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The cross section of the cores of electrical wires and cables used to connect lighting and household appliances, power plants and various equipment depends on the magnitude of the electrical power of these consumers and, accordingly, the electric current flowing through them. The value of the maximum allowable current flowing through the current-carrying core for different brands of wires and cables, in accordance with their cross section and method of laying, is regulated by the "Electrical Installation Rules" (PUE) chapter 1.3 "Selection of conductors for heating, economic current density and corona conditions" . About how to choose a cable for home wiring, as well as a table of cable power by cross section, which is useful for many jobs, we will talk about this in today's publication site
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 the passports of these products or technical specifications posted on the Internet;
- use the average values for each category of household appliances.
The average values of various household appliances are shown in the following table.
| Device name | Electric power, kW |
|---|---|
| Dishwasher | 1,8 |
| Electric kettle | 1,2 |
| Oven | 2,3 |
| hair dryer | 1,3 |
| Microwave | 1,5 |
| Iron | 1,1 |
| Air conditioner | 4 |
| Washing machine | 0,5 |
| Television | 0,3 |
| Fridge | 0,2 |
| Satellite TV | 0,15 |
| A computer | 0,12 |
| Printer | 0,05 |
| Monitor | 0,15 |
| Hand electric tool | 1,2 |
This table does not list all types of household appliances and tools, because their nomenclature is quite large, so if you need to find the required values, you should turn to the Internet, where using the "search engine" to find the power value of the desired 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 - the current flowing through the current-carrying conductors when devices of a given power are turned on.
Note! 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 strength of the current flowing through the conductor when the maximum possible load is connected to a given section of the electrical circuit, its cross section can be determined.
Important! For copper and aluminum conductors, the values of the maximum allowable current differ, so this must be taken into account without fail when selecting the cable (wire) section.
Selection of the cross-section of copper or aluminum wire by power and current strength
As can be seen from the formula (by which the electric current was determined), when a certain power is connected, the current value directly depends on the voltage of the electrical network on which the connected devices operate. In this regard, the values of the maximum allowable current for different voltage classes are given in the technical literature separately, as well as for different brands of current-carrying conductors, namely:
- For aluminum conductors.
- For copper conductors.
- For conductors used in low voltage classes (12/24 V).
Note! AWG is the American Wire Gauge System, which is determined by the technology of their manufacture and determines the dependence of the AWG index on the thickness of the current-carrying core. The smaller the AWG, the thicker the wire.
The choice of cable cross-section according to the PUE
As already written above, in the preamble to this article, the correspondence of the cable (wire) cross-section and other electrical quantities (current and power, length and laying method) are regulated by the "Electrical Installation Rules". In accordance with this technical document, the values of permissible currents, in addition to the indicators considered above, are also classified according to the method of laying them, as well as the type of insulation used in the manufacture of wires and cables, namely:
- For copper conductors.
Below I will give a table of wire cross-sections, but I recommend that you be patient by reading this small theoretical part to the end.
This will allow you to be more conscious in choosing wires for wiring, in addition, you can independently make wire section calculation, moreover, even "in the mind."
The passage of current through the conductor is always accompanied by the release of heat (respectively, heating), which is directly proportional to the power dissipated in the wiring section. Its value is determined by the formula P=I 2 *R, where:
- I - the value of the flowing current,
- R is the resistance of the wire.
Excessive heat may cause insulation failure, resulting in a short circuit and/or fire.
The current flowing through the conductor depends on the load power (P), defined by the formula
I=P/U
(U is the voltage, which for a household electrical network is 220V).
The wire resistance R depends on its length, material and section. For electrical wiring in an apartment, cottage or garage, the length can be neglected, but the material and cross section must be taken into account when choosing wires for electrical wiring.
CALCULATION OF THE SECTION OF THE WIRE
The cross section of the wire S is determined by its diameter d as follows (hereinafter, I will simplify the formulas as much as possible):
S=π*d 2 /4=3.14*d 2 /4=0.8*d 2.
This may come in handy if you already have a wire, and without a marking that immediately indicates the cross section, for example, VVG 2x1.5, here 1.5 is the cross section in mm 2, and 2 is the number of cores.
The larger the cross section, the greater the current load the wire can withstand. With the same sections of copper and aluminum wires - copper can withstand more current, in addition, they are less brittle, oxidize worse, therefore they are most preferable.
Obviously, with a hidden installation, as well as wires laid in a corrugated hose, an electrical box, due to poor heat transfer, they will heat up more strongly, which means that their cross section should be chosen with a certain margin, so it's time to consider such a value as current density (let's denote it Iρ).
It is characterized by the amount of current in amperes flowing through the unit section of the conductor, which we will take as 1mm 2. Since this value is relative, it is convenient to use it to calculate the cross section using the following formulas:
- d=√ 1.27*I/Iρ =1.1*√I/Iρ- get the value of the wire diameter,
- S \u003d 0.8 * d 2 - previously obtained formula for calculating the section,
We substitute the first formula into the second, round everything that is possible, we get a very simple ratio:
S=I/Iρ
It remains to determine the value of the current density Iρ), since the operating current I) is determined by the power of the load, I gave the formula above.
The permissible value of the current density is determined by many factors, the consideration of which I will omit and give the final results, and with a margin:
Calculation example:
We have: the total load power in the line is 2.2 kW, the wiring is open, the wire is copper. For the calculation we use the following units of measurement: current - Ampere, power - Watt (1kW = 1000W), voltage - Volt.
S=I/Iρ=(2200/220)/10=1mm 2
If you carry out the appropriate calculations for the entire range of wire cross-sections, you can get the corresponding table.
WIRE SIZE TABLE
I bring to your attention the table promised at the beginning of the article:
I warn you right away, data from different sources may vary. This difference is determined by the power margin.
Making calculations, I took this reserve to the maximum, bearing in mind that it is better to buy more powerful, respectively more expensive wires than to redo the burned-out electrical wiring later.
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Electricity can be generated by a generator at a voltage of 6, 10, 18 kV. Then it goes through busbars or complete busbars to transformers, which increase this value to 35-330kV. The higher the voltage, the further this energy can be transmitted. Then electricity goes through power lines to consumers. There it is again transformed through step-down transformers to a value of 0.4 kV. And between all these transformations, electricity goes through overhead, cable lines of various voltages. The choice of the section of these cables is a separate issue, which is discussed in this article.
If we turn to the basics of the question, then it can immediately be divided into two parts. Part one, the choice of section in networks up to 1kV, and the second part (in a separate article) - the choice of section in networks above 1kV. In addition, we will consider a common question for these voltage classes - determining the cable cross-section by diameter. I warn you right away that there are a lot of tables ahead, but don't let that scare you, because sometimes a table is better than a thousand words.
Selection and calculation of the cross-section of cables with voltage up to 1 kV (for an apartment, house)
Electric networks up to 1 kV are the most numerous - it's like a web that wraps around the entire electric power industry and in which there are so many automatic machines, circuits and devices that an unprepared person's head can spin. In addition to 0.4 kV networks of industrial enterprises (factories, thermal power plants), these networks also include wiring in apartments and cottages. Therefore, the question of choosing and calculating the cable cross-section is also asked by people who are far from electricity - simple property owners.
The cable is used to transfer electricity from the source to the consumer. In apartments, we consider the area from the electrical panel, where the introductory circuit breaker is installed to the apartment, to which our appliances (TVs, washing machines, kettles) are connected. Everything that moves away from the machine to the side of the apartment in the department of the service organization, we have no right to climb there. That is, we are considering the issue of laying cables from the introductory machine to sockets in the wall and switches on the ceiling.
In the general case, 1.5 squares are taken for lighting, 2.5 for sockets, and calculation is necessary if you want to connect something non-standard with high power - a washing machine, a boiler, a heating element, a stove.
The choice of cable cross-section by power
I will continue to consider an apartment, since the people at the enterprises are literate and know everything. To estimate the power, you need to know the power of each electrical receiver, add them together. The only disadvantage when choosing a cable with a larger cross section than necessary is the economic inexpediency. Since a larger cable costs more, but it heats up less. And if you choose the right one, it will come out cheaper and will not warm up much. It is impossible to round it down, since the cable will heat up more from the current flowing in it and will quickly go into a faulty state, which can lead to a malfunction of the electrical appliance and all wiring.
The first step in choosing the cable section will be to determine the power of the loads connected to it, as well as the nature of the load - single-phase, three-phase. Three-phase it can be a stove in an apartment or a machine in a garage in a private house.
If all devices have already been purchased, then you can find out the power of each according to the passport that comes with the kit, or, knowing the type, you can find a passport on the Internet and see the power there.
If the devices are not purchased, but buying them is included in your plans, then you can use the table where the most popular devices are listed. We write out the power values and add up those values \u200b\u200bthat can simultaneously be included in one outlet. The values given below are for reference only, the larger value should be used in the calculation (if the power range is specified). And it is always better to look at the passport than to take averages from tables.
The switches that come after the introductory are conveniently divided into groups. Separate switches for powering the stove, washing machine, boiler and other powerful appliances. Separate for powering lighting of individual rooms, separate for groups of room outlets. But this is ideal, in reality it is just an introductory and three machines. But I got distracted...
Knowing the value of the power that will be connected to this outlet, we select the cross section from the table with rounding up.
I will take as a basis tables 1.3.4-1.3.5 from the 7th edition of the PUE. These tables are given for wires, aluminum or copper cords with rubber and (or) PVC insulation. That is, what we use in home wiring - copper NYM and VVG, and aluminum AVVG, beloved by electricians, are also suitable for this type.
In addition to the tables, we need two active power formulas: for a single-phase (P = U * I * cosf) and a three-phase network (the same formula, just multiply by the root of three, which is 1.732). We take the cosine to the unit, we will have it for the reserve.
Although there are tables where for each type of socket (a socket for a machine tool, a socket for this, for this) its own cosine is described. But it cannot be greater than one, so it’s not scary if we accept it as 1.
Even before looking at the table, it is worth deciding how and in what quantity our wires will be laid. The options are as follows - open or in the pipe. And in the pipe you can have two or three or four single-core, one three-core or one two-core. For an apartment, we have a choice of either two single-core in a pipe - this is for 220V, or four single-core in a pipe - for 380V. When laying in a pipe, it is necessary that 40 percent of free space remains in this very pipe, this is to avoid overheating. If you need to lay wires in a different quantity or in a different way, then feel free to open the PUE and recalculate for yourself, or choose not by power, but by current, which will be discussed a little later in this article.
You can choose from both copper and aluminum cable. Although, recently copper has been more widely used, since a smaller section will be required for the same power. In addition, copper has the best electrically conductive properties, mechanical strength, is less susceptible to oxidation, and, in addition, the service life of copper wire is higher compared to.
Decided on whether copper or aluminum, 220 or 380V? Well, look at the table and select the section. But we take into account that in the table we have values \u200b\u200bfor two or four single-core wires in a pipe.
we calculated the load, for example, at 6kW for a 220V socket and look at 5.9 a little, although close, we choose 8.3kW - 4mm2 for copper. And if you decide on aluminum, then 6.1 kW is also 4mm2. Although copper is worth choosing, since the current with the same cross section will be 10A more allowable.
Selection of the cable cross-section by current
The essence of the choice is similar, only now we have the PUE, where the currents are registered, but the currents themselves are unknown to us. Although, wait… After all, we know the power of the devices and can calculate the magnitude of the currents using the formula. Yes, and currents can be written in the passports for products. Similarly, look at the tables below. These are already tables from official documents, so there is nothing to complain about.
Selection of the cross section of the wire with rubber or PVC insulation according to the permissible current
These wires are the most common, and therefore this table is given. In the PUE, there are other tables for all occasions for wires, cables, cords with and without a sheath when laying in water, land and air. But these are special cases. By the way, the table that is given when calculating the power is completely a special case of the current selection tables, which are official and are described in the PUE.
Cable calculation by power and length
If you are laying a cable for a long distance (well, 15 meters or more), then you need to take into account the voltage drop, which is caused by the resistance of the cable line.
Why is the voltage drop at the end of the cable line unfavorable for us? For a light bulb, this is a deterioration in the luminous flux with a decrease in voltage, or a decrease in service life with increased voltage. There are acceptable voltage deviations. But basically for electrical appliances it is plus or minus five percent.
In this case, it is required to make a calculation, and if the voltage is lower than the nominal by 5% or more, then you will have to increase the cross section and re-calculate. Or use another table.
Now let's delve a little into the materiel. The voltage drop for a three-phase network is determined by the formula:
This value consists of two parts, active (R) and inductive (X). The inductive part can be neglected in the following cases:
- DC network
- AC mains, at cos=1
- networks made with cables or insulated wires laid in pipes, if their cross section is not more than a certain value, but we will not go further.
In general, we neglect the inductive component, we take the cosine equal to 1. The value of R is determined by the formula:
where p is the resistivity (for - 0.0175, and for aluminum - 0.03)
a) according to the given value of the voltage drop, we find the permissible cross section and select the next larger value.
b) according to the given value of power or current, we determine the voltage drop in the section, and if it is more than 5%, we select another section and repeat the calculation.
In the formulas above, length is in meters, current is in amps, voltage is in volts, area is in mm2. The very magnitude of the voltage drop in relative terms, dimensionless. The formulas are suitable for calculations in the absence of an inductive component and a cosine equal to 1. A number of cable sections are standard. In principle, with the obtained cross-section value, you can go to the market and see what suits you with rounding up.
Or you can use tables on the Internet, but these tables ... It is not clear where and for what case they were built. Formulas are everything!
Determining the cable cross-section by diameter
If you have the opportunity to measure the diameter of the cable core, naturally bare, without insulation, then you can determine the cross section of this core. Again we have two ways: formula or table. Let everyone choose what is more convenient for him.
Formula: pide square four. Everyone knows this. We measure the diameter of the wire (ruler, caliper, micrometer), again cleaned. We square the value, multiply by pi (equal to 3.14) and divide by 4. We get the value of the section. Approximate, because the errors here are both in the number pi and in the measurement itself. If you want, here is an elementary table - we measure the diameter, see if it corresponds to the section declared on the tag.
If the wire is stranded, then we either measure each core, and then count their number. Well, we multiply the number by the diameter of one and then according to the scheme above. Or, if they are well twisted in the form of a circle at the end, we measure as on a single-core.
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This article will talk about how to calculate the wire cross-section for power consumption yourself. You need to know this not only when in the house, but also when working in cars, for example. If the wire section is insufficient, it will start to heat up very much, which will lead to a significant loss of safety level. Given all the recommendations that will be outlined below, you will be able to independently calculate the parameters of the wires for installing the power supply in the house. But if you are not confident in your abilities, it is better to contact specialists in this field. Moreover, it should be noted that the calculation of the wire cross-section for power consumption (12V and 220V) is carried out similarly.
Carrying out the calculation of the length of the wiring
For any type of electronic system, the most important condition for stable and trouble-free operation is the competent calculation of the cross sections of all wires for current and power. The first step is to calculate the maximum length of the entire wiring. There are several ways to do this:
- Measuring the distance from shields to sockets, switches according to the installation diagram. Moreover, this can be done with a ruler on a pre-prepared wiring plan - it is enough to multiply the obtained length values by the scale.
- And the second, more accurate way is to arm yourself with a ruler and walk through all the rooms, taking measurements. Moreover, it must be borne in mind that the wires must somehow be connected, so there must always be a margin - at least one or two centimeters from each edge of the wiring.
Now you can proceed to the next step.
Calculation of the load on the wiring
To calculate the total load, you need to add up all the minimum power consumers in the house. Let's say you are doing a calculation for the kitchen, it has lamps, a microwave oven, an electric kettle and stove, a dishwasher, and so on. All powers must be summed up (see the power consumption on the back covers, but you will have to calculate the current yourself from this parameter). Then multiply by a correction factor of 0.75. It is also called the simultaneity factor. Its essence is clear from the name itself. This figure, which will be obtained as a result of calculations, you will need in the future to calculate the parameters of the wires. Please note that the entire power supply system must be safe, reliable and durable. These are the basic requirements that must be taken into account when calculating the wire cross-section for power consumption of 12V and 220V.
Current consumption of electrical installations
Now about how to calculate the current consumption of an electrical device. You can do this in your mind, or you can use a calculator. See the instructions for the device, what is the value of the power consumption of it. Of course, in the household electrical network flows alternating current with a voltage of 220 volts. Therefore, using a simple formula (power consumption divided by supply voltage), you can calculate the current. For example, an electric kettle has a power of 1000 watts. So, if we divide 1000 by 220, we get a value approximately equal to 4.55 amperes. It is produced very simply in terms of power consumption. How to do this is described in the article. In the operating mode, the kettle consumes 4.55 amperes from the network (for protection, you must install a circuit breaker of a larger rating). But note that this is not always the exact value. For example, if there is a motor in the design of an electrical appliance, the value obtained can be increased by about 25% - the current consumption of the motor in the start mode is much greater than during idling.
But you can use a set of rules and standards. There is such a document as the Rules for the Installation of Electrical Installations, it is he who regulates all the standards for wiring not only in private estates, but also in factories, factories, etc. According to these rules, the wiring standard is the ability to withstand a load of 25 amperes for a long time. Therefore, in apartments, all electrical wiring should be carried out only using copper wire, its cross section is not less than 5 square meters. mm. Each core must have a cross section of more than 2.5 square meters. mm. The conductor diameter must be 1.8 mm.
In order for all electrical wiring to work as safely as possible, an automatic switch is installed at the input. It will protect the apartment from short circuits. Also, recently, most homeowners have been installing residual current devices that instantly act on a change in resistance in the circuit. In other words, if you accidentally touch them while energized, they will instantly de-energize and you won't get hit. it is necessary to calculate by current, and be sure to choose with a margin, so that it is always possible to install any electrical appliance in the house. A competent calculation of the wire cross-section according to the power consumption (how to make the right choice of wires, you will learn from this material) is a guarantee that the power supply will function correctly and efficiently.
Materials for the manufacture of wires
As a rule, wiring in a private house or apartment is done using three-core wires. Moreover, each core has a separate insulation, they all have different colors - brown, blue, yellow-green (standard). The core is the part of the wire through which the current flows. It can be both single-wire and multi-wire. Some brands of wire use a cotton braid over the strands. Materials for the manufacture of wire cores:
- Steel.
- Copper.
- Aluminum.
Sometimes you can find combined ones, for example, a stranded copper wire with several steel conductors. But these were used for field telephone communications - a signal was transmitted over copper, and steel was used for the most part for fastening to supports. Therefore, in this article we will not talk about such wires. For apartments and private houses, copper wire is ideal. It is durable, reliable, the characteristics are much higher than that of cheap aluminum. Of course, the price of copper wire bites, but it is worth mentioning that its service life (guaranteed) is 50 years.
Wire Marks
For laying electrical wiring, it is best to use two brands of wires - VVGng and VVG. The first has the ending "-ng", which indicates that the insulation does not burn. It is used for electrical wiring inside structures and buildings, as well as in the ground, in the open air. Works stably in the temperature range -50 ... +50. Guaranteed service life - not less than 30 years. The cable can be with two, three or four cores, the cross section of each is in the range of 1.5 ... 35 square meters. mm. Please also note that it is necessary to calculate the wire cross-section according to the power consumption and length (in the case of an overhead long line).
Pay attention to the fact that there is no letter “A” before the name of the wire (for example, АВВГ). This suggests that the cores inside are made of aluminum. There are also foreign analogues - the NYM brand cable, which has a round shape, complies with the standards adopted in Germany (VDE0250). The conductors are copper, the insulation is not subject to combustion. The round shape of the wire is much more convenient if you need to install through the wall. But for wiring indoors, it turns out to be more convenient than a flat domestic one.
aluminum wires
They are lightweight and, most importantly, low cost. Therefore, they are useful for those cases when you need to lay long lines through the air. If all work is carried out correctly and correctly, you will get an ideal air line, since aluminum has one huge advantage - it is not subject to oxidation (unlike copper). But often aluminum wiring was also used in houses (usually in old ones). The wire used to be easier to get, and it cost a penny. It should be noted that the calculation of the wire cross-section according to the power consumption (the features of this process are known to every electrician) is the main step in creating a house power supply project. But you need to pay attention to one feature - the cross section of the aluminum wire must be larger than the copper wire in order to withstand the same load.
Table for calculating the power section
It is also necessary to mention that the maximum permissible current load is much less than for copper ones. The table below will help calculate the cross section of the cores
Cross section of wires depending on the type of wiring
There are two types of electrical wiring in homes - open and closed. As you understand, this nuance must be taken into account when making calculations. Hidden is mounted inside ceilings, as well as in grooves and channels, in pipes, etc. Closed wiring has higher requirements, since it has less cooling capacity. And any wire with prolonged exposure to a large load heats up very much. Therefore, in the case when you calculate the cross section of the wire according to the power consumption, be sure to take into account the effect on heating. The following parameters must also be taken into account:
- continuous current load.
- Loss of voltage.
As the wire length increases, the voltage decreases. Therefore, in order to reduce voltage losses, it is necessary to increase the cross section of the wire cores. If we are talking about a small house or even a room, then the loss value is extremely low, they can be neglected. But if a long line is calculated, this cannot be avoided. After all, the calculation of the wire cross-section according to the power consumption (the influence of the length is very large) depends on such a parameter as the length of the line.
Calculation of the wire by power
So, you need to know the following characteristics:
- The material of which the cable cores are made.
- Maximum power consumption.
- Supply voltage.
Please note that when any current flows, the temperature rises and some heat is released. Moreover, the amount of heat is proportional to all the power that is dissipated on a piece of electrical wiring. If you choose the wrong section, then excessive heating will occur, and the result can be disastrous - ignition of the electrical wiring and fire. Therefore, it is worth making an accurate calculation of the wire cross-section according to the power consumption. The risk factors are too big, and there are many of them.
Optimal parameters
Optimal sections:
- For wiring sockets - 2.5 square meters. mm.
- Lighting group - 1.5 sq. mm.
- High power electrical appliances (electric stove) - 4-6 sq. mm.
At the same time, pay attention to the fact that copper wires can withstand the following loads:
- Wire 1.5 sq. mm - up to 4.1 kW (current load - 19 amperes).
- 2.5 sq. mm - up to 5.9 kW (current - up to 27 amperes).
- 4-6 sq. mm - more than 8-10 kW.
Therefore, when the load increases, you will always have a fairly large reserve.
Conclusion
Now you know how to calculate the cross section of the wire according to the power consumption (the definition of important characteristics and other small factors is now known to you). Based on all of the above data, you can independently, without resorting to the help of professionals, draw up the correct power supply plan for your house or apartment.
The cross section of the cable at the cut is standardized in all countries. This applies to both the CIS countries and Europe. This issue is regulated in our country by the document "Electrical Installation Rules", which are called PUE. The calculation of the cable cross-section by power is selected using special tables. Of course, many calculate the necessary parameters of the conductor "by eye", but this is not entirely correct. For each apartment, this figure may be different. 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 the apartment.
Cable device
To determine the cable cross-section by power, one should understand its principle and structure. It can be compared, for example, with a water or gas pipeline. In the same way as through these communications, a stream flows through the electrical conductor. Its power limits the cross section of the conductor.
The cable cross-section using the power indicator can be incorrect 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. Such a state of the conductor over time will be characterized by the presence of weak points where leakage is possible. This condition of the channel can cause a fire.
- Conductor too wide. This, of course, is not the worst option. The space for transporting the electrical flow will allow more functional and durable use of the conductor. However, as the cross section increases, so does the cost of the cable.
The first option is a danger to life, health and property. The second method is safe, but the materials are quite expensive to purchase.
The easy way
The calculation of the cable cross-section by power is based on the well-known law developed by Ohm. He says that the current flow times the voltage equals 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 in terms of current, as well as power, only two variables remain.
Next, the current values \u200b\u200band the expected load are calculated. Moreover, the size of the cable according to its power can be selected according to the PUE table. This indicator is calculated for a wire suitable for 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 oven, electric kettle, etc. are connected to the outlet group. It is necessary to distribute the load and correctly calculate the cable cross-section in terms of power, correlating the diameter and load.
If it is not possible to break up the socket groups, then many electricians will recommend immediately installing a cable with a copper core up to 6 mm 2.
Cross-sectional area and diameter
Calculation of the cable cross-section by power, diameter and load are not equivalent concepts. The first indicator is calculated in mm 2, and the second is simply in mm. You can choose the power and allowable current according to the table both by the cable cross section and by 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 diameter of the cable, the missing indicator can be found using the following formula:
S \u003d 3.14D 2 / 4 \u003d 0.785D 2,
where: S is the cross section of the wire and D is the diameter.
If the wire in the section 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 wire cross section is by summing up the capacities 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 are likely to function simultaneously. Next, you need to look into the data sheets of each of these units. It will be necessary to calculate the sum of the capacities of those electrical consumers that must work simultaneously.
Then the indicator obtained as a result of the calculations performed is rounded up. This will provide a safe supply of electrical wiring power. The cross section of the wire or cable is calculated further using the 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 in the power calculation table is performed.
Table of power, current and section of copper wires
According to the PUE, in residential buildings it is necessary to use only copper conductors for arranging wiring. The power supply of some electrical equipment, which belongs to the engineering types of receivers, can be connected to the network with aluminum conductors with a cross section of at least 2.5 mm 2.
Table of power, current and section of aluminum wires
The specialist will also be able to make correction factors for the type of wire location, ambient temperature, for a cable in the ground, etc. The table for calculating cable power, cross-section or current strength refers to conductors in plastic or rubber insulation. These include such common brands as VVP, PVS, PPV, VPP, AVVG, VVG, APPV, etc. Uninsulated or paper-screened cables should be calculated according to the table related to them.
Length and section
The calculation of the cable cross-section by power simply needs to be used to determine its length. This data is important when creating long extensions. The obtained exact values must be increased by 10-15 cm. This margin is necessary for switching by soldering, welding or crimping.
In construction, the cable cross-section is calculated in terms of power and length at the design stage of electrical wiring. This is very important, especially for those communications that will be subject to significant or additional loads.
In everyday life, the calculation of the length of the wire is carried out according to the following formula:
I=P/U*cosφ, where:
- P - power (W);
- I - current strength (A);
- U - voltage (V);
- cosφ - coefficient, which 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 derived empirically. This value is calculated for the current flowing through 1 mm 2 of the copper core.
This statement means that the calculation of the cable cross-section in terms of power and current is based on a copper cable with a cross section of 1 mm 2, through which current from 6 to 10 A can flow to waiting household appliances without melting and overheating.
According to the PUE code, for each wire a margin of 40% is allocated for overheating that is safe for the sheath. If the value of 6 A characterizes the operation of the presented conductor for an infinitely long term without time limits, then the indicator of 10 A is suitable for the short-term flow of current through the core.
If a current of 12 A flows through a 1 mm 2 copper conductor, it will be cramped in such a core. This will increase the current density. The core will begin to heat up and will melt the insulation.
Therefore, such calculations are mandatory when choosing a cable section for each type of wiring.
Having familiarized yourself with the methods that allow you to calculate the cable cross-section by power and current strength, you can lay or repair old wiring that will last a long time and be completely safe for people living in the house. A lot of fairly simple, but effective ways will help you accurately determine the required cross-sectional size for the power grid.
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