Calculate the cross-section of wires by current or power. How to choose a cable section. Calculation of the cross-section of copper wires and cables

The table shows power, current and cross sections of cables and wires, For calculations and selection of cables and wires, cable materials and electrical equipment.

The calculation used data from the PUE tables and active power formulas for single-phase and three-phase symmetrical loads.

Below are tables for cables and wires with copper and aluminum wire cores.

Table for selecting cable cross-section for current and power with copper conductors

	Copper conductors of wires and cables
	Voltage, 220 V		Voltage, 380 V
	current, A	power, kW	current, A	power, kW
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	33,0
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	66,0	260	171,6

Table for selecting cable cross-section for current and power with aluminum conductors

Cross-section of current-carrying conductor, mm 2	Aluminum conductors of wires and cables
	Voltage, 220 V		Voltage, 380 V
	current, A	power, kW	current, A	power, kW
2,5	20	4,4	19	12,5
4	28	6,1	23	15,1
6	36	7,9	30	19,8
10	50	11,0	39	25,7
16	60	13,2	55	36,3
25	85	18,7	70	46,2
35	100	22,0	85	56,1
50	135	29,7	110	72,6
70	165	36,3	140	92,4
95	200	44,0	170	112,2
120	230	50,6	200	132,0

Example of cable cross-section calculation

Task: to power the heating element with a power of W=4.75 kW with copper wire in the cable channel.
Current calculation: I = W/U. We know the voltage: 220 volts. According to the formula, the flowing current I = 4750/220 = 21.6 amperes.

We focus on copper wire, so we take the value of the diameter of the copper core from the table. In the 220V - copper conductors column we find a current value exceeding 21.6 amperes, this is a line with a value of 27 amperes. From the same line we take the cross-section of the conductive core equal to 2.5 squares.

Calculation of the required cable cross-section based on the type of cable or wire

№	Number of veins section mm. Cables (wires)	Outer diameter mm.							Pipe diameter mm.		Acceptable long current (A) for wires and cables when laying:		Permissible continuous current for rectangular copper bars sections (A) PUE
№	Number of veins section mm. Cables (wires)	VVG	VVGng	KVVG	KVVGE	NYM	PV1	PV3	PVC (HDPE)	Met.tr. Du	in the air	in the ground	Section, tires mm	Number of buses per phase
1	1x0.75							2,7	16	20	15	15	Section, tires mm	1	2	3
2	1x1							2,8	16	20	17	17	15x3	210
3	1x1.5	5,4	5,4				3	3,2	16	20	23	33	20x3	275
4	1x2.5	5,4	5,7				3,5	3,6	16	20	30	44	25x3	340
5	1x4	6	6				4	4	16	20	41	55	30x4	475
6	1x6	6,5	6,5				5	5,5	16	20	50	70	40x4	625
7	1x10	7,8	7,8				5,5	6,2	20	20	80	105	40x5	700
8	1x16	9,9	9,9				7	8,2	20	20	100	135	50x5	860
9	1x25	11,5	11,5				9	10,5	32	32	140	175	50x6	955
10	1x35	12,6	12,6				10	11	32	32	170	210	60x6	1125	1740	2240
11	1x50	14,4	14,4				12,5	13,2	32	32	215	265	80x6	1480	2110	2720
12	1x70	16,4	16,4				14	14,8	40	40	270	320	100x6	1810	2470	3170
13	1x95	18,8	18,7				16	17	40	40	325	385	60x8	1320	2160	2790
14	1x120	20,4	20,4						50	50	385	445	80x8	1690	2620	3370
15	1x150	21,1	21,1						50	50	440	505	100x8	2080	3060	3930
16	1x185	24,7	24,7						50	50	510	570	120x8	2400	3400	4340
17	1x240	27,4	27,4						63	65	605		60x10	1475	2560	3300
18	3x1.5	9,6	9,2			9			20	20	19	27	80x10	1900	3100	3990
19	3x2.5	10,5	10,2			10,2			20	20	25	38	100x10	2310	3610	4650
20	3x4	11,2	11,2			11,9			25	25	35	49	120x10	2650	4100	5200
21	3x6	11,8	11,8			13			25	25	42	60	rectangular copper bars (A) Schneider Electric IP30
22	3x10	14,6	14,6						25	25	55	90
23	3x16	16,5	16,5						32	32	75	115
24	3x25	20,5	20,5						32	32	95	150
25	3x35	22,4	22,4						40	40	120	180	Section, tires mm	Number of buses per phase
26	4x1			8	9,5				16	20	14	14	Section, tires mm	1	2	3
27	4x1.5	9,8	9,8	9,2	10,1				20	20	19	27	50x5	650	1150
28	4x2.5	11,5	11,5	11,1	11,1				20	20	25	38	63x5	750	1350	1750
29	4x50	30	31,3						63	65	145	225	80x5	1000	1650	2150
30	4x70	31,6	36,4						80	80	180	275	100x5	1200	1900	2550
31	4x95	35,2	41,5						80	80	220	330	125x5	1350	2150	3200
32	4x120	38,8	45,6						100	100	260	385	Permissible continuous current for rectangular copper bars (A) Schneider Electric IP31
33	4x150	42,2	51,1						100	100	305	435
34	4x185	46,4	54,7						100	100	350	500
35	5x1			9,5	10,3				16	20	14	14
36	5x1.5	10	10	10	10,9	10,3			20	20	19	27	Section, tires mm	Number of buses per phase
37	5x2.5	11	11	11,1	11,5	12			20	20	25	38	Section, tires mm	1	2	3
38	5x4	12,8	12,8			14,9			25	25	35	49	50x5	600	1000
39	5x6	14,2	14,2			16,3			32	32	42	60	63x5	700	1150	1600
40	5x10	17,5	17,5			19,6			40	40	55	90	80x5	900	1450	1900
41	5x16	22	22			24,4			50	50	75	115	100x5	1050	1600	2200
42	5x25	26,8	26,8			29,4			63	65	95	150	125x5	1200	1950	2800
43	5x35	28,5	29,8						63	65	120	180
44	5x50	32,6	35						80	80	145	225
45	5x95	42,8							100	100	220	330
46	5x120	47,7							100	100	260	385
47	5x150	55,8							100	100	305	435
48	5x185	61,9							100	100	350	500
49	7x1			10	11				16	20	14	14
50	7x1.5			11,3	11,8				20	20	19	27
51	7x2.5			11,9	12,4				20	20	25	38
52	10x1			12,9	13,6				25	25	14	14
53	10x1.5			14,1	14,5				32	32	19	27
54	10x2.5			15,6	17,1				32	32	25	38
55	14x1			14,1	14,6				32	32	14	14
56	14x1.5			15,2	15,7				32	32	19	27
57	14x2.5			16,9	18,7				40	40	25	38
58	19x1			15,2	16,9				40	40	14	14
59	19x1.5			16,9	18,5				40	40	19	27
60	19x2.5			19,2	20,5				50	50	25	38
61	27x1			18	19,9				50	50	14	14
62	27x1.5			19,3	21,5				50	50	19	27
63	27x2.5			21,7	24,3				50	50	25	38
64	37x1			19,7	21,9				50	50	14	14
65	37x1.5			21,5	24,1				50	50	19	27
66	37x2.5			24,7	28,5				63	65	25	38

So, the known power of each electrical appliance in the house, the known number of lighting fixtures and lighting points allow us to calculate the total power consumed. This is not an exact sum, since most values for the powers of various devices are averages. Therefore, you should immediately add 5% of its value to this figure.

Average power readings for common electrical appliances

Consumer	Power, W
TV	300
Printer	500
Computer	500
Hair dryer	1200
Iron	1700
Electric kettle	1200
Toaster	800
Heater	1500
Microwave oven	1400
Oven	2000
Fridge	600
Washing machine	2500
Electric stove	2000
Lighting	2000
Instantaneous water heater	5000
Boiler	1500
Drill	800
Hammer	1200
Welding machine	2300
Lawnmower	1500
Water pump	1000

And many believe that this is enough to select almost standard copper cable options:

cross section 0.5 mm2 for wires for lighting spotlights;
cross section 1.5 mm2 for lighting wires for chandeliers;
cross-section 2.5 mm2 for all sockets.

At the level of household use of electricity, such a scheme looks quite acceptable. Until the refrigerator and electric kettle decided to turn on in the kitchen at the same time, while you were watching TV there. The same unpleasant surprise overtakes you when you plug in a coffee maker, washing machine and microwave into one outlet.

Thermal calculation using correction factors

For several lines in one cable channel, the tabulated values of the maximum current should be multiplied by the appropriate coefficient:

0.68 — for the number of conductors from 2 to 5 pcs.
0.63 — for conductors from 7 to 9 pcs.
0.6 — for conductors from 10 to 12 pcs.

The coefficient refers specifically to the wires (cores), and not to the number of passing lines. When calculating the number of laid wires, the neutral working wire or grounding wire is not taken into account. According to PUE and GOST 16442-80, they do not affect the heating of wires during the passage of normal currents.

Summarizing the above, it turns out that in order to correctly and accurately select the wire cross-section, you need to know:

The sum of all maximum powers of electrical appliances.
Network characteristics: number of phases and voltage.
Characteristics of cable material.
Tabular data and coefficients.

At the same time, power is not the main indicator for an individual cable line or the entire internal power supply system. When selecting a cross-section, be sure to calculate the maximum load current, and then check it with the rated current of the home circuit breaker.

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 installation 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.

Cable length

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, kW		Power, kW












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

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.

How to calculate a cable by current, voltage and length. , as you know, come in different sections, materials and with different numbers of cores. Which one should you choose so as not to overpay, and at the same time ensure the safe, stable operation of all electrical appliances in the house? To do this, it is necessary to calculate the cable. The cross section is calculated by knowing the power of the devices powered from the network and the current that will flow through the cable. You also need to know a few other wiring parameters.

Basic rules

When laying electrical networks in residential buildings, garages, and apartments, rubber or PVC insulated cables designed for a voltage of no more than 1 kV are most often used. There are brands that can be used outdoors, indoors, in walls (grooves) and pipes. Usually this is a VVG or AVVG cable with different cross-sectional areas and number of cores.
PVA wires and SHVVP cords are also used to connect electrical appliances.

After calculation, the maximum permissible cross-section value is selected from a number of cable grades.

Basic recommendations for choosing a cross-section are found in the Electrical Installation Rules (PUE). The 6th and 7th editions have been released, which describe in detail how to lay cables and wires, install protection, distribution devices and other important points.

For violation of the rules, administrative fines are provided. But the most important thing is that violation of the rules can lead to failure of electrical appliances, fire of wiring and serious fires. Fire damage is sometimes measured not in monetary terms, but in human casualties.

The importance of choosing the right section

Why is cable sizing so important? To answer, you need to remember your school physics lessons.

Current flows through the wires and heats them. The stronger the power, the greater the heating. Active current power is calculated using the formula:

**P=UI cos φ=I²*R**

R– active resistance.

As you can see, power depends on current and resistance. The greater the resistance, the more heat is generated, that is, the more the wires heat up. Same for current. The larger it is, the more the conductor heats up.

Resistance in turn depends on the material of the conductor, its length and cross-sectional area.

**R=ρ*l/S**

ρ – specific resistance;

l– length of the conductor;

S– cross-sectional area.

It can be seen that the smaller the area, the greater the resistance. And the greater the resistance, the more the conductor heats up.

If you buy a wire and measure its diameter, do not forget that the area is calculated using the formula:

**S=π*d²/4**

d– diameter.

Don't forget resistivity either. It depends on the material from which the wires are made. The resistivity of aluminum is greater than that of copper. This means that with the same area, aluminum will heat up more strongly. It immediately becomes clear why it is recommended to use aluminum wires with a larger cross-section than copper wires.

In order not to go into a long calculation of the cable cross-section each time, standards for selecting the cross-section of wires in tables were developed.

Calculation of wire cross-section by power and current

The calculation of the wire cross-section depends on the total power consumed by electrical appliances in the apartment. It can be calculated individually, or use average characteristics.

For the accuracy of calculations, a block diagram is drawn up that shows the devices. You can find out the power of each from the instructions or read on the label. Electric stoves, boilers, and air conditioners have the highest power. The total figure should be in the range of approximately 5-15 kW.

Knowing the power, the rated current is determined using the formula:

**I=(PK)/(Ucos φ)**

P– power in watts

U=220 Volt

K=0.75 – simultaneous switching factor;

cos φ=1 for household electrical appliances;

If the network is three-phase, then a different formula is used:

**I=P/(U√3cos φ)**

U=380 Volt

Having calculated the current, you need to use the tables that are presented in the PUE and determine the cross-section of the wire. The tables indicate the permissible continuous current for copper and aluminum wires with various types of insulation. Rounding is always done upward to allow for margin.

You can also refer to tables in which the cross-section is recommended to be determined only by power.

Special calculators have been developed that can be used to determine the cross-section, knowing the power consumption, network phases and cable line length. You should pay attention to the installation conditions (in a pipe or outdoors).

Influence of wiring length on cable selection

If the cable is very long, then additional restrictions arise on the choice of cross-section, since voltage losses occur over an extended section, which in turn lead to additional heating. To calculate voltage losses, the concept of “load torque” is used. It is defined as the product of power in kilowatts and length in meters. Next, look at the value of losses in the tables. For example, if the power consumption is 2 kW and the cable length is 40 m, then the torque is 80 kW*m. For copper cable with a cross-section of 2.5 mm². this means that the voltage loss is 2-3%.

If the losses exceed 5%, then it is necessary to take a cross section with a margin greater than that recommended for use at a given current.

Calculation tables are provided separately for single-phase and three-phase networks. For three-phase load torque increases, since the load power is distributed over three phases. Consequently, losses are reduced and the effect of length is reduced.

Voltage losses are important for low-voltage devices, in particular gas-discharge lamps. If the supply voltage is 12 V, then with a loss of 3% for a 220 V network, the drop will be little noticeable, and for a low-voltage lamp it will be almost halved. Therefore, it is important to place ballasts as close as possible to such lamps.

Calculation of voltage losses is performed as follows:

∆U = (P∙r0+Q∙x0)∙L/ Un

P— active power, W.

Q— reactive power, W.

r0— active resistance of the line, Ohm/m.

x0— line reactance, Ohm/m.

Un– rated voltage, V. (it is indicated in the characteristics of electrical appliances).

L— line length, m.

Well, if it’s simpler for everyday conditions:

**ΔU=I*R**

R– cable resistance, calculated using the well-known formula R=ρ*l/S;

I– current strength, found from Ohm’s law;

Let's say we have it that I=4000 W/220 IN=18.2 A.

The resistance of one strand of copper wire with a length of 20 m and an area of 1.5 mm2. amounted to R=0.23 Ohm. The total resistance of the two wires is 0.46 Ohms.

Then ΔU=18.2*0.46=8.37 V

Percentage

8,37*100/220=3,8%

On long lines against overloads and short circuits they are installed with thermal and electromagnetic releases.

When renovations are planned in a house or apartment, replacing the wiring is one of the most important jobs. Not only the durability of the electrical wiring, but also its functionality depends on the correct choice of wire cross-section. The correct calculation of the cable cross-section by power can be carried out by a qualified electrician who can not only select a suitable cable, but also carry out installation. If the wires are chosen incorrectly, they will heat up, and under high loads they can lead to negative consequences.

As you know, when a wire overheats, its conductivity decreases, which ultimately leads to even greater overheating. When a wire overheats, its insulation can become damaged and lead to a fire. In order not to worry about your home after installing new electrical wiring, you should initially perform a correct calculation of the cable power and pay special attention to this issue.

Why carry out cable calculations based on load current?

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.

An incorrectly selected cable cross-section will lead to overheating of the wire and, as a result, after a short time you will have to call a specialist to troubleshoot electrical wiring problems. Calling a specialist today costs a lot, so in order to save money, you need to do everything correctly from the beginning, in which case you can not only save money, but also protect your home.

It is important to remember that the electrical and fire safety of the room and those who are or live in it depends on the correct choice of cable cross-section.

Safe operation lies in the fact 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 affects the calculation of the cross-section of a wire or cable

There are many factors influencing, which are fully described in paragraph 1.3 of the PUE. This paragraph provides for the calculation of cross-section for all types of conductors.

In this article, dear readers of the “Electrician in the House” website, we will consider the calculation of the wire cross-section based on power consumption for copper conductors in PVC and rubber insulation. Today, such wires are mainly used in houses and apartments for installing electrical wiring.

The main factor for cable cross-section calculation The load used in the network or the current is considered. Knowing the power of the electrical equipment, we will obtain the rated current as a result of a simple calculation using the formulas below. Based on this, it turns out that the cross-section of the wires is directly related to the estimated power of the electrical installation.

When calculating the cable cross-section, the choice of conductor material is also important. Perhaps every person knows from physics lessons at school that copper has much higher conductivity than the same wire made of aluminum. If we compare copper and aluminum wires of the same cross-section, the former will have higher performance.

Also important when calculating the cable cross-section is the number of cores in the wire. A large number of cores heats up much higher than a single-core wire.

The method of laying the wires is also of great importance when choosing a cross-section. As you know, earth is considered a good heat conductor, unlike air. Based on this, it turns out that a cable laid under the surface of the earth can withstand a greater electrical load, unlike those in the air.

When calculating the cross section, do not forget that when wires are in a bundle and placed in special trays, they can heat up against each other. Therefore, it is quite important to take this point into account when making calculations, and, if necessary, make appropriate adjustments. If there are more than four cables in a box or tray, then when calculating the wire cross-section, it is important to enter a correction factor.

As a rule, the correct choice of wire cross-section is also influenced by the air temperature at which it will be operated. In most cases, the calculation is made from the average ambient temperature + 25 degrees Celsius. If the temperature regime does not meet your requirements, then in Table 1.3.3 of the PUE there are correction factors that must be taken into account.

The calculation of the cable cross-section is also affected by the voltage drop. If a voltage drop of more than 5% is expected in an extended cable line, then these indicators must be taken into account in the calculations.

Calculation of wire cross-section based on power consumption

Each cable has its own power rating, which it can withstand when an electrical appliance is connected.

In the case when the power of the appliances in the house exceeds the load capacity of the wire, then in this case an emergency situation cannot be avoided and sooner or later the wiring problem will make itself felt.

To independently calculate the power consumption of appliances, you need to write down on a piece of paper the power of all available electrical appliances that can be connected at the same time (electric kettle, TV, vacuum cleaner, hob, computer, etc.).

Once the power of each device is known, all values must be summed up to understand the total consumption.

Where K o is the simultaneity coefficient.

Let's look at an example calculating wire cross-section for an ordinary two-room apartment. The list of necessary devices and their approximate power is indicated in the table.

Based on the obtained value, you can continue calculations with the choice of wire cross-section.

If the house has powerful electrical appliances with a load of 1.5 kW or more, it is advisable to use a separate line to connect them. When making your own calculations, it is important not to forget to take into account the power of the lighting equipment that is connected to the network.

When properly produced, each room will provide approximately 3 kW, but do not be afraid of these figures, since all devices will not be used at the same time, and, therefore, this value has a certain margin.

When calculating the total power consumed in the apartment, it turned out result 15.39 kW, now this indicator should be multiplied by 0.8, which will result in 12.31 kW actual load. Based on the obtained power indicator, you can use a simple formula to calculate the current strength.

Calculation of cable cross-section for current

The main indicator by which a wire is calculated is its longevity. Simply put, this is the amount of current that it can pass for a long time.

Knowing the current load, you can obtain more accurate calculations of the cable cross-section. Besides, everything cross-section selection tables in GOST and regulatory documents are based on current values.

The meaning of calculation is similar to that of power, but only in this case it is necessary to calculate the current load. To calculate the current cable cross-section, the following steps must be carried out:

- select the power of all devices;
- calculate the current that passes through the conductor;
- Use the table to select the most suitable cable cross-section.

To find the rated current value, you need to calculate the power of all connected electrical appliances in the house. What you and I, friends, have already done in the previous section.

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 strength for single-phase network 220 V:

- P - total power of all electrical appliances, W;
- U - network voltage, V;
- for household electrical appliances cos (φ) = 1.

2) Formula for calculating the current in three-phase network 380 V:

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 from the table the nearest larger 27 A - with a cross-section of 2.5 mm2 (for stranded copper wire laid through the air).

I present to your attention tables of permissible current loads of cables with copper and aluminum conductors with insulation made of polyvinyl chloride plastic.

All data is taken not from the head, but from the regulatory document GOST 31996-2012 “PLASTIC INSULATION POWER CABLES”.

For example, you have a three-phase load with a power of P = 15 kV. It is necessary to select a copper cable (over-the-air installation). How to calculate the cross section? First, you need to calculate the current load based on the given power; for this we use the formula for a three-phase network: I = P / √3 380 = 22.8 ≈ 23 A.

According to the table of current loads, we select a cross-section of 2.5 mm2 (for it the permissible current is 27A). But since you have a four-core cable (or five, there is not much difference), according to the instructions of GOST 31996-2012, the selected current value must be multiplied by a factor of 0.93. I = 0.93 * 27 = 25 A. What is permissible for our load (design current).

Although, due to the fact that many manufacturers produce cables with a reduced cross-section, in this case I would advise taking a cable with a reserve, with a cross-section an order of magnitude higher - 4 mm2.

Which wire is better to use: copper or aluminum?

Today, for the installation of both open and hidden electrical wiring, copper wires are, of course, very popular. Copper, compared to aluminum, is more effective:

1) it is stronger, softer and does not break in places of inflection compared to aluminum;

2) 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;

3) 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.

As for the conductor material, only copper wire is subject to consideration in this article, since in most cases it is used as electrical wiring in houses and apartments. Among the advantages of this material, durability, ease of installation and the ability to use a smaller cross-section compared to aluminum, with the same current, should be highlighted. If the cross-section of the wire is large enough, then its cost exceeds all the advantages and the best option would be to use an aluminum cable rather than a copper one.

For example, if the load is more than 50 A, then in order to save money, it is advisable to use cables with an aluminum core. Usually these are areas where electricity enters the house, where the distance exceeds several tens of meters.

An example of calculating the cable cross-section for an apartment

Having calculated the load and decided on the material (copper), consider an example calculating wire cross-section for certain consumer groups, 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, living rooms and bathroom. Since the most powerful equipment is installed there (electric kettle, microwave, refrigerator, boiler, washing machine, etc.).

1. Water cable

Input cable cross-section(the section from the switchboard on the site to the distribution board of the apartment) is selected based on the total power of the entire apartment, which we received in the table.

First, we find the rated current in this section relative to a given load:

The current is 56 Amperes. Using the table, we find the cross section corresponding to a given current load. We choose the nearest larger value - 63 A, which corresponds to a cross section of 10 mm2.

2. Room No. 1

Here the main load on the socket group will be such equipment as a TV, computer, iron, vacuum cleaner. The load on the wiring section from the apartment panel to the distribution box in this room is 2990 W (rounded up to 3000 W). We find the rated current using the formula:

Using the table, we find a cross section that corresponds to 1.5 mm2 and the permissible current is 21 Amperes. Of course, you can take this cable, but it is recommended to lay the socket group with a cable with a cross-section of AT LEAST 2.5 mm2. This is also related to the rating of the circuit breaker that will protect the cable in question. It is unlikely that you will power this area from a 10 A machine? And most likely install the machine at 16 A. Therefore, it is better to take it with a reserve.

Friends, as I already said, we power the socket group with a cable with a cross-section of 2.5 mm2, so for wiring directly from the box to the sockets we choose it.

3. Room No. 2

Here, equipment such as a computer, vacuum cleaner, iron, and possibly a hair dryer will be connected to the sockets.

The load in this case is 4050 W. Using the formula we find the current:

For this current load, a wire with a cross-section of 1.5 mm2 is suitable for us, but here, similarly to the previous case, we take it with a margin and accept 2.5 mm2. We also do the connection of sockets.

4. Kitchen

In the kitchen, the socket group powers the electric kettle, refrigerator, microwave, electric oven, electric stove and other appliances. Perhaps a vacuum cleaner will be connected here.

The total power of kitchen consumers is 6850 W, the current is:

For such a load, according to the table, select the nearest larger cable cross-section - 4 mm2, with a permissible current of 36 A.

Friends, I stipulated above that it is advisable to connect powerful consumers with a separate independent line (your own). The electric stove is just that, for her cable cross-section calculation performed separately. When installing electrical wiring for such consumers, an independent line is laid from the switchboard to the connection point. But our article is about how to correctly calculate the cross-section and in the photo I did not do this on purpose for better assimilation of the material.

5. Bath

The main consumers of electricity in this room are st. car, water heater, hair dryer, vacuum cleaner. The power of these devices is 6350 W.

Using the formula we find the current:

Using the table, we select the nearest higher current value - 36 A, which corresponds to a cable cross-section of 4 mm2. Here again, friends, it is advisable to power powerful consumers with a separate line.

6. Hallway

In this room, portable equipment is usually used, for example, a hair dryer, vacuum cleaner, etc. There are no particularly powerful consumers expected here, but we also accept a wire with a cross-section of 2.5 mm2 for the socket group.

7. Lighting

According to the calculations in the table, we know that the total lighting power in the apartment is 500 W. The rated current for such a load is 2.3 A.

In this case, the entire lighting load can be 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 6 - 10 mm2.

Currently, for installation of electrical wiring, it is preferable to use cables of the following brands: VVGng, VVG, NYM. The “ng” indicator indicates that the insulation is not subject to combustion - “non-flammable”. These types of wires can be used both indoors and outdoors. The operating temperature range of these wires varies from “+/-” 50 degrees Celsius. The warranty period is 30 years, but the service life may be longer.

If you know how to correctly calculate the current cross-section of a conductor, you can install electrical wiring in your house without any problems. If all requirements are met, the safety and security of your home will be guaranteed to be as high as possible. By choosing the right conductor cross-section, you will protect your home from short circuits and fires.