Wire and cable cross-section diagram. Calculation of cable cross-section by power. What is wire cross-section and how to determine it

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.

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

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.

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:

Supply voltage ( single-phase or three-phase).
Conductor material.
Load current measured in amperes ( A), or power - in ( kW).
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 for current, use the PUE tables.

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

Conductor cross-sectional area, mm²
	open	in one pipe
	open	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
	open	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:

Wire length, unit of measurement - m. As it increases, losses increase.
Cross-sectional area, measured in mm². As it increases, the voltage drop decreases.
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:

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.
Using PUE tables, the current cross-section of the wire is determined.
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.
We find the voltage drop from the relationship: ΔU=I*R.
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.

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The cross-section of the conductors of electrical wires and cables used to connect lighting and household appliances, power plants and various equipment depends on the amount of electrical power of these consumers and, accordingly, the electric current flowing through them. The value of the maximum permissible current flowing through the current-carrying core for different brands of wires and cables, in accordance with their cross-section and method of installation, is regulated by the “Rules for Electrical Installations” (PUE) Chapter 1.3 “Selection of conductors for heating, economic current density and corona conditions” . We will tell you about how to choose a cable for home electrical wiring, as well as a table of cable power by cross-section, which is useful for many jobs, in today’s publication website

PUE is the main document regulating all areas of work in electrical installations for various purposes

In order to determine the permissible cable cross-section, it is necessary to know the power of the load connected using it. To do this, you can use two methods:

collect information about connected devices using data sheets of these products or technical specifications posted on the Internet;
use average values for each category of household appliances.

The average values of various household appliances are given in the following table.

Device name	Electric power, kW
Dishwasher	1,8
Electric kettle	1,2
Oven	2,3
Hairdryer	1,3
Microwave	1,5
Iron	1,1
Air conditioner	4
Washing machine	0,5
TV	0,3
Fridge	0,2
Satellite TV	0,15
Computer	0,12
Printer	0,05
Monitor	0,15
Hand power tool	1,2

This table does not show all types of household appliances and tools, because... their range is quite large, so if you need to find the required values, you should turn to the Internet, where, using a “search engine,” you can find the power value of the required load object.

Knowing the power values of the electrical load, it is possible to calculate the value of the current that will flow through the conductors during their use. To do this, use the formula:

I=P/U , Where

P – power of connected household appliances and electric lighting;
U – voltage of the electrical network;
I – current flowing through current-carrying conductors when devices of a given power are turned on.

For your information! When performing this calculation, the power value is taken in kilowatts (kW), and when summing this value in Watts (W), the resulting value must be converted to kW, for which it should be divided by one thousand.

By calculating the current flowing through the conductor when connecting the maximum possible load in a given section of the electrical circuit, you can determine its cross-section.

Important! For copper and aluminum current-carrying conductors, the values of the maximum permissible current differ, so this must be taken into account when selecting the cross-section of the cable (wire).

Selecting the cross-section of copper or aluminum wire based on power and current

As can be seen from the formula (by which the electric current was determined), when a certain power is connected, the value of the current directly depends on the voltage of the electrical network at which the connected devices operate. In this regard, the values of the maximum permissible current at different voltage classes are given separately in the technical literature, as well as for different brands of current-carrying conductors, namely:

Today there is a wide range of cable products, with a cross-section of cores from 0.35 mm2. and higher.

If you choose the wrong cable cross-section for household wiring, the result can have two results:

An overly thick core will “hit” your budget, because... its linear meter will cost more.
If the conductor diameter is inappropriate (smaller than necessary), the conductors will begin to heat up and melt the insulation, which will soon lead to a short circuit.

As you understand, both the results are disappointing, so in front of and in the apartment it is necessary to correctly calculate the cable cross-section depending on the power, current strength and line length. Now we will look at each of the methods in detail.

Calculation of power of electrical appliances

For each cable there is a certain amount of current (power) that it can withstand when operating electrical appliances. If the current (power) consumed by all devices exceeds the permissible value for the conductor, then an accident will soon be unavoidable.

To independently calculate the power of electrical appliances in the house, you need to write down the characteristics of each appliance separately (stove, TV, lamps, vacuum cleaner, etc.) on a piece of paper. After this, all the values are summed up and the resulting number is used to select a cable with cores with the optimal cross-sectional area.

The calculation formula looks like:

Ptotal = (P1+P2+P3+…+Pn)*0.8,

Where: P1..Pn – power of each device, kW

Please note that the resulting number must be multiplied by a correction factor of 0.8. This coefficient means that only 80% of all electrical appliances will work at the same time. This calculation is more logical, because, for example, you will definitely not use a vacuum cleaner or hair dryer for a long time without a break.

Tables for selecting cable cross-section by power:

These are given and simplified tables; more accurate values can be found in paragraphs 1.3.10-1.3.11.

As you can see, for each specific type of cable the table values have their own data. All you need is to find the nearest power value and look at the corresponding cross-section of the cores.

So that you can clearly understand how to correctly calculate the cable power, we will give a simple example:

We calculated that the total power of all electrical appliances in the apartment is 13 kW. This value must be multiplied by a factor of 0.8, which will result in 10.4 kW of actual load. Next in the table we look for a suitable value in the column. We are satisfied with the figure “10.1” for a single-phase network (voltage 220V) and “10.5” if the network is three-phase.

This means that you need to choose a cross-section of cable cores that will power all the calculation devices - in an apartment, room or some other room. That is, such a calculation must be carried out for each outlet group powered from one cable, or for each device if it is powered directly from the panel. In the example above, we calculated the cross-sectional area of the input cable cores for the entire house or apartment.

In total, we select a cross-section with a 6-mm conductor for a single-phase network or a 1.5-mm conductor for a three-phase network. As you can see, everything is quite simple and even a novice electrician can cope with this task on his own!

Current load calculation

Calculation of cable cross-section by current is more accurate, so it is best to use it. The essence is similar, but only in this case it is necessary to determine the current load on the electrical wiring. To begin with, we calculate the current strength for each of the devices using formulas.

If the house has a single-phase network, you must use the following formula for calculation:For a three-phase network, the formula will look like:Where, P – power of the electrical appliance, kW

cos Phi - power factor

More details about the formulas associated with calculating power can be found in the article:.

We draw your attention to the fact that the values of the table values will depend on the conditions of laying the conductor. At , the permissible current loads and power will be significantly greater than at .

Let us repeat, any cross-section calculation is carried out for a specific device or group of devices.

Table for selecting cable cross-section for current and power:

Calculation by length

Well, the last way to calculate the cable cross-section is by length. The essence of the following calculations is that each conductor has its own resistance, which contributes as the length of the line increases (the greater the distance, the greater the losses). In the event that the loss value exceeds 5%, it is necessary to choose a conductor with larger conductors.

The following methodology is used for calculations:

It is necessary to calculate the total power of electrical appliances and current strength (we provided the corresponding formulas above).
The electrical wiring resistance is calculated. The formula is as follows: conductor resistivity (p) * length (in meters). The resulting value must be divided by the selected cable cross-section.

R=(p*L)/S, where p is the tabular value

We draw your attention to the fact that the length of the current must be doubled, because The current initially flows through one core, and then returns back through the other.

Voltage losses are calculated: the current is multiplied by the calculated resistance.

U losses =I load *R wires

LOSSES=(U losses /U nom)*100%

The amount of losses is determined: voltage losses are divided by the network voltage and multiplied by 100%.
The final number is analyzed. If the value is less than 5%, we leave the selected core cross-section. Otherwise, we select a “thicker” conductor.

Let's say we calculated that the resistance of our cores is 0.5 Ohm, and the current is 16 Amperes, then:

U losses =16*0.5=8 Volts

LOSSES=(8/220)*100%=0.03636*100%=3.6%

Resistivity table:

Often, before purchasing cable products, there is a need to independently measure its cross-section in order to avoid deception on the part of manufacturers, who, due to savings and setting a competitive price, may slightly underestimate this parameter.

It is also necessary to know how the cable cross-section is determined, for example, when adding a new energy-consuming point in rooms with old electrical wiring that does not have any technical information. Accordingly, the question of how to find out the cross-section of conductors always remains relevant.

General information about cable and wire

When working with conductors, it is necessary to understand their designation. There are wires and cables that differ from each other in their internal structure and technical characteristics. However, many people often confuse these concepts.

A wire is a conductor that has in its design one wire or a group of wires woven together and a thin common insulating layer. A cable is a core or a group of cores that has both its own insulation and a common insulating layer (sheath).

Each type of conductor will have its own methods for determining cross sections, which are almost similar.

Conductor materials

The amount of energy that a conductor transmits depends on a number of factors, the main one of which is the material of the current-carrying conductors. The following non-ferrous metals can be used as the core material of wires and cables:

Aluminum. Cheap and lightweight conductors, which is their advantage. They are characterized by such negative qualities as low electrical conductivity, a tendency to mechanical damage, high transient electrical resistance of oxidized surfaces;
Copper. The most popular conductors, which have a high cost compared to other options. However, they are characterized by low electrical and transition resistance at the contacts, fairly high elasticity and strength, and ease of soldering and welding;
Aluminum copper. Cable products with aluminum cores coated with copper. They are characterized by slightly lower electrical conductivity than their copper counterparts. They are also characterized by lightness, average resistance and relative cheapness.

Important! Some methods for determining the cross-section of cables and wires will depend specifically on the material of their conductor component, which directly affects the throughput power and current strength (method of determining the cross-section of conductors by power and current).

Measuring the cross-section of conductors by diameter

There are several ways to determine the cross-section of a cable or wire. The difference in determining the cross-sectional area of wires and cables will be that in cable products it is necessary to measure each core separately and summarize the indicators.

For information. When measuring the parameter under consideration with instrumentation, it is necessary to initially measure the diameters of the conductive elements, preferably removing the insulating layer.

Instruments and measurement process

The measuring instruments can be a caliper or a micrometer. Mechanical devices are usually used, but electronic analogues with a digital screen can also be used.

Basically, the diameter of wires and cables is measured using a caliper, since it is found in almost every household. It can also measure the diameter of wires in a working network, for example, a socket or panel device.

The diameter of the wire cross-section is determined using the following formula:

S = (3.14/4)*D2, where D is the diameter of the wire.

If the cable contains more than one core, then it is necessary to measure the diameter and calculate the cross-section using the above formula for each of them, then combine the result obtained using the formula:

Stotal= S1 + S2 +…+Sn, where:

Stotal – total cross-sectional area;
S1, S2, …, Sn – cross sections of each core.

On a note. To ensure the accuracy of the results obtained, it is recommended to take measurements at least three times, turning the conductor in different directions. The result will be the average.

In the absence of a caliper or micrometer, the diameter of the conductor can be determined using a regular ruler. To do this, you need to perform the following manipulations:

Clean the insulating layer of the core;
Wind the turns around the pencil tightly to each other (there should be at least 15-17 pieces);
Measure the winding length;
Divide the resulting value by the number of turns.

Important! If the turns are not laid evenly on the pencil with gaps, then the accuracy of the obtained results of measuring the cable cross-section by diameter will be in doubt. To increase the accuracy of measurements, it is recommended to take measurements from different sides. It will be difficult to wind thick wires onto a simple pencil, so it is better to resort to a caliper.

After measuring the diameter, the cross-sectional area of the wire is calculated using the formula described above or determined using a special table, where each diameter corresponds to the cross-sectional area.

It is better to measure the diameter of the wire, which contains ultra-thin cores, with a micrometer, since a caliper can easily break it.

The easiest way to determine the cable cross-section by diameter is using the table below.

Table of correspondence between wire diameter and wire cross-section

Diameter of conductor element, mm	Cross-sectional area of the conductor element, mm2
0,8	0,5
0,9	0,63
1	0,75
1,1	0,95
1,2	1,13
1,3	1,33
1,4	1,53
1,5	1,77
1,6	2
1,8	2,54
2	3,14
2,2	3,8
2,3	4,15
2,5	4,91
2,6	5,31
2,8	6,15
3	7,06
3,2	7,99
3,4	9,02
3,6	10,11
4	12,48
4,5	15,79

Segment cable cross-section

Cable products with a cross-section of up to 10 mm2 are almost always produced in a round shape. Such conductors are quite sufficient to meet the domestic needs of houses and apartments. However, with a larger cross-section of the cable, the input cores from the external electrical network can be made in segment (sector) form, and it will be quite difficult to determine the cross-section of the wire by diameter.

In such cases, it is necessary to resort to a table where the size (height, width) of the cable takes the corresponding value of the cross-sectional area. Initially, it is necessary to measure the height and width of the required segment with a ruler, after which the required parameter can be calculated by correlating the obtained data.

Table for calculating the area of an electric cable core sector

Cable type	Sectional area of the segment, mm2
	S	35	50	70	95	120	150	185	240
Four-core segment	V	-	7	8,2	9,6	10,8	12	13,2	-
Four-core segment	w	-	10	12	14,1	16	18	18	-
Three-core segmental stranded, 6(10)	V	6	7	9	10	11	12	13,2	15,2
Three-core segmental stranded, 6(10)	w	10	12	14	16	18	20	22	25
Three-core segmental single-wire, 6(10)	V	5,5	6,4	7,6	9	10,1	11,3	12,5	14,4
Three-core segmental single-wire, 6(10)	w	9,2	10,5	12,5	15	16,6	18,4	20,7	23,8

Dependence of current, power and core cross-section

It is not enough to measure and calculate the cross-sectional area of the cable based on the diameter of the core. Before installing wiring or other types of electrical networks, it is also necessary to know the capacity of the cable products.

When choosing a cable, you must be guided by several criteria:

the strength of the electric current that the cable will pass;
power consumed by energy sources;

Power

The most important parameter during electrical installation work (in particular, cable laying) is throughput. The maximum power of electricity transmitted through it depends on the cross-section of the conductor. Therefore, it is extremely important to know the total power of the energy consumption sources that will be connected to the wire.

Typically, manufacturers of household appliances, appliances and other electrical products indicate on the label and in the documentation accompanying them the maximum and average power consumption. For example, a washing machine can consume electricity ranging from tens of W/h during rinsing mode to 2.7 kW/h when heating water. Accordingly, a wire with a cross-section that is sufficient to transmit electricity of maximum power must be connected to it. If two or more consumers are connected to the cable, then the total power is determined by adding the limit values of each of them.

The average power of all electrical appliances and lighting devices in an apartment rarely exceeds 7500 W for a single-phase network. Accordingly, the cable cross-sections in the electrical wiring must be selected to this value.

So, for a total power of 7.5 kW, it is necessary to use a copper cable with a core cross-section of 4 mm2, which is capable of transmitting about 8.3 kW. The cross-section of the conductor with an aluminum core in this case must be at least 6 mm2, passing a current power of 7.9 kW.

In individual residential buildings, a three-phase power supply system of 380 V is often used. However, most equipment is not designed for such electrical voltage. A voltage of 220 V is created by connecting them to the network through a neutral cable with an even distribution of the current load across all phases.

Electric current

Often the power of electrical equipment and equipment may not be known to the owner due to the absence of this characteristic in the documentation or completely lost documents and labels. There is only one way out in such a situation - to calculate using the formula yourself.

Power is determined by the formula:

P = U*I, where:

P – power, measured in watts (W);
I – electric current strength, measured in amperes (A);
U is the applied electrical voltage, measured in volts (V).

When the strength of the electric current is unknown, it can be measured with control and measuring instruments: an ammeter, a multimeter, and a clamp meter.

After determining the power consumption and electric current, you can use the table below to find out the required cable cross-section.

Calculation of the cross-section of cable products based on current load must be carried out to further protect them from overheating. When too much electric current passes through conductors for their cross-section, destruction and melting of the insulating layer can occur.

The maximum permissible long-term current load is the quantitative value of the electric current that can pass the cable for a long time without overheating. To determine this indicator, it is initially necessary to sum up the powers of all energy consumers. After this, calculate the load using the formulas:

I = P∑*Ki/U (single-phase network),
I = P∑*Kи/(√3*U) (three-phase network), where:

P∑ – total power of energy consumers;
Ki – coefficient equal to 0.75;
U – electrical voltage in the network.

Tablitz for matching the cross-sectional area of copper conductorsconductor products current and power *

Section of cable and wire products	Electrical voltage 220 V		Electrical voltage 380 V
	Current strength, A	power, kWt	Current strength, A	power, kWt
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	50	11	40	26,4
10	70	15,4	50	33
16	90	19,8	75	49,5
25	115	25,3	90	59,4
35	140	30,8	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

*Important! Conductors with aluminum conductors have different values.

Determining the cross-section of a cable product is a particularly important process in which miscalculations are unacceptable. You need to take into account all factors, parameters and rules, trusting only your calculations. The measurements taken must coincide with the tables described above - if they do not contain specific values, they can be found in the tables of many electrical engineering reference books.

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Using the PUE table, you can select the correct cable cross-section for current. So, for example, if the cable is of a smaller cross-section, this can lead to premature failure of the entire wiring system or damage to the included equipment. Also, an incorrect choice of cable thickness can cause a fire, which will occur due to melting of the wire insulation when it overheats due to high power.

In the reverse process, when the cable thickness is taken with a significant power reserve, there may be an unnecessary waste of money to purchase a more expensive wire.

As practice shows, in most cases the current cable cross-section should be selected based on its density.

PUE and GOST tables

Current Density

When choosing a wire cross-section, you need to know some indicators. So, for example, the current density in a material such as copper ranges from 6 to 10 A/mm2. This indicator is the result of many years of experience by specialists and is adopted based on the basic rules governing the design of electrical installations.

In the first case, with a density of six units, the electrical network is provided for long-term operation. If the indicator is ten units, then it should be understood that network operation is not possible for a long time during periodic short turns on.

Therefore, it is necessary to select the thickness precisely according to this permissible indicator.

The above data is for copper cable. Aluminum wires are still used in many electrical networks. At the same time, copper cable has its undeniable advantages in comparison with the latter type of wire.

These include the following:

Copper cable has much greater softness and at the same time its strength is higher.
Products made from copper are not subject to oxidation processes for a longer period of time.
Perhaps the most important indicator of a copper cable is its higher degree of conductivity, and therefore a better indicator of current density and power.

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The most important disadvantage of such a cable is its higher price.

The current density indicator for aluminum wire is in the range from four to six A/mm2. Therefore, it can be used in less critical structures. This type of wiring was also actively used in the last century in the construction of residential buildings.

Carrying out current cross-section calculations

When calculating the working indicator of cable thickness, it is necessary to know what current will flow through the network of a given room. For example, in the most ordinary apartment it is necessary to sum up the power of all electrical appliances that are connected to the network.

As an example for calculation, we can give a standard table of power consumption by the main household appliances used in an ordinary apartment.

Based on the total power, the current that will flow through the network cables is calculated.

In this formula, P means the total power, measured in Watts, K1 is the coefficient that determines the simultaneous operation of all household appliances (its value is usually 0.75) and U is the voltage in the home network, usually equal to 220 Volts.

This current calculation indicator will help to estimate the required cross-section for the general network. In this case, it is also necessary to take into account the operating current density.

This calculation can be taken as an approximate choice. In this case, more accurate indicators can be obtained using a selection from a special PUE table. This PUE table is an element of special rules for the design of electrical installations.

Below is an example of a PUE table that can be used to select a section.

As you can see, such a PUE table, in addition to the dependence of cross-sections on the current indicator, also provides for taking into account the material from which the wires are made, as well as its location. In addition, the table regulates the number of cores and the voltage value, which can be either 220 or 380 Volts.

Current calculation using additional parameters

When calculating the cross section based on current using the PUE table, you can also use additional parameters.

For example, it is possible to take into account the core diameter. Therefore, when determining the cross-section of the conductor, special equipment called a micrometer is used. Based on its data, the thickness of each core is determined. Then, using the values of previously obtained currents and a special table, the final selection of the cross-sectional value of the wire core is made.

If the cable consists of several cores, then you should measure one of them and calculate its cross-section. After this, to find the final thickness value, the indicator obtained for one core is multiplied by their number in the wire.

The value of the cable cross-section obtained in this way using calculations and the PUE table will allow you to create wiring in a house or apartment that will serve the owners for quite a long period of time without the occurrence of emergency or emergency situations.