How to calculate the wire size for home wiring

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The installation of a household power grid should be carried out in such a way that users can simultaneously switch on several powerful electrical appliances at the same time. Therefore, it is necessary to select the cross-section of the wire for home wiring on the basis of a competent calculation of the parameters of the apartment and house electrical network.

There are several methods of calculation. We offer to get acquainted with different approaches and choose the best option. In addition to the technology for calculating the cross-section of the wire, the article describes the main parameters for the selection of electrical wiring and specifies the regulatory restrictions on the maximum power of electrical appliances.

The content of the article:

  • Why know the parameters of the wire
  • Wiring Section Selection Factors
  • Method for determining the cross-section of home wiring
    • Calculation of power devices
    • Determination of the cable section by tables
    • Voltage drop calculation
  • Regulatory restrictions
  • Conclusions and useful video on the topic
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Why know the parameters of the wire

Standard power sockets are designed for a continuous current of 16 A, which corresponds to the maximum power of the switched on device 3.52 kW. Usually they are supplied with a copper cable with a cross section of 2.5 mm2that can be misleading in choosing the type of wire for the rest of the wiring.

Different sections of copper cables

In parallel with the increase in the cross-sectional area of ​​the cable increases and its price. However, saving on wiring is not worth it - it can lead to much greater financial costs in the future

When electrons move along the metal part of the energy is dissipated as heat. With a large current and a small cable cross-section, the heat component can lead to overheating of the metal and the melting of its shell.

In a domestic environment, this can initiate both intra-wall short-circuits, as well as ignition of open wires, especially in places of bends.

As a result, the following situations may occur:

  1. Large-scale fireif there is flammable material near the cable.
  2. Current leakage in case of incomplete fusion of the core of the core. This leads to meaningless power consumption and the likelihood of electric shock to residents.
  3. Inconspicuous wire break in the wall. As a result, part of the apartment or the entire room is de-energized. After that, it is necessary to search for a break point and then replace the wiring with a local repair of the wall.

The choice of a thick electric wire for an apartment, with a margin, also has one drawback - an overrun of funds, which does not make sense. Therefore, it is better to select the wiring section using calculation methods to avoid all the above problems.

Wiring Section Selection Factors

Not only the power of the device determines the nature of the required electrical wiring. There are other factors, the influence of which is necessarily taken into account when calculating the required cable cross-section. They may affect the heat buildup in the conductor, its fire hazard and performance.

To such wire selection factors include:

  1. Core material: copper, aluminum.
  2. Type of insulation: PTFE, PVC, PE and other plastics.
  3. The length of the wire from the current source to the device.
  4. Wire laying method: outdoor installationhidden in a wall or using cable channels.
  5. The temperature in the room.
  6. Number of phases and line voltage.
  7. Wiring layout

Copper has less resistance than aluminum, and therefore calculations for these materials are made separately. The cross section of the copper conductor can be about 1.5 times smaller than aluminum.

Insulation material also influences electrical wire selection. There are special shells that withstand high temperatures without reflow and change. resistance, therefore, such cables may be subject to increased loads and be used with increased temperatures.

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Single and Stranded Cable

Single-core wires are cheaper, but bend worse, so they are often used in fixed wiring.

Laying of electrical cable in the corrugation

Electric cable in wooden houses should be laid in a metal corrugation to protect adjacent materials from fire

Different types of wire insulation

Thick insulation not only protects the metal core from external influences, but also prevents heat dissipation

Three-core cable for home wiring

The three-core circuit allows reducing the load on the wiring and extending its operational life.

Single and Stranded Cable

Single and Stranded Cable

Laying of electrical cable in the corrugation

Laying of electrical cable in the corrugation

Different types of wire insulation

Different types of wire insulation

Three-core cable for home wiring

Three-core cable for home wiring

The degree of voltage drop depends on the length of the wire and its cross section; therefore, for the operation of sensitive electronics, it is necessary to take these parameters into account.

Closed in boxes or plastered in the wall of an electric wire to a lesser extent lose heat during prolonged loads, so they overheat faster and require a larger design section.

The wiring going from the meter to the junction boxes can generally experience simultaneous loads from several devices plugged into different sockets. Therefore, the calculation of the cross section of these cable sections must be made separately.

Also, the load on the electric cable depends on the voltage and the number of connected phases. But as in everyday life mainly single-phase wiring with a voltage of 220 V is used, the influence of this factor will not be considered.

Method for determining the cross-section of home wiring

When calculating the conductor cross section of the cable with installing home wiring Many factors are considered. There are special computer programs that allow you to take into account all the features of the house and the needs of its tenants. But it is possible to determine the cross-section required for the wiring independently using the described method.

It is important to understand that the diameter of the wires in the apartment may differ from room to room. At the entrance to the meter it is one, at the junction box the wire size may already be less, at sockets and fixtures it is even less.

At each section of the wiring, it is desirable to determine the parameters necessary for it so as not to overpay for excessively thick wires.

Calculation of power devices

The simplest method for determining the required wire cross-section is to calculate it, taking into account the power of the appliances being operated and the correction factors. This technique involves several stages.

Stage number 1.Power summation of electrical appliances. Ideally, you need to know the nominal energy consumption of each device, which is indicated on its label. If the dwelling is not yet equipped, then the estimated need for electricity can be calculated using the following table №1.

List of power household appliances

Equal in functionality and size household appliances can have a power consumption that is 2-3 times different, so its value should be looked at on each device (+)

When calculating, you can also use the parameters of devices that are located in similar apartments of relatives or friends. There is another option - to go to the store of household appliances, to see its characteristics, and at the same time to look for a suitable model of equipment for the home.

Stage number 2. Determination of the coefficient of simultaneity. It can be expressed as a percentage or as a numerical value from 0 to 1. The coefficient shows the ratio of electricity consumption simultaneously included in the network devices to the total power of all household devices, calculated in the first stage.

Usually the coefficient is 0.8, but you can calculate it yourself, based on the habits of the home residents.

Simultaneous power on

Do not abuse portable sockets, tees and extension cords. It is advisable to use only equipment with a built-in safety mechanism that turns off electricity at high currents.

Stage number 3. Determination of the safety factor. This indicator takes into account the possible growth of electricity consumption in a few years. Usually it is assumed to be 1.5-2, but if the house already has a full set of electrical appliances, then the value of the coefficient can be taken 1.2-1.3. The main thing is not to regret a small section of wires in the future.

Stage number 4. Calculation of the maximum permissible load.

It is produced according to the formula:

P = (P (1) + P (2) +.. P (N)) * J * K,


  • P - maximum permissible load in W;
  • P (1) + P (2) +.. P (N) - the sum of the nominal powers of all electrical appliances;
  • K - coefficient of simultaneity;
  • J - safety factor.

For example, if the total power of the devices is 7500 W, the simultaneity factor is 0.8, the safety factor is 1.5, then the maximum permissible load will be:

P = 7500 * 0.8 * 1.5 = 9000 watts.

This indicator will be used in subsequent calculations.

Stage number 5. Determination of the maximum allowable current.

The indicator is determined by a simple formula:

I = p / u,


  • I - permissible current strength;
  • P - maximum permissible load in W;
  • U - mains voltage - 220 V.

Using data from the fourth stage, you can determine the maximum allowable current:

I = 9000W / 220V41A.

The method of calculating the cable section for power and current is described in detail in this article.

Stage number 6. Calculation of the cable section on the table. Since the optimal choice of wire for home wiring is influenced not only by the parameters of the devices, but also by external factors. (the core material, its shell, installation scheme, etc.), then for each case there are different tables, which are considered Further.

Determination of the cable section by tables

To determine the optimal cross-section of wire for home wiring, there are special tables. All of them are focused on the value of the permissible current, which is calculated separately by the above method. Next will be considered the table options. definition of the wiring section.

The calculation of the cross section of conventional household wires is presented in the tables:

Calculation of the cross section for copper electrical cables

Due to the fragility of aluminum, wires are made of this material only with a cross section of 2 mm. Also, there are no stranded aluminum wires from thin wires (+)

Below is a calculation of the wire section for carriers and extension cords.

Calculation for carriers and extenders

Extension cords in stores are rarely with a wire cross-section of more than 1.5 mm2, so you should not load them with powerful electrical appliances (+)

The current load on the electrical cable with open and closed laying is different. But they are considered the same if the wire is laid in the ground in a wide tray. This allows the cable to give off heat to the surrounding air and to heat less.

The calculation of the cross section for copper and aluminum conductors, depending on the method of laying the cable, is given in the table.

Calculation of the copper wiring cross section

The maximum current depends on the number of lived in the cable, because each of them generates heat, summed under a single sheath (+)

Similar tables are used in the calculation of electrical wiring and in industry. Household cables are usually arranged much simpler, so the number of calculated materials for them is quite limited. The parameters listed in the tables are not invented, but are indicated in industry standards, for example, in GOST 31996-2012.

Voltage drop calculation

Not only the degree of heating of the core, but also the voltage at the far end of the wire depends on the cross-section of the electrical cable. Household appliances are designed for certain parameters of the power grid, and their constant discrepancy may lead to a decrease in the life of the equipment.

Voltage drop at the end of the wire

When the voltage drops on the boiler, it is advisable to install a stabilizer so that the equipment does not experience additional loads due to the mismatch of the operating characteristics of the power grid

When the cable is lengthened, a voltage drop occurs. This effect can be reduced by increasing the cross section of the wiring. It is considered critical to lower the voltage at the end of the wire by 5%, compared to its value at the current source.

This indicator can be calculated using the well-known formula:

Upad = I * 2 * (ρ * L) / S,


  • ρ - resistivity of metal, Ohm * mm2 / m;
  • L - cable length, m;
  • S - conductor cross section in mm2;
  • Upad - voltage drop, Volt;
  • I - current flowing through a conductor.

If the calculated voltage drop is more than 5% of the nominal, then a cable with a large cross-section is required. This will ensure stable operation of the equipment.

Boilers, washing machines and other devices with multiple relays and sensors are especially sensitive to the voltage value. This feature must be considered when using the carrier.

Regulatory restrictions

Utilities that provide the population with electricity, have the right to impose restrictions on the maximum total power devices in the apartment. This can be achieved by installing electricity meters with a certain bandwidth.

Automatic one-time or reusable fuses are installed on the device, which are triggered when the current threshold is exceeded.

Outdated power meter

Electric meters of the Soviet type are massively replaced by electronic ones. They are even more sensitive to overloads, due to which they quickly fail.

If you remove the plug from the meter and connect it to the apartment wiring directly, then it is guaranteed to burn in case of a long violation of the operating mode. Most Soviet meters installed in apartments withstand a peak load of 25 A to 1 minute.

After that, they burn, which is fraught with payment of the installation of a new device and a fine for violating the rules of operation.

Not able to withstand high loads and wiring at the entrance, burnout which can de-energize several apartments at once. Therefore, when connecting an apartment to the house network with a 2.5 mm cable, you should not expect that a thicker cable inside the apartment will be able to withstand high loads.

It is especially important to consider the factor of regulatory restrictions at the planning stage of the installation of electric heating, underfloor heating, infrared saunas and other energy-intensive equipment.

First you need to consult about the possibilities of electrical equipment installed in front of the apartment, in the relevant utilities.

If you decide to calculate the parameters of the wiring yourself, then it will be useful for you to understand such concepts as: current strength, power and voltage. Read more in the article - How to calculate power, current and voltage: principles and examples of calculation for living conditions

Conclusions and useful video on the topic

Videos contain practical electrical tips on choosing and purchasing home wiring. They will help you to purchase equipment appropriate to the cable that will precisely protect the housing from possible problems with overloads in the network.

Selection of cable section in the store:

Compliance with the cable section and the parameters of the circuit breaker:

Selection of cable section and machine:

Errors when choosing an electrical cable:

The main factors when choosing a cable for home wiring are the power of household appliances and the limitation of electrical networks that provide electrical power to the apartment.

Having correctly picked up the cross-section of the wire, it is possible to include all the necessary electrical appliances in the network. This eliminates the inconvenience of operating equipment and helps prevent the wiring from burning.

Is there anything to supplement, or have any questions on the calculation of the wiring section? Please leave comments on the publication, participate in discussions of the material. The form for communication is in the lower block.

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