The cross-section of the core is one of the main quantities that allows you to correctly perform electrical wiring, taking into account the total load on the network.

Knowing what wire cross-section is needed for 6 kW, you can easily choose the cable product that is optimal in terms of values.

Conductor material

A competent choice of material for electrical wiring is not only a matter of affordable price, but also a guarantee of uninterrupted “delivery” of electricity, as well as safety, fire resistance and reliability during operation.

Currently, about three hundred brands and several thousand varieties of conductor are manufactured, differing in the type of material and other technical characteristics.

Aluminum

Aluminum is a soft and light, silver-white metal widely used in the manufacture of cable products. The most significant advantages of aluminum wiring include:

  • light weight of the material, which is especially important if it is necessary to install electrical transmission lines over several kilometers;
  • the cost of a high-quality cable product affordable to a wide range of consumers;
  • resistance to oxidation under the negative influence of open air and atmospheric conditions;
  • the presence of a protective layer that forms on aluminum during operation.

Aluminum is not without some disadvantages that limit the scope of use of wires of this type. The disadvantages of the material include a high level of resistivity and a predisposition to heating with weakening of contact. The film formed on the surface of aluminum reduces current conductivity, and the metal itself becomes excessively brittle as a result of frequent overheating.

As the practice of using aluminum electrical wiring shows, the standard service life is about a quarter of a century, after which it is mandatory to replace such a network.

Copper

Electrical wiring in residential premises or industrial buildings most often involves the installation of stranded copper wires.

This option is characterized by good flexibility and ease of use.

Copper wires are an order of magnitude more expensive than aluminum cable, but such electrical wiring is more reliable and much more durable. In addition, the advantages of copper wires include a high level of strength and softness, which minimizes the risk of breakage at bends and contact connections, resistance to harmful corrosive changes, and excellent current conductivity.

Copper armored cable products VBBShV are characterized by double PVC insulation and fire resistance, due to which such wiring is in great demand in outdoor work.

What wire cross-section is needed for a 6 kW load?

In order to be competent, it is necessary to calculate the total power of all electrical appliances in use.

Full operation of a significant part of household appliances will require the use of a wire that can withstand a load of 6 kW or more.

In this case, the optimal option would be to use a copper round wire with a cross-section of at least 2.5 mm and double insulation.

Also, under conditions of such power indicators, it is permissible to perform work on the basis of round copper wire in the form of twisted cores and double insulation.

The presence of aluminum wiring in a household, in order to ensure power indicators of 6 kW, will require the installation of an aluminum flat wire with a cross-section of 4.0 mm and single insulation.

Criterias of choice

The main characteristics that you should pay attention to when choosing a conductor are represented by the material of the cores and their cross-section, design, thickness of the core insulation and sheath.

A high-quality cable product must be marked and have a certificate of conformity.

The most important technical characteristics of the electrical wire for a load of 6 kW:

  • Durability. Cable products with single insulation last for about 15 years, and with double insulation - for a quarter of a century.
  • Oxidation resistance. Aluminum is a metal that reacts very actively with oxygen, which is accompanied by the formation of a thin film on the surface, which impairs current conductivity. To insulate contacts, special terminal blocks with a conductive paste composition are used.
  • Strength indicators. The copper cable product can be used repeatedly in bending/unbending mode. Copper wires can withstand just under a hundred such modes, and aluminum wires can withstand about ten.
  • Resistivity level. This indicator for copper cable products is 0.018 Ohm*sq.mm/m, and aluminum wires have a resistance of 0.028 Ohm*sq.mm/m.

Equally important is the ease of performing installation work yourself. In this regard, copper wires are more convenient, since they do not require the use of special elements in the form of a termination, terminal block or bolted connection.

It should be remembered that copper cable products with a cross-section of 2.5 mm 2 are designed for 27 A, while the thickness of the aluminum wiring should not be less than 4.0 mm 2.

Calculation of cross-sectional area

Proper selection of wire cross-section allows you to ensure the reliability and safety of electrical wiring. The main indicator on which the standard calculation of the core area or its cross-section is based is the level of the long-term permissible current value.

Calculating the wire cross-section in accordance with the load involves summing the power of all connected electrical appliances, expressing the power in the same units of measurement - W or kW.

According to the calculations obtained, the optimal cross-sectional indicators are determined using tabular data for 6 kW:

  • 27 A and 220 V - the diameter of the copper conductor is 2.26 mm with a cross section of 4.0 mm 2;
  • 15 A and 380 V - the diameter of the copper conductor is 1.38 mm with a cross section of 1.5 mm 2;
  • 26 A and 220 V - the diameter of the aluminum conductor is 2.76 mm with a cross section of 6.0 mm 2;
  • 16 A and 380 V - the diameter of the aluminum conductor is 1.78 mm with a cross section of 2.5 mm 2.

When choosing a cross-section, you need to remember that a discrepancy between the core area and current loads can cause overheating, melting of the insulation, short circuit and a fire hazard.

Video on the topic

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

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

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

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

Calculation of total power

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

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

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

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

How to determine the wire cross-section?

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

  • S=π D²/4;
  • D= √(4×S/π).

Where π = 3.14.

S = N×D²/1.27.

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

How to choose a cable based on power?

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

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

Which cables are better?

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

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

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

Determination of current load

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

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

I = P/(U∙cosφ).

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

Current example

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

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

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

The input currents are determined:

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

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

I f = 162/3 = 54 A.

I f = 54 + 38 = 92 A.

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

I f = 92×0.75×1.5 = 103.5 A.

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

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

Cable voltage drop

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

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

The following notations are used in the formulas:

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

Coefficient 2 shows that current flows through two wires.

Example of cable calculation based on voltage drop

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

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

Conclusion

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

First of all, an electrician must be able to correctly calculate the cross-section of the cable to be laid, since if the cross-section is chosen incorrectly, the electrical network will not last long. In everyday life, this knowledge will be useful to everyone who makes repairs, changes wiring, purchases new electrical equipment, and at the same time thinks about the reliability of the electrical network and their own safety.

A precisely selected wiring cross-section will ensure the following:

  1. Will provide long-term, uninterrupted operation of your equipment.
  2. Will exclude the possibility of fires.
  3. Will deliver from the need to replace the wiring.
  4. Will allow avoid additional costs for purchasing a product with a large cross-section.

How to choose cable cross-section based on power?


 For correct calculation you need:

  1. Calculate the number of household appliances in the room (it is advisable to take into account the appliances that you plan to purchase in the future), their total power.
  2. All devices divide into 2 groups: those that will operate continuously, and those that will be used rarely, then sum up their powers and determine the approximate operating time of the wiring at full load.
  3. Add to the resulting value of 5% - “margin of safety”.
  4. Final value must be divided by the network operating coefficient, the result will be the required wire power indicator, after which, using a special current flow table, we determine the cross-section of the cores for the resulting value.
  5. Select product made of aluminum, copper, or aluminum-copper, the cross-section of which is suitable for your power value, taking into account the network voltage (220V for a household power supply, 380V for an industrial power supply).

You need to know that the materials for conductive products are aluminum, copper and aluminum-copper, and each of them has advantages and disadvantages.

Features of Aluminum Cable:

  1. Lighter and cheaper than copper ones.
  2. Possess 1.73 times less conductive than copper.
  3. Susceptible to oxidation, after which they lose conductivity.
  4. After long-term use stop keeping their shape.
  5. At home soldering is not possible.

Features of copper cable:

  1. Possess high elasticity and mechanical strength.
  2. Are different small amount of electrical resistance.
  3. Great amenable soldering and tinning.
  4. They're standing much more than aluminum ones.

An aluminum-copper cable is an aluminum conductor clad on the outside with copper (the amount of copper is 10-30%) using a thermomechanical method.

Features of aluminum-copper cable:

  1. Conductivity is better than that of an aluminum product, but worse than that of a copper product.
  2. With time, the characteristics of this product do not deteriorate, unlike aluminum wires.
  3. Much lower cost, compared to copper.
  4. Aluminum copper, unlike copper and aluminum, is not of interest to thieves, since non-ferrous metal collectors do not accept aluminum-copper due to the difficulty of separating the two metals.

How to find out the power?

Power is measured in watts, kilowatts (W, kW, w, kWt). On every modern electrical equipment (household and industrial), the power is indicated on the tag along with other characteristics of the product. If this parameter is missing for some reason, we recommend using Table 1.

Table 1 – average power values ​​of household electrical appliances:

electrical appliance Average power, W
1. Boiler1500
2. Water heater (instantaneous)5000
3. Lawnmower1500
4. Drill800
5. Oven2000
6. Oil fireplace900
7. Computer (laptop)500
8. Microwave1500
9. Water pump1000
10. Welding machine2500
11. Washing machine2500
12. Hammer1300
13. Printer500
14. TV300
15. Toaster800
16. Fridge700
17. Household hair dryer1200
18. Industrial hair dryer1500
19. Electric fryer (oven)2000
20. Electric stove2000
21. Electric kettle1400

Calculation examples

Permissible current for cables and wires:

Example 1. Calculation for a single-phase 220V network.

Most often, apartment buildings are powered from a single-phase network with a voltage of 220V. Let’s say the total power of household electrical appliances, taking into account an additional 5% - the “safety margin”, is 7.6 kW (average electrical load in an apartment) - now you can start choosing the cable material.

To do this, we find the value of the nearest suitable cable cross-section in the corresponding table of the publication “Rules for Electrical Installations” (Table 2), in our case it will be:

  • 4 mm sq. for copper (designed for continuous loads of 8.3 kW);
  • 6 mm. sq. for aluminum (designed for continuous loads of 7.9 kW);
  • 6 mm. sq. for aluminum copper (see section on advice from professionals);

Example 2. Calculation for a three-phase network with a voltage of 380V.

In this case, the connection is made to one of the 3 phases and a common “zero” - this rule applies exclusively to single-phase devices, of which the vast majority are found in a modern home.

Do not forget about three-phase home appliances - pumps, welding machines, motors, etc., when connecting the load must be evenly distributed between 3 phases (7.6 kW / 3 phases = 2.6 kW per phase).

Therefore, when connecting a load to a 3-phase network, the value of the total power is multiplied by a special coefficient, due to which the cross-sectional value decreases. For example, when connecting a load of 7.6 kW, for a 1-phase network you will need a copper wire - 4 mm sq., for a 3-phase network - 1.5 mm sq.

Note that it is much easier to carry out calculations for home conditions than for industrial facilities, since in the latter case the following are added to the indicators that must be taken into account when calculating:

  • seasonal loads;
  • simultaneity factor;
  • demand factor;

Online calculators

To facilitate calculations and accurately select the required cross-section size, we have selected working online calculators that will quickly and accurately perform calculations for you to determine the required cross-section:

Consequences of incorrect selection of section

Selection of cross-section by power– an extremely responsible process. For example, if the cross-section of the home electrical network cable is designed for a power of up to 6 kW, at a load of 7.5 kW (only connecting just one household appliance, such as a microwave oven or electric kettle, to the home electrical network), the cable will overheat.

When overheating reaches a critical value, it will first begin to melt and then the cable insulation will ignite:

  1. It is the incorrectly selected wire cross-section is the most common cause of domestic fires.
  2. Also, if the insulation fails, a short circuit may occur, as a result of which all household appliances may fail.
  3. Anyway, you will have to spend a lot of money to restore and replace, at least the wiring of the house.
  4. At an industrial enterprise Incorrectly selected cables can lead to much more tragic consequences.

That is why this issue must be taken very seriously.

  1. Aluminum wiring it is best to replace with aluminum-copper one of the same diameter (this rule also applies to Table 2). If you replace a copper cable with an aluminum-copper one, the cross-section of the new cable should correspond to the copper one as 5 to 6.
  2. With three-phase power supply It is best to divide the devices into groups so that the load on each phase is approximately the same.
  3. At the time of buying, you need to pay attention to the markings, since sellers can cheat - passing off aluminum-copper cables as copper, thereby causing significant damage to your wallet. To prevent this from happening, you must:
    • Pay attention to the markings (domestic aluminum-copper products are marked with the letter combination AM).
    • If there is no marking, or the cable was manufactured abroad (not taking into account the CIS countries), it is enough to scrape off the top layer - the copper core is homogeneous, unlike aluminum copper.
  4. Last time Laying cables using corrugated pipes (corrugations) is becoming increasingly common. Below are the advantages of corrugation, as well as operating features:
    • The reduced flammability of the corrugations minimizes the likelihood of a fire when the wiring is shorted.
    • The corrugation protects the wiring from mechanical stress and damage.
    • Threading a wire into a corrugation becomes more difficult the longer it is; therefore, its end is first attached to a thin wire, which is much easier to thread through the corrugation.
  5. For household electrical wiring, it is recommended to use stranded wires as they are more flexible.

Selection of the optimal cross-section of cable or wire for creating electrical wiring in houses and apartments, taking into account the installation method, the total power of connected devices and the protective circuit breaker; practical recommendations

What factors influence the cross section?

Selecting the correct cable section for electrical wiring influence factors such as:

  • material of current-carrying conductors;
  • insulation material;
  • laying method;
  • total power of connected devices.

Similar material is presented in 9 minute video:

Conductor material

  1. conducts current 1.64 times worse (has a resistivity of 0.02828 Ohm mm 2 /m compared to 0.01724 Ohm mm 2 /m);
  2. when closed, it may “leak” from the contact connection due to the low melting point (657 and 1083 ° C, respectively);
  3. fragile (with several bends the core will break);
  4. causes overheating of contact connections due to the formation of an oxide film, which has a high contact resistance.

We counter argument 1 - aluminum is 3 times cheaper than copper. With equal current load, if, according to calculations, a copper core is required with a cross-section of 1.5 mm 2, aluminum - 2.5 mm 2; if the copper core is 2.5 mm 2, then the aluminum core is 4.0 mm 2 and so on due to the 1.64 times greater resistivity. Still, the economic gain is 3/1.64 ≈ 1.83 times.
We counter argument 4 - to reduce the contact resistance, quartz-vaseline pastes are used, which prevent the appearance of an oxide film upon contact with air.

Insulation material

The operating current of the electrical wiring is limited by the maximum permissible heating temperature of the core when current flows through it.
Most often used in wiring PVC insulation(optimal ratio of price and maximum heating temperature), its maximum heating temperature with rated current is +70 °C. When this temperature is exceeded for a certain time, varying degrees of changes occur*:

Table 1

Core and insulation temperature, °C Exposure time Implications for isolation
+80 > 8 hours deformed
+160 > 4 seconds cracks
+350 any deteriorates irretrievably


*Information sources:

  • standard tables 8 and 9 on page 7, clauses 2.6.4 and 2.6.5 on page 9, tables 21 and 22 on page 16;
  • standard table 18 on page 24;
  • standard table 2 on page 3 (last column).

Laying method

Conductors are placed in cable ducts, corrugated pipes, rigid pipes or grooves. All these installation methods in PUE-7 are united by a single term - in a pipe.

Total power of connected devices

Higher power requires a larger cross-section of the core. Examples of electrical appliance capacities and counter sections.
If you compare the current power with the volume of water in the pipe, then the more water you need to “drive”, the larger the diameter of the pipe is needed.

Comprehensive selection of core cross-section and circuit breaker

Let's consider electrical wiring in apartments, houses, cottages, cottages, garages and other domestic and commercial buildings (single-phase network with a modular input circuit breaker for a current of ≤100A without powerful electric motors). To create it, a two-core or three-core copper cable is used (phase + zero or phase + zero + ground, respectively).

Table choosing the optimal section veins, based on for practical reasons:

table 2


And now Let's justify it.

Table 3

Permissible continuous current for wires and cords with rubber and PVC insulation with copper conductors
Core cross-section, mm 2 Current in amperes for wires laid:
open in one pipe
two single-core three single-core four single-core one two-wire one three-wire
0.50 11 - - - - -
0.75 15 - - - - -
1.00 17 16 15 14 15 14
1.5 23 19 17 16 18 15
2.5 30 27 25 25 25 21
4 41 38 35 30 32 27
6 50 46 42 40 40 34
10 80 70 60 50 55 50
16 100 85 80 75 80 70
25 140 115 100 90 100 85
35 170 135 125 115 125 100
50 215 185 170 150 160 135
70 270 225 210 185 195 175
95 330 275 255 225 245 215
120 385 315 290 260 295 250
150 440 360 330 - - -
185 510 - - - - -
240 605 - - - - -

According to table 3 (exactly corresponds to table 1.3.4 from) Let's determine the rated current loads for each section. Since the grounding conductor is not involved in the calculations (that is, a three-core cable is assumed to be a two-core cable) and most often the conductor is placed in the groove, we select the current values ​​from the 6th column (“one two-core”). Let's summarize the results:


Table 4

Cross section of one core*, mm 2 Permissible current I cable, A
1.5 18
2.5 25
4 32
6 40
10 55
16 80

* If you choose a cross-section, knowing the current load, you should take into account that when choosing a cross-section, it is necessary to take into account the requirements for the mechanical strength of the conductors. According to table 7.1.1 on page 412 of PUE-7, for internal electrical wiring in residential buildings, the minimum cross-section of group line conductors should be 1.5 mm 2. That is, if according to calculations it turns out that a cross-section of 1.0 mm 2 or less is required, then it is necessary to use a wire of 1.5 mm 2.


Let's calculate the rated current of the machine, necessary to protect a cable of a certain cross-section (the formula corresponds to clause 433.1 of the GOST 50571.4.43 standard):

I av =I cab /1.45(1), where:

  • I av - the rated current of the circuit breaker, which is necessary to protect the electrical wiring;
  • I cable - permissible current per cable core;
  • 1.45 - coefficient selected based on table 5.

The circuit breaker has been tested and adjusted so that cause guaranteed shutdown for 1 hour with an overload that exceeds the rated current by 45% (or a factor of 1.45). If you install a circuit breaker with a rated current equal to the permissible current on the cable core, then at overloads of up to 45% the switch will be inactive and the cable will overheat. Regular overheating is dangerous due to accelerated aging of the insulation (plasticizers, which are responsible for electrical resistance, evaporate from the composition) with subsequent breakdown and short circuit.


Table 5

Time-current characteristics thermal release of the circuit breaker
Test current Trigger Shutdown time
or non-disconnection
1.13·I n No t > 60 min at I n< 63А
t > 120 min at I n > 80A
1.45·I n There is t< 60 мин при I n < 63А
t< 120 мин при I n >80A
2.55·I n There is 1 s< t < 60 c при I n < 32А
1 s< t < 120 c при I n >40A

Partial reproduction of Table 6 on page 19 of the MCB standard.

For example, if, to protect a wire with a conductor cross-section of 4 mm 2, we install a 32 ampere circuit breaker (from Table 4 we see that the conductor will withstand the same long-term current), then if there is an overload, the circuit breaker will not turn off immediately, but will pass a current of 32 1 within an hour, 45 = 46.4 A. During this time, the wire insulation will become overheated, which can lead to cable failure.
To ensure safety (margin of “strength”), reliability and durability of electrical wiring for domestic use, the optimal ratio of the cross-section of the wire used and the rating of the circuit breaker to protect the laid cable is as in Table 6.

The calculated current is determined by formula (1), rated current of the machine We select the one closest to the calculated one from the existing line of rated currents: 3, 4, 5, 6, 8, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80, 100 A.

Table 6

Cross section of one core, mm 2 Permissible current I cable, A Rated current of the machine, A Rated current of the circuit breaker Iav, A
1,5 18 12,41 10*
2,5 25 17,24 16
4 32 22,07 20**
6 40 27,59 25
10 55 37,93 40
16 80 55,17 50
Maximum power P, W Rounded value P, kW 1,5 10 2200 2,2 2,5 16 3520 3,5 4 20 4400 4,4 6 25 5500 5,5 10 40 8800 8,8 16 50 11000 11,0


From here it is clear what cross-section is needed for a specific rounded power:

  • 1.5 mm 2 - 1 and 2 kW;
  • 2.5 mm 2 - 3 kW;
  • 4 mm 2 - 4 kW;
  • 6 mm 2 - 5 kW;
  • 10 mm 2 - 6, 7 and 8 kW;
  • 16 mm 2 - 9, 10 and 11 kW.

For lighting We use a wire with a cross-section of 1.5 mm2, protected by a 10 A circuit breaker. A load of 2.2 kW is allowed on such a wire, that is, it is enough for 22 incandescent lamps of 100 W each, which is more than enough for an apartment.

For indoor sockets, in which it is planned to include devices low power(phone, tablet, laptop, computer, speakers - all these consumers up to 100 W) we use one wire with a cross-section of 2.5 mm 2, protected by a 16 A circuit breaker. The principle is the same, the total power of the devices plugged into the outlet, and therefore applied to the cable, should not exceed 3.5 kW.
Important rule: To 1 socket (with 1-5 places for plugs) we connect 1 cable, protected by 1 circuit breaker.
If you want to connect two or more sockets to one cable with a cross-section of 2.5 mm 2, then when you turn on a 2.1 kW iron and a 2.0 kW room heater at the same time, the total load on the cable will be 4.1 kW, which is clearly more than permissible 3.5 kW (breaker tripped).
In the case of one double socket, when you want to turn on the iron and heater together, you will think - is it worth doing this?

For direct connection of powerful devices or for sockets into which they will obviously be connected (for example, a socket in the bathroom for connecting a washing machine or boiler), cables with a cross-section of 4, 6 or 10 mm 2 should be used, and it is imperative separate cable to a separate consumer. We select the section according to the same principle. The power of a particular device is indicated in its manufacturer's passport, but you can navigate using Table 8 (also part of Appendix 7.2 in RM-2696-01).

Table 8


Thus we see that to connect:

  • a washing machine with a cross section of 2.5 mm 2 is sufficient,
  • flow heater with power up to 5.5 kW - 6 mm 2, from 5.6 to 8.8 - 10 mm 2
  • but for an electric stove you will already need a cross-section of 16 mm 2.

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

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

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

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

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

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

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

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

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

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

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

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

I = (P × K u) / (U × cos(φ))

    I- current strength;

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

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

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

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

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

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

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

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

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

I = P / (√3 × U × cos(φ))

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

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

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

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

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

U linear = √3 × U phase

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

Concept of continuous current

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

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

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

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