Cross section of 3 phase cable by power. How to calculate the required wire cross-section based on load power? Example of cable calculation based on voltage drop

Conductor cross-section for power and current for electrical wiring in an apartment

Electrical installation work is a complex and responsible undertaking. If your qualifications are sufficient to do the electrical wiring in the apartment with your own hands, useful tips will come in handy. If not, then use the services of electrical installation specialists. So, let's talk about choosing the cross-section of wires for current and power in detail.

Calculation of the length and maximum load of electrical wiring

Correct calculation of the wire cross-section for power and current is an important condition for the uninterrupted and trouble-free operation of the electrical system. First, calculate the total wiring length. The first way is to measure the distances between panels, switches and sockets on the wiring diagram, multiplying the number by the scale. The second way is to determine the length according to the location where the electrical wiring is designed. It includes all wires, installation and installation cables along with fastenings, support and protective structures. Each segment must be extended by at least 1 cm, taking into account the wire connections.

Next, the total load of consumed electricity is calculated. This is the sum of the rated powers of all electrical appliances that will operate in the house (*see table at the end of the article). For example, if in the kitchen an electric kettle, electric stove, microwave, lamps, and dishwasher are turned on at the same time, we sum up the power of all appliances and multiply by 0.75 (simultaneity coefficient). The load calculation must always have a margin of reliability and strength. We remember this figure to determine the cross-section of the wire cores.

A simple formula will help you determine the current consumption of any electrical appliance yourself. Divide the power consumption (see the instructions for the device) by the network voltage (220 V). For example, according to the passport, the power of the washing machine is 2000 W; 2000/220 = maximum current during operation will not exceed 9.1A.

Another option is to use the recommendations of the PUE (Electrical Installation Rules), according to which standard apartment wiring with a continuous load of 25A is calculated for the maximum current consumption and is carried out with copper wire with a cross-section of 5mm 2. According to the PUE, the cross-section of the core must be at least 2.5 mm 2, which corresponds to a conductor diameter of 1.8 mm.

This current is set to circuit breaker at the entrance of wires into the apartment to prevent accidents. In residential buildings, single-phase current with a voltage of 220 V is used. We divide the calculated total load by the voltage value (220 V) and obtain the current that will pass through the input cable and the machine. You need to buy a machine with exact or similar parameters, with a margin of current load.

Choosing a cable for electrical wiring in an apartment

* Table of power consumption and current
household electrical appliances with a supply voltage of 220V

Household electrical appliance	Power consumption depending on the model of the electrical appliance, kW (BA)	Current consumption, A	Note
Incandescent lamp
Electric kettle			Continuous operation time up to 5 minutes
Electric stove			For power greater than 2 kV, separate wiring is required
Microwave oven
Electric meat grinder

Coffee grinder			During operation, the current consumption varies depending on the load.
Coffee maker
Electric oven			During operation, the maximum current is consumed periodically
Dishwasher
Washing machine			Maximum current consumed from the moment of switching on until the water is heated
			During operation, the maximum current is consumed periodically
			During operation, the current consumption varies depending on the load.
Desktop computer			During operation, the maximum current is consumed periodically
Power tools (drill, jigsaw, etc.)			During operation, the current consumption varies depending on the load.

The ability to choose the right cable cross-section can be useful to anyone over time, and you don’t have to be a qualified electrician to do this. By incorrectly calculating the cable, you can expose yourself and your property to serious risk - too thin wires will get very hot, which can lead to a fire.

Why do you need to calculate the cable cross-section?

First of all, carrying out this slightly complicated procedure is necessary to ensure the safety of both the premises itself and the people in it. Today, humanity has not invented a more convenient method of distributing and delivering electrical energy to the consumer, like through wires. People need the services of an electrician almost every day - someone needs to connect an outlet, someone needs to install a lamp, etc. From this it turns out that even such a seemingly insignificant procedure as installing a new lamp is associated with the operation of selecting the required cross-section . What then can we say about connecting an electric stove or water heater?

Failure to comply with the standards can lead to damage to the integrity of the wiring, which often causes a short circuit or even electric shock.

If you make a mistake when choosing a cable cross-section and purchase a cable with a smaller conductor area, this will lead to constant heating of the cable, which will cause destruction of its insulation. Naturally, all this negatively affects the life of the wiring - there are often cases when, a month after successful installation, the electrical wiring stopped working and specialist intervention was required.

It should be remembered that the electrical and fire safety in the building, and therefore the lives of the residents themselves, directly depends on the correctly selected cable cross-section.

Of course, every owner wants to save as much as possible, but you should not do this at the cost of your life, putting it at risk - after all, as a result of a short circuit, a fire can occur, which may well destroy all property.

To avoid this, before starting electrical installation work, you should select a cable with an optimal cross-section. For selection, several factors must be taken into account:

the total number of electrical devices located in the room;
the total power of all devices and the load they consume. To the obtained value you should add 20–30% “in reserve”;
then, through simple mathematical calculations, convert the resulting value into the cross-section of the wire, taking into account the material of the conductor.

Attention! Due to lower electrical conductivity, wires with aluminum conductors must be purchased with a larger cross-section than copper ones.

What affects the heating of wires

If the wiring heats up during the operation of household appliances, then you should immediately take all necessary measures to eliminate this problem. There are many factors influencing the heating of wires, but the main ones include the following:

Insufficient cable cross-sectional area. To put it in accessible language, we can say this: the thicker the cable’s cores, the more current it can transmit without overheating. The value of this value is indicated in the marking of cable products. You can also measure the cross-section yourself using a caliper (you should make sure that the wire is not live) or by the type of wire.
Material from which the wire is made. Copper conductors transmit voltage better to the consumer and have lower resistance compared to aluminum conductors. Naturally, they heat up less.
Core type. The cable can be single-core (the core consists of one thick rod) or multi-core (the core consists of a large number of small wires). A multi-core cable is more flexible, but is significantly inferior to a single-core cable in terms of the permissible strength of the transmitted current.
Cable laying method. Tightly laid wires located in the pipe heat up noticeably more than open wiring.
Material and quality of insulation. Inexpensive wires, as a rule, have low quality insulation, which negatively affects their resistance to high temperatures.

How to calculate power consumption

You can calculate the approximate cable cross-section yourself - it is not necessary to seek the help of a qualified specialist. The data obtained as a result of the calculations can be used to purchase wires, however, the electrical installation work itself should be trusted only to an experienced person.

The sequence of actions when calculating the section is as follows:

A detailed list of all electrical appliances in the room is compiled.
The passport data of the power consumption of all found devices is established, after which the continuity of operation of a particular equipment is determined.
Having identified the value of power consumption from devices that operate constantly, you should sum this value by adding to it a coefficient equal to the value of electrical appliances that turn on periodically (that is, if the device will work only 30% of the time, then you should add a third of its power).
Next, we look for the obtained values in a special table for calculating the wire cross-section. For greater guarantee, it is recommended to add 10-15% to the obtained power consumption value.

To determine the necessary calculations for selecting the cross-section of electrical wiring cables according to their power within the network, it is important to use data on the amount of electrical energy consumed by devices and current appliances.

At this stage, it is necessary to take into account a very important point - the data of electrically consumed devices does not give an exact, but an approximate, average value. Therefore, about 5% of the parameters specified by the equipment manufacturer must be added to this mark.

The majority of not the most competent and qualified electricians are confident in one simple truth - in order to correctly install electrical wires for lighting sources (for example, for lamps), it is necessary to take wires with a cross-section equal to 0.5 mm², for chandeliers - 1, 5 mm², and for sockets – 2.5 mm².

Only incompetent electricians think about this and think so. But what if, for example, a microwave, kettle, refrigerator and lighting operate simultaneously in the same room, which require wires with different cross-sections? This can lead to a variety of situations: short circuit, rapid damage to wiring and insulating layer, as well as fire (this is a rare case, but still possible).

Exactly the same not very pleasant situation can happen if a person connects a multicooker, a coffee maker and, say, a washing machine to the same outlet.

Features of calculating the power of hidden wiring

If the design documentation implies the use of hidden wiring, then it is necessary to purchase cable products “with a reserve” - about 20–30% should be added to the obtained value of the cable cross-section. This is done to avoid heating the cable during operation. The fact is that in conditions of cramped space and lack of air access, heating of the cable occurs much more intensely than when installing open wiring. If in closed channels it is planned to lay not one cable, but several at once, then the cross-section of each wire should be increased by at least 40%. It is also not recommended to tightly lay various wires - ideally, each cable should be contained in a corrugated pipe, which provides it with additional protection.

Important! It is by the value of power consumption that professional electricians are guided when choosing a cable cross-section, and only this method is correct.

How to calculate cable cross-sections by power

If the cable cross-section is sufficient, the electric current will pass to the consumer without causing heating. Why does heating occur? We will try to explain as clearly as possible. For example, a kettle with a power consumption of 2 kilowatts is plugged into the outlet, but the wire going to the outlet can only transmit a current of 1 kilowatt for it. The capacity of a cable is related to the resistance of the conductor - the greater it is, the less current can be transmitted through the wire. As a result of high resistance in the wiring, the cable heats up, gradually destroying the insulation.

With the appropriate cross-section, the electric current reaches the consumer in full, and the wire does not heat up. Therefore, when designing electrical wiring, you should take into account the power consumption of each electrical device. This value can be found from the technical data sheet for the electrical device or from the label affixed to it. By summing the maximum values and using a simple formula:

and get the value of the total current.

Pn denotes the power of the electrical appliance indicated in the passport, 220 is the rated voltage.

For a three-phase system (380 V), the formula looks like this:

I=(P1+P2+....+Pn)/√3/380.

The resulting I value is measured in Amperes, and based on it, the appropriate cable cross-section is selected.

It is known that the throughput of a copper cable is 10 A/mm; for an aluminum cable the throughput is 8 A/mm.

For example, let’s calculate the cable cross-section for connecting a washing machine, the power consumption of which is 2400 W.

I=2400 W/220 V=10.91 A, rounding up we get 11 A.

11 A+5 A=16 A.

If we take into account that three-core cables are used in apartments and look at the table, then the value close to 16 A is 19 A, so to install a washing machine you will need a wire with a cross-section of at least 2 mm².

Table of cable cross-sections relative to current values

Current cross-section wire length of core(mm 2)		Current (A), for wires laid
	Open That		in one pipe
		two one- vein	three one- vein	four one- vein	one two- vein	one three- vein
0,5	11	-	-	-	-	-
0,75	15	-	-	-	-	-
1	17	16	15	14	15	14
1,2	20	18	16	15	16	14,5
1,5	23	19	17	16	18	15
2	26	24	22	20	23	19
2,5	30	27	25	25	25	21
3	34	32	28	26	28	24
4	41	38	35	30	32	27
5	46	42	39	34	37	31
6	50	46	42	40	40	34
8	62	54	51	46	48	43
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	-	-	-	-	-
300	695	-	-	-	-	-
400	830	-	-	-	-	-

How to choose conductor cross-sections

There are several more criteria that the cross-section of the wires used must meet:

Cable length. The longer the wire, the greater the current loss observed in it. This again occurs as a result of an increase in resistance, which increases as the length of the conductor increases. This is especially noticeable when using aluminum wiring. When using copper wires to organize electrical wiring in an apartment, the length, as a rule, is not taken into account - a standard margin of 20–30% (for hidden wiring) is more than enough to compensate for possible increases in resistance associated with the length of the wire.
Type of wires used. There are 2 types of conductors used in household electricity supply - copper or aluminum based. Copper wires are of better quality and have less resistance, but aluminum wires are cheaper. In full compliance with the standards, aluminum wiring copes with its tasks no worse than copper, so you need to carefully weigh your choice before purchasing a wire.
Electrical panel configuration. If all the wires supplying consumers are connected to one circuit breaker, then it will be the weak point in the system. A heavy load will lead to heating of the terminal blocks, and non-compliance with the rating will lead to its constant operation. It is recommended to divide the electrical wiring into several “beams” with the installation of a separate machine.

In order to determine the exact data for choosing the cross-section of electrical wiring cables, it is necessary to take into account any, even the most insignificant parameters, such as:

Type and type of insulation of electrical wiring;
Length of sections;
Laying methods and options;
Features of temperature conditions;
Humidity level and percentage;
The maximum possible value of superheat;
The difference in the powers of all current receivers belonging to the same group. All these and many other indicators can significantly increase the efficiency and benefits of energy use on any scale. In addition, correct calculations will help avoid cases of overheating or rapid abrasion of the insulating layer.

In order to correctly determine the optimal cable cross-section for any human household needs, it is necessary in all general cases to use the standardized following rules:

for all sockets that will be installed in the apartment, it is necessary to use wires with an appropriate cross-section of 3.5 mm²;
for all spotlighting elements, it is necessary to use electrical wiring cables with a cross-section of 1.5 mm²;
As for high-power devices, cables with a cross-section of 4-6 mm² should be used.

If some doubts arise during the installation or calculation process, it is better not to act blindly. The ideal option would be to refer to the appropriate table of calculations and standards.

Copper cable cross-section table

Cross-section of conductors (mm)	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
16	80	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	265	57,2	220	145,2
120	300	66	260	171,6

Aluminum Cable Section Table

When installing a home electrical network, it is important to choose the right wires.

The material and diameter of the cores must match the load, otherwise overheating will occur followed by melting of the insulation, then a short circuit and fire.

The selection methodology is outlined in this article, the topic of which is by power: table.

The throughput of the conductor is characterized by the maximum permissible current density.

The latter is defined as the relation in the conductor to its. Unit of measurement - A/sq. mm (amps per square millimeter).

But since current is related to power and voltage (W=U*I), and the voltage is constant, then it is more convenient to select the cross-section of the wires according to the power of the consumer. After all, this parameter is usually indicated in the passport or on the nameplate.

It’s not scary to make a mistake when choosing a wire in the direction of increase: it will only lead to unjustified material costs. An error in the other direction is more expensive: due to overheating, the insulation melts, which leads to current leakage, followed by a short circuit and fire.

Line type and parameter

The maximum permissible current density for a conductor depends on 3 factors:

material of current-carrying conductors;
installation method (external/hidden);
number of phases for which the consumer is designed.

The electrical resistance of the core, and therefore the amount of heat released during the flow of current, depends on the material. Electrical copper has the lowest resistance. For aluminum this parameter is 1.73 times higher. Because of this, the maximum permissible current density for aluminum wires is 1.73 times lower than for copper wires.

The intensity of heat removal depends on the installation method. With the open type, the wires cool better than those placed in a sleeve, box or groove, therefore the permissible current density for them is increased.

Cable options

The effect of phasing is as follows: with equal power, single-phase and three-phase devices consume different currents. Therefore, the permissible current density for different numbers of phases is different.

Speaking about the permissible current density, there are two values:

Short-term permissible: such a current density that the conductor can withstand without overheating for a limited period. Such overloads occur, for example, when starting an electric motor.
Long-term permissible: a current with such a density, the core conducts for an indefinitely long time without being subject to overheating.

According to the PUE, the long-term permissible current density is 40% less than the short-term permissible one.

The purpose of the line is also taken into account. The electrical network is divided into two parts:

lighting;
power

The power line is calculated based on the load.

The latest edition of the “Rules for the Design and Connection of Electrical Installations” (PUE) prohibits the use of aluminum wires in residential premises.

Power

For a line supplying one electrical appliance, selecting a cross-section is not difficult; you just need to look into and find the cross-section of the core that corresponds to the known ones:

power;
phasing;
laying method.

This is how a wire is selected for laying from the distribution board to the boiler or air conditioner, or from the distribution box to one of the sockets.

The situation is different when several consumers are connected to one line. For example, a wire is powered by a socket group of several points, which include a refrigerator, microwave oven, electric heater and TV.

If you simply sum up their power, the cross-section of the wire will be overestimated, and the wire itself will be unreasonably expensive, because the devices are operated differently and not at the same time.

Therefore, when calculating the total load on a line from several consumers, two coefficients are used - simultaneity and demand.

Simultaneity coefficient (Co)

Takes into account that consumers usually work at different times. For different groups of consumers, the PUE assigns its own simultaneity coefficient. Here, for example, is how it changes depending on the number of apartments connected to the line:

It can be seen that in the case of one apartment, it is considered possible to turn on all devices synchronously - the simultaneity coefficient is equal to one. But as the number of apartments increases, the probability of simultaneously turning on all consumers becomes less and less, which is reflected in a decrease in this coefficient.

Demand factor (Ks)

Takes into account the operating time of the device. Some of them work constantly, others turn on occasionally and for a short period. For example, for a TV the demand coefficient is equal to one, for a vacuum cleaner it is 0.1. Data for some consumers are shown in the table:

On the nameplate or in the passport of consumers that include an electric motor or transformer, only the useful power (in watts) is indicated. The power consumption will be higher, since part of it is spent on overcoming the reactance of the windings (reactive power).

To determine the total power, the useful power must be divided by cosϕ - this value is also given in the passport and on the nameplate. If it is not indicated, you can take the average value: cosϕ = 0.7. Total power is usually measured in volt-amperes (VA).

Line current

If the table is based on load current and not power, first find it using the formula I = W / U, where: W is the power of the device in watts (W), U is the voltage in volts (V) and then find the cross section. Power is determined taking into account the correction factors described above.

For example, when connecting a heater with a power of 1.1 kW, a current of I = 1100 / 220 = 5A will flow in the circuit.

Protection apparatus

Three types of protection devices are used in household electrical networks.

Automatic switch (VA)

Disconnects a circuit if the current in it exceeds the permissible value.

Protects a network section from short circuits and overloads.

In function, the VA is similar to a fuse, but unlike it, it is reusable: after eliminating the malfunction that caused the machine to turn off, it is brought back into operation using a button or switch.

VA is selected in accordance with the maximum current allowed for the protected circuit and depending on the cross-section of the wires.

Residual current switch or residual current device (RCD)

Disconnects the circuit in case of current leakage, that is, when the user touched live parts or if, due to an insulation breakdown, they came into contact with a grounded conductor - building structures, device housing, etc.

They differ in two parameters:

Rated current. This is the maximum current that can flow through a given RCD without damaging it. The rated current of the RCD must be at least one step higher than the rated current of the VA protecting it (that is, set above).
Sensitivity. This is the minimum leakage current value that triggers the RCD.

Based on sensitivity, RCDs are divided into the following categories:

Fire: Low sensitivity ratings of 100, 300, or 500 mA provide no protection against electric shock. Through such RCDs, for example, lighting in wooden houses is connected.
Protecting people and animals from electric shock.

RCD and diffavtomat

The latter are divided into two subgroups with a leakage current setting:

10 mA: intended for consumers in rooms with high humidity;
30 mA: for consumers in dry rooms.

Through such RCDs, consumers are connected that can cause electrical injury. They are not required for lighting and appliances such as air conditioning installed in an inaccessible location.

There are imported RCDs on sale with a leakage current setting of 6 mA. This value corresponds to the standards of the European Union and the USA.

The higher the sensitivity of the RCD, the greater the likelihood of false alarms (depending on the quality of the power supply).

Differential automatic

Two-in-one device: combined. Costs less and is more compact than two devices separately.

Conductor selection

Wires with aluminum conductors have a similar marking - AVVG. They are not used in everyday life now, but are sometimes found in old houses.

The most preferred wires are VVGng brand.

The prefix “ng” indicates the use of non-combustible insulation. For installation behind a suspended ceiling, in a floor or wall structure, wires with reduced smoke emission are recommended. They are recognized by the letters “LS” in the markings.

The choice in favor of copper wires is due to the following advantages over aluminum:

low electrical resistance: copper wires heat up less and therefore allow a higher current density;
ductility: copper wire can have a cross-section from 1.5 square meters. mm and bend repeatedly, while aluminum breaks after several twists, and the minimum cross-section for it is 2.5 square meters. mm.

Aluminum wires are used in power lines because they are lightweight and inexpensive.

Cable cross-section by power: table

In conclusion, we present a table showing the dependence of the required cross-sectional area of the wires on the load, material and installation method.

Selection of cable cross-section, mm 2
Open gasket							Gasket in pipe
Copper			Aluminum				Copper			Aluminum
Current, A	Power, kW		Current, A	Power, kW			Current, A	Power, kW		Current, A	Power, kW
Current, A	220 V	380 V	Current, A	220 V	380 V	*mm 2*	Current, A	220 V	380 V	Current, A	220 V	380 V
11	2,4	–	–	–	–	*0,5*	–	–	–	–	–	–
15	3,3	–	–	–	–	*0,75*	–	–	–	–	–	–
17	3,7	6,4	–	–	–	*1,0*	–	–	–	–	–	–
23	5,0	8,7	–	–	–	*1,5*	14	3,0	5,3	–	–	–
26	5,7	9,8	21	4,6	7,9	*2,0*	19	4,1	7,2	14	3,0	5,3
30	6,6	11	24	5,2	9,1	*2,5*	21	4,6	7,9	16	3,5	6,0
50	11	19	39	8,5	14	*6,0*	34	7,4	12	26	5,7	9,8

The correct choice of wire cross-section is, first of all, a safety issue. At the same time, it is advisable to provide a reserve in case of connecting new electrical appliances in the future.

In this article I will tell you how choose the right cable section for a house or apartment. If- this is the “heart” of our power supply system, then the cables connected to the electrical panel circuit breakers are"blood vessels" that supplyelectricity from our household electrical receivers.

When installing electrical wiring in a house or apartment, all stages, starting from designing the electrical supply of a private house or apartment, and ending with the final installation of sockets or switches, must be approached with full responsibility, because your personal electrical safety, as well as the fire safety of your house or apartment, depends on this . Therefore, we approach the choice of cable cross-section with all seriousness, because no other method of transmitting electricity in a private house or apartment has yet been invented.

It is important to choose the correct cable cross-section, specifically for a specific line (group) of electrical receivers. Otherwise, if we choose a lower section cable is will lead to overheating, destruction of insulation and further to a fire If you touch a cable with damaged insulation, you will receive an electric shock. If you choose a cable cross-section that is too high for a house or apartment, this will lead to increased costs, and difficulties will arise during the electrical installation of cable lines, because the larger the cable cross-section, the more difficult it is to work with it; not every socket will “fit” a cable with a cross-section of 4 sq. mm .

I bring common universal table, which I myself use to select the rated current of automatic cable protection machinesblue

I won’t fill your head with abstruse formulas for calculating cable cross-sections from books on electrical engineering, so that you can choose the right cable cross-section. Everything has long been calculated and tabulated.

Please note that with different wiring installation methods(hidden or open) , cables with the same cross-section have different continuous-permissible currents.

Those. at open way installation of electrical wiring, the cable heats up less due to better cooling. At h covered way installation of electrical wiring (in grooves, pipes, etc.), on the contrary, it heats up more. This is an important point, because if you choose the wrong machine to protect the cable, the rating of the machine may be overestimated relative to the long-term permissible current of the cable, which is why the cable can get very hot, but the machine will not turn off.

I'll bring you example, for example, we have a cable cross-section of 6 sq. mm:

with the open method, its long-term permissible current is 50A, therefore the machine must be set to 40A;
with the hidden method, its long-term permissible current is 34A, in this case the machine is 32A.

Suppose we chose a cable cross-section for an apartment, which are laid in grooves or under plaster (in a closed way). If we mix it up and install 50A circuit breakers for protection, the cable will overheat, because... with a closed method of laying it, In = 34 A, which will lead to the destruction of its insulation, then a short circuit and fire.

TABLES ARE NOT CURRENT. WHEN SELECTING A MACHINE FOR CABLES, USE THE TABLE ABOVE.

Cable cross-section for hidden electrical wiring

Cable cross-section for open electrical wiring

To use the tables and choose the right cable cross-section for a house or apartment, we need to know the current strength, or know the power of all household electrical receivers.

The current is calculated using the following formulas:

— for a single-phase network with a voltage of 220 Volts:

where P is the sum of all powers of household electrical receivers, W;

U - single-phase network voltage 220 V;

Cos(phi) - power factor, for residential buildings it is 1, for production it will be 0.8, and on average 0.9.

— for a three-phase network with a voltage of 380 Volts:

in this formula everything is the same as for a single-phase network, only in the denominator, because The network is three-phase, add root 3 and the voltage will be 380 V.

To select the cable cross-section for a house or apartment using the above tables, it is enough to know the sum of the power receivers of a given cable line (group). We will still need current calculations when designing an electrical panel (choosing automatic machines, RCDs or differential circuit breakers).

Below are the average power values of the most common household electrical appliances:

Knowing the power of electrical receivers, you can accurately select the cable cross-section for a specific cable line (group) in a house or apartment, and therefore an automatic device (difavtomatic) to protect this line, whose rated current must be lower than the continuous-permissible current of the cable of a certain cross-section. If we choose a copper cable cross-section of 2.5 sq. mm, which conducts current up to 21 A for as long as desired ( hidden installation method), then the automatic circuit breaker (difavtomat) in the electrical panel for this cable must have a rated current of 20 A so that the circuit breaker turns off before the cable begins to overheat.

Typical cable sections for household electrical installations:

In apartments, cottages or private houses, for socket groups laying copper cable 2.5 sq.mm.;
For lighting group- copper cable cross-section 1.5 sq.mm;
For single phase hob(electric stoves) - cable section 3x6 sq. mm., for a three-phase electric stove - 5x2.5 sq. mm. or 5x4 sq. mm. depending on power;
For other groups (ovens, boilers, etc.) - by their power. And also on the connection method, through a socket or through terminals. For example, if the oven power is more than 3.5 kW, then lay a 3x4 cable and connect the oven through the terminals; if the oven power is less than 3.5 kW, then a 3x2.5 cable and connection through a household outlet is sufficient.

To select the correct cable cross-section and ratings of circuit breakers for the electrical panel of a private house, apartment, you need to know important points, not knowing which can lead to dire consequences.

For example:

For socket groups, select a cable cross-section of 2.5 sq. mm, but the machine is chosen with a rated current of not 20A, but 16A, because household sockets are designed for a current of no more than 16 A.
For lighting I use a 1.5 sq. mm cable, but automatic machine no more than 10A, because switches are designed for a current of no more than 10A.
You need to know that the machine passes current up to 1.13 times its nominal value, for as long as you like, and if the nominal value is exceeded up to 1.45 times, it can turn off only after 1 hour. And all this time the cable will heat up.
The cable cross-section should be selected correctly according to the hidden installation method, so that there is the necessary safety margin.
PUE clause 7.1.34. prohibits the use aluminum wiring inside buildings.

Thank you for your attention.

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 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 is capable of passing 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 greater 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. Particularly powerful consumers are not expected here, therefore, we also accept a socket group with a wire with a cross-section of 2.5 mm2.

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.