How to choose the correct cable cross-section for power. Calculation of wire cross-section by power and current density: rules, algorithm, electrical details

When repairing and designing electrical equipment, it becomes necessary to choose correctly. You can use a special calculator or reference book. But for this you need to know the load parameters and cable laying features.

The following requirements apply to electrical networks:

• safety;
• reliability;
• efficiency.

If the selected cross-sectional area of ​​the wire is small, then the current loads will not be large, which will lead to overheating. As a result, an emergency may occur that will damage all electrical equipment and become dangerous to the life and health of people.

If you install wires with a large cross-sectional area, then safe use is ensured. But from a financial point of view there will be cost overruns. The correct choice of wire cross-section is the key to long-term safe operation and rational use of financial resources.

A separate chapter in the PUE is devoted to the correct selection of a conductor: “Chapter 1.3. Selection of conductors based on heating, economic current density and corona conditions.”

The cable cross-section is calculated based on power and current. Let's look at examples. To determine what wire gauge is needed for 5 kW, you will need to use PUE tables (“ Rules for electrical installations“). This directory is a regulatory document. It states that the choice of cable cross-section is made according to 4 criteria:

1. Supply voltage ( single-phase or three-phase).
2. Conductor material.
3. Load current measured in amperes ( A), or power - in ( kW).
4. Cable location.

There is no meaning in the PUE 5 kW, so you have to choose the next larger value -- 5.5 kW. For installation in an apartment today it is necessary. In most cases, installation is by air, so a cross-section of 2.5 mm² is suitable from the reference tables. In this case, the maximum permissible current load will be 25 A.

The above reference book also regulates the current for which the input circuit breaker is designed ( VA). According to " Rules for electrical installations“, with a load of 5.5 kW, the VA current should be 25 A. The document states that the rated current of the wire that is suitable for a house or apartment should be an order of magnitude greater than that of VA. In this case, after 25 A there is 35 A. The last value must be taken as the calculated value. A current of 35 A corresponds to a cross section of 4 mm² and a power of 7.7 kW. So, the choice of the cross-section of the copper wire according to power is completed: 4 mm².

To find out what wire gauge is needed for 10 kW, let's use the reference book again. If we consider the case for open wiring, then we need to decide on the cable material and the supply voltage.

For example, for an aluminum wire and a voltage of 220 V, the nearest higher power will be 13 kW, the corresponding cross-section will be 10 mm²; for 380 V the power will be 12 kW and the cross-section will be 4 mm².

Choose by power

Before choosing a cable cross-section based on power, you need to calculate its total value and make a list of electrical appliances located in the territory to which the cable is laid. The power must be indicated on each of the devices; the corresponding units of measurement will be written next to it: W or kW ( 1 kW = 1000 W). Then you will need to add up the power of all equipment and get the total.

If you select a cable to connect one device, then only information about its energy consumption is sufficient. You can select wire cross-sections based on power in the PUE tables.

Table 1. Selection of wire cross-section based on power for cables with copper conductors

	For cable with copper conductors
	Voltage 220 V		Voltage 380 V
	Current, A	power, kWt	Current, A	power, kWt
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	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	260	171,6

Table 2. Selection of wire cross-section based on power for cables with aluminum conductors

Conductor cross-section, mm²	For cable with aluminum conductors
	Voltage 220 V		Voltage 380 V
	Current, A	power, kWt	Current, A	power, kWt
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	132,2

In addition, you need to know the network voltage: three-phase corresponds to 380 V, and single-phase corresponds to 220 V.

The PUE provides information for both aluminum and copper wires. Both have their advantages and disadvantages. Advantages of copper wires:

• high strength;
• elasticity;
• oxidation resistance;
• electrical conductivity is greater than that of aluminum.

Lack of copper conductors-- high price. In Soviet houses, aluminum electrical wiring was used during construction. Therefore, if a partial replacement occurs, it is advisable to install aluminum wires. The only exceptions are those cases when, instead of all the old wiring ( to the distribution board) a new one is installed. Then it makes sense to use copper. It is unacceptable for copper and aluminum to come into direct contact, as this leads to oxidation. Therefore, a third metal is used to connect them.

You can independently calculate the wire cross-section according to power for a three-phase circuit. To do this you need to use the formula: I=P/(U*1.73), Where P-- Power, W; U-- voltage, V; I-- current, A. Then the cable cross-section is selected from the reference table depending on the calculated current. If the required value is not there, then the closest one is selected, which exceeds the calculated one.

How to calculate by current

The amount of current passing through a conductor depends on the length, width, resistivity of the latter and on temperature. When heated, the electric current decreases. Reference information is given for room temperature ( 18°C). To select the cable cross-section by current, use the PUE tables (PUE-7 clause 1.3.10-1.3.11 PERMISSIBLE CONTINUOUS CURRENTS FOR WIRES, CORDS AND CABLES WITH RUBBER OR PLASTIC INSULATION).

Table 3. Electric current for copper wires and cords with rubber and PVC insulation

Conductor cross-sectional area, mm²
	open	in one pipe
		two single-core	three single-core	four single-core	one two-wire	one three-wire
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	-	-	-	-	-

A table is used to calculate aluminum wires.

Table 4. Electric current for aluminum wires and cords with rubber and PVC insulation

Conductor cross-sectional area, mm²	Current, A, for wires laid
	open	in one pipe
		two single-core	three single-core	four single-core	one two-wire	one three-wire
2	21	19	18	15	17	14
2,5	24	20	19	19	19	16
3	27	24	22	21	22	18
4	32	28	28	23	25	21
5	36	32	30	27	28	24
6	39	36	32	30	31	26
8	46	43	40	37	38	32
10	60	50	47	39	42	38
16	75	60	60	55	60	55
25	105	85	80	70	75	65
35	130	100	95	85	95	75
50	165	140	130	120	125	105
70	210	175	165	140	150	135
95	255	215	200	175	190	165
120	295	245	220	200	230	190
150	340	275	255	-	-	-
185	390	-	-	-	-	-
240	465	-	-	-	-	-
300	535	-	-	-	-	-
400	645	-	-	-	-	-

In addition to the electric current, you will need to select the conductor material and voltage.

For an approximate calculation of the cable cross-section for current, it must be divided by 10. If the resulting cross-section is not in the table, then it is necessary to take the nearest larger value. This rule is only suitable for cases where the maximum permissible current for copper wires does not exceed 40 A. For the range from 40 to 80 A, the current must be divided by 8. If aluminum cables are installed, then it must be divided by 6. This is because for to ensure equal loads, the thickness of the aluminum conductor is greater than that of copper. Each conductor is characterized by electrical resistance. This parameter is affected by:

1. Wire length, unit of measurement - m. As it increases, losses increase.
2. Cross-sectional area, measured in mm². As it increases, the voltage drop decreases.
3. Material resistivity (reference value). Shows the resistance of a wire measuring 1 square millimeter per 1 meter.

The voltage drop is numerically equal to the product of resistance and current. It is acceptable that the specified value does not exceed 5%. Otherwise, you need to take a cable with a larger cross-section. Algorithm for calculating wire cross-section based on maximum power and length:

1. Depending on power P, voltage U and coefficient cosф we find the current using the formula: I=P/(U*cosф). For electrical networks used in everyday life, cosф = 1. In industry, cosph is calculated as the ratio of active power to total power. The latter consists of active and reactive powers.
2. Using PUE tables, the current cross-section of the wire is determined.
3. We calculate the conductor resistance using the formula: Ro=ρ*l/S, where ρ is the resistivity of the material, l is the length of the conductor, S is the cross-sectional area. It is necessary to take into account the fact that current flows through the cable not only in one direction, but also back. Therefore the total resistance is: R = Ro*2.
4. We find the voltage drop from the relationship: ΔU=I*R.
5. Determine the voltage drop as a percentage: ΔU/U. If the obtained value exceeds 5%, then select the nearest larger cross-section of the conductor from the reference book.

Open and closed wiring

Depending on the placement, wiring is divided into 2 types:

• closed;
• open.

Today, hidden wiring is installed in apartments. Special recesses are created in the walls and ceilings to accommodate cables. After installing the conductors, the recesses are plastered. Copper wires are used. Everything is planned in advance, because over time, to build up electrical wiring or replace elements, you will have to dismantle the finishing. For hidden finishing, wires and cables that have a flat shape are often used.

When laid open, the wires are installed along the surface of the room. Advantages are given to flexible conductors that have a round shape. They are easy to install in cable channels and pass through the corrugation. When calculating the load on the cable, the method of laying the wiring is taken into account.

For correct and safe installation of wiring cables, it is imperative to make a preliminary calculation of the expected power consumption. Failure to comply with the requirements for selecting the cross-section of the cable used for wiring can lead to insulation melting and fire.

Calculating the cable cross-section for a specific electrical wiring system can be divided into several stages:

1. breakdown of electricity consumers by groups;
2. determining the maximum current for each segment;
3. selection of cable cross-section.

All consuming electrical appliances should be divided into several groups so that the total power consumption of one group does not exceed approximately 2.5-3 kW. This will allow you to select a copper cable with a cross-section of no more than 2.5 square meters. mm. The power ratings of some major household appliances are shown in Table 1.

Table 1. Power values ​​of major household appliances.

Consumers combined into one group must be geographically located in approximately the same place, since they are connected to the same cable. If the entire connected object is powered by a single-phase network, then the number of groups and distribution of consumers do not play a significant role. If the power supply is three-phase, then it is recommended to divide consumers into groups so that each phase receives approximately the same power.
Then the percentage of discrepancy can be calculated using the formula = 100% — (Pmin/Pmax*100%), where Pmax is the maximum total power per phase, Pmin is the minimum total power per phase. The lower the power discrepancy percentage, the better.

Calculation of the maximum current for each consumer group

Once the power consumption has been found for each group, the maximum current can be calculated. It is better to take the demand coefficient (Kc) equal to 1 everywhere, since the use of all elements of one group at the same time is not excluded (for example, you can turn on all household appliances belonging to one group of consumers at the same time). Then the formulas for single-phase and three-phase networks will look like:

Icalc = Pcalc / (Unom * cosφ)
for a single-phase network, in this case the network voltage is 220 V,

Icalc = Pcalc / (√3 * Unom * cosφ)
for three-phase network, network voltage 380 V.

When installing electrical wiring in recent decades, the method using. This is explained by a whole set of properties that a corrugated pipe has, but at the same time, when working with it, you must adhere to certain rules.

You can often come across both in theory and in practice the terms delta and star connection, phase and linear voltage - an interesting one will help you understand their differences.

The cosine value for household appliances and incandescent lighting is assumed to be 1, for LED lighting - 0.95, for fluorescent lighting - 0.92. The arithmetic mean cosine is found for the group. Its value depends on the cosine of the device that consumes the most power in a given group. Thus, knowing the currents in all sections of the wiring, you can begin to select the cross-section of wires and cables.

Selection of cable cross-section based on power

Once the calculated maximum current is known, you can begin selecting cables. This can be done in two ways, but the easiest way is to select the desired cable cross-section using the tabular data. The parameters for selecting copper and aluminum cables are given in the table below.

Table 2. Data for selecting the cross-section of a cable with copper conductors and a cable made of aluminum.

When planning electrical wiring, it is preferable to choose cables from the same material. Connecting copper and aluminum wires using conventional twisting is prohibited by fire safety rules, since when temperature fluctuates, these metals expand differently, which leads to the formation of gaps between the contacts and the generation of heat. If there is a need to connect cables made of different materials, then it is best to use terminals specially designed for this.

Video with formulas for calculating cable cross-section

Content:

Before connecting the load to the network, it is important to ensure that the supply cable cores are thick enough. If the permissible power is significantly exceeded, the insulation and even the core itself may be destroyed due to overheating.

Before calculating the cable cross-section by power, you should calculate the sum of the powers of the connected electrical appliances. In most modern apartments, the main consumers are:

• Refrigerator 300 W
• Washing machine 2650 W
• Computer 550 W
• Lighting 500 W
• Electric kettle 1150 W
• Microwave oven 700 W
• TV 160 W
• Water heater 1950 W
• Vacuum cleaner 600 W
• Iron 1750 W
• Total 10310 W = 10.3 kW

In total, most modern apartments consume approximately 10 kW. Depending on the time of day, this parameter can decrease significantly. However, when choosing a conductor cross-section, it is important to focus on a larger value.

You need to know the following: the calculation of cable cross-section for single-phase and three-phase networks is different. But in both cases, three parameters should be taken into account first:

• Current strength(I),
• Voltage(U),
• Power consumption (P).

There are also several other variables, their meaning varies from case to case.

Calculation of wire cross-section for a single-phase network

Calculation of wire cross-section by power is carried out using the following formula:

I = (P × K u) / (U × cos(φ))

Where,

• I- current strength;
• P- power consumption of all electrical appliances in total;
• K and- simultaneity coefficient, usually the standard value of 0.75 is taken for calculations;
• U- phase voltage, it is 220 (V), but can range from 210 to 240 (V);
• Cos(φ)- for household single-phase appliances this value is unchanged and equals 1.

If you need to quickly calculate the current, you can omit the value of cos (φ) and even K and. The resulting value will differ downward (by 15%) if a formula of this type is applied:

I=P/U

Having found the current using the calculation formula, you can safely proceed to selecting the power cable. More precisely, its cross-sectional area. There are special tables that present data that allows you to compare the current value, power consumption and cable cross-section.

The data varies greatly for conductors made from different metals. Today, for residential electrical wiring, only hard copper cable, aluminum is practically not used. Although in many old houses all lines are laid using aluminum.

The cross-section of the copper cable is selected according to the following parameters:

Calculation of wire cross-section in an apartment - Table

It often happens that the calculation results in a current that is between the two values ​​​​presented in the table. In this case, the nearest larger value must be used. If, as a result of calculations, the current value in a single-core wire is 25 (A), it is necessary to select a cross-section of 2.5 mm 2 or more.

Calculation of cable cross-section for a three-phase network

To calculate the cross-section of the power cable used in a three-phase network, you must use the following formula:

I = P / (√3 × U × cos(φ))

Where,

• I- current strength by which the cross-sectional area of ​​the cable will be selected;
• U- phase voltage, 220 (V);
• Cosφ- phase shift angle;
• P- an indicator of the total power of all electrical appliances.

Cosφ is very important in this formula. Since it directly affects the current strength. It is different for different equipment; most often this parameter can be found in the technical accompanying documentation, or it is indicated on the case.

The total power of consumers is found very simply: all powers are added up, the resulting value is used for calculations.

A distinctive feature of the choice of cable cross-sectional area for use in a three-phase network is that a thinner core can withstand a larger load. The required section is selected according to the standard table.

Selection of cable cross-section for a three-phase network - Table

Calculation of the wire cross-section for power in a three-phase network is carried out using a value such as √3 . This value is necessary to simplify the appearance of the formula.

U linear = √3 × U phase

Thus, if necessary, you can replace the product of the root and phase voltage with linear voltage. This value is equal to 380 (V) (U linear = 380 V).

When choosing a cable cross-section, both for a three-phase network and for a single-phase network, it is necessary to take into account permissible continuous current . This parameter indicates the current strength (measured in amperes) that the conductor can withstand for an unlimited amount of time. It is determined using special tables, they are available in the PUE. For aluminum and copper conductors, the data differs significantly.

Permissible current duration - Table

When the value specified in the table is exceeded, the conductor begins to heat up. The heating temperature is inversely proportional to the current strength.

The temperature in a certain area can increase not only due to an incorrectly selected cross-section, but also due to poor contact.For example, in the place where wires are twisted. Quite often this happens as a result of direct contact between aluminum cables and copper cables. The surface of metals oxidizes and becomes covered with an oxide film, which significantly impairs contact. This is where the cable gets hot.

In order for the electrical wiring to function flawlessly, it is important to select the correct cross-section of wires and make a competent power calculation, because other characteristics depend on these indicators. Current moves through wires in the same way that water moves through pipes.

The safety of the entire premises depends on the quality of the electrical installation work. Here it is especially important to choose the right parameter such as cable cross-section. In order to calculate the cable cross-section by power, you need to know the technical characteristics of all electricity consumers that will be connected to it. You should also consider the length of the wiring and how it will be installed.

Selecting a cable for electrical wiring

Current moves through wires just like water flows through a pipe. Just as it is impossible to place a larger volume of liquid into a water pipe, it is also impossible to pass more than a certain amount of current through a cable. In addition, the cost of the cable directly depends on its cross-section. The larger the cross-section, the higher the price of the cable.

A water pipe with a cross-section larger than necessary is more expensive, and one that is too narrow will not allow the required amount of water to pass through. The same thing happens with current, with the only difference being that choosing a cable with a cross-section smaller than the specified value is much more dangerous. Such a wire overheats all the time, and the current power in it increases. Because of this, the light in the room will randomly turn off, and in the worst case, a short circuit will occur and a fire will start.

There is nothing wrong with the fact that the selected cable cross-section will be larger than necessary. On the contrary, wiring where the power and cross-section exceed the required value will last much longer, but the cost of all electrical installation work will immediately increase by at least 2-3 times, because the main cost of power supply lies precisely in the cost of the wires.
A correctly selected section will allow:

• avoid overheating of wires;
• prevent short circuit;
• save on repair costs.

Calculation using formulas

A sufficient cross-sectional area will allow maximum current to pass through the wires without overheating. Therefore, when designing electrical wiring, first of all, find the optimal wire cross-section depending on the power consumption. To calculate this value, the total current must be calculated. It is determined based on the power of all devices connected to the cable.

To choose the optimal wire cross-section, knowing the power, you should remember Ohm's law, as well as the rules of electrodynamics and other electromechanical formulas. Thus, the current strength (I) for a section of a network with a voltage of 220 Volts, namely this voltage is used for a home network, is calculated by the formula:

I=(P1+P2+…+Pn)/220, where:

(P1+P2+…+Pn) – the total power of each electrical appliance used.

For networks with a voltage of 380 Volts:

I=(P1+P2+…+Pn)/ √3/380.

Power ratings of some household electrical appliances

electrical appliance	Power, W	electrical appliance	Power, W
Blender	up to 500	Heated towel rail	900-1700
Fan	750-1700	Dishwasher	2000
Video recorder	up to 500	Vacuum cleaner	400-2000
Storage water heater	1200-1500	Juicer	up to 1000
Instantaneous water heater	2000-5000	Washing machine	3000
Hood (ventilation)	500-1000	Washer and dryer	3500
Grill	1200-2000	Hand dryer	800
Oven	1000-2000	TV	100-400
Computer	400-750	Toaster	600-1500
Air conditioner	1000-3000	Humidifier	200
Coffee maker	800-1500	Iron	500-2000
Food processor	up to 100	Hair dryer	450-2000
Microwave	850	deep fryer	1500
Microwave oven combination	2650	Fridge	200-600
Mixer	up to 500	Electric shaver	up to 100
Meat grinder	500-1000	Electric lamps	20-250
Heater	1000-2400	Electric stove	8000-10000
Double boiler	500-1000	Electric kettle	1000-2000

But these are vague formulas and simplified calculations. Detailed calculations take into account the permissible loads, which for a copper cable will be 10 A/mm², and for an aluminum cable – 8 A/mm². The load determines how much current can pass through a unit area unhindered.

Correction of power indicators

Also, when calculating, an amendment is added in the form of the demand coefficient (Kс). This coefficient shows which devices are used on the network constantly, and which for a certain time. A special calculator and tables showing power calculations simplify all these calculations.

Demand coefficients of auxiliary receivers (Kс)

But what to do if the characteristics indicate 2 types of power: active and reactive? Moreover, the first of them measures in the usual kV, and the second - kVA. Our networks carry alternating current, the magnitude of which varies over time. Therefore, for all consumers there is active power, which is calculated as the average value of all instantaneous current and power variables. Devices with active power include incandescent lamps and electric heaters. For such energy consumers, the phases of current and voltage coincide. If the electrical circuit involves units that accumulate energy, for example, transformers or electric motors, then they may exhibit deviations in amplitude. Due to this phenomenon, reactive power arises.

For networks where there is reactive and active power, one more correction must be taken into account - the power factor (cosφ) or the reactive component.

Thus, the formula is obtained:

S= Kс*(P1+P2+…+Pn)/(220*cosφ*Рд), where:

• S – cross-sectional area,
• Рд – permissible load value.

In addition, possible current power losses that occur during passage through the wires are considered. When using a cable with several cores, you need to multiply the loss by the number of these cores.

Important! For all these calculations you will need not just a calculator, but also deep knowledge of physics. It will not be possible to make an accurate calculation right away without theoretical knowledge.

Finding area by diameter

Sometimes even a scrupulous calculation does not help; a short circuit occurs in the circuit. This is due to the fact that the stated technical characteristics often do not correspond to the actual value. Therefore, in order to find out how to make a power calculation, it is important to be sure that the store will offer a suitable electrical wire cross-section. To do this, we use a simple formula:

S=0.785d 2 , where:

• d is the diameter of the core;
• S – cross-sectional area.

You can determine the exact diameter of the wire and calculate the cross-section using a caliper or a micrometer, which is more accurate.

If the cable consists of several thin wires, then first look at the diameter of one of them, and then multiply the obtained data by their number:

Stotal=n*0.785di 2, where:

• di is the area of ​​an individual wire;
• n – number of wires;
• Stotal – total cross-sectional area.

Tables for calculations

It is not entirely correct to resort to complex calculations for calculations every time. The industry produces wires of a certain cross-section. If, after accurate calculations and calculations, the cable cross-section for power is 3.2 square millimeters, then it will not be possible to find such a wire, because there are wires with a cross-section of 2.5 mm 2, 3 or 4 mm 2.

Attention! In order to find out the cable cross-sections, you need a table where all the data is regulated and compiled in accordance with the PUE - rules for the design of electrical installations.

In order to determine the cable cross-section at a known load, you need to:

• calculate the current strength;
• round up to a higher value according to the data in the table;
• then find the closest standard section size.

Permissible continuous current for wires and cords with rubber and polyvinyl chloride insulation with copper conductors

Current cross-section provo- conductor, 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	-	-	-	-	-

It's easy to make this calculation. First you need to determine the total power of all electrical appliances used in the network. For this you will need a table, and the missing data for each electrical appliance can be taken from the product passport. The resulting amount must be multiplied by 0.8 - the demand coefficient, if the electrical appliances will not be used all at once, or left unchanged during constant operation. Now the resulting value must be divided by the voltage in the network and add a constant value of 5. This will be the required current indicator. Let's say the current is 20A.

Note! In residential areas, three-wire electrical wiring and enclosed wiring are used. This must be remembered when calculations are made using the table.

Next you will need a table from the PUE. We take the column where the current values ​​for a three-core core are given, and select the closest ones: 17 and 22. It is better to take the cross-section with a margin, so in the example under consideration the required value will be equal to 22. As you can see, this value corresponds to a three-core cable with a cross-section of 2 mm 2 .

You can additionally consider how this calculation is made for an aluminum cable according to the PUE, although for safety reasons such wires cannot be used in residential buildings. Old houses still have aluminum wiring, but it is recommended to replace it during major renovations. In addition, aluminum electrical wire crumbles at bends and has less conductivity at the joints. Exposed parts of aluminum quickly oxidize in air, which leads to significant losses of electricity at the joints.

Calculator

Today, specialists use not only a table, but also a special calculator to determine the cross-section. This calculation greatly simplifies the calculations. The calculator is easy to find on the Internet. To calculate the cross-sectional size, you need to know the following parameters:

• AC or DC current is used;
• wire material;
• power of all devices used;
• mains voltage;
• power supply system (single or three-phase);
• type of wiring.

These indicators are loaded into the calculator and the required cross-sectional value of the wires is obtained.

Calculation by length

Calculating the cross-section along the length is important when constructing industrial-scale networks, when areas are subject to constant heavy load, and the cable must be pulled over significant distances. After all, during the passage of current through the wires, power losses occur due to electrical resistance in the circuit. Power loss (dU) is calculated as follows:

dU = I*p*L/S, where:

• I – current strength;
• p – resistivity (copper – 0.0175, aluminum – 0.0281);
• L – cable length;
• S is the cross-sectional area we have already calculated.

According to the technical specifications, the maximum voltage drop along the length of the wire should not exceed 5 percent. Otherwise, you should select a wire with a larger cross-section.

Peculiarities

There are certain standards according to which the cable cross-section is calculated. If you are not sure which electrical wire is needed, then you can use these rules: electrical appliances in the apartment are divided into lighting group and others; for powerful electrical appliances, for example, washing machines or electric ovens, a connection from separate wires is used; the standard wire cross-section for a lighting group in an apartment is 1.5 mm 2, and for other wires – 2.5 mm 2. Such standards are used because the rated power of the incoming current cannot be greater.

Three-phase current is required when high-power industrial devices are used. Therefore, to determine the cable cross-section at enterprises, it is necessary to accurately calculate all additional coefficients, and also be sure to take into account power losses and voltage fluctuations. For electrical work in an apartment or private house, such complex calculations are not carried out.

For installation of acoustic equipment, wires with minimal resistance are used. This is necessary in order to eliminate distortion as much as possible and improve the quality of the transmitted signal. Therefore, for speaker systems, cables measuring 2x2.5 or 2x1.5 with a length of at least 3 meters are better suited, and the subwoofer is connected with the shortest cable 2.5-4 mm 2.

Examples

Let's consider a general diagram for choosing the cable cross-section in an apartment:

• First you need to determine the places where the sockets and lighting fixtures will be located;
• Next, you need to determine which devices will be used at each output;
• Now you can draw up a general connection diagram and calculate the cable length, adding at least 2 cm for wire connections;
• Based on the data obtained, we calculate the size of the cable cross-section using the formulas given above.

I=2400W/220V=10.91A, round up and get 11A.

As we already know, different coefficients are used to accurately determine the cross-sectional area, but almost all of this data refers to a network with a voltage of 380V. To increase the safety margin, we add another 5A to our current value:

For apartments, three-core cables are used. The table will show a current value close to our 16A, it will be 19A. We find that to install one washing machine you need a wire with a cross-section of at least 2 mm 2.

General theory

To determine the optimal cable cross-section for domestic needs, the following rules are generally used:

• sockets require wires with a cross section of 2.5 mm²;
• for lighting – 1.5 mm²;
• for devices with increased power – 4-6 mm².

If there are doubts about the calculation of the cross-section, then the PUE table is used. To determine the exact data on the cable cross-section, all factors affecting the passage of current through the circuit are taken into account. These include:

• type of wire insulation;
• length of each section;
• laying method;
• temperature regime;
• humidity;
• permissible value of overheating;
• difference in power of current receivers in one group.

All these indicators make it possible to increase the efficiency of energy use on an industrial scale, as well as to avoid overheating.

Selection of section. Video

In this video, the master shares his experience in choosing the cable cross-section and machine rating. He points out possible mistakes and gives practical advice to beginners.

If after reading the article you still have any doubts, then the table or calculator described above will help you find the exact power cross-section of the wire.

Cable power table required to correctly calculate the cable cross-section, if the power of the equipment is large and the cable cross-section is small, then it will heat up, which will lead to the destruction of the insulation and loss of its properties.

To calculate the conductor resistance, you can use the conductor resistance calculator.

For the transmission and distribution of electric current, the main means are cables; they ensure the normal operation of everything related to electric current, and how good this work will be depends on the right choice cable cross-section by power. A convenient table will help you make the necessary selection:

Current cross-section conductive lived mm
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt

Section Toko- conductive lived mm	Aluminum conductors wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt

But in order to use the table, you need to calculate the total power consumption of devices and equipment that are used in a house, apartment or other place where the cable will be laid.

Example of power calculation.

Let's say you are installing closed electrical wiring in a house using an explosive cable. You need to write down a list of equipment used on a piece of paper.

But how now find out power? You can find it on the equipment itself, where there is usually a label with the main characteristics recorded.

Power is measured in Watts (W, W) or Kilowatts (kW, KW). Now you need to write down the data and then add it up.

The resulting number is, for example, 20,000 W, which would be 20 kW. This figure shows how much energy all electrical receivers together consume. Next, you should consider how many devices will be used simultaneously over a long period of time. Let’s say it turns out to be 80%, in which case the simultaneity coefficient will be equal to 0.8. We calculate the cable cross-section based on power:

20 x 0.8 = 16 (kW)

To select a cross-section, you will need a cable power table:

Current cross-section conductive lived mm	Copper conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt
10		15.4

If the three-phase circuit is 380 Volts, then the table will look like this:

Current cross-section conductive lived mm	Copper conductors of wires and cables
	Voltage 220V		Voltage 380V
	Current. A	Power. kW	Current. A	Power, kWt
				16.5
10		15.4

These calculations are not particularly difficult, but it is recommended to choose a wire or cable with the largest cross-section of conductors, because it may be that it will be necessary to connect some other device.

Additional cable power table.