How to calculate the cross section of the wiring. How to choose a cable cross section
How to calculate cable for current, voltage and length. As you know, there are different sections, material and with different quantities lived. Which one needs to be chosen 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 grids in residential buildings, garages, apartments most often use a 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 with a different cross section area and 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.
Importance right choice Sections
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 the smaller the area, 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) / (u * cos 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 mm². 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:
ΔU \u003d I * R
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.
In the process of repair, they usually always replace the old wiring. This is due to the fact that many useful household appliances have recently appeared, which facilitate the life of housewives. Moreover, they consume quite a few energy, which is old wiring, just may not stand. Such electrical appliances should be attributed washing machines, Electric ovens, electric kettle, microwaves, etc.
Locking the electric pipe, you should know what section the wire should be paved to power the electrical appliance or group of electrical appliances. As a rule, the choice is carried out both by power consumption and the strength of the current, which consume electrical appliances. At the same time, it is necessary to take into account how the laying method and the length of the wire.
It is quite simple to select the secting of the cable paved for load power. This may be one load or totality of loads.
Each household appliance, the more new, is accompanied by a document (passport), where its main technical data is indicated. In addition, the same data is available on special signs attached to the body of the product. On this plate, which is located on the side or back of the device, is indicated by the country of manufacturer, its factory number and, of course, its power consumption in wats (W) and current that consumes the device in amperes (A). On products of the domestic producer, power may be indicated in watts (W) or kilowatts (kW). In import models there is a letter W. In addition, the power consumption is indicated as "that" or "that max".
An example of such a sign, where the main information on the device is indicated. Such a sign can be found on any technical device. In the event that you cannot recognize the desired information (the inscription fell on the plate or household appliances Not yet) You can find out about what power has the most common household appliances. All this data is actually found in the table. Basically, the electrical appliances are standardized by power consumed and there is no special data scatter.
The table selects those electrical appliances that are planned to be purchased and their consumed current 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 calculate and wiring will be more reliable. The fact is that the thicker the cable, the better because the wiring is warm much less.
How to choose from
When the wire is selected, all loads should be summed up to this wire. At the same time, it should be monitored so that all the indicators are discharged or in watts, or kilowatts. To translate the indicators to one value, the numbers are followed or divided, or multiply by 1000. For example, to translate into watts, all numbers follow (if they are in kilowatts) to multiply by 1000: 1.5 kW \u003d 1.5x1000 \u003d 1500 W. When reverse rendering actions are made in reverse order: 1500 W \u003d 1500/1000 \u003d 1.5 kW. Usually, all calculations are made in wats. After such calculations, the cable is selected by using the corresponding table.
You can use the table as follows: Find the corresponding column, where the supply voltage is indicated (220 or 380 volts). In this column there is a digit that corresponds to the power of consumption (you need to take a little greater value). In the line that corresponds to the power consumption, the first column shows the cross section of the wire that is allowed to be used. Going to the store for the cable, you should search for the wire, the cross section of which corresponds to the records.
What wire is to use - aluminum or copper?
In this case, it all depends on power consumption. In addition, copper wire Withstands the load twice as much as aluminum. If the load is large, it is better to give preference to the copper wire, as it will be thinner and easier to lay it. In addition, it is easier to connect it to electrical equipment, including to sockets, and to switches. Unfortunately, the copper wire has a significant minus: it is much more expensive than the wire from aluminum. Despite this, he will serve much longer.
How to calculate the current cable cross section
Most of the masters calculate the diameters of the current consumption. Sometimes it simplifies the task, especially if you know which current withstands a wire having one or another thickness. To do this, write all the indicators of the current consumed and summing up. The wire section can be chosen along the same table, only now you need to look for a column where the current is specified. As a rule, the greater value is always selected for reliability.
For example, to connect a hob that can consume a maximum current to 16a, a copper wire is required. By contacting the table, the desired result can be found in the third column on the left. Since there is no value 16a, then choose the nearest, greater - 19a. By this current is suitable for the cable cross section, equal to 2.0 mm square.
As a rule, connecting powerful household appliances, they are powered by separate wires, with the installation of individual inclusion machines. This greatly simplifies the process of selection of wires. In addition, this is part modern demands To wiring. Plus, it is practical. In an emergency, you do not have to turn off the electricity completely, in the whole housing. It is not recommended to choose wires along a smaller value. If the cable will constantly work at maximum loads, it can lead to emergency situations in electrical network. The result can be a fire if automatic switches are incorrectly selected. At the same time, you should know that they are not protected from the shell ignition, and it is not possible to choose exactly the current so that it can protect the wires from overload. The fact is that they are not regulated and manufactured on a fixed current value. For example, on 6a, on 10a, on 16a, etc.
The selection of the wire with a margin will allow you to further install another electrical appliance on this line or even a few if it will correspond to the current consumption rate.
Calculation of power cable and length
If you take into account the average apartment, then the length of the wires does not reach such values \u200b\u200bto take into account this factor. Despite this, there are cases when when choosing a wire should be taken into account and their length. For example, you need to connect a private house From the nearest pillar, which can be at a considerable distance from the house.
With significant consumption currents, the long wire can influence the quality of the power. This is associated with losses in the Wire itself. The more the length of the wire, the greater the loss in the wire itself. In other words, the more the length of the wire, the greater the voltage drops in this area will be. With regard to our time, when the quality of the power supply leaves much to be desired, such a factor plays a significant role.
To know this, you will 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 of determining the thickness of the wire, depending on the power and distance.
Open and closed wire laying method
The current passing through the conductor causes it to heat up, as it has a certain resistance. So, the larger the current, the more heat on it it is distinguished, under conditions of the same cross section. With the same current consumption, heat is released on extensions of a smaller diameter greater than on conductors with a greater thickness.
Depending on the laying conditions, the amount of heat released on the conductor changes. When the gasket is open, when the wire is actively cooled with air, you can give preference to a thin wire, and when the wire is laid closed and cooling it minimized, it is better to choose thicker wires.
Such information can also be found in the table. The principle of choice is the same, but taking into account another factor.
And finally, the most important thing. The fact is that in our time the manufacturer is trying to save on everything, including on the material for wires. Very often, the claimed section does not respond true. If the seller does not inform the buyer, then it is better to measure the thickness of the wire, if it is critical. To do this, it is enough to take with me the caliper and measure the thickness of the wire in millimeters, after which it is to calculate its cross section along the simple formula 2 * Pi * d or Pi * R in the square. Where Pi is a constant number of equal to 3.14, and D is the diameter of the wire. In another formula, respectively, pi \u003d 3.14, and R in the square is a radius in a square. The radius is very simple, a diameter is enough to share for 2.
Some sellers directly indicate the inconsistency of the stated section and valid. If the wire is selected with a large margin - it is not at all significantly. The main problem is that the price of the wire, compared with its cross section, is not underestimated.
Cable products are now presented on the market in a wide range, the cross section of the vein is from 0.35 mm. and above, this article will see an example. calculation of cable cross section.
To calculate the resistance of the conductor, you can use the calculator for calculating the resistance of the conductor.
Wrong selecting a cable cross section For household wiring, may result in such results:
1. The temporon meter of too thick casualties will cost more, which will cause a significant "blow" by budget.
2. The cores will soon begin to heat up and will melt the insulation if the inappropriate diameter of the conductor (smaller than necessary) will be selected and it can soon lead to short closure or self-burning wiring.
In order not to spend the means to be wasted, it is necessary before starting the installation of wiring in an apartment or house, perform the right calculation of cable cross section Depending on the strength of the current, power and length of the line.
Calculation of cable cross-section for electrical appliances.
Each cable has a rated power that it is able to withstand during the operation of the electrical appliances. When the power of all electrical appliances in the apartment will exceed the calculation of the conductor, the accident will not be avoided soon.
You can calculate the power of electrical appliances in an apartment or house yourself, for this it is necessary to write onto a sheet of paper. The characteristics of each device separately (TV, vacuum cleaner, plates, lamps). Then all obtained values \u200b\u200bare summed up, and the finished number is used to select the optimal diameter.
The formula for calculating power has this kind:
Pont \u003d (p1 + p2 + p3 + ... + pn) * 0.8, where: P1..pn-power of each electrical appliance, kW
It is worth paying attention to the fact that the number that needed to multiply on the correction factor is 0.8. Indicates this coefficient that only 80% of all electrical appliances will work at the same time. This calculation will be more logical, because, vacuum cleaner or hairdryer, will definitely not be in use for a long time without a break.
An example of calculating the cable cross-section in power is listed in the tables:
For conductor with aluminum veins.
For conductor with copper veins.
As can be seen from the tables, their data is values \u200b\u200bfor each specific view of cableIt will only be necessary to find the nearest of power values \u200b\u200band see the corresponding cross section lived.
For example calculation of the cable cross section looks like that:
Suppose that the total capacity of all devices is 13 kW. It is necessary to multiply the resulting value to the coefficient of 0.8, as a result, it will give 10.4 kW of the actual load. Then a suitable value must be found in the table column. The nearest figure is 10.1 with a single-phase network (220V voltage) and with a three-phase Network of the figure 10.5. So stop the selection of section with a single-phase network on a 6-milimmeter conductor or with a three-phase on 1.5-milemmetrov.
Calculation of the cable cross-section.
More accurate Calculation of cable cross-sectionSo it is best to use it. The essence of the calculation is similar, but in this case it is necessary only to determine which current load on the electrical wiring. First you need to calculate the current strength for each of the electrical appliances.
The average power of household electrical appliances
An example of a power display of an electrical appliance (in this case, the LCD TV)
To calculate, it is necessary to use such a formula if a single-phase network is in the apartment:
I \u003d p / (u × cosφ)
When the network is three-phase, then the formula will have this kind:
I \u003d p / (1.73 × u × cosφ), where p is the electrical capacity of the load, W;
- U - actual voltage in the network, in;
- cosφ - power factor.
It should be noted that the values \u200b\u200bof table values \u200b\u200bwill depend on the conditions of the conductor laying. Power and current loads will be significantly large when installing open wiring than if the wiring laying is in the pipe.
The resulting total value of current currents is recommended to multiply by 1.5 times, because with time more powerful electrical appliances can be purchased into the apartment.
Calculation of the cross section of the cable in length.
You can also to calculate the cable cross section. The essence of such calculations is that each of the conductors has its own resistance, which contributes to current loss with increasing line length. It is necessary to choose a conductor with cores greizing if the magnitude of the loss exceeds 5%.
Calculations occur as follows:
- The total power of all electrical appliances and the current is calculated.
- The electrical wiring resistance is then calculated by the formula: the resistivity of the conductor (P) * length (in meters).
- It is necessary to divide the resulting value to the selected cross-section of the cable:
R \u003d (P * L) / S, where P is a table value
It should be paid to the fact that the current length is multiplying by 2 times, since initially the current goes on one dwell, and back it is returned on another.
- Voltage loss is calculated: the current is multiplied by the calculated resistance.
- Next, the amount of losses is determined: voltage loss is divided into voltage in the network and multiply 100%.
- Analyzed the final number. If the resulting value is less than 5%, then the selected section of the core can be left, but if more, then you need to select the conductor more "thick".
Table of specific resistivity.
Be sure to make the calculation, taking into account the loss in length, if the line is stretched on a fairly extended distance, otherwise there is a high probability select a cable cross section wrong.
The cable for which electricity comes into the apartment is a very responsible plot of electrical wiring. It is on this cable that the load is located on all electrical appliances operating in the room. The parameters of the introductory cable depends on how many instruments and which power can be served in the room. Consider the key parameter - the cable cross section and the method of its choice.
Section diameter - cable power index
Physical laws suggest that the maximum current of the current is depends on the diameter of the conductor, which is capable of conducting this conductor without heating. If you try to spend the current more than the boundary digit, it will lead to the heating of the conductor, and the greater the current and the duration of the "session", the higher the temperature.
For the apartment subscriber, said interpreted as follows.
The diameter of the cable cross section means the maximum allowable number of kilowatts (kW), which can be consumed in the apartment. That is, what and how many electrical appliances can work simultaneously. The larger the diameter, the more appliances can be used at the same time without any fears for life and health. Theoretically, you can "hang" to the cable and greater power than its diameter allows. But in this case, the heating of the conductive conductors is inevitable, the insulation damage, and the effects of bravery, ignition ... ignition.
Therefore, it is necessary to approach the choice of the secting of the introductory cable with all seriousness: because it depends on both the safety and the ease of operation of domestic electrical appliances.
Algorithm for calculating section
There is a spent scheme for calculating the cross section of the introductory cable, which is used when designing. It is based on the discharge that the diameter of the entering cable section is selected depending on the estimated power of all devices running in the apartment.
Stage 1: Inventory
At the first stage, a list of electrical appliances is drawn up, which are present in the apartment. It is assumed which technique will be purchased in perspective and the list is complemented. Assumption, of course, is better to do with a reserve for a long-term future within reasonable limits. Each of the devices is put in touch with the approximate power consumption.
You can use a table in which the list of typical domestic electrical appliances is indicative and their approximate power consumed.
| The name of the electrical appliance | Approximate power, W | The name of the electrical appliance | Approximate power, W |
| television | 300 | air conditioning | 1500 |
| printer | 500 | flowing water heater | 5000 |
| a computer | 500 | boiler | 1500 |
| hair dryer | 1200 | drill | 800 |
| iron | 1700 | perforator | 1200 |
| electric kettle | 1200 | powerful | 900 |
| fans | 1000 | circular Saw | 1300 |
| toaster | 800 | electrolabanok. | 900 |
| coffee maker | 1000 | electropolitanzik | 700 |
| a vacuum cleaner | 1600 | grinder machine | 1700 |
| heater | 1500 | a circular saw | 2000 |
| Microwave | 1400 | compressor | 2000 |
| oven | 2000 | lawn mower | 1500 |
| electric stove | 3000 | electric welding machine | 2300 |
| refrigerator | 600 | water pump | 1000 |
| washer | 2500 | electromotors | 1500 |
| lighting | 2000 |
Stage 2: Simple Arithmetic
Next calculates the total power of our list. The approximate power required for lighting is added, depending on the size of the apartment, the intended lighting intensity, the intended type of lighting devices.
The resulting digit is an assessment of the power consumption in the apartment for the case if all the devices are included simultaneously. However, this situation is very unlikely, and therefore in electrical engineering it is believed that at the same time a maximum of 75% of the existing technique is included. And the resulting total power is multiplied by the coefficient of 0.75, and the resulting digit is taken as the basis for calculating the cross section of the input cable.
Stage 3: Logic and Physics
Currently veins electrical cables Performed from copper and aluminum. There are formula ratios that bind the maximum allowable current (and, accordingly, power) for a copper cable with a diameter of its cross section. For standard copper cable sections, there are calculated values \u200b\u200bof the permissible current and the maximum allowable power for AC voltage 220 V and 380 V. The following table provides these numbers in the "extensible" form.
| Section of conductive veins, mm | Voltage 220 B. | Voltage 380 B. | ||
| talk, A. | power, kWt | talk, A. | power, kWt | |
| 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 | 40 | 33,0 |
| 16 | 85 | 18,7 | 75 | 49,5 |
Suppose that the calculated power of all devices was 12 kW, and with a coefficient of 0.75 - 9 kW. It turns out that you need to select a cable for which the maximum allowable power will be at least 9 kW. For voltage 220 V, it is necessary to cross section with a diameter of 6 mm - it can skip the current 46 A and the power of 10.1 kW. For a smaller cross section from the table - 4 mm - the maximum allowable current is 38 A, and the power is 8.3 kW. It is less than necessary, so the cable of such a section will not fit and stop follows 6mm.
If you choose a larger cable than necessary, this will provide a good ground for the future (for example, the emergence of new powerful household appliances) and stock for wear. However, it should not be too exceeding the calculated power: this will be reflected at the cost of the introductory cable, and the introductory cable may turn out to be more powerful internal wiring, which is not reasonable and safe.
What else is needed
At the input cable you need to put the machine to which it will be charged to disconnect the power supply in the event of a current approximation to the maximum allowable mark. The nominal machine is selected slightly smaller than the maximum allowable current through the input cable: this way provides an additional degree of protection. In this example, an automatic machine should be put on 40 A.
So, the parameters of the introductory cable require a careful choice. Errors threaten, for example, the situation of the "bottle neck" - when all the home wiring is quite powerful, but the inlet cable is not capable of providing the desired power. The diameter of the cross section of the introductory cable is selected taking into account the total power of the electrical appliances that will be operated in the room. In order for all the nuances to be taken into account and the introductory cable served for many years without all sorts of emergencies, it is better to trust the reconstruction of electrical wiring by professional electricians.
In the modern technological world, electricity has almost become one level with water and air. It is used in almost any field of human activity. There was such a concept as electricity back in the distance 1600, before that we knew about electricity no more ancient Greeks. But over time, it began to spread more widely, and only in 1920 it began to push the kerosene lamps from the lighting of the streets. Since then, the electric current began to spread rapidly, and now it is even in the most deaf wooden village at least highlighting the house and for communications by phone.
Electricity itself is a flow of directional charges moving through the conductor. The conductor is the substance capable of passing through itself the electrical charges themselves, but each conductor has there is resistance (In addition to the so-called superconductors, the resistance in superconductors is zero, such a state is achieved by lowering the temperature to -273.4 degrees Celsius).
How to figure out the sections of copper and aluminum cables, for wiring?
This article is designed to teach you how to calculate the cross section of the wire. It's like the more water you want to file, the more pipe diameter you need. So here, the more electric current consumption, the greater the cross section of cables and wires should be. In short, I will describe what it is: if you have a snack cable or wire, and look at it from the end, then you will just see its cross section, that is, the thickness of the wire that determines the power that this wire is capable of skipping, warming up to a permissible temperature.
In order to properly choose a cross section power wire us need to take into account the maximum value of the current current. It is possible to determine the values \u200b\u200bof the currents, knowing the passport power of the consumer, is determined by such a formula: I \u003d P / 220, where P is the power of the current consumer, and 220 is the amount of volts in your outlet. Accordingly, if the socket is 110 or 380 volts, then we substitute this value.
It is important to know that the calculation of the value for single-phase, and three-phase networks differs. In order to learn how many phases you need, you need to calculate the total amount of current consumption in your dwelling. Let us give an example of an average set of equipment that can be at home.
A simple example of calculating the cable cross section for current consumed, now we calculate the sum of the capacities of the connected electrical appliances. The main consumers in the average apartment are the following devices:
- TV - 160 W
- Refrigerator - 300 W
- Lighting - 500 W
- Personal computer - 550 W
- Vacuum cleaner - 600 W
- Microwave oven - 700 W
- Electric kettle - 1150 W
- Iron - 1750 W
- Boiler (Water Heater) - 1950 W
- Washing machine - 2650 W
- Total 10310 W \u003d 10.3 kW.
When we learned the total consumption of electricity, we can calculate the wire cross section by the formula for the normal functioning of the wiring. It is important to remember that for single-phase and three-phase formula networks will be different.
Calculation of the cross section of the wire for the network with one phase (single-phase)
The calculation of the cross section of the wire is carried out using the following formula:
I \u003d (p × k and) / (u × cos (φ))
- P. - power of all consumers of energy in the amount
- K I. - The coefficient of simultaneity is usually the generally accepted value of 0.75 is taken for calculations.
- U. - Phase voltage, which is 220V, but may vary from 210V to 240V.
- cOS (φ) - For household single-phase appliances, this value is becoming 1 and equals 1.
I. - current strength;
When we found current consumption by the formula, you can start choosing a cable, which suits us by power. Rather, its cross-section area. Below is a special table in which the data is provided, where the current value, the cable cross section and power consumption are compared.
Data may vary for wires made from different metals. Today, copper, hard cable is used for use in residential premises. Aluminum cable is practically no applied. But still in many old houses, the aluminum cable is still present.
Table of current cable power cable. The selection of the copper cable cross section is made according to the following parameters:
We also give a table to calculate the current consumed of the aluminum cable:
If the power value turned out between the two indicators, it is necessary to select the value of the wire cross section in the biggest. Since the power supply must be present.
Calculation of the cross section of the wire wire with three phases (three-phase)
And now we will analyze the calculation formula of the cross section of the wire for three-phase networks.
To calculate the cross section of the feed cable, we use the following formula:
I \u003d p / (√3 × u × cos (φ))
- I. - The current of the current on which the cable cross section is selected
- U. - phase voltage, 220V
- Cos φ - Phase shift angle
- P. - shows the total consumption of all electrical appliances
Cos φ. - In the above formula, it is extremely important, since it affects the current strength. It differs for different equipment, with this parameter most often can be found in the technical documentation, or the corresponding labeling on the housing.
The total capacity is very simple, we summarize the value of all power indicators, and we use the resulting number in the calculations.
A distinctive feature in a three-phase network is that a thinner wire is able to withstand a larger load. It is selected by the secession of the wire, according to the table below.
Calculation of the cross section of the current-consumption used in a three-phase network is used using such a magnitude as √3 . This value is needed to simplify external view Formula itself:
U linear \u003d √3 × u phase
In this way, when itemies occurs, the product of the root and phase voltage on linear voltage is replaced. This value is 380V (U linear \u003d 380V).
The concept of long-term current
Also one at least important moment When choosing a cable for a three-phase and single-phase network, it is necessary to consider such a concept that sounds like a permissible long-term current. This parameter shows us the current strength in the cable that the wire can withstand during an unlimited amount of time. You can determine the ego in a special table. Also for aluminum and copper conductors, they differ significantly.
In the case when this parameter exceeds the allowable values, the conductor overheating begins. The heating temperature is inversely proportional to the strength of the current.
Temperature in some areas may increase not only because of the wrong selected cross section of the wire, and even with bad contact. For example, in the place of twist of the wires. This is quite often happening at the point of contact of copper cables and aluminum. In this regard, the surface of the metals is subjected to oxidation, covered with an oxide film, which greatly worsens contact. In such a place, the cable will be heated above the permissible temperature.
When we spent all the calculations, and checked with data from the tables, you can safely go to a specialized store and buy the cables you need to lay the network at home or at the cottage. The main thing is your advantage before, for example, your neighbor will be that you have completely understood in this matter with the help of our article, and save a lot of money, not overpaying for what you wanted to sell the store. Yes, and to know how to calculate the current cross-section for copper or aluminum wires will never be superfluous, and we are sure that knowledge received from us will repeat on your life path.
