When a home power supply device is important to choose the right wire.

The material and diameter of the liveli must match the load, otherwise the overheating will happen with the subsequent melting of insulation, then a short circuit and a fire.

The selection technique is set forth in this article, the theme of which is in power: the table.

The throughput of conductive conductors is characterized by a maximum permissible current density.

The latter is defined as an attitude in the conductor to it. Unit of measurement - A / sq. mm (ampere per square millimeter).

But since the current is linked with power and voltage (W \u003d u * i)And the voltage is permanent, then the cross-section of the wires is more convenient to select the power of the consumer. After all, this parameter is usually indicated in the passport or on a signboard.

It is not terrible to make mistake when choosing a wire: it will only lead to unjustified material costs. Error in the other side is more expensive: insulation is mounted due to overheating, which leads to current leaks, followed by short circuit and fire.

Type and line parameter

The maximum allowable current density for the conductor depends on the 3 factors:

1. conductive vehicle material;
2. packing method (outer / hidden);
3. the number of phases on which the consumer is designed.

The electrical resistance of the core depends on the material, which means the amount of heat released when the heat flow occurs. Electrotechnical copper has the smallest resistance. Aluminum this parameter is 1.73 times higher. Because of this, the maximum allowable current density for aluminum wires is 1.73 times lower than for copper.

The heat sink intensity depends on the method of gasket. With an open type, the wires are cooled better than the sleeve, a box or a stroke, because the permissible current density increases for them.

Cable options

The effect of phase content is as follows: with equal power, single-phase and three-phase instruments consume different currents. Therefore, the permissible current density for a different number of phases is different.

Speaking of the permissible current density, two quantities distinguish:

1. Short-term permissible: such a current density, the conductor is able to withstand without overheating for a limited period. Such overloads occur, for example, when starting the electric motor.
2. A long permissible: current with such a density, the lived spends arbitrarily for a long time without exposed to overheating.

According to the PUE, a long-term current density is 40% less short-term permissible.

The line is also taken into account. The power grid is divided into two parts:

• lighting;
• power.

The power line is calculated based on the load.

The last edition of the "Rules of the device and connecting electrical installations" (PUE) prohibits the use of aluminum wires in residential premises.

Power

For a line that feeds one electrical appliance, the selection of the section is not labor, it is necessary to simply look into and find a cross-section of the vein that corresponds to known:

• power;
• phasnosts;
• method of laying.

This is how the wire is selected for laying from the switchboard to the boiler or air conditioner or from the junction box to one of the outlets.

Otherwise, things are concluded when connecting to one line of several consumers. For example, the wire is powered by a filling group of several points, which includes a refrigerator, microwave, electrical heater and TV.

If you simply summarize their power, the cross section of the wire will be overestimated, and he is unreasonably expensive, because the devices are operated differently and not at the same time.

Therefore, when calculating the total load on line from several consumers, two coefficients are used - simultaneity and demand.

Simultaney coefficient (KO)

It takes into account consumers usually work at different times. For different groups PUE consumers assigns their coefficient of simultaneity. Here, for example, how it changes depending on the number of apartments connected to the line:

It can be seen that in the case of one apartment, it is considered possible to synchronous inclusion of all devices - the simultaneous coefficient equal to unity. But with an increase in the number of apartments, the probability of simultaneous inclusion of all consumers is becoming less, which is reflected in the reduction of this coefficient.

Demand ratio (COP)

Considers the duration of the device. Some of them work constantly, others are increasing occasionally and for a short period. For example, for the TV demand coefficient is equal to one, for a vacuum cleaner - 0.1. Data for some consumers are shown in the table:

On a signboard or in the passport of consumers who have an electric motor or a transformer in its composition, only useful power (in watts) is indicated. The power consumed will be higher, since part of it is spent on overcoming the reactive resistance of the windings (reactive power).

To determine the full capacity, it is necessary to divide on cosφ - this value is also given in the passport and on the nameplate. If it is not specified, you can take averaged value: cosφ \u003d 0.7. Complete power is made to measure in Volt-amperes (BA).

Current line

If the table is built on a load current, and not power, first find it according to the formula i \u003d w / u, where: W is the power of the device in watts (W), U is voltage in volts (B) and then find a cross section. Power is determined taking into account the correction coefficients described above.

For example, when the heater is connected with a power of 1.1 kW in the chain, the current of power I \u003d 1100/220 \u003d 5A will flow.

Defense apparatus

In household power grids, three species protection devices are used.

Automatic switch (VA)

Disconnects the circuit if the current of the current in it exceeds the allowable value.

Protects the network site from short circuits and overloads.

According to the function of the VA, the fuse is similar, but in contrast to it, is a reusable: after eliminating a malfunction, which caused the disablement of the machine, it is again driven into the operating state using the or switch button.

Va is selected in accordance with the maximum current allowed for the protected chain and depending on the cross section of the wires.

Differential Current Switch or Protective Disconnection Device (UZO)

Disconnects the circuit during current leaks, that is, when the user touched the current parts or if they are due to the breakdown of insulation, they came into contact with a grounded conductor - construction structures, the case of the device, etc.

Different with two parameters:

1. Rated current. This is the maximum current that can proceed through this UDO, without damaging it. The rated current of the UZO should be at least one step above the rated current of its protecting it (that is, the above) va.
2. Sensitivity. This is the minimum leakage current, which causes the triggering of the RCD.

The sensitivity of the UZO is divided into the following categories:

• Firerests: have low sensitivity at 100, 300 or 500 mA, not protecting against electric shock. Through such UzOs are connected, for example, lighting in wooden houses.
• Protecting by electric shocks of people and animals.

Uzo and Diffabtomat

The latter are divided into two subgroups with leakage current setting:

1. 10 mA: Designed for consumers in rooms with high humidity;
2. 30 mA: For consumers in dry rooms.

Through such RCOs are connected by consumers who can cause an electrician. For lighting and devices, like air conditioning installed in an inaccessible place, they are not required.

There are imported Uzo on sale with the setting current of leakage of 6 mA. This value complies with European Union and USA standards.

The higher the sensitivity of the UZO, the greater the likelihood of false positives (depends on the quality of the power supply).

Differential automatic

The device "two in one": combined. It is less and more compact than two devices separately.

Selection of conductor

Wires with aluminum cores have similar labeling - AVVG. They do not apply to life now, but sometimes found in old houses.

The most preferred wires of the WGG brand.

The prefix "NG" indicates the use of non-combustible isolation. For laying for suspended ceilingIn the design of the floor or walls recommended wires with reduced smoke. They are recognized by the letters "LS" in marking.

The choice in favor of copper wires is due to the following advantages in comparison with aluminum:

• low electrical resistance: copper wires are heated less and therefore allowing higher current density;
• plasticity: Copper wire can have a cross section from 1.5 square meters. mm and bend repeatedly, while the aluminum after several stars breaks, and the minimum section for it is 2.5 square meters. mm.

Aluminum wires are used in power lines, as they weigh little and cheap.

Power cable cross section: Table

In conclusion, we give a table reflecting the dependence of the required area of \u200b\u200bthe cross-section of the wires from the load, material and the gasket method.

The right choice of wire section is, first of all, the issue of security. At the same time, it is desirable to provide a reserve in case of connecting new electrical appliances in the future.

An online calculator considers the cross section of the wire and power, as long as long. It believes both aluminum wiring and power copper conductors. Makes the selection of section (core diameter) depending on the load. Does not consider for 12V. To calculate, fill in all the fields and select the desired parameters in all drop-down lists. Important! We draw your attention - the calculations of this selection program are not direct guidelines for the use of electrical conductors, with the size of the cross section calculated here. They are only a preliminary reference to the sequence of section. The final accurate calculation of the selection of the section should make a qualified specialist who will make the right choice in each case. Remember, with the right calculations you will receive the result for the minimum section. power cables. Exceed this result for settlement electric wiringallowed.

Pue Table Calculation Table Cable Cable and Current

Allows you to select a maximum current and maximum load.

for copper wires:

for aluminum wires:

Formula for calculating cable cross section

Allows you to choose a section on power consumption and voltage.

For single-phase electrical networks (220 V):

I \u003d (p × k and) / (u × cos (φ))

• cOS (φ) - for household appliances, equals 1.
• U - phase voltage, can vary in the range from 210 V to 240 V
• I - Current Power
• P - Total power of all electrical appliances
• K and - the coefficient of simultaneity, for calculations is made 0.75

For 380 in three-phase networks:

I \u003d p / (√3 × u × cos (φ))

• COS Φ - phase shift angle
• P - the sum of the power of all electrical appliances
• I - current strength on which the cross section of the wire is selected
• U - phase voltage, 220V

Calculation of the automatic power and current

The table below shows the vehicle currents by means of connection depending on the voltage.

Calculation of the cross section of the wire It is a very important component of high-quality and reliable wiring. After all, these calculations include the power consumption of electrical equipment and long-permissible currents that can withstand the wire in normal operating mode. In addition, we all want to have a guarantee and be confident in electricity and fire safety electrical wiring, so calculation of the cross section of the wire It is important.

Let's see what the wrong segment of the wire can cause.

In most cases, electricians operating on the market in this service sector do not bother themselves to perform any calculations at all, but simply overestimate or underestimate the cross section of the wire. It is usually due to the fact that they are after a long time after graduation educational institutions Do not remember how this is done, since the knowledge gained was not fixed in time. Most of these knowledge has some part of the energy and main engineers and then due to the fact that their knowledge is operated in this direction every day.

If the cross section of the wire is smaller than the required

Consider an example if the cross section of the wire is underestimated, that is, less power consumption is selected.

This case is the most dangerous of all considered, as it can lead to a damage of electrical equipment, fire, affecting people electric shock, and often fatal outcome. Why this happens, everything is very simple. Suppose we have electric water heater 3 kW with a capacity, and the wire laid by a specialist is able to withstand only 1.5 kW. When the water heater is turned on, the wire will be very hot that over time will damage the insulation, and in the future and its complete destruction, a short circuit will occur.

If the wire section is larger than the required

Now, consider an example with an overestimated cross section of a wire selected more than required for equipment. About the reserve of the people even the sayings are all sorts of different, not extra might. In reasonable pasties, he is really not superfluous, but it will cost much more expensive. On the 3 kW water heater above, according to the calculation, we need a 2.5 mm 2 wire cross section, we look at Table 1.3.4 in PUE (rules of electrical installations). And in our case, the wire 6 mm 2 was used to be used, the cost of this wire is 2.5 times higher than 2.5 mm 2, allow 2.5 28 rubles, and 6 costs 70 rubles per meter. We will need 20 meters to be allowed, in the first case we will spend 560 rubles, and in the second 1400 rubles, the difference in money is obvious. And imagine if you do Make overestimated wires all the apartment, how much money in this case you throw on the wind. Hence the question, do you need such a stock?

Summing up the intermediate results, we learned that the wrong calculation of the cross-section of the wires is very unpleasant, and in some cases serious consequences, so it is simply necessary to approach the sequence of the wire sections correctly, competently and seriously.

Formula for calculating the cross section of the wire

I calcul \u003d p / u nom

where i is calculated current

P - equipment power,

U nom - rated voltage \u003d 220 volts

For example, we calculate the electric water heater of 3 kW.

3 kW \u003d 3000 W, I calc \u003d 3000/220 \u003d 13,636363 ..., rounded i calcul \u003d 14 a

There are also various correction coefficients, according to the conditions of the environment and laying of the wire, as well as the coefficient of re-short-term inclusion. To a greater extent, these coefficients have a weight in three-phase networks of 380 volts at the production, where large launchers are present. And in our case, we have household appliances designed for a voltage of 220 volts, so we will not count it, but must take into account it and we define it with an average value equal to 5 A and add to the calculated current.

As a result, I calc \u003d 14 + 5 \u003d 19 A,

the wire used copper three-core (phase, zero, ground), look at the table.

Copper wire cross sections on a long permissible current (Pue Table 1.3.4)

If, the value is in the interval between the two currents of different sections, in our case 15 A and 21 A, always take more. The calculated cross section of the wire required to connect the water heater with a power of 3 kW 2.5 mm 2.

So, on the 3 kW water heater provided in the example, we calculated the cross sections of the wires, found out why it is impossible to undress and overstate the cross-section of the wires. We learned how to determine the long-term valid currents, as well as correctly choose the cross section of the wire.

Similarly, according to the formula, it is also possible to perform, so you achieve the optimal illumination of non-strain vision and the high-quality distribution of the light flux.

By calculating the cross section of the wire with your own hands, you will save:

• On the purchase of wires, the cost of the wire increases with the cross section. For example, 1 meter of the non-combustible wire of the brand quite well-proven itself in the installation of the inner wiring cross section of 1.5 square costs 15 rubles, and the same wire with a cross section of 2.5 square costs 23 rubles, the difference of 8 rubles from one meter, from 100 meters is already 800 rubles.
• At the purchase of protection devices, circuit breakers, RCD. The larger the operation of the device, the greater the price. For example, a single-pole circuit breaker for 16 amps costs 120 rubles, and 25 amps are already 160 rubles, a difference of 40 rubles. The average power shield is gaining order of 12 circuit breakers from each 40 rubles to be 480 rubles. The difference in the value of the UZO will be even more, about 200-300 rubles.

Conduct power tablerequires to correctly calculate the cross section of the wire, if the power of the equipment is large, and the cross section of the wire is small, then it will be heated, which will result in the destruction of the insulation and the loss of its properties.

For transmission and distribution of electric current, the main means are wires, they provide the normal operation of everything that is connected with the electric current and how high-quality this work will be depends on right choice conducting wireby power. Comfortable table will help make the necessary selection:

But to use the table, it is necessary to calculate the overall power consumption of instruments and equipment that are used in the house, apartment or elsewhere where the wire will be conducted.

An example of calculating power.

Suppose it is performed in the house installation of closed wiring wires of explosives. On a sheet of paper you need to rewrite a list of equipment used.

But now learn power? It is possible to find it on the equipment itself, where there is usually a tag with recorded basic characteristics.

Power is measured in watts (W, W) or kilowatts (kW, kW). Now you need to write data, and then fold them.

The resulting number is, for example, 20,000 W, it will be 20 kW. This figure shows how many electrical acceptors together consume energy. Next, you should think about how the number of devices during a long period of time will be used simultaneously. Suppose it turned out 80%, in which case, the simultaneity coefficient will be 0.8. We produce power to calculate the cross section of the wire:

20 x 0.8 \u003d 16 (kW)

To select a section, you will need a wire power table:

If the three-phase chain is 380 volts, then the table will look like this:

These calculations do not constitute a special difficulty, but it is recommended to choose a wire or cable of the greatest section lived, because it may be so that it will be necessary to connect some device yet.

Additional wire power table.

As you know, there are different sections, material and with different quantities lived. Which one should choose not to overpay, and at the same time ensure the safe stable operation of all electrical appliances in the house? To do this, make a cable calculation. The calculation of the section is carried out, knowing the power of devices that feed on the network, and the current that will pass through the cable. You also need to know several other posting parameters.

Fundamental rules

When laying power grid in residential buildings, garages, apartments most often use cable with rubber or PVC insulation, designed for voltage of no more than 1 kV. There are brands that can be used in the open air, indoors, in the walls (strokers) and pipes. Usually this cable VVG. or AVVG S. different area Sections and quantities lived.
The PVA wires and the ShVVP cords are also used to connect electrical appliances.

After the calculation, the maximum allowable section of the cross section from a series of cable brands is selected.

The basic guidelines for the choice of sections are in the rules of the electrical installation device (PUE). The 6th and 7th editions were released, in which it is described in detail how to lay cables and wires, to establish protection, distributing devices and other important points.

For violation of the rules, administrative fines are provided. But the most important thing is that the violation of the rules can lead to the failure of the electrical appliances, wiring and serious fires. The damage from the fire is measured sometimes not the sum of money, but by human victims.

The importance of the right segment

Why is the calculation of the cable cross section so important? To answer, you need to remember the school lessons of physics.

The current proceeds along the wires and heats them. The stronger the power, the greater the heating. The active power of the current is calculated by the formula:

P \u003d U. I. cos φ \u003d ² * r

R. - Active resistance.

As can be seen, power depends on the strength of the current and resistance. The more resistance, the more heat allocates, that is, the stronger the wires are heated. Similar to current. What he is more, the more heated the conductor.

Resistance in turn depends on the material of the conductor, its length and cross-sectional area.

R \u003d ρ * L / S

ρ - resistivity;

l. - the length of the conductor;

S.- Cross-section area.

It can be seen that less square, the more resistance. And the more resistance, ther the conductor is stronger than it.

If you buy the wire and measure it with diameter, do not forget that the area is calculated by the formula:

S \u003d π * d² / 4

d. - diameter.

You should also not forget the specific resistance. It depends on the material from which the wires are made. The resistivity of aluminum is greater than copper. So, with the same area, aluminum will be heighted harder. It immediately becomes clear why aluminum wires are recommended to take a larger cross section than copper.

To do not go into the long calculation of the cable cross section, the rules of sections of the wire section were developed in tables.

Calculation of the cross section of the power and current

The calculation of the cross section of the wire depends on the total power consumed by electrical appliances in the apartment. It can be calculated individually, or use the average characteristics.

The accuracy of calculations constitute the structural scheme, which depicts devices. You can learn the power of each from the instructions or read on the label. The greatest power in electric ovens, boilers, air conditioners. The total digit should turn out in the range of approximately 5-15 kW.

Knowing power, according to the formula determines the rated current strength:

I \u003d (p K) / (ucos φ)

P. - Power in watts

U.\u003d 220 Volt.

K.\u003d 0.75 - the coefficient of simultaneous inclusion;

cos φ \u003d 1 for household electrical appliances;

If the network is three-phase, then use another formula:

I \u003d p / (u √3 cos φ)

U.\u003d 380 VOLT.

Calculating the current, you need to use the tables that are presented in PUE, and determine the cross section of the wire. The tables specify the allowable long-term current for copper and aluminum wires with isolation of various types. Rounding is always produced in the biggest, so that there is a stock.

You can also refer to the tables in which the section is recommended to determine only in power.

Special calculators are developed, which determine the section, knowing the power consumption, the phase of the network and the length of the cable line. Attention should be paid to the laying conditions (in the pipe or outdoors).

Influence of wiring length on cable selection

If the cable is very long, then there are additional limitations on the sequence of section, since there are voltage losses on the extended portion, which in turn leads to additional heating. To calculate the loss of voltage use the concept of "moment of load". It is determined as a product of power in kilowatts for length in meters. Next, look at the loss value in the tables. For example, if the power consumption is 2 kW, and the cable length is 40 m, then the moment is equal to 80 kW * m. For a copper cable with a cross section of 2.5 mm square. This means that voltage losses are 2-3%.

If the losses will exceed 5%, then it is necessary to take a segment with a margin, more recommended for use at a given current.

Estimated tables are provided separately for a single-phase and three-phase network. For a three-phase moment of load increases, since the load capacity is distributed over the three phases. Consequently, losses are reduced, and the effect of length decreases.

Voltage losses are important for low-voltage devices, in particular, gas-discharge lamps. If the supply voltage is 12 V, then with a loss of 3% for the network 220 to the fall will be much noticeable, and for a low-voltage lamp it will decrease almost twice. Therefore, it is important to place start-adjusting devices as close as possible to such lamps.

The calculation of the loss of voltage is performed as follows:

ΔU \u003d (P ∙ R0 + Q ∙ x0) ∙ L / UON

P. - active power, W.

Q. - reactive power, W.

r0 - Active line resistance, OM / m.

x0. - reactive line resistance, OM / m.

UAN - Rated voltage, V. (It is indicated in the characteristics of electrical appliances).

L. - Length line, m.

Well, if easier for living conditions:

R. - cable resistance, calculated according to the well-known formula R \u003d ρ * L / S;

I. - the current is found from the Ohm law;

Suppose we happened that I.\u003d 4000 W / 220 IN\u003d 18.2 A.

Resistance to one copper wire vein with a length of 20 m and an area of \u200b\u200b1.5 mm square. amounted to R.\u003d 0.23 ohms. The total resistance of the two veins is 0.46 ohms.

Then ΔU.\u003d 18.2 * 0.46 \u003d 8.37 V

In percentage ratio

8,37*100/220=3,8%

On long lines from overload and short circuits are installed with thermal and electromagnetic releases.