What is the resistance of copper wire. Wire resistance. Influence of adjacent conductors

When an electrical circuit is closed, on the terminals of which there is a potential difference, an electric current arises. Free electrons under the influence of electric field forces move along the conductor. In their motion, free electrons collide with the atoms of the conductor and give them a reserve of their kinetic energy.

Thus, electrons passing through the conductor meet resistance to their movement. When an electric current passes through a conductor, the latter heats up.

The electrical resistance of the conductor (it is denoted by the Latin letter r) is due to the phenomenon of converting electrical energy into thermal energy when an electric current passes through the conductor. In the diagrams, electrical resistance is indicated as shown in Fig. 18.

The unit of resistance is 1 ohm. Om is often denoted by the Greek capital letter Ω (omega). Therefore, instead of writing: "The resistance of the conductor is 15 ohms," you can simply write: r = 15 Ω.

1000 ohm is called 1 kilo ohm (1 kom, or 1 kΩ).

1,000,000 ohms is called 1 meg (1 mg, or 1 MΩ).

Appliance, having a variable electrical resistance and serving to change the current in the circuit, is called a rheostat. In the diagrams, rheostats are designated as shown in fig. 18. As a rule, a rheostat is made from a wire of one or another resistance, wound on an insulating base. The slider or lever of the rheostat is placed in a certain position, as a result of which the desired resistance is introduced into the circuit.

A long conductor of small cross-section creates a high resistance to current. Short conductors of large cross-section have little resistance to current.

If we take two conductors of different materials, but of the same length and section, then the conductors will conduct current in different ways. This shows that the resistance of a conductor depends on the material of the conductor itself.

The temperature of the conductor also affects its resistance. As the temperature rises, the resistance of metals increases, and the resistance of liquids and coal decreases. Only some special metal alloys (manganin, constantan, nickeline, etc.) almost do not change their resistance with increasing temperature.

So, we see that the electrical resistance of the conductor depends on the length of the conductor, the cross section of the conductor, the material of the conductor, the temperature of the conductor.

When comparing the resistances of conductors from different materials, it is necessary to take a certain length and section for each sample. Then we will be able to judge which material conducts electric current better or worse.

The resistance (in ohms) of a conductor 1 m long, with a cross section of 1 mm 2 is called resistivity and is denoted by the Greek letter ρ (po).

Conductor resistance can be determined by the formula

where r is the resistance of the conductor, ohm;

ρ - specific resistance of the conductor;

l- conductor length, m;

S - conductor cross section, mm2.

From this formula, we obtain the dimension for resistivity

In table. 1 shows the resistivity of some conductors.

The table shows that an iron wire with a length of 1 m and a cross section of 1 mm2 has a resistance of 0.13 ohms. To get 1 ohm of resistance, you need to take 7.7 m of such wire. Silver has the lowest resistivity - 1 ohm of resistance can be obtained by taking 62.5 m of silver wire with a cross section of 1 mm 2. Silver is the best conductor, but the high cost of silver precludes its widespread use. After silver in the table comes copper: 1 m of copper wire with a cross section of 1 mm "has a resistance of 0.0175 ohms. To get a resistance of 1 ohm, you need to take 57 m of such wire.

Chemically pure, obtained by refining, copper has found widespread use in electrical engineering for the manufacture of wires, cables, windings of electrical machines and apparatus. Aluminum and iron are also widely used as conductors.

A detailed description of metals and alloys is given in Table. 2.

Example 1 Determine the resistance of 200 m of iron wire with a cross section of 5 mm 2:

Example 2 Calculate the resistance of 2 km of aluminum wire with a cross section of 2.5 mm2:

From the resistance formula, you can easily determine the length, resistivity and cross section of the conductor.

Example3. For a radio receiver, it is necessary to wind a resistance of 30 ohms from nickel wire with a cross section of 0.21 mm2. Determine the required wire length:

Example 4 Determine the cross section of a nichrome wire with a length of 20 W, if its resistance is 25 ohms:

Example 5 A wire with a cross section of 0.5 mm2 and a length of 40 m has a resistance of 16 ohms. Determine the material of the wire.

The material of the conductor characterizes its resistivity

According to the table of resistivity, we find that lead has such resistance.

It was previously stated that the resistance of conductors depends on temperature. Let's do the following experiment. We wind several meters of thin metal wire in the form of a spiral and turn this spiral into a battery circuit. An ammeter is included in the circuit to measure current. When heating the spiral in the flame of the burner, you can notice that the ammeter readings will decrease. This shows that the resistance of the metal wire increases with heating.

For some metals, when heated by 100 °, the resistance increases by 40-50%. There are alloys that slightly change their resistance with heat. Some special alloys hardly change resistance with temperature. The resistance of metal conductors increases with increasing temperature, the resistance of electrolytes (liquid conductors), coal and some solids, on the contrary, decreases.

The ability of metals to change their resistance with temperature changes is used to construct resistance thermometers. Such a thermometer is a platinum wire wound on a mica frame. By placing a thermometer, for example, in a furnace and measuring the resistance of the platinum wire before and after heating, the temperature in the furnace can be determined.

The change in the resistance of the conductor when it is heated, per 1 ohm of the initial resistance and 1 0 of the temperature, is called temperature coefficient of resistance and is denoted by the letter α (alpha).

If at a temperature t 0 the resistance of the conductor is r 0, and at a temperature t it is r t, then the temperature coefficient of resistance

The concept of electrical resistance and conductivity

Any body through which an electric current flows, has a certain resistance to it.The property of a conductor material to prevent the passage of electric current through it is called electrical resistance.

Electronic theory explains the essence of the electrical resistance of metal conductors in this way. When moving along a conductor, free electrons encounter atoms and other electrons countless times on their way and, interacting with them, inevitably lose part of their energy. The electrons experience, as it were, resistance to their movement. Different metal conductors having different atomic structure have different resistance to electric current.

Exactly the same explains the resistance of liquid conductors and gases to the passage of electric current. However, one should not forget that in these substances, not electrons, but charged particles of molecules meet resistance during their movement.

Resistance is indicated by Latin letters R or r.

The ohm is taken as the unit of electrical resistance.

Ohm is the resistance of a mercury column 106.3 cm high with a cross section of 1 mm2 at a temperature of 0 ° C.

If, for example, the electrical resistance of the conductor is 4 ohms, then it is written as follows: R = 4 ohms or r = 4 ohms.

To measure the resistance of a large value, a unit called megohm is adopted.

One meg is equal to one million ohms.

The greater the resistance of the conductor, the worse it conducts electric current, and, conversely, the lower the resistance of the conductor, the easier it is for the electric current to pass through this conductor.

Therefore, to characterize the conductor (in terms of the passage of electric current through it), one can consider not only its resistance, but also the reciprocal of the resistance and is called conductivity.

electrical conductivity The ability of a material to pass an electric current through itself is called.

Since conductivity is the reciprocal of resistance, it is expressed as 1 / R, the conductivity is denoted by the Latin letter g.

Influence of conductor material, its dimensions and ambient temperature on the value of electrical resistance

The resistance of various conductors depends on the material from which they are made. To characterize the electrical resistance of various materials, the concept of the so-called resistivity has been introduced.

Resistivity is the resistance of a conductor 1 m long and with a cross-sectional area of ​​1 mm2. Resistivity is denoted by the Greek letter p. Each material from which the conductor is made has its own resistivity.

For example, the resistivity of copper is 0.017, that is, a copper conductor 1 m long and 1 mm2 in cross section has a resistance of 0.017 ohms. The resistivity of aluminum is 0.03, the resistivity of iron is 0.12, the resistivity of constantan is 0.48, the resistivity of nichrome is 1-1.1.

The resistance of a conductor is directly proportional to its length, that is, the longer the conductor, the greater its electrical resistance.

The resistance of a conductor is inversely proportional to its cross-sectional area, that is, the thicker the conductor, the lower its resistance, and, conversely, the thinner the conductor, the greater its resistance.

To better understand this relationship, imagine two pairs of communicating vessels, with one pair of vessels having a thin connecting tube and the other having a thick one. It is clear that when one of the vessels (each pair) is filled with water, its transition to another vessel through a thick tube will occur much faster than through a thin one, i.e., a thick tube will offer less resistance to the flow of water. In the same way, it is easier for an electric current to pass through a thick conductor than through a thin one, that is, the first one offers him less resistance than the second.

The electrical resistance of a conductor is equal to the specific resistance of the material from which this conductor is made, multiplied by the length of the conductor and divided by the area of ​​the cross-sectional area of ​​the conductor:

R = pl / S ,

Where - R - conductor resistance, ohm, l - conductor length in m, S - conductor cross-sectional area, mm 2.

Cross-sectional area of ​​a round conductor calculated by the formula:

S \u003d Pi x d 2 / 4

Where is Pi - constant value equal to 3.14; d is the diameter of the conductor.

And so the length of the conductor is determined:

l = S R / p ,

This formula makes it possible to determine the length of the conductor, its cross section and resistivity, if the other quantities included in the formula are known.

If it is necessary to determine the cross-sectional area of ​​\u200b\u200bthe conductor, then the formula is reduced to the following form:

S = pl / R

Transforming the same formula and solving the equality with respect to p, we find the resistivity of the conductor:

R = R S / l

The last formula has to be used in cases where the resistance and dimensions of the conductor are known, and its material is unknown and, moreover, difficult to determine by appearance. To do this, it is necessary to determine the resistivity of the conductor and, using the table, find a material that has such a resistivity.

Another reason that affects the resistance of conductors is temperature.

It has been established that with increasing temperature, the resistance of metal conductors increases, and decreases with decreasing. This increase or decrease in resistance for pure metal conductors is almost the same and averages 0.4% per 1°C. The resistance of liquid conductors and coal decreases with increasing temperature.

The electronic theory of the structure of matter gives the following explanation for the increase in the resistance of metallic conductors with increasing temperature. When heated, the conductor receives thermal energy, which is inevitably transferred to all atoms of the substance, as a result of which the intensity of their movement increases. The increased movement of atoms creates more resistance to the directed movement of free electrons, which is why the resistance of the conductor increases. With a decrease in temperature, better conditions are created for the directed movement of electrons, and the resistance of the conductor decreases. This explains an interesting phenomenon - superconductivity of metals.

Superconductivity, i.e., a decrease in the resistance of metals to zero, occurs at a huge negative temperature - 273 ° C, called absolute zero. At a temperature of absolute zero, the metal atoms seem to freeze in place, without impeding the movement of electrons at all.

Electrical resistance is the main characteristic of conductive materials. Depending on the scope of the conductor, the value of its resistance can play both a positive and a negative role in the functioning of an electrical system. Also, the features of the use of the conductor may cause the need to take into account additional characteristics, the influence of which in a particular case cannot be neglected.

Conductors are pure metals and their alloys. In a metal, atoms fixed in a single "strong" structure have free electrons (the so-called "electron gas"). It is these particles in this case that are charge carriers. Electrons are in constant random movement from one atom to another. When an electric field appears (a voltage source is connected to the ends of the metal), the movement of electrons in the conductor becomes ordered. Moving electrons encounter obstacles on their way, caused by the peculiarities of the molecular structure of the conductor. When colliding with the structure, charge carriers lose their energy, giving it to the conductor (heating it). The more obstacles the conductive structure creates for charge carriers, the higher the resistance.

With an increase in the cross section of the conducting structure for one number of electrons, the “transmission channel” will become wider, and the resistance will decrease. Accordingly, with an increase in the length of the wire, there will be more such obstacles and the resistance will increase.

Thus, the basic formula for calculating the resistance includes the length of the wire, the cross-sectional area and a certain coefficient that relates these dimensional characteristics to the electrical values ​​of voltage and current (1). This coefficient is called resistivity.
R=r*L/S (1)

Resistivity

Resistivity unchanged and is a property of the substance from which the conductor is made. Units of measurement r - ohm * m. Often, the resistivity value is given in ohm * mm sq. / m. This is due to the fact that the cross section of the most commonly used cables is relatively small and is measured in mm square. Let's take a simple example.

Task number 1. Copper wire length L = 20 m, section S = 1.5 mm. sq. Calculate the wire resistance.
Solution: specific resistance of copper wire r = 0.018 ohm*mm. sq./m. Substituting the values ​​into formula (1) we get R=0.24 ohm.
When calculating the resistance of the power system, the resistance of one wire must be multiplied by the number of wires.
If aluminum with a higher resistivity (r = 0.028 ohm * mm sq. / m) is used instead of copper, then the resistance of the wires will increase accordingly. For the example above, the resistance would be R = 0.373 ohm (55% more). Copper and aluminum are the main materials for wires. There are metals with lower resistivity than copper, such as silver. However, its use is limited due to the obvious high cost. The table below lists the resistances and other basic characteristics of conductor materials.
Table - the main characteristics of the conductors

Thermal losses of wires

If, using the cable from the above example, a load of 2.2 kW is connected to a single-phase 220 V network, then the current I \u003d P / U or I \u003d 2200/220 \u003d 10 A will flow through the wire. The formula for calculating the power loss in the conductor:
Ppr \u003d (I ^ 2) * R (2)
Example No. 2. Calculate active losses during power transmission of 2.2 kW in a network with a voltage of 220 V for the mentioned wire.
Solution: by substituting the values ​​of the current and resistance of the wires into the formula (2), we get Ppr \u003d (10 ^ 2) * (2 * 0.24) \u003d 48 W.
Thus, when transferring energy from the network to the load, the losses in the wires will be slightly more than 2%. This energy is converted into heat released by the conductor into the environment. According to the condition of heating the conductor (according to the magnitude of the current), its cross section is selected, guided by special tables.
For example, for the above conductor, the maximum current is 19 A or 4.1 kW in a 220 V network.

Increased voltage is used to reduce active losses in power lines. In this case, the current in the wires decreases, the losses fall.

Temperature effect

An increase in temperature leads to an increase in the oscillations of the crystal lattice of the metal. Accordingly, the electrons encounter more obstacles, which leads to an increase in resistance. The value of the "sensitivity" of the resistance of the metal to a rise in temperature is called the temperature coefficient α. The formula for taking into account the temperature is as follows
R=Rн*, (3)
where Rn is the resistance of the wire under normal conditions (at temperature t°n); t° is the temperature of the conductor.
Usually t°n = 20°C. The value of α is also indicated for the temperature t°n.
Task 4. Calculate the resistance of a copper wire at a temperature of t ° \u003d 90 ° C. α copper \u003d 0.0043, Rn \u003d 0.24 Ohm (task 1).
Solution: substituting the values ​​in formula (3) we get R = 0.312 Ohm. The resistance of the analyzed heated wire is 30% greater than its resistance at room temperature.

Frequency effect

With an increase in the frequency of the current in the conductor, the process of displacing charges closer to its surface occurs. As a result of an increase in the concentration of charges in the surface layer, the resistance of the wire also increases. This process is called the “skin effect” or surface effect. Skin coefficient– the effect also depends on the size and shape of the wire. For the above example, with an AC frequency of 20 kHz, the resistance of the wire will increase by approximately 10%. Note that high-frequency components can have a current signal of many modern industrial and domestic consumers (energy-saving lamps, switching power supplies, frequency converters, and so on).

Influence of adjacent conductors

Around any conductor through which current flows, there is a magnetic field. The interaction of the fields of neighboring conductors also causes energy losses and is called the "proximity effect". Also note that any metal conductor has an inductance created by a conductive core, and a capacitance created by insulation. These parameters also have a proximity effect.

Technologies

High voltage zero resistance wires

This type of wire is widely used in car ignition systems. The resistance of high-voltage wires is quite small and amounts to a few fractions of an ohm per meter of length. Recall that the resistance of such a value cannot be measured with a general-purpose ohmmeter. Often, measuring bridges are used for the task of measuring low resistances.
Structurally, such wires have a large number of copper conductors with insulation based on silicone, plastics or other dielectrics. The peculiarity of the use of such wires is not only in operation at high voltage, but also in the transfer of energy in a short period of time (pulse mode).

Bimetal cable

The main scope of the mentioned cables is the transmission of high-frequency signals. The core of the wire is made of one type of metal, the surface of which is coated with another type of metal. Since only the surface layer of the conductor is conductive at high frequencies, it is possible to replace the inside of the wire. This saves expensive material and improves the mechanical characteristics of the wire. Examples of such wires are silver-plated copper, copper-plated steel.

Conclusion

Wire resistance is a value that depends on a group of factors: type of conductor, temperature, current frequency, geometric parameters. The significance of the influence of these parameters depends on the operating conditions of the wire. Optimization criteria depending on the tasks for wires can be: reduction of active losses, improvement of mechanical characteristics, price reduction.

Electrical resistance -a physical quantity that shows what kind of obstacle is created by the current when it passes through the conductor. The units of measurement are ohms, after Georg Ohm. In his law, he derived a formula for finding resistance, which is given below.

Consider the resistance of conductors using the example of metals. Metals have an internal structure in the form of a crystal lattice. This lattice has a strict order, and its nodes are positively charged ions. The charge carriers in the metal are “free” electrons, which do not belong to a particular atom, but randomly move between lattice sites. It is known from quantum physics that the movement of electrons in a metal is the propagation of an electromagnetic wave in a solid. That is, an electron in a conductor moves at the speed of light (practically), and it has been proven that it exhibits properties not only as a particle, but also as a wave. And the resistance of the metal arises as a result of the scattering of electromagnetic waves (that is, electrons) on the thermal vibrations of the lattice and its defects. When electrons collide with the nodes of the crystal lattice, part of the energy is transferred to the nodes, as a result of which energy is released. This energy can be calculated at direct current, thanks to the Joule-Lenz law - Q \u003d I 2 Rt. As you can see, the greater the resistance, the more energy is released.

Resistivity

There is such an important concept as resistivity, this is the same resistance, only in a unit of length. Each metal has its own, for example, for copper it is 0.0175 Ohm*mm2/m, for aluminum it is 0.0271 Ohm*mm2/m. This means that a copper bar with a length of 1 m and a cross-sectional area of ​​1 mm2 will have a resistance of 0.0175 Ohm, and the same bar, but made of aluminum, will have a resistance of 0.0271 Ohm. It turns out that the electrical conductivity of copper is higher than that of aluminum. Each metal has its own resistivity, and the resistance of the entire conductor can be calculated using the formula

Where p is the resistivity of the metal, l is the length of the conductor, s is the cross-sectional area.

Resistivity values ​​are given in metal resistivity table(20°C)

Substance	p, Ohm * mm 2 / 2	α,10 -3 1/K
Aluminum	0.0271
Tungsten	0.055
Iron	0.098
Gold	0.023
Brass	0.025-0.06
Manganin	0.42-0.48	0,002-0,05
Copper	0.0175
Nickel
Constantan	0.44-0.52	0.02
Nichrome		0.15
Silver	0.016
Zinc	0.059

In addition to resistivity, the table contains TCR values, more on this coefficient a little later.

Dependence of resistivity on deformations

During cold working of metals by pressure, the metal undergoes plastic deformation. During plastic deformation, the crystal lattice is distorted, the number of defects becomes larger. With an increase in the defects of the crystal lattice, the resistance to the flow of electrons through the conductor increases, therefore, the resistivity of the metal increases. For example, a wire is made by drawing, which means that the metal undergoes plastic deformation, as a result of which, the resistivity increases. In practice, to reduce the resistance, recrystallization annealing is used, this is a complex technological process, after which the crystal lattice, as it were, “straightens out” and the number of defects decreases, therefore, the resistance of the metal too.

When stretched or compressed, the metal undergoes elastic deformation. With elastic deformation caused by stretching, the amplitudes of thermal vibrations of the crystal lattice nodes increase, therefore, the electrons experience great difficulties, and in connection with this, the resistivity increases. With elastic deformation caused by compression, the amplitudes of thermal oscillations of nodes decrease, therefore, it is easier for electrons to move, and the resistivity decreases.

Effect of Temperature on Resistivity

As we have already found out above, the cause of resistance in a metal is the nodes of the crystal lattice and their vibrations. So, with an increase in temperature, the thermal fluctuations of the nodes increase, which means that the resistivity also increases. There is such a value as temperature coefficient of resistance(TCS), which shows how much the resistivity of the metal increases or decreases when heated or cooled. For example, the temperature coefficient of copper at 20 degrees Celsius is 4.1 10 − 3 1/degree. This means that when, for example, a copper wire is heated by 1 degree Celsius, its resistivity will increase by 4.1 · 10 − 3 Ohm. Resistivity with temperature change can be calculated by the formula

where r is the resistivity after heating, r 0 is the resistivity before heating, a is the temperature coefficient of resistance, t 2 is the temperature before heating, t 1 is the temperature after heating.

Substituting our values, we get: r=0.0175*(1+0.0041*(154-20))=0.0271 Ohm*mm2/m. As you can see, our bar of copper, 1 m long and with a cross-sectional area of ​​1 mm 2, after heating to 154 degrees, would have resistance, like the same bar, only made of aluminum and at a temperature of 20 degrees Celsius.

The property of changing resistance with temperature, used in resistance thermometers. These instruments can measure temperature based on resistance readings. Resistance thermometers have high measurement accuracy, but small temperature ranges.

In practice, the properties of conductors prevent the passage current are used very widely. An example is an incandescent lamp, where a tungsten filament is heated due to the high resistance of the metal, large length and narrow cross section. Or any heating device where the coil is heated due to high resistance. In electrical engineering, an element whose main property is resistance is called - resistor. The resistor is used in almost any electrical circuit.

When designing electrical circuits, it is important to choose the right material and wire size. Most often, copper is used for these purposes, which has less resistance.

What determines the resistance of a metal

Electric current is the directed movement of charged particles. In metals, these are free electrons. They move between the atoms of the crystal lattice. The resistance to their movement depends on the metal or alloy, as well as its temperature - as it increases, the resistance of the wire to electric current increases.

The exception is special alloys used in measuring instruments. Resistors are made from them that do not change their parameters when the temperature changes. In addition, two-wire wires are used to connect thermocouples, the resistance of one of which increases with increasing temperature, and the other decreases. As a result, the cable parameters do not change.

Resistivity of various metals

Different metals have different properties and are used for different purposes.

Copper and aluminum

The most common wires are copper and aluminum. Copper has a lower electrical resistance than the resistance of aluminum wire, cables from it have a smaller cross section. It is stronger, this allows you to make the cable thinner, as well as flexible and stranded. In addition, copper is soldered with tin solders.

But aluminum has one advantage: it is much cheaper. Therefore, it is used for winding transformers and laying wiring, during operation of which there are no bends, movement or vibration.

Other metals

• Gold. It has the lowest electrical resistance, but due to its price it is used only in certain places in military and space technology;
• Silver. It has a better price / quality ratio than gold, but it is also used to a limited extent, mainly for the manufacture of contacts and connectors - it does not oxidize;
• Nichrome (an alloy of nickel and chromium) and Fechral (iron, chromium and aluminum). They have a high melting point. The resistance of nichrome and nichrome wire is large enough to make heaters and resistance wires;
• Tungsten. It has a high resistivity and is very refractory - 3422 degrees. It is used to make filaments in light bulbs;
• Constantan. An alloy of copper, nickel and manganese that does not change its properties with temperature changes. It is used for the manufacture of resistors in measuring instruments;
• Compensatory. These alloys are used to make cables for connecting thermocouples and other sensors. As the temperature rises, the electrical resistance of one conductor increases and that of the other decreases. As a result, the total value remains unchanged.

Interesting. In the 1950s, transformers for high-voltage substations with silver windings were designed. Given the reduced losses, this was beneficial. But due to the increase in the price of silver on the world market, these projects were not implemented.

Cable section selection

When calculating the cross section of a conductive core, heating and voltage drop in long cables are taken into account. You can calculate the resistance of the wire using special tables or using online calculators.

The cross section calculated from losses can be larger or smaller than that calculated from heating. It depends on the length of the cable. For padding, a larger value is selected.

Selection of the conductor section according to the allowable heating

When electric current flows through the cable, it heats up. This heating can melt the insulation, which will lead to its destruction and the short circuit of adjacent wires to each other or to grounded structural parts.

Important! Destruction of insulation and K.Z. (short circuit) may cause a fire.

In order to prevent this situation, the cable cross-section must be suitable for the load current, insulation type and laying conditions. Open or heat-insulated wires can carry more current than vinyl or rubber-jacketed pipes.

Selection of cross-section according to voltage losses

When an electric current flows through the cable, the voltage near the load decreases. This is due to the fact that, although the resistance of a small piece of wire and the voltage drop across it is small, over a long length it can reach a significant value.

For example, the specific resistance of a copper wire is 0.017 ohm mm²/m. But in a single-core cable 100 m long with a cross section of 10 mm², it will be 0.17 Ohm. At a current of 80A (admissible for heating), the voltage drop in the 220V network will be 27V (100 m of phase wire and 100 m of zero with a drop of 13V in each conductor). Therefore, with a permissible voltage drop of 2% or 5V, the cable cross-section must be at least 66 mm², or the nearest higher standard value - 75 mm².

If the calculation of the section for heating is carried out according to the operating current of the electric motor and in the section from the introductory machine to the device, then the calculation for losses must be made according to the starting current, taking into account the entire length of the cables: from the main to the electric machine.

The resistance of a copper wire is a value that affects the choice of cables and wires for winding coils when designing electrical circuits, as well as electric motors and transformers. Knowing how the conductor resistance is calculated and the necessary formulas will help to correctly design the wiring and avoid accidents.

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