When installing electrical wiring in a new house or replacing an old one during renovation, everyone House master I wonder: what cross-section of wire is needed? And this question has great importance, since not only the reliable operation of electrical appliances, but also the safety of all family members largely depends on the correct choice of cable cross-section, as well as the material of its manufacture.
Which wire to choose - the material of manufacture comes first
The most common types of wiring in our homes are aluminum and copper. Which one is better is a question that still haunts users of numerous forums. For some, copper is a priority, while others say that there is no need to overpay and aluminum will do for a home network. In order not to be unfounded, let's do a little analysis of these options and then everyone can choose an option for themselves.
Aluminum wiring is lightweight, due to which it is widely used in the electrical power industry. It is used for laying power lines, since in this way the load on the supports can be minimized. In addition, it has gained popularity due to its low cost. Aluminum cable costs several times less than its copper counterpart. During times Soviet Union Aluminum wiring was very common and can still be found in houses built some 15-20 years ago.
However, aluminum cable also has its downsides. One of these points that is definitely worth mentioning is the short service life. After two decades, aluminum wiring becomes highly susceptible to oxidation and overheating, which often leads to fires. Therefore, if you still have such cables in your home, think about replacing them. In addition, the oxidation to which aluminum is susceptible reduces the useful cross-section of the cable with a simultaneous increase in resistance, and this leads to overheating. Another significant disadvantage of aluminum is its fragility. It breaks quickly if the cable is bent several times.
Important! PUE prohibits the use of aluminum cable for installation in electrical networks if its cross-section is less than 16 mm.
Copper cable bends well and does not break
As for copper wire, its advantages include a long service life - more than half a century, excellent conductivity and mechanical strength. It is much easier to work with copper cable, because it bends without breaking and can withstand repeated twisting. The disadvantage of copper cable wiring is the cost. For replacement power cable in the entire apartment you will need a significant number Money. To save money, some craftsmen combine the laying of aluminum wires with copper ones. The entire lighting part is mounted from aluminum, and the socket part is made from copper, since lighting does not require such a large load as electrical appliances powered into the network.
Choosing a section - what you need to know and what to pay attention to
If previously the equipment in an apartment was limited to a refrigerator and a TV, then nowadays you won’t find anything in an apartment: vacuum cleaners, computers, hair dryers, microwave ovens, etc. All this requires power, and depending on the time of day, the load from devices connected to the network can vary greatly. And in order to choose the right cable for each point to which the device is powered, you need to know:
- current strength;
- voltage;
- power consumption of the device in watts or kilowatts.
For single-phase networks that are present in our apartments, there is a certain formula that allows you to determine the current strength of the devices:
I = (P × K u) / (U × cos(φ)), where
I – current strength;
P – power consumption of all electrical appliances (it is necessary to add their nominal value):
| Single-phase boiler | 5–7 kW |
| Fan | up to 900 W |
| Oven | from 5 kW |
| Computer | 600-800 W |
| Microwave | 1.2–2 kW |
| Mixer | 300 W |
| Freezer | 150–300 W |
| Lighting | 100–1000 W |
| Grill oven | 1 kW |
| Dishwasher | 1.8–2.5 kW |
| Vacuum cleaner | 1200 W |
| Juicer | 250 W |
| Washing machine | 600–2500 W |
| TV | 100–200 W |
| Warm floor | 0.7–1.5 kW |
| Toaster | 750–1000 W |
| Iron | 1000–2000 W |
| Hairdryer | 500–1000 W |
| Fridge | 150–300 W |
| Electric hob | from 5 kW |
| Electric coffee maker | 700–1000 W |
| Electric meat grinder | 1000 W |
| Electric stove | 9–12 kW |
| Electric fireplace | 9–24 kW |
| Electric boiler | 9–18 kW |
| Electric kettle | 2 kW |
K and is the simultaneity coefficient (often, for simplicity, a value of 0.75 is used);
U – phase voltage, it is 220 (V), but can range from 210 to 240 (V);
Cos (φ) – for household appliances the value is unchanged and equals 1.
For simplicity, you can use the formula: I = P / U.
When the current is determined, the wire cross-section can be determined using the following table:
Table of power, current and cross-section of cable and conductor materials
ALUMINUM |
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Voltage, 220 V | Voltage, 380 V |
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power, kWt | power, kWt |
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Conductor cross-section, mm | ||||
Voltage, 220 V | Voltage, 380 V |
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power, kWt | power, kWt |
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If during the calculations it turns out that the value does not coincide with any one given in the table, then the next larger number should be taken as a basis. For example, if your value is 30 A, then when using aluminum wiring you should choose a wire cross-section of 6 mm 2, and 4 mm 2 will be enough for copper.
Usually modern apartment consumes approximately 10 kW.
We determine the cross-section of the wire by diameter and by the method of wiring
When buying a wire, it would be useful to check its cross-section, since many manufacturers work according to specifications. Because of this, not all products meet the declared characteristics. Therefore, it is necessary to stock up on calipers and measure the diameter of the core, which will help us determine the real value of the wire cross-section. To simplify the work, we present the most simple formula, thanks to which you will not need to make additional calculations: S=0.785d 2, where S is the desired section; d – core diameter. The final value must be rounded to 0.5. So, if you get a value of 2.4, then you should choose a cable with a cross-section of 2.5 mm 2.
In most of our houses, the cable is laid in the walls. It is called closed wiring. Wires can run through cable ducts, pipes, or simply be walled into the wall. In some houses, and this concerns wooden buildings and old housing stock, you can find open wiring. It is noteworthy that for open installation you can use a cable of a smaller cross-section, since such a wire heats up less than the one that is walled into the wall. For this reason, when laying wires in grooves, it is recommended to choose a cable with a larger cross-section. This way the cable will heat up less, which means it will wear out more slowly. In the table below you can find out how many squares of cable you need to take for devices of different power, be it 1 or 6 kW:
Cable cross-section, mm 2 | Open wiring | Gasket in channels |
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Aluminum | Aluminum |
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Below I will provide a table of wire cross-sections, but I recommend being patient by reading this small theoretical part to the end. This will allow you to be more conscious in choosing wires for electrical wiring installation, in addition, you will be able to do it yourself wire cross section calculation, and even “in the mind.”
The passage of current through a conductor is always accompanied by the release of heat (respectively, heating), which is directly proportional to the power dissipated in the electrical wiring section. Its value is determined by the formula P=I 2 *R, where:
- I is the magnitude of the flowing current,
- R is the wire resistance.
Excessive heating can lead to insulation failure, as a result - short circuit and/or fire.
The current flowing through the conductor depends on the load power (P), determined by the formula
I=P/U
(U is the voltage, which for a household electrical network is 220V).
The wire resistance R depends on its length, material and cross-section. For electrical wiring in an apartment, cottage or garage, the length can be neglected, but the material and cross-section must be taken into account when choosing wires for electrical wiring.
CALCULATION OF WIRE SECTION
The cross-section of the wire S is determined by its diameter d as follows (hereinafter I will simplify the formulas as much as possible):
S=π*d 2 /4=3.14*d 2 /4=0.8*d 2.
This may be useful to you if you already have a wire, without markings that immediately indicate the cross-section, for example, VVG 2x1.5, where 1.5 is the cross-section in mm 2, and 2 is the number of cores.
The larger the cross-section, the greater the current load the wire can withstand. With the same cross-sections of copper and aluminum wires, copper can withstand more current, in addition, they are less brittle and oxidize less easily, so they are most preferable.
Obviously, with a hidden installation, as well as wires laid in a corrugated hose or electrical box, due to poor heat transfer, they will heat up more strongly, which means their cross-section should be selected with a certain margin, so it’s time to consider such a value as current density (let’s denote it Iρ).
It is characterized by the amount of current in Amperes flowing through a unit cross-section of a conductor, which we will take as 1 mm 2. Since this value is relative, it is convenient to use it to calculate the cross section using the following formulas:
- d=√ 1.27*I/Iρ =1.1*√I/Iρ- we get the value of the wire diameter,
- S=0.8*d 2 - previously obtained formula for calculating the cross section,
We substitute the first formula into the second, round everything possible, and we get a very simple ratio:
S=I/Iρ
It remains to determine the value of the current density Iρ), since the operating current I) is determined by the load power, I gave the formula above.
The permissible value of the current density is determined by many factors, the consideration of which I will omit and present the final results, and with a margin:
Calculation example:
We have: the total load power in the line is 2.2 kW, the wiring is open, the wire is copper. For calculation we use the following units of measurement: current - Ampere, power - Watt (1kW = 1000W), voltage - Volt.
All materials presented on this site are exclusively informational in nature and cannot be used as guidelines and normative documents
Understanding all the parameters and processes occurring with electricity is the key to choosing the right cable. This article explains step by step the relationships between physical quantities that affect reliable operation energy network and its safe operation.
It is known that all metals have free electrons that move in the presence of an applied electrical voltage, creating an electric current. When they hit atoms, they lose energy, which turns into heat. The greater the current, the denser the flow of particles, and the smaller the cross section of the conductor through which they pass, the more crowded they are; collisions are more frequent, useful energy is lost, and the release of useless and often dangerous heat increases.
Avalanche of heat
Important! As the temperature rises, the resistivity increases and heat release increases, which leads to an avalanche-like process of rapid heating with catastrophic consequences.
Exist complex formulas, calculating the heat balance, using the melting coefficient and thermal coefficient of resistance of the conductor to determine the cross-sectional area of the conductor.
But, in everyday life, ready-made tables are used, which take into account the possibility of cable overheating in hidden wiring- in this case for identical values in terms of current and power, the cross-section is prescribed to be large for the cable in poorly ventilated and thermally insulated places so that the heating does not exceed the permissible limit.
Solution in practice
It is carried out using special tables and PUE standards, according to which the cable cross-section is selected. The cross-sectional value of the conductor is selected in several ways:
- Calculation of wire cross-section by power;
- Selecting a current wire;
- If there is already a wire, but of unknown cross-section.
Selection by power
Each electrical appliance indicates its rated power. By summing up the power of electrical appliances that are planned to be connected to the designed electrical network at the same time, get a certain number and, using the table, select the appropriate cross-section of copper or aluminum cable, choosing suitable value power.
First of all, it is necessary to take into account the expected load on the electrical wiring that we are going to lay. If there are several electrical appliances on one section of the electrical network, then to calculate the expected load we add up all their capacities. After calculating this indicator, we analyze the way in which we will lay the electrical networks (open or closed), as well as the impact of which temperature regime will appear on the wires.
It is also very important to calculate the correct cable cross-section because errors in calculations will lead to power losses in the wires. If this is not so significant for household appliances, then on an industrial scale this can lead to quite serious waste.
So, take a piece of paper and a pen, write down all the electrical appliances in your apartment and add up their power:
P=P1+P2+P3+…Pn (W),
where P1 is the power of, for example, a kettle of 1.5 kW, P2 is the power of a vacuum cleaner of 1.6 kW, etc.
After all the powers have been added up, it is necessary to multiply the total power by the simultaneity factor K=0.8. This coefficient shows that during a certain period of time all electrical appliances in the apartment will work, but not for a long time, but for a short period of time, this must be taken into account, because if you choose a wire cross-section based only on power, you will choose a larger wire cross-section, and this may turn out to be significantly more expensive.
So, we get:
Ptotal=P*K (W)
After calculating the total power, select the wire cross-section (copper or aluminum) in Table 1:
Table 1 - Selection of wire cross-section by power
Important! If in the future you are going to increase the load, then you must increase the wire cross-section in advance; this remark applies to all methods of determining the wire cross-section.
Current selection
In Table 2 you can find the correspondence between cross sections and rated current. Selection based on this parameter is considered more accurate. It is necessary to look at the passports and labels of electrical appliances; the rated power is usually indicated, and then follow the same procedures as in the method described above.
where Ptot. — total power of electrical appliances (W).
It is possible to measure the current with an ammeter for each consumer individually with your own hands and then simply sum the current.
To do this, the tester is connected to an open circuit - in practice, you can take a piece of network cable with a plug, connect one core to the socket terminal, and apply the other to measuring device. Connect the other ammeter probe to a free terminal of the socket, and plug the existing one into it one by one. household appliances, in different operating modes, checking the parameters declared by the manufacturers.
If you have a three-phase network, you need to find the current using this formula:
After we have summed up the currents of electrical appliances, we select the conductor cross-section from the table:
Table 2 Relationship between current and conductor cross-section One more point, if your three-phase network contains electric motors, then the current of this motor is determined by the formula:
where - P is the engine power, n is the engine efficiency (available on the engine tag), COS f is the power factor (also look at the tag).
And lastly, in a three-phase network, we sum up the calculated motor currents and the calculated currents of electrical appliances and select the conductor cross-section from Table 2.
One more point needs to be taken into account - this. She may be open type or closed, respectively, the current loads will differ, so when choosing the wire cross-section, pay attention to this. In Table 2 you can analyze this point
The wire is already there
In the opposite situation, when there is a cable, but the markings are not visible, you need to find out its rated current and power; to do this, measure the diameter of the wire with a caliper or micrometer. You can get by with a ruler, if the core is flexible enough, wind it around a thin rod, measure the length of the resulting spiral, divide by the number of turns - the result will correspond to the diameter.
Using the formula, we calculate the cross-sectional area of the conductor:
S=πD²/4 (mm²) ,
where π- 3.14, D is the diameter of the conductor, you can take a caliper and measure the diameter (mm)
Using the cross-section selection method from Table 1, you can find out for what power the existing cable is suitable.
It is better to choose the cable cross-section with a margin.
It is prohibited to operate a cable wound into a coil due to its inductive reactance.
Installation of aluminum cables should be carried out with extreme caution - frequent bending and straightening produces invisible cracks that reduce the cross-section, resistance increases in this place and spot overheating occurs.
Length check
The conductor length factor l also increases the resistance in the network. It can be neglected at a short distance, but as it increases, the voltage drop across the load will be increasingly noticeable, and it may become lower than the nominal value - 5%.
Let's take a closer look; to avoid this, calculate the cross-sectional area of the entire cable, allowing for a certain value and using it in the formula for determining the resistance:
where l is the length of the wire (m), ϱ is the resistivity of the conductor (Ohm*mm²/m) (see Table 2), S is the cross-sectional area of the conductor, determined from the method described above (mm²)
Table 3- resistivity metals:
Next, using Ohm's law, we find the voltage drop:
where I is the total current in your network (A), R is the calculated resistance (Ohm).
And lastly, we determine network losses. We divide the calculated voltage drop by the network voltage and multiply by 100%.
If the obtained value exceeds 5% of the network voltage, the cable cross-section must be increased according to table 1.
Content:
Of great importance in electrical engineering is the quantity cross section wires and load. Without this parameter, it is impossible to carry out any calculations, especially those related to laying cable lines. A table of the dependence of power on wire cross-section, used in the design of electrical equipment, helps to speed up the necessary calculations. Correct calculations provide normal work devices and installations, contribute to the reliable and long-term operation of wires and cables.
Rules for calculating cross-sectional area
In practice, calculating the cross-section of any wire does not present any difficulty. It is enough just to use a caliper, and then use the resulting value in the formula: S = π (D/2)2, in which S is the cross-sectional area, the number π is 3.14, and D is the measured diameter of the core.
Currently, predominantly copper wires are used. Compared to aluminum ones, they are more convenient to install, durable, have a significantly smaller thickness, with the same current strength. However, with an increase in cross-sectional area, the cost copper wires begins to increase, and all advantages are gradually lost. Therefore, when the current value is more than 50 amperes, it is practiced to use cables with aluminum conductors. Square millimeters are used to measure wire cross-section. The most common indicators used in practice are areas of 0.75; 1.5; 2.5; 4.0 mm2.
Table of cable cross-section by core diameter
The main principle of calculations is the sufficiency of the cross-sectional area for normal flow through it. electric current. That is, the permissible current should not heat the conductor to a temperature above 60 degrees. The voltage drop should not exceed the permissible value. This principle is especially relevant for long-distance power lines and high strength current. Ensuring the mechanical strength and reliability of the wire is achieved by optimal thickness wires and protective insulation.
Wire cross-section for current and power
Before considering the ratio of cross-section and power, you should focus on an indicator known as the maximum operating temperature. This parameter must be taken into account when choosing the cable thickness. If this indicator exceeds its permissible value, then due to strong heating, the metal core and insulation will melt and collapse. Thus, the operating current for a particular wire is limited by its maximum operating temperature. An important factor is the time during which the cable can function in such conditions.
The main influence on the stable and durable operation of the wire is the power consumption and. For speed and convenience of calculations, special tables have been developed that allow you to select the required cross-section in accordance with the expected operating conditions. For example, with a power of 5 kW and a current of 27.3 A, the cross-sectional area of the conductor will be 4.0 mm2. The cross-section of cables and wires is selected in the same way if other indicators are available.
It is also necessary to take into account the influence environment. When the air temperature is 20 degrees higher than the standard, it is recommended to select a larger section, the next one in order. The same applies to the presence of several cables contained in one bundle or the operating current value approaching the maximum. Ultimately, the table of the dependence of power on the wire cross-section will allow you to select suitable parameters in case of a possible increase in the load in the future, as well as in the presence of large starting currents and significant temperature differences.
Formulas for calculating cable cross-section
Quality of electrical conduction installation work affects the safety of the entire building. The determining factor when carrying out such work is the cable cross-section. To carry out the calculation, you need to find out the characteristics of all connected electricity consumers. It is necessary to calculate the cable cross-section based on power. The table is needed to see the required indicators.
High quality and suitable cable ensures safe and durable operation of any network
The optimal cross-sectional area of the cable allows for leakage maximum number current and does not heat up. When carrying out an electrical wiring project, it is important to find the correct value for the wire diameter that would fit the certain conditions power consumption. To perform the calculations, you need to determine the total current. In this case, you need to find out the power of all equipment that is connected to the cable.
Before work, the wire cross-section and load are calculated. The table will help you find these values. For a standard 220 volt network, the approximate current value is calculated as follows: I(current)=(P1+P2+….+Pn)/220, Pn – power. For example, the optimal current for an aluminum wire is 8 A/mm, and for a copper wire is 10 A/mm.
The table shows how to carry out calculations, knowing the technical characteristics
Load calculation
Even having determined desired value, you can make certain adjustments for the load. After all, it’s not often that all devices work simultaneously on the network. To make the data more accurate, it is necessary to multiply the cross-sectional value by Kc (correction factor). If all equipment is turned on at the same time, then this coefficient does not apply.
To perform calculations correctly, use the table for calculating cable cross-section by power. It should be taken into account that there are two types of this parameter: reactive and active.
IN electrical networks an alternating current flows, the indicator of which can change. Active power is needed to calculate the average. Electric heaters and incandescent lamps have active power. If there are electric motors and transformers in the network, then some deviations may occur. At the same time, reactive power is generated. In calculations, the reactive load indicator is reflected as a coefficient (cosф).
Helpful information! In everyday life, the average cosph value is 0.8. But for a computer this figure is 0.6-0.7.
Calculation by length
Calculations of parameters along the length are necessary when constructing production lines, when the cable is subjected to heavy loads. For calculations, use a table of cable cross-sections for power and current. When current moves along highways, power losses appear, which depend on the resistance appearing in the circuit.
By technical parameters, the largest voltage drop value should not be more than five percent.
Using a table of wire cross-sections by power
In practice, a table is used to carry out calculations. Calculation of the cable cross-section for power is carried out taking into account the shown dependence of the current and power parameters on the cross-section. There are special standards for the construction of electrical installations, where you can view information on the required measurements. The table shows common values.
To select a cable for a specific load, you need to make some calculations:
- calculate the current strength indicator;
- round to the highest using the table;
- select the closest standard parameter.
Related article:
Video step-by-step installation will allow you to do all the work yourself without turning to specialists. We will tell you in this article what you need to prepare for work and how to avoid mistakes.
Formula for calculating power by current and voltage
If you already have some cables available, you should use a caliper to find out the required value. In this case, the cross section is measured and the area is calculated. Since the cable has a round shape, the calculation is made for the area of the circle and looks like this: S(area)= π(3.14)R(radius)2. You can correctly determine, using the table, the cross-section of a copper wire by power.
Important information! Most manufacturers reduce the section size to save material. Therefore, when making a purchase, use a caliper and measure the wire yourself, and then calculate the area. This will avoid problems with overload. If the wire consists of several twisted elements, then you need to measure the cross-section of one element and multiply by their number.
What are some examples?
A certain scheme will allow you to do right choice cable sections for your apartment. First of all, plan the places where the light sources and outlets will be placed. You should also find out which equipment will be connected to each group. This will allow you to draw up a plan for connecting all elements, as well as calculate the length of the wiring. Don't forget to add 2 cm at the joints of the wires.
Determination of wire cross-section taking into account different types loads
Using the obtained values, the current value is calculated using formulas and the cross section is determined from the table. For example, you need to know the wire cross-section for household appliance, whose power is 2400 W. We calculate: I = 2400/220 = 10.91 A. After rounding, 11 A remains.
To determine the exact cross-sectional area, different coefficients are used. These values are especially relevant for a 380 V network. To increase the safety margin, it is worth adding another 5 A to the obtained indicator.
It is worth considering that three-core wires are used for apartments. Using the tables, you can select the closest current value and the corresponding wire cross-section. You can see what wire cross-section is needed for 3 kW, as well as for other values.
At the wires different types there are some subtleties of calculations. Three-phase current is used where equipment of significant power is needed. For example, this is used for production purposes.
To identify the necessary parameters in production, it is important to accurately calculate all coefficients, as well as take into account power losses due to voltage fluctuations. Carrying out electric installation work at home, no need to carry out complex calculations.
You should be aware of the differences between aluminum and copper wire. The copper version is more different at a high price, but at the same time surpasses its analogue in terms of technical specifications. Aluminum products can crumble on bends, and also oxidize and have a lower thermal conductivity. For safety reasons, only copper products are used in residential buildings.
Basic cable materials
Because alternating current moves along three channels, a three-core cable is used for installation work. When installing acoustic devices, cables with a minimum resistance value are used. This will help improve signal quality and eliminate possible interference. To connect similar designs wires are used, the size of which is 2*15 or 2*25.
Some average values will help you choose the optimal cross-sectional indicator for everyday use. For sockets it is worth purchasing a 2.5 mm2 cable, and for lighting design - 1.5 mm2. Equipment with higher power requires a cross-section size of 4-6 mm2.
A special table will help if you have any doubts during the calculations. To determine accurate indicators, you need to take into account all the factors that influence the current in the circuit. These are the length of individual sections, installation method, type of insulation and permissible overheating value. All data helps to increase productivity on a production scale and use electrical energy more efficiently.
Calculation of cable and wire cross-sections based on power and current for connecting a private house (video)
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