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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 installation method, 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 oven | 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 cores, namely:
- For aluminum conductors.
- For copper conductors.
- For conductors used at low voltage classes (12/24 V).
For your information! AWG is an American wire sizing system (American Wire Gauge System), determined by their manufacturing technology and determining the dependence of the AWG indicator on the thickness of the current-carrying core. The smaller the AWG, the thicker the wire.
Selection of cable cross-section according to PUE
As was already written above, in the preamble to this article, the compliance of the cross-section of the cable (wire) and other electrical quantities (current and power, length and installation method) is regulated by the “Rules for Electrical Installations”. 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 their installation, as well as the type of insulation used in the manufacture of wires and cables, namely:
- For copper conductors.
During the repair process, old electrical wiring is usually always replaced. This is due to the fact that recently many useful household appliances have appeared that make the life of housewives easier. Moreover, they consume a lot of energy, which old wiring simply cannot withstand. Such electrical appliances include washing machines, electric ovens, electric kettles, microwave ovens, etc.
When laying electrical wires, you should know what cross-section of wire you need to lay in order to power a particular electrical appliance or group of electrical appliances. As a rule, the choice is made both by power consumption and by the current strength consumed by electrical appliances. In this case, you need to take into account both the laying method and the length of the wire.
It is quite simple to select the cross-section of the cable to be laid according to the load power. This can be a single load or a collection of loads.
Each household appliance, especially a new one, is accompanied by a document (passport), which indicates its basic technical data. In addition, the same data is available on special plates attached to the product body. This plate, which is located on the side or back of the device, indicates the country of manufacture, its serial number and, of course, its power consumption in watts (W) and the current that the device consumes in amperes (A). On products from domestic manufacturers, power may be indicated in watts (W) or kilowatts (kW). On imported models there is the letter W. In addition, the power consumption is designated as “TOT” or “TOT MAX”.
An example of such a plate showing basic information about the device. Such a plate can be found on any technical device. If you cannot find out the necessary information (the inscription on the plate is worn out or there are no household appliances yet), you can find out approximately what power the most common household appliances have. All this data can actually be found in the table. Basically, electrical appliances are standardized in terms of power consumption and there is no particular variation in the data.
In the table, exactly those electrical appliances that you plan to purchase are selected, and their current consumption and power are recorded. From the list it is better to choose indicators that have maximum values. In this case, it will not be possible to miscalculate and the wiring will be more reliable. The fact is that the thicker the cable, the better, since the wiring heats up much less.
How the choice is made
When choosing a wire, you should sum up all the loads that will be connected to this wire. At the same time, you should ensure that all indicators are written out either in watts or kilowatts. To convert the indicators to one value, you should either divide the numbers or multiply by 1000. For example, to convert to watts, you should multiply all the numbers (if they are in kilowatts) by 1000: 1.5 kW = 1.5x1000 = 1500 W. When converting back, the actions are performed in the reverse order: 1500 W = 1500/1000 = 1.5 kW. Usually, all calculations are made in watts. After such calculations, a cable is selected using the appropriate table.
You can use the table as follows: find the corresponding column where the supply voltage is indicated (220 or 380 volts). This column contains a number that corresponds to the power consumption (you need to take a slightly higher value). In the line that corresponds to power consumption, the first column indicates the wire cross-section that can be used. When going to the store to buy a cable, you should look for a wire whose cross-section matches the notes.
Which wire to use - aluminum or copper?
In this case, everything depends on the power consumption. In addition, copper wire can withstand twice the load than aluminum wire. If the loads are large, then it is better to give preference to copper wire, as it will be thinner and easier to lay. In addition, it is easier to connect it to electrical equipment, including sockets and switches. Unfortunately, copper wire has a significant disadvantage: it costs much more than aluminum wire. Despite this, it will last much longer.
How to calculate cable cross-section by current
Most craftsmen calculate wire diameters based on current consumption. Sometimes this simplifies the task, especially if you know what current a wire of a particular thickness can withstand. To do this, you need to write down all the indicators of current consumption and sum them up. The wire cross-section can be selected using the same table, only now you need to look for the column where the current is indicated. As a rule, a larger value is always selected for reliability.
For example, to connect a hob, which can consume a maximum current of up to 16A, a copper wire must be selected. If you turn to the table for help, the desired result can be found in the third column from the left. Since there is no value 16A, we choose the nearest, larger one - 19A. A cable cross-section of 2.0 mm square is suitable for this current.
As a rule, when connecting powerful household appliances, they are powered by separate wires, with the installation of separate automatic switches. This greatly simplifies the process of selecting wires. In addition, this is part of modern electrical wiring requirements. Plus, it's practical. In an emergency, you do not have to turn off the electricity completely in your entire home. It is not recommended to select wires with a lower value. If the cable constantly operates at maximum loads, this can lead to emergency situations in the electrical network. The result can be a fire if the circuit breakers are incorrectly selected. At the same time, you should know that they do not protect the wire sheath from fire, and it will not be possible to select the exact current so that it can protect the wires from overload. The fact is that they are not regulated and are issued at a fixed current value. For example, 6A, 10A, 16A, etc.
Choosing a wire with a reserve will allow you to later install another electrical appliance on this line, or even several, if this corresponds to the current consumption rate.
Cable calculation by power and length
If we take into account the average apartment, the length of the wires does not reach such values as to take this factor into account. Despite this, there are cases when when choosing wires, their length should be taken into account. For example, you need to connect a private house from the nearest pole, which may be located at a considerable distance from the house.
With significant current consumption, a long wire can affect the quality of power transmission. This is due to losses in the wire itself. The longer the wire, the greater the losses in the wire itself. In other words, the longer the wire, the greater the voltage drop in this section. In our time, when the quality of power supplies leaves much to be desired, this factor plays a significant role.
To know this, you will again have to refer to the table, where you can determine the cross-section of the wire, depending on the distance to the power point.
Table for determining wire thickness, depending on power and distance.
Open and closed method of laying wires
Current passing through a conductor causes it to heat up, since it has a certain resistance. So, the greater the current, the more heat is generated on it, under conditions of the same cross section. At the same current consumption, more heat is generated on conductors of smaller diameter than on conductors with a larger thickness.
Depending on the laying conditions, the amount of heat generated on the conductor also changes. When laying open, when the wire is actively cooled by air, you can give preference to a thinner wire, and when the wire is laid closed and its cooling is minimized, it is better to choose thicker wires.
Similar information can also be found in the table. The principle of selection is the same, but taking into account one more factor.
And finally, the most important thing. The fact is that nowadays the manufacturer is trying to save on everything, including the material for the wires. Very often, the declared cross-section does not correspond to reality. If the seller does not inform the buyer, then it is better to measure the thickness of the wire on the spot if this is critical. To do this, just take a caliper with you and measure the thickness of the wire in millimeters, and then calculate its cross-section using the simple formula 2*Pi*D or Pi*R squared. Where Pi is a constant number equal to 3.14, and D is the diameter of the wire. In another formula - respectively, Pi = 3.14, and R squared is the radius squared. The radius is very easy to calculate; just divide the diameter by 2.
Some sellers directly point out the discrepancy between the declared cross-section and the actual one. If the wire is chosen with a large margin, then this is not at all significant. The main problem is that the price of the wire, compared to its cross-section, is not underestimated.
In theory and practice, the choice of transverse area current wire cross-section(thickness) is given special attention. In this article, analyzing reference data, we will get acquainted with the concept of “sectional area”.
Calculation of wire cross-section.
In science, the concept of “thickness” of a wire is not used. The terminology used in literary sources is diameter and cross-sectional area. Applicable to practice, the thickness of the wire is characterized by cross-sectional area.
Quite easy to calculate in practice wire cross section. The cross-sectional area is calculated using the formula, having first measured its diameter (can be measured using a caliper):
S = π (D/2)2 ,
- S - wire cross-sectional area, mm
- D is the diameter of the conductive core of the wire. You can measure it using a caliper.
A more convenient form of the wire cross-sectional area formula:
S=0.8D.
A small correction - it is a rounded factor. Exact calculation formula:
In electrical wiring and electrical installations, copper wire is used in 90% of cases. Copper wire has a number of advantages compared to aluminum wire. It is more convenient to install, has the same current strength, is thinner, and is more durable. But the larger the diameter ( cross-sectional area), the higher the price of copper wire. Therefore, despite all the advantages, if the current exceeds 50 Amperes, aluminum wire is most often used. In a specific case, a wire with an aluminum core of 10 mm or more is used.
Measured in square millimeters wire cross-sectional area. Most often in practice (in household electrics), the following cross-sectional areas are found: 0.75; 1.5; 2.5; 4 mm.
There is another system for measuring cross-sectional area (wire thickness) - the AWG system, which is used mainly in the USA. Below is section table wires according to the AWG system, as well as conversion from AWG to mm.
It is recommended to read the article about choosing the wire cross-section for direct current. The article provides theoretical data and discussions about voltage drop and wire resistance for different cross-sections. Theoretical data will indicate which wire cross-section for current is most optimal for different permissible voltage drops. Also, using a real example of an object, the article on the voltage drop on long three-phase cable lines provides formulas, as well as recommendations on how to reduce losses. Wire losses are directly proportional to the current and the length of the wire. And they are inversely proportional to resistance.
There are three main principles when choosing the wire cross-section.
1. For the passage of electric current, the cross-sectional area of the wire (wire thickness) must be sufficient. The concept sufficiently means that when the maximum possible, in this case, electric current passes, the heating of the wire will be acceptable (no more than 600C).
2. Sufficient cross-section of the wire so that the voltage drop does not exceed the permissible value. This mainly applies to long cable lines (tens, hundreds of meters) and large currents.
3. The cross-section of the wire, as well as its protective insulation, must ensure mechanical strength and reliability.
To power, for example, a chandelier, they mainly use light bulbs with a total power consumption of 100 W (current slightly more than 0.5 A).
When choosing the thickness of the wire, you need to focus on the maximum operating temperature. If the temperature is exceeded, the wire and the insulation on it will melt and, accordingly, this will lead to the destruction of the wire itself. The maximum operating current for a wire with a certain cross-section is limited only by its maximum operating temperature. And the time that the wire can work in such conditions.
The following is a table of wire cross-sections, with the help of which, depending on the current strength, you can select the cross-sectional area of the copper wires. The initial data is the cross-sectional area of the conductor.
Maximum current for different thicknesses of copper wires. Table 1.
|
Conductor cross-section, mm 2 |
Current, A, for wires laid |
||
|
open |
in one pipe |
||
|
one two core |
one three core |
||
The ratings of wires that are used in electrical engineering are highlighted. “Single two-wire” is a wire that has two wires. One is Phase, the other is Zero - this is considered to be single-phase power supply to the load. “One three-wire” - used for three-phase power supply to the load.
The table helps to determine at what currents, as well as under what conditions it is operated. wire of this section.
For example, if the socket says “Max 16A”, then a wire with a cross-section of 1.5 mm can be laid to one socket. It is necessary to protect the outlet with a switch for a current of no more than 16A, preferably even 13A, or 10 A. This topic is covered in the article “About replacing and choosing a circuit breaker.”
From the table data it can be seen that a single-core wire means that no more wires pass nearby (at a distance of less than 5 wire diameters). When two wires are side by side, as a rule, in the same common insulation, the wire is two-core. There is a more severe thermal regime here, so the maximum current is lower. The more collected in a wire or bundle of wires, the less the maximum current should be for each conductor separately, due to the possibility of overheating.
However, this table is not entirely convenient from a practical point of view. Often the initial parameter is the power of the electricity consumer, and not the electric current. Therefore, you need to choose a wire.
We determine the current, having the power value. To do this, divide the power P (W) by the voltage (V) - we get the current (A):
I=P/U.
To determine power, having a current indicator, it is necessary to multiply the current (A) by voltage (V):
P=IU
These formulas are used in cases of active load (consumers in residential premises, light bulbs, irons). For reactive loads, a coefficient of 0.7 to 0.9 is mainly used (for the operation of powerful transformers, electric motors, usually in industry).
The following table suggests the initial parameters - current consumption and power, and the determined values - wire cross-section and tripping current of the protective circuit breaker.
Based on power consumption and current - choice wire cross-sectional area and circuit breaker.
Knowing the power and current, in the table below you can select wire cross section.
Table 2.
|
Max. power, |
Max. load current, |
Section |
Machine current, |
Critical cases in the table are highlighted in red; in these cases, it is better to play it safe without saving on the wire, choosing a thicker wire than indicated in the table. On the contrary, the current of the machine is less.
From the table you can easily select current wire cross-section, or wire cross-section by power. Select a circuit breaker for the given load.
In this table, all data is given for the following case.
- Single phase, voltage 220 V
- Ambient temperature +300С
- Laying in the air or in a box (located in a closed space)
- Three-core wire, in general insulation (wire)
- The most common TN-S system is used with a separate ground wire
- In very rare cases the consumer reaches maximum power. In such cases, the maximum current can operate for a long time without negative consequences.
Recommended choose a larger section(next in a series), in cases where the ambient temperature is 200C higher, or there are several wires in the harness. This is especially important in cases where the operating current is close to the maximum.
In doubtful and controversial points, such as:
high starting currents; possible future increase in load; fire hazardous premises; large temperature changes (for example, the wire is in the sun), it is necessary to increase the thickness of the wires. Or, for reliable information, refer to formulas and reference books. But basically, tabular reference data is applicable for practice.
You can also find out the thickness of the wire using an empirical (experienced) rule:
The rule for choosing the cross-sectional area of the wire for the maximum current.
The right one cross-sectional area for copper wire, based on the maximum current, can be selected using the rule:
The required wire area is equal to the maximum current divided by 10.
Calculations according to this rule do not have a margin, so the result must be rounded up to the nearest standard size. For example, you need wire cross section mm, and the current is 32 Amperes. It is necessary to take the nearest one, of course, in the larger direction - 4 mm. It can be seen that this rule fits well into the tabular data.
It should be noted that this rule works well for currents up to 40 Amperes. If the currents are greater (outside the living room, such currents are at the input) - you need to choose a wire with an even larger margin, and divide it not by 10, but by 8 (up to 80 A).
The same rule applies to finding the maximum current through a copper wire, if its area is known:
The maximum current is equal to the cross-sectional area, multiplied by 10.
About the aluminum wire.
Unlike copper, aluminum conducts electric current less well. For aluminum ( wire of the same section, as copper), at currents up to 32 A, the maximum current will be less than for copper by 20%. At currents up to 80 A, aluminum transmits current worse by 30%.
Rule of thumb for aluminum:
The maximum current of an aluminum wire is cross-sectional area, multiply by 6.
With the knowledge gained in this article, you can choose a wire based on the ratios “price/thickness”, “thickness/operating temperature”, as well as “thickness/maximum current and power”.
The main points about the cross-sectional area of the wires are covered, but if something is not clear, or you have something to add, write and ask in the comments. Subscribe to the SamElectric blog to receive new articles.
The Germans approach the maximum current depending on the cross-sectional area of the wire somewhat differently. A recommendation for choosing an automatic (protective) switch is located in the right column.
Table of the dependence of the electric current of the circuit breaker (fuse) on the cross-section. Table 3.
This table is taken from “strategic” industrial equipment, which may therefore give the impression that the Germans are playing it safe.
When designing the circuit of any electrical installation and installation, choosing the cross-section of wires and cables is a mandatory step. In order to correctly select the power wire of the required cross-section, it is necessary to take into account the maximum consumption.
Wire cross-section is measured in square millimeters or "squares". Each “square” of aluminum wire is capable of passing through itself for a long time, heating up to permissible limits, a maximum of only 4 amperes, and copper wires 10 amperes of current. Accordingly, if some electrical consumer consumes power equal to 4 kilowatts (4000 watts), then at a voltage of 220 volts the current strength will be equal to 4000/220 = 18.18 amperes and to power it it is enough to supply electricity to it with a copper wire with a cross-section of 18.18/ 10=1.818 square. True, in this case the wire will work to the limit of its capabilities, so you should take a margin of at least 15% for the cross-section. We get 2.091 squares. And now we will select the nearest wire of standard cross-section. Those. We must conduct wiring to this consumer with a copper wire with a cross-section of 2 square millimeters, called the current load. Current values can be easily determined by knowing the rated power of consumers using the formula: I = P/220. The aluminum wire will be correspondingly 2.5 times thicker.
Based on the calculation of sufficient mechanical strength, open power wiring is usually carried out with a wire with a cross-section of at least 4 square meters. mm. If you need to know with greater accuracy the long-term permissible current load for copper wires and cables, you can use the tables.
|
Copper conductors of wires and cables |
||||
| Voltage, 220 V | Voltage, 380 V | |||
| current, A | power, kW | current, A | power, kW | |
| 1,5 | 19 | 4,1 | 16 | 10,5 |
| 2,5 | 27 | 5,9 | 25 | 16,5 |
| 4 | 38 | 8,3 | 30 | 19,8 |
| 6 | 46 | 10,1 | 40 | 26,4 |
| 10 | 70 | 15,4 | 50 | 33,0 |
| 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 | 66,0 | 260 | 171,6 |
|
Aluminum conductors of wires and cables |
||||
| Cross-section of current-carrying conductor, mm. | Voltage, 220 V | Voltage, 380 V | ||
| current, A | power, kW | current, A | power, kW | |
| 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 | 132,0 |
|
Permissible continuous current for wires and cords with rubber and polyvinyl chloride insulation with copper conductors, for example |
||||||
| Cross-section of current-carrying conductor, mm. | 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 | - | - | - | - | - |
|
Permissible continuous current for wires and cords with rubber and polyvinyl chloride insulation with aluminum conductors |
||||||
| Cross-section of current-carrying conductor, mm. | Open | Current, A, for wires laid in one pipe | ||||
| Two single-core | Three single-core | Four single-core | One two-wire | One three-wire | ||
| 2 | 21 | 19 | 18 | 15 | 17 | 14 |
| 2,5 | 24 | 20 | 19 | 19 | 19 | 16 |
| 3 | 27 | 24 | 22 | 21 | 22 | 18 |
| 4 | 32 | 28 | 28 | 23 | 25 | 21 |
| 5 | 36 | 32 | 30 | 27 | 28 | 24 |
| 6 | 39 | 36 | 32 | 30 | 31 | 26 |
| 8 | 46 | 43 | 40 | 37 | 38 | 32 |
| 10 | 60 | 50 | 47 | 39 | 42 | 38 |
| 16 | 75 | 60 | 60 | 55 | 60 | 55 |
| 25 | 105 | 85 | 80 | 70 | 75 | 65 |
| 35 | 130 | 100 | 95 | 85 | 95 | 75 |
| 50 | 165 | 140 | 130 | 120 | 125 | 105 |
| 70 | 210 | 175 | 165 | 140 | 150 | 135 |
| 95 | 255 | 215 | 200 | 175 | 190 | 165 |
| 120 | 295 | 245 | 220 | 200 | 230 | 190 |
| 150 | 340 | 275 | 255 | - | - | - |
| 185 | 390 | - | - | - | - | - |
| 240 | 465 | - | - | - | - | - |
| 300 | 535 | - | - | - | - | - |
| 400 | 645 | - | - | - | - | - |
|
Permissible continuous current for wires with copper conductors with rubber insulation in metal protective sheaths and cables with copper conductors with rubber insulation in lead, polyvinyl chloride, |
|||||||
| Cross-section of current-carrying conductor, mm. | Current*, A, for wires and cables | ||||||
| single-core | two-wire | three-wire | |||||
| when laying | |||||||
| in the air | in the air | in the ground | in the air | in the ground | |||
| 1,5 | 23 | 19 | 33 | 19 | 27 | ||
| 2,5 | 30 | 27 | 44 | 25 | 38 | ||
| 4 | 41 | 38 | 55 | 35 | 49 | ||
| 6 | 50 | 50 | 70 | 42 | 60 | ||
| 10 | 80 | 70 | 105 | 55 | 90 | ||
| 16 | 100 | 90 | 135 | 75 | 115 | ||
| 25 | 140 | 115 | 175 | 95 | 150 | ||
| 35 | 170 | 140 | 210 | 120 | 180 | ||
| 50 | 215 | 175 | 265 | 145 | 225 | ||
| 70 | 270 | 215 | 320 | 180 | 275 | ||
| 95 | 325 | 260 | 385 | 220 | 330 | ||
| 120 | 385 | 300 | 445 | 260 | 385 | ||
| 150 | 440 | 350 | 505 | 305 | 435 | ||
| 185 | 510 | 405 | 570 | 350 | 500 | ||
| 240 | 605 | - | - | - | - | ||
* Currents refer to cables and wires with and without a neutral core.
|
Permissible continuous current for cables with aluminum conductors with rubber or plastic insulation in lead, polyvinyl chloride and rubber sheaths, armored and unarmored |
|||||||
| Cross-section of current-carrying conductor, mm. | Current, A, for wires and cables | ||||||
| single-core | two-wire | three-wire | |||||
| when laying | |||||||
| in the air | in the air | in the ground | in the air | in the ground | |||
| 2,5 | 23 | 21 | 34 | 19 | 29 | ||
| 4 | 31 | 29 | 42 | 27 | 38 | ||
| 6 | 38 | 38 | 55 | 32 | 46 | ||
| 10 | 60 | 55 | 80 | 42 | 70 | ||
| 16 | 75 | 70 | 105 | 60 | 90 | ||
| 25 | 105 | 90 | 135 | 75 | 115 | ||
| 35 | 130 | 105 | 160 | 90 | 140 | ||
| 50 | 165 | 135 | 205 | 110 | 175 | ||
| 70 | 210 | 165 | 245 | 140 | 210 | ||
| 95 | 250 | 200 | 295 | 170 | 255 | ||
| 120 | 295 | 230 | 340 | 200 | 295 | ||
| 150 | 340 | 270 | 390 | 235 | 335 | ||
| 185 | 390 | 310 | 440 | 270 | 385 | ||
| 240 | 465 | - | - | - | - | ||
Permissible continuous currents for four-core cables with plastic insulation for voltages up to 1 kV can be selected according to this table as for three-core cables, but with a coefficient of 0.92.
| Summary table of wire cross-sections, current, power and load characteristics | |||||
| Cross-section of copper conductors of wires and cables, sq. mm | Permissible continuous load current for wires and cables, A | Rated current of the circuit breaker, A | Maximum current of the circuit breaker, A | Maximum single-phase load power at U=220 V | Characteristics of an approximate single-phase household load |
| 1,5 | 19 | 10 | 16 | 4,1 | lighting and alarm group |
| 2,5 | 27 | 16 | 20 | 5,9 | socket groups and electric floors |
| 4 | 38 | 25 | 32 | 8,3 | water heaters and air conditioners |
| 6 | 46 | 32 | 40 | 10,1 | electric stoves and ovens |
| 10 | 70 | 50 | 63 | 15,4 | input supply lines |
The table shows data based on the PUE for selecting cross-sections of cable and wire products, as well as rated and maximum possible currents of circuit breakers for single-phase household loads most often used in everyday life.
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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 core, 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 volatile 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 the 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.