Cable with a large cross section. How to choose a cable section

Conductor cross section for power and current for wiring in an apartment

Electrical work is a complex and responsible undertaking. If your qualifications are enough to do the wiring in the apartment with your own hands, they will come in handy helpful tips. If not, then use the services of specialists in electrical work. So, let's talk about the choice of wire cross-section for current and power in detail.

Calculation of the length and maximum load of electrical wiring

Correct calculation of the cross section of wires for power and current - important condition uninterrupted and trouble-free operation of the electrical system. First, calculate the total wiring length. The first way is to measure the distances between shields, switches and sockets on the wiring diagram, multiplying the number by the scale. The second way is to determine the length at the place where the wiring is designed. It includes all wires, installation and installation cables along with fasteners supporting and protective structures. Each segment must be extended by at least 1 cm, taking into account the wire connections.

Next, the total load of the consumed electricity is calculated. This is the sum of the rated capacities of all electrical appliances that will work in the house (*see table at the end of the article). For example, if an electric kettle, electric stove, microwave, lamps are turned on in the kitchen at the same time, Dishwasher, sum up the power of all devices and multiply by 0.75 (simultaneity factor). The calculation of the load must always have a margin of safety and strength. We remember this figure to determine the cross section of the wires.

A simple formula will help you independently determine the current consumption of any electrical appliance. Divide the power consumption (see the instructions for the device) by the mains voltage (220 V). For example, according to the passport power washing machine 2000 W; 2000/220 = maximum current during operation will not exceed 9.1A.

Another option is to use the recommendations of the PUE (Electrical Installation Rules), according to which standard apartment wiring with a continuous load of 25A is calculated for the maximum current consumption, is carried out with a copper wire with a cross section of 5mm 2. According to the PUE, the cross section of the core must be at least 2.5 mm 2, which corresponds to a conductor diameter of 1.8 mm.

This current is set and circuit breaker at the input of wires to the apartment to prevent accidents. AT residential buildings a single-phase current with a voltage of 220 V is used. The calculated total load is divided by the voltage value (220 V) and we get the current that will pass through the input cable and the machine. You need to buy an automatic machine with exact or close parameters, with a margin for current load.

The choice of cable for electrical wiring in the apartment

* Table of power consumption and current
household electrical appliances with a supply voltage of 220V

household appliance	Power consumption depending on the model of the electrical appliance, kW (BA)	Consumed current, A	Note
incandescent lamp
Electric kettle			Continuous operation time up to 5 minutes
electric stove			Above 2 kV, separate wiring is required
Microwave
Electric meat grinder
coffee grinder			During operation, depending on the load, the consumed current varies
Coffee maker
Electric oven			During operation, the maximum current is consumed intermittently
Dishwasher
Washing machine			The maximum current is consumed from the moment of switching on until the water is heated
			During operation, the maximum current is consumed intermittently
			During operation, depending on the load, the consumed current varies
Desktop computer			During operation, the maximum current is consumed intermittently
Power tools (drill, jigsaw, etc.)			During operation, depending on the load, the consumed current varies

The cross section of the cable at the cut is standardized in all countries. This applies to both the CIS countries and Europe. This issue is regulated in our country by the document "Electrical Installation Rules", which are called PUE. The calculation of the cable cross-section by power is selected using special tables. Of course, many calculate the necessary parameters of the conductor "by eye", but this is not entirely correct. For each apartment, this figure may be different. This is due to the number of electrical consumers and their power. Without proper calculation, many unpleasant situations can occur, costly repairs of both wiring and the apartment.

Cable device

To determine the cable cross-section by power, one should understand its principle and structure. It can be compared, for example, with water or gas pipeline. In the same way as through these communications, a stream flows through the electrical conductor. Its power limits the cross section of the conductor.

The cable cross-section using the power indicator can be incorrect in two cases:

1. The current-carrying channel will be too narrow. This will lead to an increase in current density and, consequently, to overheating of the insulation. Such a state of the conductor over time will be characterized by the presence weaknesses where leakage is possible. This condition of the channel can cause a fire.
2. Conductor too wide. This, of course, is not the worst option. The space for transporting the electrical flow will allow more functional and durable use of the conductor. However, as the cross section increases, so does the cost of the cable.

The first option is a danger to life, health and property. The second method is safe, but the materials are quite expensive to purchase.

The easy way

The calculation of the cable cross-section by power is based on the well-known law developed by Ohm. He says that the current flow times the voltage equals the power. Voltage in everyday life is considered a constant value. In a single-phase network, it is equal to 220 V. Therefore, to determine the cable cross-section in terms of current, as well as power, only two variables remain.

Next, the current values ​​\u200b\u200band the expected load are calculated. Moreover, the size of the cable according to its power can be selected according to the PUE table. This indicator is calculated for a wire suitable for sockets. Traditionally, for lighting lines, a wire with a cross section of 1.5 mm 2 is laid.

However, it happens that devices such as a hair dryer, microwave oven, electric kettle, etc. are connected to the outlet group. It is necessary to distribute the load and correctly calculate the cable cross-section in terms of power, correlating the diameter and load.

If it is not possible to break up the socket groups, then many electricians will recommend immediately installing a cable with a copper core up to 6 mm 2.

Cross-sectional area and diameter

Calculation of the cable cross-section by power, diameter and load are not equivalent concepts. The first indicator is calculated in mm 2, and the second is simply in mm. You can choose the power and allowable current according to the table both by the cable cross section and by its diameter.

If the table takes into account only the size of the cross-sectional area in mm 2, and there is data only on the diameter of the cable, the missing indicator can be found using the following formula:

S \u003d 3.14D 2 / 4 \u003d 0.785D 2,

where: S is the cross section of the wire and D is the diameter.

If the wire in the section is not round, but rectangular, its cross-sectional area is calculated by multiplying the length by the width (just like the area of ​​a rectangle).

Load Based Calculation

The easiest way to calculate the cable wire cross section is by summing up the capacities of all units that will be connected to the line. To do this, you will need to perform a certain sequence of actions.

First, it is determined which electrical appliances will be used in the home, which of them are likely to function simultaneously. Next, you need to look into the data sheets of each of these units. It will be necessary to calculate the sum of the capacities of those electrical consumers that must work simultaneously.

Then the indicator obtained as a result of the calculations performed is rounded to big side. This will provide a safe supply of electrical wiring power. The cross section of the wire or cable is calculated further using the PUE tables.

In a similar way, you can summarize the current strength, which is indicated in the data sheets electrical equipment. Rounding and searching in the power calculation table is performed.

Table of power, current and section of copper wires

According to the PUE, in residential buildings it is necessary to use only copper conductors for arranging wiring. The power supply of some electrical equipment, which belongs to the engineering types of receivers, can be connected to the network with aluminum conductors with a cross section of at least 2.5 mm 2.

Table of power, current and section of aluminum wires

The specialist will also be able to make correction factors for the type of wire location, temperature environment, for a cable in the ground, etc. The table for calculating cable power, cross-section or current strength applies to conductors in plastic or rubber insulation. These include such common brands as VVP, PVS, PPV, VPP, AVVG, VVG, APPV, etc. Uninsulated or paper-screened cables should be calculated according to the table related to them.

Length and section

The calculation of the cable cross-section by power simply needs to be used to determine its length. This data is important when creating long extensions. Received exact values at the same time, it is necessary to increase by 10-15 cm. This margin is necessary for switching by soldering, welding or crimping.

In construction, the cable cross-section is calculated in terms of power and length at the design stage of electrical wiring. This is very important, especially for those communications that will be subject to significant or additional loads.

In everyday life, the calculation of the length of the wire is carried out according to the following formula:

I=P/U*cosφ, where:

• P - power (W);
• I - current strength (A);
• U - voltage (V);
• cosφ - coefficient, which is equal to 1.

The cable cross section must first be found in the table. The formula will help determine the correct wire length.

current density

The current strength varies in the range of 6-10 A, which was derived empirically. This value is calculated for the current flowing through 1 mm 2 of the copper core.

This statement means that the calculation of the cable cross-section in terms of power and current is based on a copper cable with a cross section of 1 mm 2, through which current from 6 to 10 A can flow to waiting household appliances without melting and overheating.

According to the PUE code, for each wire a margin of 40% is allocated for overheating that is safe for the sheath. If the value of 6 A characterizes the operation of the presented conductor for an infinitely long term without time limits, then the indicator of 10 A is suitable for the short-term flow of current through the core.

If a current of 12 A flows through a 1 mm 2 copper conductor, it will be cramped in such a core. This will increase the current density. The core will begin to heat up and will melt the insulation.

Therefore, such calculations are mandatory when choosing a cable section for each type of wiring.

Having familiarized yourself with the methods that allow you to calculate the cable cross-section by power and current strength, you can lay or repair old wiring that will last a long time and be completely safe for people living in the house. Many fairly simple, but effective ways help you determine exactly required size sections for the electrical network.

From right choice section of electrical wiring depends on the comfort and safety in the house. When overloaded, the conductor overheats and the insulation may melt, resulting in a fire or short circuit. But it is unprofitable to take a cross section larger than necessary, since the price of the cable increases.

In general, it is calculated depending on the number of consumers, for which the total power used by the apartment is first determined, and then the result is multiplied by 0.75. The PUE uses a table of loads for the cable section. From it, you can easily determine the diameter of the cores, which depends on the material and the passing current. As a rule, copper conductors are used.

The cross section of the cable core must exactly match the calculated one - in the direction of increasing the standard size range. It's most dangerous when it's low. Then the conductor constantly overheats, and the insulation quickly fails. And if you set the appropriate one, it will be triggered frequently.

If you overestimate the cross section of the wire, it will cost more. Although a certain margin is necessary, since in the future, as a rule, you have to connect new equipment. It is advisable to apply a safety factor of about 1.5.

Calculation of total power

The total power consumed by the apartment falls on the main input, which is included in switchboard, and after it branches into lines:

• lighting;
• socket groups;
• separate powerful electrical appliances.

Therefore, the largest section power cable- at the entrance. On the outlet lines, it decreases, depending on the load. First of all, the total power of all loads is determined. It is not difficult, because on the cases of all household appliances and in the passports to them it is indicated.

All powers add up. Similarly, calculations are made for each contour. Experts suggest multiplying the amount by 0.75. This is due to the fact that at the same time all devices are not included in the network. Others suggest choosing a section bigger size. Due to this, a reserve is created for the subsequent commissioning of additional electrical appliances that may be purchased in the future. It should be noted that this cable calculation option is more reliable.

How to determine the wire size?

In all calculations, the cable section appears. It is easier to determine its diameter by using the formulas:

• S=π D²/4;
• D= √(4×S/π).

Where π = 3.14.

S = N × D² / 1.27.

Stranded wires are used where flexibility is required. Cheaper solid conductors are used in permanent installations.

How to choose a cable by power?

In order to select the wiring, the table of loads for the cable section is used:

• If the line open type is energized at 220 V, and the total power is 4 kW, a copper conductor with a cross section of 1.5 mm² is taken. This dimension is usually used for lighting wiring.
• With a power of 6 kW, conductors of a larger cross section are required - 2.5 mm². The wire is used for sockets to which household appliances are connected.
• A power of 10 kW requires the use of 6 mm² wiring. Usually it is intended for the kitchen, where it is connected electric stove. The supply to such a load is made on a separate line.

Which cables are best?

Electricians are well aware of the cable of the German brand NUM for office and residential premises. In Russia, brands of cables are produced that are lower in characteristics, although they may have the same name. They can be distinguished by the leakage of the compound in the space between the cores or by its absence.

The wire is produced monolithic and stranded. Each core, as well as the entire twist, is insulated from the outside with PVC, and the filler between them is made non-combustible:

• So, the NUM cable is used indoors, since the insulation on the street is destroyed by sunlight.
• And as an internal cable, the VVG brand is widely used. It is cheap and fairly reliable. It is not recommended for laying in the ground.
• Wire brand VVG is made flat and round. Filler is not used between the cores.
• do with outer shell that does not sustain combustion. The cores are made round up to a section of 16 mm², and above - sectoral.
• Cable brands PVS and ShVVP are made multi-wire and are used mainly for connecting household appliances. It is often used as home electrical wiring. It is not recommended to use stranded conductors on the street due to corrosion. In addition, the insulation cracks when bent at low temperatures.
• On the street, armored and moisture-resistant cables AVBShv and VBShv are laid underground. The armor is made of two steel tapes, which increases the reliability of the cable and makes it resistant to mechanical stress.

Determining the current load

A more accurate result is given by the calculation of the cable cross-section in terms of power and current, where the geometric parameters are related to electrical ones.

For home wiring, not only active load, but also reactive load should be taken into account. The current strength is determined by the formula:

I = P/(U∙cosφ).

Reactive load is created fluorescent lamps and motors of electrical appliances (refrigerator, vacuum cleaner, power tools, etc.).

Current example

Let's find out what to do if it is necessary to determine the cross-section of a copper cable for connecting household appliances with a total power of 25 kW and three-phase machines for 10 kW. Such a connection is made by a five-core cable laid in the ground. The meals at home are from

Taking into account the reactive component, the power of household appliances and equipment will be:

• P life. = 25 / 0.7 = 35.7 kW;
• P rev. \u003d 10 / 0.7 \u003d 14.3 kW.

Input currents are determined:

• I life. \u003d 35.7 × 1000 / 220 \u003d 162 A;
• I rev. \u003d 14.3 × 1000 / 380 \u003d 38 A.

If you distribute single-phase loads evenly over three phases, one will have a current:

I f \u003d 162/3 \u003d 54 A.

I f \u003d 54 + 38 \u003d 92 A.

All appliances will not work at the same time. Taking into account the margin, each phase has a current:

I f \u003d 92 × 0.75 × 1.5 \u003d 103.5 A.

In a five-core cable, only phase cores are taken into account. For a cable laid in the ground, a conductor cross section of 16 mm² can be determined for a current of 103.5 A (table of loads for the cable cross section).

A more accurate calculation of the current strength saves money, since a smaller cross section is required. With a rougher calculation of the cable in terms of power, the cross section of the core will be 25 mm², which will cost more.

Cable voltage drop

Conductors have resistance that must be taken into account. This is especially important for long cable lengths or small cross-sections. PES standards have been established, according to which the voltage drop on the cable should not exceed 5%. The calculation is done as follows.

1. The resistance of the conductor is determined: R = 2×(ρ×L)/S.
2. The voltage drop is found: U pad. = I×R. In relation to the linear percentage, it will be: U% \u003d (U fall / U line) × 100.

The following notations are accepted in the formulas:

• ρ - resistivity, Ohm×mm²/m;
• S - area cross section, mm².

The coefficient 2 shows that the current flows through two wires.

Example of cable calculation for voltage drop

• The wire resistance is: R \u003d 2 (0.0175 × 20) / 2.5 \u003d 0.28 Ohm.
• The strength of the current in the conductor: I \u003d 7000/220 \u003d 31.8 A.
• Carry voltage drop: U pad. = 31.8×0.28 = 8.9V.
• Voltage drop percentage: U% \u003d (8.9 / 220) × 100 \u003d 4.1 %.

Carrying suit for welding machine according to the requirements of the rules for the operation of electrical installations, since the percentage of voltage drop on it is within the normal range. However, its value on the supply wire remains large, which can adversely affect the welding process. Here it is necessary to check the lower permissible limit of the supply voltage for the welding machine.

Conclusion

To reliably protect the wiring from overheating when the rated current is exceeded for a long time, the cable cross-sections are calculated according to the long-term permissible currents. The calculation is simplified if the load table for the cable section is used. A more accurate result is obtained if the calculation is based on the maximum current load. And for stable and long-term operation, a circuit breaker is installed in the wiring circuit.

Content:

Reliable and safe operation of any electrical appliances and equipment largely depends on the correct choice of wires. Great importance has a section copper wire, the table allows you to determine its necessary parameters, depending on the current load and power. Incorrect selection of cable products can cause a short circuit and subsequent fire. If the wire section is small and the power of the equipment is too high, it will overheat, which will cause an emergency.

Cross section and wire power

When choosing cable products, it is first necessary to take into account the significant differences between copper and aluminum wires.

And power table

Copper is more resistant to various kinds of bending, it has a higher electrical conductivity and is less susceptible to corrosion. Therefore, the same load provides for a smaller cross section of copper wire compared to aluminum. In any case, when purchasing an electrical wire, you need to make a certain margin of its cross section, in case of increased loads in the future, when a new one is installed. Appliances. In addition, the section must match maximum load, or other protective devices.

The magnitude of the current refers to the main indicators that affect the calculations of the cross-sectional area of ​​\u200b\u200bthe wires. That is, a certain area has the ability to pass a certain amount of current through itself for a long time. This parameter is also called continuous load capacity.

The section itself is total area, which has a cut of the conductive core. To determine it, the formula for calculating the area of ​​​​a circle is used. Thus, Skr. \u003d π × r2, where the number π \u003d 3.14, and r - will be the radius of the circle being measured. If available in cable core several conductors at once, the diameter of each of them is measured, and then the data obtained are summarized. To find the radius, you must first use a micrometer or caliper. Most effective method the determination of the cross-sectional area according to special tables is considered, taking into account the necessary indicators.

First of all, specific operating conditions are taken into account, as well as the expected value maximum current that will flow through this cable for a long time.

Cross section of copper wires and power of electrical equipment

Before installing any electrical equipment, all calculations must be completed. They are carried out taking into account the full capacity of future consumers of electricity. If several pieces of equipment are mounted at once, then the calculations are carried out in accordance with their total capacity.

The power of each device is indicated on the case or in technical documentation per product and are reported in watts (W) or kilowatts (kW). In order to calculate the cross section of a copper wire by power, a table with special parameters will help you choose the best option.

In standard city apartments, as a rule, a single-phase power supply system operates, the voltage of which is 220 volts. The calculations are carried out taking into account the so-called simultaneity factor, which is 0.7. This indicator means that about 70% of the installed equipment can be turned on at the same time. This coefficient must be multiplied by the value of the total power of all available devices. According to the result obtained in the table is determined required section wiring in accordance with the specified technical and operational conditions.

How to determine the cross section for a stranded wire

Content:

Before connecting the load to the network, it is important to make sure that the cores of the supply cable are of sufficient thickness. In the case of a significant excess of the permissible power, the destruction of the insulation and even the core itself is possible due to its overheating.

Before calculating the cable cross-section by power, you should calculate the sum of the powers of the connected electrical appliances. Most modern apartments the main consumers are:

• Refrigerator 300 W
• Washing machine 2650 W
• Computer 550W
• Lighting 500 W
• Electric kettle 1150 W
• Microwave oven 700 W
• TV 160 W
• Water heater 1950 W
• Vacuum cleaner 600 W
• Iron 1750 W
• Total 10310 W = 10.3 kW

In sum, most modern apartments consume approximately 10 kW. Depending on the time of day, this parameter can be significantly reduced. However, when choosing a conductor cross section, it is important to focus on a large value.

You need to know the following: the calculation of the cable cross-section for single-phase and three-phase networks is different. But in both cases, three parameters should be taken into account first of all:

• current strength(I)
• Voltage(U)
• Power consumption (P).

There are also several other variables, their meaning differs for each specific case.

Calculation of the wire cross section for a single-phase network

The calculation of the wire cross-section by power is carried out using the following formula:

I = (P × K and) / (U × cos(φ))

Where,

• I- current strength;
• P- power consumption of all electrical appliances in total;
• K and- coefficient of simultaneity, usually a standard value of 0.75 is taken for calculations;
• U- phase voltage, it is 220 (V), but can range from 210 to 240 (V);
• Cos(φ)- for household single-phase appliances, this value is unchanged and equals 1.

If you need to quickly calculate the current, you can omit the value of cos (φ) and even K and. The resulting value will differ downward (by 15%) if a formula of this type is applied:

I=P/U

Having found the current according to the calculation formula, you can safely proceed to the choice of the supply cable. More precisely, its cross-sectional area. There are special tables that provide data that allow you to compare the amount of current, power consumption and cable cross-section.

Data vary greatly for conductors made from different metals. To date, for residential electrical wiring is usually used only rigid copper cable, aluminum is practically not used. Although in many old houses all lines are laid using aluminum.

The cross section of the copper cable is selected according to the following parameters:

Calculation of the wire cross section in the apartment - Table

It often happens that as a result of calculations, a current is obtained that is between the two values ​​\u200b\u200bpresented in the table. In this case, the nearest higher value should be used. If, as a result of calculations, the current value in a single-core wire is 25 (A), it is necessary to select a cross section of 2.5 mm 2 or more.

Calculation of the cable cross-section for a three-phase network

To calculate the cross section of the supply cable used in three-phase network, you need to use the following formula:

I = P / (√3 × U × cos(φ))

Where,

• I- current strength, according to which the cross-sectional area of ​​\u200b\u200bthe cable will be selected;
• U- phase voltage, 220 (V);
• Cos φ- phase shift angle;
• P- an indicator of the total power of all electrical appliances.

Cos φ in this formula is very important. Since it directly affects the strength of the current. It is different for different equipment, most often this parameter can be found in the technical accompanying documentation, or it is indicated on the case.

The total power of consumers is very simple: all powers are added up, the resulting value is used for calculations.

A distinctive feature of the choice of cable cross-sectional area for use in a three-phase network is that a thinner core can withstand a greater load. The required section is selected according to the standard table.

The choice of cable cross-section for a three-phase network - Table

The calculation of the wire cross-section by power in a three-phase network is performed using a value such as √3 . Given value needed to simplify appearance formulas.

U linear = √3 × U phase

Thus, if necessary, you can replace the product of the root and the phase voltage with a linear voltage. This value is 380 (V) (U linear = 380 V).

When choosing a cable section, both for a three-phase network and for a single-phase network, it is necessary to take into account permissible continuous current . This parameter indicates the amount of current (measured in amperes) that the conductor can withstand for an unlimited amount of time. It is determined according to special tables, they are available in the PUE. For aluminum and copper conductors, the data differ significantly.

Permissible current duration - Table

If the value specified in the table is exceeded, the conductor starts to heat up. The heating temperature is inversely proportional to the current strength.