Choosing a cable cross-section for an apartment, house, or cottage. Calculation of cable cross-section
The installation of a household electrical network must be carried out in such a way that users can simultaneously turn on several powerful electrical appliances without any problems. Therefore, it is necessary to select the wire cross-section for home wiring based on a competent calculation of the parameters of the apartment and house electrical networks.
There are several calculation methods. We suggest that you familiarize yourself with different approaches and choose the best option. In addition to the technology for calculating the wire cross-section, the article describes the main parameters for choosing electrical wiring and indicates regulatory restrictions on the maximum power of electrical appliances.
Standard electrical sockets are designed for a continuous current of 16 A, which corresponds to a maximum power of 3.52 kW when the device is turned on. Usually they are connected to a copper cable with a cross-section of 2.5 mm 2, which can be misleading when choosing the type of wire for the rest of the electrical wiring.
In parallel with the increase in the cross-sectional area of the cable, its price also increases. However, you should not save on electrical wiring - this can lead to much greater financial costs in the future.
When electrons move through a metal, some of the energy is dissipated as heat. With a large current and a small cross-section of the cable, the thermal component can lead to overheating of the metal and melting of its sheath.
In domestic conditions, this can initiate both an intra-wall short circuit and a fire in exposed wires, especially in kinked areas.
As a result, the following situations may arise:
- Large-scale fire if there is flammable material near the cable.
- Leakage current in case of incomplete melting of the core shell. This leads to wasted energy consumption and the possibility of electric shock to residents.
- Unnoticeable. As a result, part of the apartment or the entire room is de-energized. After this, a search for the break point and subsequent replacement of the wiring with local wall repairs are required.
Choosing a thick electrical wire for an apartment, with a margin, also has one drawback - overspending of funds, which does not make sense. Therefore, it is better to select the wiring cross-section using calculation methods in order to avoid all of the above problems.
Factors for choosing wire cross-section
It is not only the power of the device that determines the nature of the required electrical wiring. There are other factors, the influence of which must be taken into account when calculating the required cable cross-section. They can affect heat generation in the conductor, its fire hazard and performance characteristics.
Stage No. 6. Calculation of cable cross-section according to the table. Since the optimal choice of wire for home wiring is influenced not only by the parameters of the devices, but also by external factors (core material, its sheath, installation diagram, etc.), each case has its own tables, which are discussed below.
Determination of electrical cable cross-section using tables
Calculation of the cross-section of ordinary household wires is presented in the tables:
Similar tables are used when calculating electrical wiring and in industry. Household cables are usually much simpler, so the number of design materials for them is quite limited. The parameters indicated in the tables are not invented, but are indicated in industry standards, for example in GOST 31996-2012.
Voltage drop calculation
Not only the degree of heating of the core, but also the electrical voltage at the far end of the wire depends on the cross-section of the electrical cable. Household appliances are designed for certain parameters of the electrical network, and their constant discrepancy can lead to a reduction in the service life of the equipment.
If the voltage drops on the boiler, it is advisable to install a stabilizer so that the equipment does not experience additional loads due to inconsistencies in the operational characteristics of the electrical network
As the cable lengthens, a voltage drop occurs. This effect can be reduced by increasing the wire cross-section. It is considered critical to reduce the voltage at the end of the wire by 5% compared to its value at the current source.
Upad = I*2*(ρ*L)/S,
- ρ – metal resistivity, Ohm*mm2/m;
- L– cable length, m;
- S– conductor cross-section in mm2;
- Upfall– drop voltage, Volt;
- I– current flowing through the conductor.
If the calculated voltage drop is more than 5% of the rated voltage, then it is necessary to use a cable with a larger cross-section. This will ensure stable operation of the equipment.
Heating boilers, washing machines and other devices with many relays and sensors are especially sensitive to voltage values. This feature must also be taken into account when using carriers.
Regulatory restrictions
Utility companies that provide electricity to the population have the right to impose restrictions on the maximum total power of appliances in the apartment. This can be achieved by installing electricity meters with a certain capacity.
The device is equipped with automatic disposable or reusable fuses, which operate when the threshold current value is exceeded.
Soviet-style electricity meters are being massively replaced with electronic ones. They are even more sensitive to overloads, due to which they quickly fail
If you remove the plugs from the meter and connect it directly to the apartment wiring, then it is guaranteed to burn out if the operating mode is disrupted for a long time. Most Soviet meters installed in apartments can withstand a peak load of 25 A for up to 1 minute.
After this, they are burned, which can lead to payment for the installation of a new device and a fine for violating operating rules.
The wiring in the entrance is also unable to withstand high loads; if it burns out, it can cut off power to several apartments at once. Therefore, when connecting an apartment to the intra-house network with a 2.5 mm cable, you should not expect that a thicker intra-apartment wire will be able to withstand high loads.
It is especially important to take into account the factor of regulatory restrictions at the stage of planning the installation of electric heating, heated floors, infrared saunas and other energy-intensive equipment.
You must first consult with the relevant utility services about the possibilities of electrical equipment installed in front of the apartment.
Conclusions and useful video on the topic
The videos contain practical advice from electricians on choosing and purchasing home wiring. They will help you purchase equipment that matches the cable, which will definitely protect your home from possible problems with network overloads.
The main factors when choosing a cable for home wiring are the power of household appliances and the limitations of the electrical networks that supply electrical energy to the apartment.
By choosing the right wire cross-section, you can connect all the necessary electrical appliances to the network. This eliminates the inconvenience when operating equipment and helps prevent fires in the wiring.
Do you have anything to add or have questions about calculating the wiring cross-section? Please leave comments on the publication and participate in discussions of the material. The contact form is located in the lower block.
Electricity has become such a part of our lives that when there is a sudden power outage, our lives seem to freeze, and we impatiently wait for it to be restored. We are surrounded by a huge number of different electrical appliances that connect to the home network either directly through sockets or through
extension cords or carriers.
Sometimes it is necessary to either move it to another outbuilding, replace the wire, or make a homemade extension cord. Or you need to calculate what is the maximum number of devices that can be simultaneously connected to one tee so that the wire does not heat up in it and a fire does not occur due to In such cases, you should first do this to be sure of the safety of the installed electrical wiring.
Which wire to choose?
It is no secret that copper has less resistance compared to aluminum, and therefore, if you compare copper and those with the same wire cross-section, then in the first case the permissible load will be slightly greater. Copper wire is stronger, softer and does not break at bend points. In addition, copper is less susceptible to oxidation and corrosion. The only advantage of aluminum wire is its cost, which is three or four times less than copper wire.
Calculation of wire cross-section by power
Any electrical wiring must be suitable for the load connected to it. The cross-section of the wire is calculated based on the maximum permissible heating of the current-carrying conductor. The amount of heating depends on the power of the connected electrical appliances. Thus, by calculating the maximum possible total power of the devices in the room, you can determine what the wire cross-section should be. In practice, it is convenient to use an online calculator or special tables that contain information about the permissible current load on the cable.
Wire cross-section, sq.mm | Copper wire (cable, core) |
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Circuit voltage, 220 V | Circuit voltage, 380 V |
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power, kWt | current strength, A | power, kWt | current strength, A |
|
Wire cross-section, sq.mm | Aluminum wire (cable, core) |
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Circuit voltage, 220 V | Circuit voltage, 380 V |
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power. kW | current strength. A | power. kW | current strength. A |
|
How to check the wire cross-section?
Since wires most often have a round cross-section, the cut area is calculated using the formula:
S = π x d²/4 or S = 0.8 x d², where
S - cross-sectional area of the core in mm2;
π - 3.14;
d—core diameter in mm.
Let's say, for example, that the diameter of the wire is 1.3 mm, then S = 0.8. 1.3² = 0.8. 1.3 x 1.3 = 1.352 mm2
If the wire consists of several cores, then the cross-section of one core is calculated and multiplied by their total number in the bundle. The diameter is usually measured with a caliper, but if you don't have one, a regular ruler will do. In this case, approximately 10-15 turns are tightly wound around a pencil, the length of the winding is measured with a ruler and the resulting value is divided by the number of turns.
When performing any electrical installation work, you must remember that electricity does not tolerate careless handling and does not forgive mistakes. Electrical safety and reliability - this is what you should always strive for when doing any work with electrical wiring in an apartment, country house or house.
In the modern technological world, electricity has almost become on the same level of importance as water and air. It is used in almost any area of human activity. The concept of electricity appeared back in 1600; before that, we knew about electricity no more than the ancient Greeks. But over time, it began to spread more widely, and only in 1920 did it begin to displace kerosene lamps from street lighting. Since then, electric current began to spread rapidly, and now it is available even in the most remote village, at least illuminating the house and for telephone communications.
Electricity itself is a stream of directed charges moving along a conductor. A conductor is a substance capable of passing these electric charges through itself, but each conductor there is resistance(except for the so-called superconductors, the resistance of superconductors is zero, this state is achievable by lowering the temperature to -273.4 degrees Celsius).
How to understand the cross-sections of copper and aluminum cables for wiring?
This article is intended to teach you how to calculate the cross-section of a wire. It's like the more water you want to supply, the larger the diameter of the pipe you need. So here, the greater the electrical current consumption, the larger the cross-section of cables and wires should be. I will briefly describe what it is: if you bite through a cable or wire and look at it from the end, you will see its cross-section, that is, the thickness of the wire, which determines the power that this wire is capable of transmitting when heated to the permissible temperature.
In order to select the correct cross-section of the power wire, we it is necessary to take into account the maximum value of the current load consumed. The current values can be determined by knowing the rated power of the consumer, which is determined by the following formula: I=P/220, where P is the power of the current consumer, and 220 is the number of volts in your outlet. Accordingly, if the outlet 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 is different. In order to find out how many phases of the network you need, you need to calculate the total amount of current consumption in your home. Let's give an example of the average set of equipment that you may have at home.
A simple example of calculating cable cross-section based on current consumption, now we will calculate the sum of the powers of connected electrical appliances. The main consumers in an 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 = 10.3 kW.
Once we know the total electricity consumption, we can use the formula to calculate the cross-section of the wire for the normal functioning of the wiring. It's important to remember that for single-phase and three-phase networks the formulas will be different.
Calculation of wire cross-section for a network with one phase (single-phase)
The wire cross-section is calculated using the following formula:
I = (P × K u) / (U × cos(φ))
- P- power of all energy consumers in total
- K and- simultaneity coefficient, as a rule, the generally accepted value for calculations is 0.75
- U- phase voltage, which is 220V but can range from 210V to 240V.
- cos(φ)- for household single-phase appliances this value is fixed and equals 1.
I- current strength;
When we have found the current consumption according to the formula, we can start choosing a cable, which suits us in terms of power. Or rather, its cross-sectional area. Below is a special table that provides data that compares the current value, cable cross-section and power consumption.
Data may vary for wires made of different metals. Today, for residential applications, copper, rigid cable is typically used. Aluminum cable is practically not used. But still, in many older houses, aluminum cable is still present.
Table of estimated cable current capacity. The choice of copper cable cross-section is made according to the following parameters:
We also provide a table for calculating the current consumption of an aluminum cable:
If the power value turns out to be an average between two indicators, then you need to select a larger wire cross-section value. Since there must be a power reserve.
Calculation of the wire cross-section of a network with three phases (three-phase)
Now let’s look at the formula for calculating the wire cross-section for three-phase networks.
To calculate the cross-section of the supply cable, we use the following formula:
I = P / (√3 × U × cos(φ))
- I- current strength by which the cross-sectional area of the cable is selected
- U- phase voltage, 220V
- Cosφ - phase angle
- P- shows the total consumption of all electrical appliances
Cosφ- in the above formula is extremely important, since it personally affects the current strength. It varies for different equipment; this parameter can most often be found in the technical documentation, or the corresponding marking on the case.
The total power is found very simply, we sum up the value of all power indicators and use the resulting number in the calculations.
A distinctive feature in a three-phase network is that a thinner wire can withstand a larger load. We select the required wire cross-section according to the table below.
Calculation of wire cross-section by current consumption used in a three-phase network is used using such a value as √3 . This value is needed to simplify the appearance of the formula itself:
U linear = √3 × U phase
In this way, if the need arises, the product of the root and phase voltage is replaced by the linear voltage. This value is equal to 380V (U linear = 380V).
Concept of continuous current
Also, one equally important point when choosing a cable for a three-phase and single-phase network is that it is necessary to take into account a concept that sounds like permissible long-term current. This parameter shows us the current strength in the cable that the wire can withstand for an unlimited amount of time. You can define the ego in a special table. They also differ significantly for aluminum and copper conductors.
When this parameter exceeds the permissible values, the conductor begins to overheat. The heating temperature is inversely proportional to the current strength.
Temperatures may increase in some areas not only due to incorrectly selected wire cross-section, and also with poor contact. For example, in the place where wires are twisted. This quite often happens at the point of contact between copper cables and aluminum cables. In this regard, the surface of the metals undergoes oxidation, becoming covered with an oxide film, which greatly impairs the contact. In such a place the cable will heat up above the permissible temperature.
When we have carried out all the calculations and checked the data from the tables, you can safely go to a specialized store and buy the cables you need for laying a network at home or in the country. Your main advantage over, for example, your neighbor will be that you have fully understood this issue with the help of our article, and you will save a lot of money without overpaying for what the store wanted to sell you. Yes, and knowing how to calculate the current cross-section for copper or aluminum wires will never be superfluous, and we are sure that the knowledge gained from us will come in handy many times on your life’s journey.
Standard apartment wiring is calculated for a maximum current consumption at a continuous load of 25 amperes (the circuit breaker that is installed at the entrance of wires into the apartment is also selected for this current strength) and is carried out with copper wire with a cross-section of 4.0 mm 2, which corresponds to a wire diameter of 2.26 mm and load power up to 6 kW.
According to the requirements of clause 7.1.35 of the PUE the cross-section of the copper core for residential electrical wiring must be at least 2.5 mm 2, which corresponds to a conductor diameter of 1.8 mm and a load current of 16 A. Electrical appliances with a total power of up to 3.5 kW can be connected to such electrical wiring.
What is wire cross-section and how to determine it
To see the cross-section of the wire, just cut it across and look at the cut from the end. The cut area is the cross-section of the wire. The larger it is, the more current the wire can transmit.
As can be seen from the formula, the cross-section of the wire is light according to its diameter. It is enough to multiply the diameter of the wire core by itself and by 0.785. For the cross-section of a stranded wire, you need to calculate the cross-section of one core and multiply by their number.
The diameter of the conductor can be determined using a caliper with an accuracy of 0.1 mm or a micrometer with an accuracy of 0.01 mm. If there are no instruments at hand, then an ordinary ruler will help out.
Section selection
copper wire electrical wiring by current strength
The magnitude of the electric current is indicated by the letter “ A" and is measured in Amperes. When choosing, a simple rule applies: The larger the cross-section of the wire, the better, so the result is rounded up.
| Table for selecting the cross-section and diameter of copper wire depending on the current strength | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Maximum current, A | 1,0 | 2,0 | 3,0 | 4,0 | 5,0 | 6,0 | 10,0 | 16,0 | 20,0 | 25,0 | 32,0 | 40,0 | 50,0 | 63,0 |
| Standard section, mm 2 | 0,35 | 0,35 | 0,50 | 0,75 | 1,0 | 1,2 | 2,0 | 2,5 | 3,0 | 4,0 | 5,0 | 6,0 | 8,0 | 10,0 |
| Diameter, mm | 0,67 | 0,67 | 0,80 | 0,98 | 1,1 | 1,2 | 1,6 | 1,8 | 2,0 | 2,3 | 2,5 | 2,7 | 3,2 | 3,6 |
The data I have provided in the table is based on personal experience and guarantees reliable operation of electrical wiring under the most unfavorable conditions of its installation and operation. When choosing a wire cross-section based on the current value, it does not matter whether it is alternating current or direct current. The magnitude and frequency of the voltage in the electrical wiring also does not matter; it can be the on-board network of a DC car at 12 V or 24 V, an aircraft at 115 V with a frequency of 400 Hz, electrical wiring 220 V or 380 V with a frequency of 50 Hz, a high-voltage power line at 10,000 IN.
If the current consumption of an electrical appliance is unknown, but the supply voltage and power are known, then the current can be calculated using the online calculator below.
It should be noted that at frequencies above 100 Hz, a skin effect begins to appear in wires when electric current flows, which means that with increasing frequency, the current begins to “press” against the outer surface of the wire and the actual cross-section of the wire decreases. Therefore, the choice of wire cross-section for high-frequency circuits is carried out according to different laws.
Determining the load capacity of 220 V electrical wiring
made of aluminum wire
In houses built a long time ago, electrical wiring is usually made of aluminum wires. If connections in junction boxes are made correctly, the service life of aluminum wiring can be one hundred years. After all, aluminum practically does not oxidize, and the service life of electrical wiring will be determined only by the service life of the plastic insulation and the reliability of the contacts at the connection points.
In the case of connecting additional energy-intensive electrical appliances in an apartment with aluminum wiring, it is necessary to determine by the cross-section or diameter of the wire cores its ability to withstand additional power. Using the table below, this is easy to do.
If your apartment wiring is made of aluminum wires and there is a need to connect a newly installed socket in a junction box with copper wires, then such a connection is made in accordance with the recommendations of the article Connecting aluminum wires.
Calculation of electrical wire cross-section
according to the power of connected electrical appliances
To select the cross-section of cable wire cores when laying electrical wiring in an apartment or house, you need to analyze the fleet of existing electrical household appliances from the point of view of their simultaneous use. The table provides a list of popular household electrical appliances indicating the current consumption depending on the power. You can find out the power consumption of your models yourself from the labels on the products themselves or data sheets; often the parameters are indicated on the packaging.
If the current consumed by an electrical appliance is unknown, it can be measured using an ammeter.
Table of power consumption and current for household electrical appliances
at supply voltage 220 V
Typically, the power consumption of electrical appliances is indicated on the housing in watts (W or VA) or kilowatts (kW or kVA). 1 kW=1000 W.
| Table of power consumption and current for household electrical appliances | |||
|---|---|---|---|
| Household electrical appliance | Power consumption, kW (kVA) | Current consumption, A | Current consumption mode |
| Incandescent light bulb | 0,06 – 0,25 | 0,3 – 1,2 | Constantly |
| Electric kettle | 1,0 – 2,0 | 5 – 9 | Up to 5 minutes |
| Electric stove | 1,0 – 6,0 | 5 – 60 | Depends on operating mode |
| Microwave | 1,5 – 2,2 | 7 – 10 | Periodically |
| Electric meat grinder | 1,5 – 2,2 | 7 – 10 | Depends on operating mode |
| Toaster | 0,5 – 1,5 | 2 – 7 | Constantly |
| Grill | 1,2 – 2,0 | 7 – 9 | Constantly |
| Coffee grinder | 0,5 – 1,5 | 2 – 8 | Depends on operating mode |
| Coffee maker | 0,5 – 1,5 | 2 – 8 | Constantly |
| Electric oven | 1,0 – 2,0 | 5 – 9 | Depends on operating mode |
| Dishwasher | 1,0 – 2,0 | 5 – 9 | |
| Washing machine | 1,2 – 2,0 | 6 – 9 | Maximum from the moment of switching on until the water is heated |
| Dryer | 2,0 – 3,0 | 9 – 13 | Constantly |
| Iron | 1,2 – 2,0 | 6 – 9 | Periodically |
| Vacuum cleaner | 0,8 – 2,0 | 4 – 9 | Depends on operating mode |
| Heater | 0,5 – 3,0 | 2 – 13 | Depends on operating mode |
| Hair dryer | 0,5 – 1,5 | 2 – 8 | Depends on operating mode |
| Air conditioner | 1,0 – 3,0 | 5 – 13 | Depends on operating mode |
| Desktop computer | 0,3 – 0,8 | 1 – 3 | Depends on operating mode |
| Power tools (drill, jigsaw, etc.) | 0,5 – 2,5 | 2 – 13 | Depends on operating mode |
Current is also consumed by the refrigerator, lighting fixtures, radiotelephone, chargers, and TV in standby mode. But in total this power is no more than 100 W and can be ignored in calculations.
If you turn on all the electrical appliances in the house at the same time, you will need to select a wire cross-section capable of passing a current of 160 A. You will need a finger-thick wire! But such a case is unlikely. It’s hard to imagine that someone is capable of grinding meat, ironing, vacuuming and drying hair at the same time.
Calculation example. You got up in the morning, turned on the electric kettle, microwave, toaster and coffee maker. The current consumption will accordingly be 7 A + 8 A + 3 A + 4 A = 22 A. Taking into account the switched on lighting, refrigerator and, in addition, for example, a TV, the current consumption can reach 25 A.
for 220 V network
You can select the wire cross-section not only by the current strength, but also by the amount of power consumed. To do this, you need to make a list of all electrical appliances planned to be connected to a given section of electrical wiring, and determine how much power each of them consumes separately. Next, add up the data obtained and use the table below.
for 220 V network |
|||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Electrical appliance power, kW (kBA) | 0,1 | 0,3 | 0,5 | 0,7 | 0,9 | 1,0 | 1,2 | 1,5 | 1,8 | 2,0 | 2,5 | 3,0 | 3,5 | 4,0 | 4,5 | 5,0 | 6,0 |
| Standard section, mm 2 | 0,35 | 0,35 | 0,35 | 0,5 | 0,75 | 0,75 | 1,0 | 1,2 | 1,5 | 1,5 | 2,0 | 2,5 | 2,5 | 3,0 | 4,0 | 4,0 | 5,0 |
| Diameter, mm | 0,67 | 0,67 | 0,67 | 0,5 | 0,98 | 0,98 | 1,13 | 1,24 | 1,38 | 1,38 | 1,6 | 1,78 | 1,78 | 1,95 | 2,26 | 2,26 | 2,52 |
If there are several electrical appliances and for some the current consumption is known, and for others the power, then you need to determine the wire cross-section for each of them from the tables, and then add up the results.
Selecting the cross-section of copper wire according to power
for the car's on-board network 12 V
If, when connecting additional equipment to the vehicle’s on-board network, only its power consumption is known, then the cross-section of the additional electrical wiring can be determined using the table below.
| Table for choosing the cross-section and diameter of copper wire according to power for vehicle on-board network 12 V |
||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Electrical appliance power, watt (BA) | 10 | 30 | 50 | 80 | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 | 1000 | 1100 | 1200 |
| Standard section, mm 2 | 0,35 | 0,5 | 0,75 | 1,2 | 1,5 | 3,0 | 4,0 | 6,0 | 8,0 | 8,0 | 10 | 10 | 10 | 16 | 16 | 16 |
| Diameter, mm | 0,67 | 0,5 | 0,8 | 1,24 | 1,38 | 1,95 | 2,26 | 2,76 | 3,19 | 3,19 | 3,57 | 3,57 | 3,57 | 4,51 | 4,51 | 4,51 |
Selecting the wire cross-section for connecting electrical appliances
to a three-phase network 380 V
When operating electrical appliances, for example, an electric motor, connected to a three-phase network, the consumed current no longer flows through two wires, but through three and, therefore, the amount of current flowing in each individual wire is somewhat less. This allows you to use a smaller cross-section wire to connect electrical appliances to a three-phase network.
To connect electrical appliances to a three-phase network with a voltage of 380 V, for example an electric motor, the wire cross-section for each phase is taken 1.75 times smaller than for connecting to a single-phase 220 V network.
Attention, when choosing a wire cross-section for connecting an electric motor based on power, it should be taken into account that the nameplate of the electric motor indicates the maximum mechanical power that the motor can create on the shaft, and not the electrical power consumed. The electrical power consumed by the electric motor, taking into account efficiency and cos φ, is approximately two times greater than that created on the shaft, which must be taken into account when choosing the wire cross-section based on the motor power indicated in the plate.
For example, you need to connect an electric motor that consumes power from a 2.0 kW network. The total current consumption of an electric motor of such power in three phases is 5.2 A. According to the table, it turns out that a wire with a cross-section of 1.0 mm 2 is needed, taking into account the above 1.0 / 1.75 = 0.5 mm 2. Therefore, to connect a 2.0 kW electric motor to a three-phase 380 V network, you will need a three-core copper cable with a cross-section of each core of 0.5 mm 2.
It is much easier to choose the wire cross-section for connecting a three-phase motor based on the current consumption, which is always indicated on the nameplate. For example, in the nameplate shown in the photograph, the current consumption of a motor with a power of 0.25 kW for each phase at a supply voltage of 220 V (the motor windings are connected in a delta pattern) is 1.2 A, and at a voltage of 380 V (the motor windings are connected in a delta pattern) "star" circuit) is only 0.7 A. Taking the current indicated on the nameplate, using the table for selecting the wire cross-section for apartment wiring, select a wire with a cross-section of 0.35 mm 2 when connecting the electric motor windings according to the "triangle" or 0.15 mm pattern 2 when connected in a star configuration.
About choosing a cable brand for home wiring
Making apartment electrical wiring from aluminum wires at first glance seems cheaper, but operating costs due to low reliability of contacts over time will be many times higher than the costs of electrical wiring made from copper. I recommend making the wiring exclusively from copper wires! Aluminum wires are indispensable when laying overhead electrical wiring, as they are light and cheap and, when properly connected, serve reliably for a long time.
Which wire is better to use when installing electrical wiring, single-core or stranded? From the point of view of the ability to conduct current per unit of cross-section and installation, single-core is better. So for home wiring you only need to use solid wire. Stranded allows multiple bends, and the thinner the conductors in it, the more flexible and durable it is. Therefore, stranded wire is used to connect non-stationary electrical appliances to the electrical network, such as an electric hair dryer, an electric razor, an electric iron and all the others.
After deciding on the cross-section of the wire, the question arises about the brand of cable for electrical wiring. The choice here is not great and is represented by only a few brands of cables: PUNP, VVGng and NYM.
PUNP cable since 1990, in accordance with the decision of Glavgosenergonadzor “On the ban on the use of wires such as APVN, PPBN, PEN, PUNP, etc., produced according to TU 16-505. 610-74 instead of APV, APPV, PV and PPV wires according to GOST 6323-79*" is prohibited for use.
Cable VVG and VVGng - copper wires in double polyvinyl chloride insulation, flat shape. Designed for operation at ambient temperatures from −50°С to +50°С, for wiring inside buildings, outdoors, in the ground when laid in tubes. Service life up to 30 years. The letters “ng” in the brand designation indicate the non-flammability of the wire insulation. Two-, three- and four-core wires are available with core cross-sections from 1.5 to 35.0 mm 2 . If in the cable designation there is a letter A (AVVG) before VVG, then the conductors in the wire are aluminum.
The NYM cable (its Russian analogue is the VVG cable), with copper cores, round in shape, with non-flammable insulation, complies with the German standard VDE 0250. Technical characteristics and scope of application are almost the same as the VVG cable. Two-, three- and four-core wires are available with core cross-sections from 1.5 to 4.0 mm 2 .
As you can see, the choice for laying electrical wiring is not large and is determined depending on what shape the cable is more suitable for installation, round or flat. A round-shaped cable is more convenient to lay through walls, especially if the connection is made from the street into the room. You will need to drill a hole slightly larger than the diameter of the cable, and with a larger wall thickness this becomes relevant. For internal wiring, it is more convenient to use a VVG flat cable.
Parallel connection of electrical wiring wires
There are hopeless situations when you urgently need to lay wiring, but there is no wire of the required cross-section available. In this case, if there is a wire with a smaller cross-section than necessary, then the wiring can be made from two or more wires, connecting them in parallel. The main thing is that the sum of the sections of each of them is not less than the calculated one.
For example, there are three wires with a cross section of 2, 3 and 5 mm 2, but according to calculations, 10 mm 2 is needed. Connect them all in parallel and the wiring will handle up to 50 amps. Yes, you yourself have repeatedly seen the parallel connection of a large number of thin conductors to transmit large currents. For example, welding uses a current of up to 150 A and in order for the welder to control the electrode, a flexible wire is needed. It is made from hundreds of thin copper wires connected in parallel. In a car, the battery is also connected to the on-board network using the same flexible stranded wire, since when starting the engine, the starter consumes current from the battery up to 100 A. And when installing and removing the battery, the wires must be taken to the side, that is, the wire must be flexible enough .
The method of increasing the cross-section of an electrical wire by connecting several wires of different diameters in parallel can be used only as a last resort. When laying home electrical wiring, it is permissible to connect in parallel only wires of the same cross-section taken from the same reel.
Online calculators for calculating the cross-section and diameter of a wire
Using the online calculator presented below, you can solve the inverse problem - determine the diameter of the conductor by cross-section.
How to calculate the cross-section of a stranded wire
Stranded wire, or as it is also called stranded or flexible, is a single-core wire twisted together. To calculate the cross-section of a stranded wire, you must first calculate the cross-section of one wire, and then multiply the resulting result by their number.
Let's look at an example. There is a multi-core flexible wire, in which there are 15 cores with a diameter of 0.5 mm. The cross-section of one core is 0.5 mm × 0.5 mm × 0.785 = 0.19625 mm 2, after rounding we get 0.2 mm 2. Since we have 15 wires in the wire, to determine the cable cross-section we need to multiply these numbers. 0.2 mm 2 ×15=3 mm 2. It remains to determine from the table that such a stranded wire will withstand a current of 20 A.
You can estimate the load capacity of a stranded wire without measuring the diameter of an individual conductor by measuring the total diameter of all twisted wires. But since the wires are round, there are air gaps between them. To eliminate the gap area, you need to multiply the result of the wire cross-section obtained from the formula by a factor of 0.91. When measuring the diameter, you need to make sure that the stranded wire does not flatten.
Let's look at an example. As a result of measurements, the stranded wire has a diameter of 2.0 mm. Let's calculate its cross-section: 2.0 mm × 2.0 mm × 0.785 × 0.91 = 2.9 mm 2. Using the table (see below), we determine that this stranded wire will withstand a current of up to 20 A.
Finally, you have decided to make repairs in your home and, of course, you will have to replace the old aluminum wiring with copper, new, which will be more reliable. First of all, you should be concerned about the nuance regarding the cross-section of the cable for the sockets. After all, the wires must be so strong that they can withstand the electrical equipment in your home. But today, almost all people have a lot of electrical equipment in their homes, and besides, each of these devices consumes a lot of electricity. Decide how many outlets you will need so that all devices can be comfortably connected.
If you choose the material from which the cable is made, you can choose aluminum. But copper is much stronger and more reliable, and it costs much more.
After you understand the issues mentioned above, you can talk and think about wires and their cross-sections. A copper wire with a solid stranded core is best suited in this case, the main thing is that it has good vinyl insulation, something like VVG. One good thing is that today the market offers a wide variety of such products, so you don’t even have to spend a lot of time searching for them. In most cases, to connect internal sockets, a wire with a cross-sectional diameter of 2.5 mm is suitable. If the sockets in your home are installed with grounding, the wires must be three-wire, with exactly the same cross-section. To replace the wires lighting the room, their diameter can be 1.5 mm square. This will be enough for you.
Which cable to choose for an apartment? How and where to lay it
Sockets consume more electricity (after all, we connect quite powerful electrical appliances to them), which is why they heat up. In this regard, the wires to them and to the room lighting from the electrical separation box must be laid separately.
If we talk about stationary electrical appliances that have quite a lot of power, it is necessary to choose the cable cross-section as large and separately as possible. What kind of devices are these? We are talking about a washing machine, electric stove, microwave, etc. The wire cross-section for such devices should be 4 mm square. When you have decided on the cross-section and type of cable, before purchasing, carefully measure the required footage for your apartment. Yes, in case of a slight shortage, the wires can be joined, but this is highly undesirable. Therefore, it is better to have a little more than not enough.
Next, you can move on to the issue of cut-off machines and distribution boxes (they are needed, one for each room of the dwelling, and it is necessary to correctly route the wires from the cut-off machine to each distribution box).
To calculate the total power that needs to be connected to the distribution box, you need to count all the electrical appliances from each room of your house that are planned to be connected to the electrical network. Then it will also be clear to you what cross-section of wire you need to buy. You will need to lay such a wire into the junction box from the distribution panel. If the total power of electrical appliances is a maximum of 3 kW, a wire with a cross-section of 2.5 mm square will be enough for you. But if we talk about the kitchen, where, as a rule, we use quite powerful electrical appliances, the wire laid from the panel to the outlet should have a cross-section of 6 square meters. mm.
In fact, to perform such types of work, you need at least minimal experience, because not everyone can do such an activity! Therefore, if it is even difficult for you to understand which cable to choose for your apartment, not to mention carrying out all the work, hire a professional specialist. Thus, you will prevent yourself from unnecessary and unnecessary troubles and worries, and even worse, from serious troubles.
Tables for calculating cable cross-section (by power)
| Copper conductors, wires and cables | ||||
| Voltage, 220 V | Voltage, 380 V | |||
| current, A | power, kWt | current, 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 | 50 | 33 |
| 16 | 85 | 18,7 | 75 | 49,5 |
| 25 | 115 | 25,3 | 90 | 59,4 |
| 35 | 135 | 29,7 | 115 | 75,9 |
| 50 | 175 | 38,5 | 145 | 95,7 |
| 70 | 215 | 47,3 | 180 | 118,8 |
| 95 | 260 | 57,2 | 220 | 145,2 |
| 120 | 300 | 66 | 260 | 171,6 |
| Cross-section of current-carrying conductor, sq. mm | Aluminum conductors, wires and cables | |||
| Voltage, 220 V | Voltage, 380 V | |||
| current, A | power, kWt | current, A | power, kWt | |
| 2,5 | 20 | 4,4 | 19 | 12,5 |
| 4 | 28 | 6,1 | 23 | 15,1 |
| 6 | 36 | 7,9 | 30 | 19,8 |
| 10 | 50 | 11 | 39 | 25,7 |
| 16 | 60 | 13,2 | 55 | 36,3 |
| 25 | 85 | 18,7 | 70 | 46,2 |
| 35 | 100 | 22 | 85 | 56,1 |
| 50 | 135 | 29,7 | 110 | 72,6 |
| 70 | 165 | 36,3 | 140 | 92,4 |
| 95 | 200 | 44 | 170 | 112,2 |
| 120 | 230 | 50,6 | 200 | 132 |
