calculations it becomes clear that for an electric stove with a power of 3 kW, it will be suitable copper cable cross section 2.5 mm². And since a separate supply line is allocated for this device with a separately installed circuit breaker in the distribution board of an apartment or house, then, as under the conditions described above, it is necessary to take into account the time-current load. That's why best option– this is a wire with a cross section of 4 mm². Exactly the same calculation can be done with any device of different power, or calculation for the whole house, regardless of technical specifications connections (it will be 10 kW or 15).

Conclusion on the topic

The question of how to choose a wire cross-section to power an apartment or private house is one of the most important. It is he who solves the problem of certain savings. Imagine if the calculations were done incorrectly. That is, you incorrectly selected and purchased several hundred meters of wire, several automatic devices and an RCD. This is, so to speak, money thrown away. That is why it is so important to understand what cross-section of wire is needed in a given case. And all this depends on the power consumption and current load, which are in direct proportion to each other according to Ohm’s law.

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For wiring in the house, let's look at the most commonly used wires today. I’ll say right away that aluminum wires when laying new wiring they are not currently used, so we will consider only copper ones. They are superior to aluminum ones in all respects, except price, and even then, this is a moot point, since copper wiring will last much longer.

Cable VVG and VVGng— their difference is that special non-flammable substances (ng) have been added to the VVGng insulation, which makes it indispensable for premises that are subject to increased requirements fire safety. it's the same power cable, in double insulation, but with single-core conductors, is used in industrial, distribution, lighting devices, as well as electrical wiring up to 1000 V in residential and commercial premises.

NYM- power cable, differs from VVG in that it contains an additional layer of chalk rubber insulation, preventing the formation of cracks during operation in unfavorable conditions. As external insulation a more elastic plastic material is used here, which also increases safety. As a result, this cable is becoming increasingly popular. This cable is also suitable for wooden country houses, it will not be chewed by mice due to special insulation.

PVS cable This power wire, multi-core, in double polyvinyl chloride plastic insulation, flexible, designed for connecting electrical appliances, power tools, electrical wiring with voltages up to 1000 V. Due to its flexibility and wear resistance, it is well suited for making extension cords and connecting garden equipment.

When laying new power wiring, a three-wire (220V, in apartments) or five-wire (380V, in some private homes) cable is used. As a rule, a cable with a cross-section of 2.5 mm² is used for sockets, 1.5 mm² for lighting, and sometimes ShVVP brand wire is used for lighting.

They are marked as follows: PVS 3x2.5, VVG 3x2.5, NYM 3x2.5, where 3 is the number of wires in the cable, 2.5 is the cross-section of one conductor in mm². Keep in mind that conductor diameter and wire gauge are two different things.

Below I will provide a table for selecting what you need sections, based on current or power, the table also contains the diameters of the conductors, which is convenient for determining sections existing cable. The data is presented for, for which you can choose a wire with a smaller (20-30%) cross-section, but it is better to put it in reserve.

As an example, I will give the average power of some household appliances: Oil radiator - 1.5 kW, iron - 2 kW, TV 0.1 kW, washing machine- 0.5 kW, microwave - 1 kW, electric kettle - 2 kW.

Most of the cost of materials when replacing electrical wiring comes from cable products. At the same time, there is a temptation to save on it. But unreasonably underestimating the cable cross-section leads to fatal results if they carry a load current that exceeds them throughput. When passing electric current any conductor heats up. When a certain heating temperature is reached, the insulation melts, the phase and neutral conductors are connected to each other, a short circuit and a fire occurs.

To avoid these troubles, before you start installation work The cable cross-section is calculated. It allows you to calculate the value that will be sufficient to ensure the safe operation of your electrical equipment.

Initial data for calculation

We need to calculate the total electrical power all electrical appliances in the house or apartment. Certainly, chargers For mobile phones can be neglected. When calculating, the assumption is made that the entire load will be turned on simultaneously. Don't think that you can never turn on a microwave oven and a kettle together if they are powered by the same socket. The time will come - they will be turned on through a tee.
This also applies to lighting. There is no guarantee that you will always use only . Use an incandescent lamp of 60 - 75 W as the equivalent load for each lamp. By multiplying this power by the total number of lamps in the house, you will get the calculated value. For country house Don’t forget about outdoor lighting and the prospects for its development.

Be sure to include household appliances that you do not have now, but are planning to purchase in the future, for example, dishwasher or another electric heater.

If your house has a 1.5 kW boiler, consider whether you would like to increase its power to 3 kW in the future.

You can find out the power of your electrical appliances from the operating instructions. If it is not there, read it on the plate located on the device body. For approximate calculations, a table of average statistical loads is used.

Such a table, compiled by you yourself for your home, will help in further calculations.

Input cable calculation

After calculating the total power of single-phase consumers, the corresponding current is calculated using the formula:

where P is the total power you calculated, W;

U – network voltage equal to 220 V;

cos (φ) – power factor, for household appliances is taken equal to unity;

Ki is the coefficient of load simultaneity, taking into account that your electrical appliances are unlikely to work at the same time. His exact value difficult to predict, so for calculations you can take Ki = 0.75.

For three-phase load in a 380 V network, the current is calculated using the formula:

Now you can find out the cross-section of the input cable through which power will be supplied to the apartment or country house. To select it, you must use the table for calculating the cross-sections of cables with polyvinyl chloride and polymer insulation. Most products used for laying household electrical wiring have such insulation. For rubber insulation and cross-linked polyethylene, a different table is needed; it can be found in GOST 31996-2012.

In order to determine permissible load for four-core and five-core cables, the data from the table must be multiplied by a factor of 0.93.

Application aluminum wires for the installation of electrical wiring in buildings has been prohibited since 2001. But bringing power into the house aluminum cable can be done if its cross-section is at least 16 mm 2.

There are also restrictions on the minimum cross-section of cable lines.

Calculation of load and cross-section of group network cables

For further calculations, it is necessary to plan the distribution network in the house. Usually input cable goes to the panel in which the input circuit breaker, electric meter and automatic switches are installed that supply separate groups of electrical receivers. You need to divide all your sockets and lamps into these groups.

In this case, the washing machine, boiler and electric stove must be powered separately. cable line and defend yourself with a separate machine gun. To connect kitchen outlets, a personal line is usually allocated. The rest of the load can be divided arbitrarily. It is better to power lighting networks separately, based on the fact that usually their power supply does not require a cross-section of more than 1.5 mm 2. And it’s more convenient to change the socket when the lighting is on.

Now we select the cable cross-section individually for each line, calculating its total load current using already known formulas. Along the way, you can select nominal data based on this current circuit breakers and RCD to protect lines from short circuits and overloads.

As you can see, the calculation of cable cross-sections is carried out comprehensively simultaneously with the design of all electrical wiring. Now all that remains is to calculate their total length, the number of sockets, switches and junction boxes, buy it all and begin installation.

Calculation of wire cross-section for a distribution panel

There remains one element of the electrical network that you need to assemble yourself. This is a distribution board. To connect the elements inside it, you will need wires.

Some conductors must have a certain color. Neutral working conductors (N) are painted blue, neutral protective conductors (PE) - yellow-green. The conductors for the corresponding purpose in the cables are painted in the same colors. Their use for other purposes is not permitted.

Application aluminum conductors cross-section below 16 mm 2 for assembling shields is prohibited.

For determining rated current For conductors, you must use the same calculation formulas as for cables, and the cross-section of the wires can be selected from the table. The data in it is applicable to wires with polyvinyl chloride and rubber insulation, both single-core and multi-core.