Table of copper cables by current. Calculation of cable and wire cross-sections for power and current
The cut-off cross-section of the cable is standardized in all countries. This applies to both the CIS countries and Europe. This issue is regulated in our country by the document “Rules for the Construction of Electrical Installations,” which are called PUE. Calculation of cable cross-section by power is selected using special tables. Of course, many calculate the necessary conductor parameters “by eye,” but this is not entirely correct. This indicator may be different for each apartment. This is due to the number of electrical consumers and their power. Without proper calculation, many unpleasant situations can occur, costly repairs of both wiring and apartments.
Cable arrangement
To determine the cable cross-section by power, you should understand its principle and design. It can be compared, for example, with a water or gas pipeline. In the same way as through these communications, a flow flows through an electrical conductor. Its power limits the cross-section of the conductor.
The cable cross-section using the power indicator can be performed incorrectly in two cases:
- The current carrying channel will be too narrow. This will lead to an increase in current density and, consequently, to overheating of the insulation. Over time, this state of the conductor will be characterized by the presence of weak points where leakage is possible. This condition of the channel can cause a fire.
- The current-carrying wire is too wide. This is certainly not the worst option. The spaciousness of transportation of the electrical flow will allow for more functional and durable use of the conductor. However, as the cross-section increases, the cost of the cable also increases.
The first option poses a danger to life, health and property. The second method is safe, but the materials will be quite expensive to purchase.
Easy way
Calculation of cable cross-section by power is based on the well-known law developed by Ohm. It tells you that the current flow multiplied by the voltage will equal the power. Voltage in everyday life is considered a constant value. In a single-phase network it is equal to 220 V. Therefore, to determine the cable cross-section based on current and power, only two variables remain.
Next, the current values and the expected load are calculated. Moreover, the cable size based on its power can be selected according to the PUE table. This indicator is calculated for the wire suitable for the sockets. Traditionally, for lighting lines, a wire with a cross section of 1.5 mm 2 is laid.
However, it happens that devices such as a hair dryer, microwave, electric kettle, etc. are connected to the socket group. It is necessary to distribute the load and correctly calculate the cable cross-section based on power indicators, correlating the diameter and load.
If it is not possible to separate the socket groups, then many electricians will recommend immediately installing a cable with a copper core of up to 6 mm 2.
Sectional area and diameter
Calculation of cable cross-section by power, diameter and load are not equivalent concepts. The first indicator is calculated in mm 2, and the second - simply in mm. You can select the power and permissible current from the table both according to the cable cross-section and its diameter.
If the table takes into account only the size of the cross-sectional area in mm 2, and there is data only on the cable diameter, the missing indicator can be found using the following formula:
S = 3.14D2/4 = 0.785D2,
where: S is the wire cross-section, and D is the diameter.
If the cross-section of the wire is not round, but rectangular, its cross-sectional area is calculated by multiplying the length by the width (just like the area of a rectangle).
Load Based Calculation
The easiest way to calculate the cable cross-section is by summing the powers of all units that will be connected to the line. To do this, you will need to perform a certain sequence of actions.
First, it is determined which electrical appliances will be used in the home, which of them will likely function simultaneously. Next, you need to look at the technical data sheets of each of these units. It will be necessary to calculate the sum of the powers of those electrical consumers that must operate simultaneously.
Then the figure obtained as a result of the calculations is rounded up. This will ensure a safe supply of power for the electrical wiring. The cross-section of the wire or cable is calculated further using PUE tables.
In a similar way, you can summarize the current strength, which is indicated in the data sheets of electrical equipment. Rounding and searching is performed using the power calculation table.
Table of power, current and cross-section of copper wires
According to the PUE, in residential buildings it is necessary to use only copper conductors for wiring. The power supply for some electrical equipment, which belongs to engineering types of receivers, can be connected to the network using aluminum conductors with a cross-section of at least 2.5 mm 2.
Table of power, current and cross-section of aluminum wires
The specialist will also be able to make correction factors based on the type of wire location, ambient temperature, for a cable in the ground, etc. The table for calculating cable power, cross-section or current applies to conductors in plastic or rubber insulation. These include such common brands as GDP, PVS, PPV, VPP, AVVG, VVG, APPV, etc. Non-insulated or paper-screened cables must be calculated according to the table relating to them.
Length and section
Calculation of the cable cross-section by power simply must be used to determine its length. This data is important when creating long extension cords. The exact values obtained must be increased by 10-15 cm. This margin is necessary for switching using soldering, welding or crimping.
In construction, the cable cross-section is calculated based on power and length at the electrical wiring design stage. This is very important, especially for those communications that will be subject to significant or additional loads.
In everyday life, the wire length is calculated using the following formula:
I=P/U*cosφ, where:
- P - power (W);
- I - current strength (A);
- U - voltage (V);
- cosφ is a coefficient that is equal to 1.
The cable cross-section must first be found in the table. The formula will help determine the correct wire length.
Current Density
The current strength varies in the range of 6-10 A, which was determined experimentally. This value is calculated for the current flowing through 1 mm 2 of copper conductor.
This statement means that the calculation of the cable cross-section for power and current takes as a basis a copper cable with a cross-sectional area of 1 mm 2, through which a current of 6 to 10 A can flow without melting or overheating to the household electrical appliances awaiting it.
According to the PUE code, a reserve of 40% is allocated for each wire for overheating that is safe for the sheath. If a value of 6 A characterizes the operation of the presented conductor for an infinitely long term without time limits, then a value of 10 A is suitable for short-term current flow through the core.
If a current of 12 A flows through a 1 mm 2 copper conductor, it will be cramped in such a conductor. This will lead to an increase in current density. The core will begin to heat up and melt the insulation.
Therefore, such calculations are required when choosing a cable cross-section for each type of wiring.
Having familiarized yourself with the methods that allow you to calculate the cable cross-section based on power and current, you can install or repair old wiring that will last a long time and will be completely safe for people living in the house. Many fairly simple but effective methods will help you accurately determine the required cross-sectional size for the electrical network.
Calculation of wire cross-section is a very important component of high-quality and reliable electrical wiring. After all, these calculations include the power consumption of electrical equipment and the long-term permissible currents that the wire can withstand in normal operating mode. In addition, we all want to have a guarantee and be confident in the electrical and fire safety of electrical wiring, so wire cross section calculation is so important.
Let's see what the wrong choice of wire cross-section can lead to.
In most cases, electricians currently working on the market in this service sector do not bother themselves with performing any calculations at all, but simply overestimate or underestimate the cross-section of the wire. This is usually due to the fact that, after a long time after graduating from educational institutions, they do not remember how to do this, since the acquired knowledge was not consolidated in practice in a timely manner. For the most part, this knowledge is possessed by a certain portion of power engineers and chief engineers, and this is due to the fact that their knowledge is exploited in this direction every day.
If the wire cross-section is less than required
Let's consider an example if the wire cross-section is underestimated, that is, less power consumption is selected.
This case is the most dangerous of all those considered, as it can lead to damage to electrical equipment, fire, electric shock to people, and often death. Why this happens is very simple. Let's say we have an electric water heater with a power of 3 kW, but the wire installed by a specialist can withstand only 1.5 kW. When you turn on the water heater, the wire will become very hot, which will eventually lead to damage to the insulation, and subsequently to its complete destruction, and a short circuit will occur.
If the wire cross-section is larger than required
Now, let's look at an example with an oversized wire cross-section, chosen larger than what is required for the equipment. People even have all sorts of sayings about reserve, they say it’s not superfluous. Within reasonable limits, it is really not superfluous, but it will cost much more than required. For the 3 kW water heater given in the example above, according to calculations, we require a wire cross-section of 2.5 mm 2, look at table 1.3.4 given in the PUE (electrical installation rules). And in our case, let’s say a 6 mm 2 wire was used, the cost of this wire will be 2.5 times higher than 2.5 mm 2, let’s say 2.5 costs 28 rubles, and 6 costs 70 rubles per meter. We will need, say, 20 meters, in the first case we will spend 560 rubles, and in the second 1400 rubles, the difference in money is obvious. Just imagine, if you over-wire the entire apartment, how much money you will throw away. Hence the question, do you need such a reserve?
Summing up the interim results, we learned that incorrect calculation of the wire cross-section has very unpleasant, and in some cases, serious consequences, so it is simply necessary to approach the choice of wire cross-section correctly, competently and seriously.
Formula for calculating wire cross-section
I calculated =P/U nom
where I calculated – calculated current,
P – equipment power,
U nom – rated voltage = 220 volts
For example, let's calculate a 3 kW electric water heater.
3 kW = 3000 W, I calculated =3000/220=13.636363 ..., round I calculation = 14 A
There are also various correction factors depending on the environmental conditions and the laying of the wire, as well as the coefficient of repeated short-term switching on. To a greater extent, these coefficients are important in three-phase networks of 380 volts in production, where large starting currents are present. And in our case, we have household electrical appliances designed for a voltage of 220 volts, so we will not calculate it, but we will definitely take it into account and determine its average value equal to 5 A and add it to the calculated current.
As a result, I calculation = 14 +5 = 19 A,
The wire used is three-core copper (phase, neutral, ground), see the table.
Table of cross-section of copper wires according to long-term permissible current (PUE table 1.3.4)
If the value is in the interval between two currents of different sections, in our case 15 A and 21 A, we always take the larger one. The calculated wire cross-section required to connect a 3 kW water heater is 2.5 mm 2.
So, using the 3 kW water heater shown in the example, we calculated the cross-section of the wires and found out why it is impossible to underestimate and overestimate the cross-section of the wires. We learned how to determine long-term permissible currents, as well as choose the correct wire cross-section.
Similarly, according to the formula, you can also perform this, thanks to which you will achieve optimal illumination without straining your eyesight and high-quality distribution of light flux.
By calculating the wire cross-section with your own hands, you will save:
- When purchasing wires, the cost of the wire increases with the cross-section. For example, 1 meter of a non-flammable wire of a brand that has proven itself quite well in the installation of internal electrical wiring with a cross-section of 1.5 squares costs 15 rubles, and the same wire with a cross-section of 2.5 squares costs 23 rubles, the difference is 8 rubles per meter, from 100 meters this is already 800 rubles.
- On the purchase of protection devices, circuit breakers, RCDs. The higher the operating current of the device, the higher the price. For example, a single-pole circuit breaker for 16 Amps costs 120 rubles, and for 25 Amps it costs 160 rubles, a difference of 40 rubles. The average power panel has about 12 circuit breakers, each costing 40 rubles, the total will be 480 rubles. The difference in the cost of the RCD will be even greater, about 200-300 rubles.
In electrical engineering, such quantities as the cross-section of the wire and the load are of great importance. Without this parameter, it is impossible to carry out any calculations, especially those related to the laying of cable lines. A table of the dependence of power on wire cross-section, used in the design of electrical equipment, helps to speed up the necessary calculations. Correct calculations ensure the normal operation of devices and installations and contribute to the reliable and long-term operation of wires and cables.
Rules for calculating cross-sectional area
In practice, calculating the cross-section of any wire does not present any difficulty. It is enough just to use a caliper, and then use the resulting value in the formula: S = π (D/2)2, in which S is the cross-sectional area, the number π is 3.14, and D is the measured diameter of the core.
Currently, predominantly copper wires are used. Compared to aluminum ones, they are more convenient to install, durable, have a significantly smaller thickness, with the same current strength. However, as the cross-sectional area increases, the cost of copper wires begins to increase, and all the advantages are gradually lost. Therefore, when the current value is more than 50 amperes, it is practiced to use cables with aluminum conductors. Square millimeters are used to measure wire cross-section. The most common indicators used in practice are areas of 0.75; 1.5; 2.5; 4.0 mm2.
Table of cable cross-section by core diameter
The main principle of calculations is that the cross-sectional area is sufficient for the normal flow of electric current through it. That is, the permissible current should not heat the conductor to a temperature above 60 degrees. The voltage drop should not exceed the permissible value. This principle is especially relevant for long-distance power lines and high current. Ensuring the mechanical strength and reliability of the wire is achieved through the optimal thickness of the wire and protective insulation.
Wire cross-section for current and power
Before considering the ratio of cross-section and power, you should focus on an indicator known as the maximum operating temperature. This parameter must be taken into account when choosing the cable thickness. If this indicator exceeds its permissible value, then due to strong heating, the metal cores and insulation will melt and collapse. Thus, the operating current for a particular wire is limited by its maximum operating temperature. An important factor is the time during which the cable can function in such conditions.
The main influence on the stable and durable operation of the wire is the power consumption and. For speed and convenience of calculations, special tables have been developed that allow you to select the required cross-section in accordance with the expected operating conditions. For example, with a power of 5 kW and a current of 27.3 A, the cross-sectional area of the conductor will be 4.0 mm2. The cross-section of cables and wires is selected in the same way if other indicators are available.
The influence of the environment must also be taken into account. When the air temperature is 20 degrees higher than the standard, it is recommended to select a larger section, the next one in order. The same applies to the presence of several cables contained in one bundle or the operating current value approaching the maximum. Ultimately, the table of the dependence of power on the wire cross-section will allow you to select suitable parameters in case of a possible increase in the load in the future, as well as in the presence of large starting currents and significant temperature differences.
Formulas for calculating cable cross-section
The smaller cross-section of the copper wire allows higher currents to pass and, accordingly, is designed for increased power or load.
This feature is due to low resistance values, which makes it possible to use a copper core in the home in the presence of a voltage of not only 220 V, but also 380 Volts.
Electrical cable products differ in the type of insulation, cross-sectional diameter and material of the conductor.
These parameters determine not only the area of use, but also the basic operating conditions.
The working element of any copper cable product is represented by a conductive core made from electrical copper.
In this case, several insulated cores are enclosed in one common shell. The outer covering is represented by the so-called “armor”, or a special protective screen.
The undeniable advantages of copper cable products are presented:
- high thermal conductivity;
- good current conductivity;
- plasticity and flexibility;
- resistance to kinking or twisting;
- ease of self-installation;
- duration of operation;
- stability to corrosive changes;
- minimal risk of fire.
Copper core
When choosing a cable product, you should pay attention to the markings. Laying in tunnels, in the open air and in the ground, is carried out with armored copper cable having durable double insulation. The mark “ng-LS” indicates the high fire safety ratings of the product.
It should be noted that single-core copper products are most often used when installing stationary wiring, and a multi-core conductor is in demand when it is necessary to use increased flexibility and elasticity, as well as resistance to vibration.
The cross-section of the copper wire is marked with the first number following the letter designation of the conductor type.
Wiring with copper conductors is used for internal and external installation in residential premises and office buildings, in industrial and production complexes, due to its high technical and quality characteristics.
Selection of wire cross-section
Copper is a reliable material with sufficient resistance to bending, a high level of electrical conductivity, and low susceptibility to corrosive changes. It is for this reason that, under conditions of the same level, a smaller cross-section of the copper core is provided compared to aluminum cable products.
The purchase of a copper-type electrical wire is carried out with a certain reserve cross-section, which reduces the risk of overheating as a result of an increase in load when connecting new volatile devices.
Cable VVGng 4x4 0.66 kV
It is important that the cross-section fully corresponds to the maximum load, as well as the current value for which automatic protective devices are designed.
The current value is one of the main indicators that influences the calculation of the wire cross-sectional area in copper cable products. A certain area determines the throughput of current over a long period of time. This parameter is called long-term permissible load. In this case, the cross-section of the copper core is the total cut area of the central part conducting current to consumers.
Determined by the main dimensions measured using a caliper:
- for a circle - S = πd 2 / 4;
- for a square - S = a 2;
- for a rectangle - S = a × b;
- for a triangle - πr 2 / 3.
Power 16-core cable
Standard design symbols: radius (r), diameter (d), width (b) and length (a) of the section, as well as π = 3.14. As a rule, the standard cross-section of the input cable is 4-6 mm 2, the wiring for connecting the socket group is 2.5 mm 2, and the cross-sectional area for connecting the main lighting system is about 1.5 mm 2.
Before installing a copper conductor, it is necessary to take into account the specific operating conditions and the expected maximum current load that will flow through the electrical wiring for a long time.
Calculation of wire cross-section
To independently determine the rated current value, you need to calculate the maximum power of all connected volatile devices.
Given the already known indicators of the power consumed by the devices, the current strength is calculated.
Standard calculation formula for a single-phase 220 V network:
I = P × K and / U × cos φ
- P - total power indicators consumed by all connected electrical appliances (W);
- U - power supply voltage indicators (V);
- K and - simultaneity coefficient equal to 0.75;
- cos φ - indicator for connected household energy-dependent appliances.
Standard calculation formula for a 380 V electrical network:
I = P / √3 × U × cos φ
After calculating the current value, you can easily determine the cross-section of the copper wire using tabular data for this purpose.
You need to select the cable cross-sectional area taking into account the current value and the required power indicators, using the table and rounding the obtained values up with the addition of 15-20% margin.
Cross-section of copper wire by power: table
Tabular data is the most convenient to use and most accurate, therefore experts recommend determining the cross-section of a copper cable product in accordance with the power indicators in the table.
| For voltage 220 V | For voltage 380 V | Copper core cross-section | ||
| Power | Current | Power | Current | |
| 4.1 kW | 19 A | 10.5 kW | 16 A | 1.5 mm |
| 5.9 kW | 27 A | 16.5 kW | 25 A | 2.5 mm |
| 8.3 kW | 38 A | 19.8 kW | 30 A | 4.0 mm |
| 10.1 kW | 46 A | 26.4 kW | 40 A | 6.0 mm |
| 15.4 kW | 70 A | 33.0 kW | 50 A | 10.0 mm |
| 18.7 kW | 80 A | 49.5 kW | 75 A | 16.0 mm |
| 25.3 kW | 115 A | 59.4 kW | 90 A | 25.0 mm |
| 29.7 kW | 135 A | 75.9 kW | 115 A | 35.0 mm |
| 38.5 kW | 175 A | 95.7 kW | 145 A | 50.0 mm |
| 47.2 kW | 215 A | 118.8 kW | 180 A | 70.0 mm |
| 57.2 kW | 265 A | 145.2 kW | 220 A | 95.0 mm |
| 66.0 kW | 300 A | 171.6 kW | 260 A | 120 mm |
How to determine the cross-section for a stranded wire?
Stranded copper wires are conductors whose cross-section is represented by several cores, which in some brands of cable products are intertwined with each other. any stranded wire is calculated using the standard formula S = π × d²/4.
In this case, the total cross-sectional area of a copper cable product will be the sum of the cross-sectional area of all its cores.
An assessment of the load capacity of a stranded wire can be made without measuring the diameter of each individual conductor.
In this case, you need to measure the overall diameter of the multi-core cable product, and then use the standard increase factor of 0.91 in the formula.
The diameter of copper wires can be measured using a caliper or a micrometer.
Maximum flexibility and a high level of elasticity are observed in copper conductors, the cores of which are woven into a dense thread.
As a result of the use of special terminals, the connection of multi-core conductors acquires high reliability and lower current resistance, but in high-frequency electrical circuits the use of such cable products is limited.
Find out the cable cross-section by power and wire length. We use an effective online wire diameter calculator. Cables are fundamental elements in the process of transmitting and distributing current. They play an important role in connecting electricity, which is why it is necessary to accurately and accurately calculate the cable cross-section according to the length and load power in order to create favorable conditions for the uninterrupted flow of electricity and avoid negative emergency consequences.
If, when designing and developing an electrical network, the wrong wiring diameter is chosen, then overheating and failure of various electrical equipment are possible. The cable insulation will also be damaged, which will lead to a short circuit and fire. There will be significant costs to restore not only the electrical wiring, but also all the electrical appliances in the room. To avoid this, you need to wisely select the cable cross-section in terms of power and length.
Online power cable selection calculator
Attention! If the data is entered incorrectly, the calculator may produce inaccurate values; for clarity, use the table of values below.
On our website you can easily make the necessary calculation of the wiring diameter in a few seconds, using a ready-made program to obtain data on the cross-section of the cable core.
To do this, you need to enter several individual parameters into the finished table:
- power of the proposed facility (total load indicators of all electrical appliances used);
- select the rated voltage (most often single-phase, 220 V, but sometimes three-phase - 380 V);
- indicate the number of phases;
- core material (technical characteristics of the wire, there are two compositions - copper and aluminum);
- line length and type.
Be sure to include all values. After that, click on the “calculate” button and get the finished result.
This value ensures that when calculating the cable cross-section by online power, the wire will not overheat under operating load. Ultimately, it is important to take into account the factor of voltage drop on the wire cores, while selecting parameters for a particular line.
Table for selecting wire cross-section depending on power (W)
How to independently calculate the cable cross-section along the length?
In domestic conditions, such data is necessary when making extension cords over long distances. However, even with accurately obtained results, you need to leave 10-15 cm in reserve for connecting wires (using welding, soldering or crimping).
In industry, the formula for calculating cable cross-section by power and length is used at the network design stage. It is important to accurately determine such data if the cable will have additional and significant loads.
Example of calculation in everyday life: I = P/U cosφ, where
I – current strength, (A);
P – power, (W);
U – network voltage, (V);
cosφ – coefficient equal to 1.
Using this calculation formula, you can find the correct wiring length, and cable cross-section indicators can be obtained using an online calculator, or manually. To convert Watts to Amps - .
Program for calculating cable cross-section by power
To find out the power of an equipment or device, you need to look at the tag, which indicates its main characteristics. After adding up the data, for example, 20,000 W, this is 20 kW. This indicator indicates how much energy all electrical appliances consume. If their percentage is used at a time about 80%, then the coefficient will be equal to 0.8. Calculation of cable cross-section by power: 20 x 0.8 = 16 kW. This is the core cross-section for a copper wire measuring 10 mm. For a three-phase circuit - 2.5 mm at a voltage of 380 V.
It is better to choose a wire of the largest cross-section in advance, in case of connecting unplanned equipment or devices. It’s better to add money today and do everything efficiently than to change the cable and buy a new kettle tomorrow.
A more detailed calculator that takes into account different coefficients.
Standard apartment wiring is designed for a maximum current consumption under continuous load of 25 amperes (copper wire with a cross-section of 5 mm and a diameter of 2.5 mm is used). The greater the planned current consumption, the more cores there should be in the cable. If the wire has a diameter of 2 mm, then its cross-section can be easily determined using the following formula: 2 mm × 2 mm × 0.785 = 3.14 mm 2. If you round the value, it turns out to be 3 mm squared.
To select a cable cross-section based on power, you need to independently determine the total current of all electrical appliances, add the result and divide by 220.
The choice for laying the cable depends on its shape; it is better to lay round wiring through walls, and for interior work, a flat cable is better suited, which is easy to install and does not create obstacles in operation. Their technical characteristics are the same.
