The ability to choose the right cable cross-section can be useful to anyone over time, and you don’t have to be a qualified electrician to do this. By incorrectly calculating the cable, you can expose yourself and your property to serious risk - too thin wires will get very hot, which can lead to a fire.
Why do you need to calculate the cable cross-section?
First of all, carrying out this slightly complicated procedure is necessary to ensure the safety of both the premises itself and the people in it. Today, humanity has not invented a more convenient method of distributing and delivering electrical energy to the consumer, like through wires. People need the services of an electrician almost every day - someone needs to connect an outlet, someone needs to install a lamp, etc. From this it turns out that even such a seemingly insignificant procedure as installing a new lamp is associated with the operation of selecting the required cross-section . What then can we say about connecting an electric stove or water heater?
Failure to comply with the standards can lead to damage to the integrity of the wiring, which often causes a short circuit or even electric shock.
If you make a mistake when choosing a cable cross-section and purchase a cable with a smaller conductor area, this will lead to constant heating of the cable, which will cause destruction of its insulation. Naturally, all this negatively affects the life of the wiring - there are often cases when, a month after successful installation, the electrical wiring stopped working and specialist intervention was required.
It should be remembered that the electrical and fire safety in the building, and therefore the lives of the residents themselves, directly depends on the correctly selected cable cross-section.
Of course, every owner wants to save as much as possible, but you should not do this at the cost of your life, putting it at risk - after all, as a result of a short circuit, a fire can occur, which may well destroy all property.
To avoid this, before starting electrical installation work, you should select a cable of the optimal cross-section. For selection, several factors must be taken into account:
- the total number of electrical devices located in the room;
- the total power of all devices and the load they consume. To the obtained value you should add 20–30% “in reserve”;
- then, through simple mathematical calculations, convert the resulting value into the cross-section of the wire, taking into account the material of the conductor.
Attention! Due to lower electrical conductivity, wires with aluminum conductors must be purchased with a larger cross-section than copper ones.
What affects the heating of wires
If the wiring heats up during the operation of household appliances, then you should immediately take all necessary measures to eliminate this problem. There are many factors influencing the heating of wires, but the main ones include the following:
- Insufficient cable cross-sectional area. To put it in accessible language, we can say this: the thicker the wires of the cable, the more current it can transmit without overheating. The value of this value is indicated in the marking of cable products. You can also measure the cross-section yourself using a caliper (you should make sure that the wire is not live) or by the type of wire.
- Material from which the wire is made. Copper conductors transmit voltage better to the consumer and have lower resistance compared to aluminum conductors. Naturally, they heat up less.
- Core type. The cable can be single-core (the core consists of one thick rod) or multi-core (the core consists of a large number of small wires). A multi-core cable is more flexible, but is significantly inferior to a single-core cable in terms of the permissible strength of the transmitted current.
- Cable laying method. Tightly laid wires located in the pipe heat up noticeably more than open wiring.
- Material and quality of insulation. Inexpensive wires, as a rule, have low quality insulation, which negatively affects their resistance to high temperatures.
How to calculate power consumption
You can calculate the approximate cable cross-section yourself - it is not necessary to seek the help of a qualified specialist. The data obtained as a result of the calculations can be used to purchase wires, however, the electrical installation work itself should be trusted only to an experienced person.
The sequence of actions when calculating the section is as follows:
- A detailed list of all electrical appliances in the room is compiled.
- The passport data of the power consumption of all found devices is established, after which the continuity of operation of a particular equipment is determined.
- Having identified the value of power consumption from devices that operate constantly, you should sum this value by adding to it a coefficient equal to the value of electrical appliances that turn on periodically (that is, if the device will work only 30% of the time, then you should add a third of its power).
- Next, we look for the obtained values in a special table for calculating the wire cross-section. For greater guarantee, it is recommended to add 10-15% to the obtained power consumption value.
To determine the necessary calculations for selecting the cross-section of electrical wiring cables according to their power within the network, it is important to use data on the amount of electrical energy consumed by devices and current appliances.
At this stage, it is necessary to take into account a very important point - the data of electrically consumed devices does not give an exact, but an approximate, average value. Therefore, about 5% of the parameters specified by the equipment manufacturer must be added to this mark.
The majority of not the most competent and qualified electricians are confident in one simple truth - in order to correctly install electrical wires for lighting sources (for example, for lamps), it is necessary to take wires with a cross-section equal to 0.5 mm², for chandeliers - 1, 5 mm², and for sockets – 2.5 mm².
Only incompetent electricians think about this and think so. But what if, for example, a microwave, kettle, refrigerator and lighting operate simultaneously in the same room, which require wires with different cross-sections? This can lead to a variety of situations: short circuit, rapid damage to wiring and insulating layer, as well as fire (this is a rare case, but still possible).
Exactly the same not very pleasant situation can happen if a person connects a multicooker, a coffee maker and, say, a washing machine to the same outlet.
Features of calculating the power of hidden wiring
If the design documentation implies the use of hidden wiring, then it is necessary to purchase cable products “with a reserve” - about 20–30% should be added to the obtained value of the cable cross-section. This is done to avoid heating the cable during operation. The fact is that in conditions of cramped space and lack of air access, heating of the cable occurs much more intensely than when installing open wiring. If in closed channels it is planned to lay not one cable, but several at once, then the cross-section of each wire should be increased by at least 40%. It is also not recommended to tightly lay various wires - ideally, each cable should be contained in a corrugated pipe, which provides it with additional protection.
Important! It is by the value of power consumption that professional electricians are guided when choosing a cable cross-section, and only this method is correct.
How to calculate cable cross-sections by power
If the cable cross-section is sufficient, the electric current will pass to the consumer without causing heating. Why does heating occur? We will try to explain as clearly as possible. For example, a kettle with a power consumption of 2 kilowatts is plugged into the outlet, but the wire going to the outlet can only transmit a current of 1 kilowatt for it. The cable capacity is related to the resistance of the conductor - the greater it is, the less current can be transmitted through the wire. As a result of high resistance in the wiring, the cable heats up, gradually destroying the insulation.
With the appropriate cross-section, the electric current reaches the consumer in full, and the wire does not heat up. Therefore, when designing electrical wiring, you should take into account the power consumption of each electrical device. This value can be found from the technical data sheet for the electrical device or from the label affixed to it. By summing the maximum values and using a simple formula:
and get the value of the total current.
Pn denotes the power of the electrical appliance indicated in the passport, 220 is the rated voltage.
For a three-phase system (380 V), the formula looks like this:
I=(P1+P2+....+Pn)/√3/380.
The resulting I value is measured in Amperes, and based on it, the appropriate cable cross-section is selected.
It is known that the throughput of a copper cable is 10 A/mm; for an aluminum cable the throughput is 8 A/mm.
For example, let’s calculate the cable cross-section for connecting a washing machine, the power consumption of which is 2400 W.
I=2400 W/220 V=10.91 A, rounding up we get 11 A.
11 A+5 A=16 A.
If you take into account that three-core cables are used in apartments and look at the table, then the value close to 16 A is 19 A, so to install a washing machine you will need a wire with a cross-section of at least 2 mm².
Table of cable cross-sections relative to current values
| Current cross-section provo- length of core(mm 2) | Current (A), for wires laid | |||||
|---|---|---|---|---|---|---|
| Open That | in one pipe | |||||
| two one- vein | three one- vein | four one- vein | one two- vein | one three- vein |
||
| 0,5 | 11 | - | - | - | - | - |
| 0,75 | 15 | - | - | - | - | - |
| 1 | 17 | 16 | 15 | 14 | 15 | 14 |
| 1,2 | 20 | 18 | 16 | 15 | 16 | 14,5 |
| 1,5 | 23 | 19 | 17 | 16 | 18 | 15 |
| 2 | 26 | 24 | 22 | 20 | 23 | 19 |
| 2,5 | 30 | 27 | 25 | 25 | 25 | 21 |
| 3 | 34 | 32 | 28 | 26 | 28 | 24 |
| 4 | 41 | 38 | 35 | 30 | 32 | 27 |
| 5 | 46 | 42 | 39 | 34 | 37 | 31 |
| 6 | 50 | 46 | 42 | 40 | 40 | 34 |
| 8 | 62 | 54 | 51 | 46 | 48 | 43 |
| 10 | 80 | 70 | 60 | 50 | 55 | 50 |
| 16 | 100 | 85 | 80 | 75 | 80 | 70 |
| 25 | 140 | 115 | 100 | 90 | 100 | 85 |
| 35 | 170 | 135 | 125 | 115 | 125 | 100 |
| 50 | 215 | 185 | 170 | 150 | 160 | 135 |
| 70 | 270 | 225 | 210 | 185 | 195 | 175 |
| 95 | 330 | 275 | 255 | 225 | 245 | 215 |
| 120 | 385 | 315 | 290 | 260 | 295 | 250 |
| 150 | 440 | 360 | 330 | - | - | - |
| 185 | 510 | - | - | - | - | - |
| 240 | 605 | - | - | - | - | - |
| 300 | 695 | - | - | - | - | - |
| 400 | 830 | - | - | - | - | - |
How to choose conductor cross-sections
There are several more criteria that the cross-section of the wires used must meet:
- Length of cable. The longer the wire, the greater the current loss observed in it. This again occurs as a result of an increase in resistance, which increases as the length of the conductor increases. This is especially noticeable when using aluminum wiring. When using copper wires to organize electrical wiring in an apartment, the length, as a rule, is not taken into account - the standard margin of 20–30% (for hidden wiring) is more than enough to compensate for possible increases in resistance associated with the length of the wire.
- Type of wires used. There are 2 types of conductors used in household electricity supply - copper or aluminum based. Copper wires are of better quality and have less resistance, but aluminum wires are cheaper. In full compliance with the standards, aluminum wiring copes with its tasks no worse than copper, so you need to carefully weigh your choice before purchasing a wire.
- Electrical panel configuration. If all the wires supplying consumers are connected to one circuit breaker, then it will be the weak point in the system. A heavy load will lead to heating of the terminal blocks, and non-compliance with the rating will lead to its constant operation. It is recommended to divide the electrical wiring into several “beams” with the installation of a separate machine.
In order to determine the exact data for choosing the cross-section of electrical wiring cables, it is necessary to take into account any, even the most insignificant parameters, such as:
- Type and type of insulation of electrical wiring;
- Length of sections;
- Laying methods and options;
- Features of temperature conditions;
- Humidity level and percentage;
- The maximum possible value of superheat;
- The difference in the powers of all current receivers belonging to the same group. All these and many other indicators can significantly increase the efficiency and benefits of energy use on any scale. In addition, correct calculations will help avoid cases of overheating or rapid abrasion of the insulating layer.
In order to correctly determine the optimal cable cross-section for any human household needs, it is necessary in all general cases to use the standardized following rules:
- for all sockets that will be installed in the apartment, it is necessary to use wires with an appropriate cross-section of 3.5 mm²;
- for all spotlighting elements, it is necessary to use electrical wiring cables with a cross-section of 1.5 mm²;
- As for high-power devices, cables with a cross-section of 4-6 mm² should be used.
If some doubts arise during the installation or calculation process, it is better not to act blindly. The ideal option would be to refer to the appropriate table of calculations and standards.
Copper cable cross-section table
| Cross-section of conductors (mm) | Copper conductors of 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 | 80 | 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 | 265 | 57,2 | 220 | 145,2 |
| 120 | 300 | 66 | 260 | 171,6 |
Aluminum Cable Section Table
Find out the cable cross-section by power and wire length. We use an effective online wire diameter calculator. Cables are fundamental elements in the process of transmitting and distributing current. They play an important role in connecting electricity, which is why it is necessary to accurately and accurately calculate the cable cross-section according to the length and load power in order to create favorable conditions for the uninterrupted flow of electricity and avoid negative emergency consequences.
If, when designing and developing an electrical network, the wrong wiring diameter is chosen, then overheating and failure of various electrical equipment are possible. The cable insulation will also be damaged, which will lead to a short circuit and fire. There will be significant costs to restore not only the electrical wiring, but also all the electrical appliances in the room. To avoid this, you need to wisely select the cable cross-section in terms of power and length.
Online power cable selection calculator
Attention! If the data is entered incorrectly, the calculator may produce inaccurate values; for clarity, use the table of values below.
On our website you can easily make the necessary calculation of the wiring diameter in a few seconds, using a ready-made program to obtain data on the cross-section of the cable core.
To do this, you need to enter several individual parameters into the finished table:
- power of the proposed facility (total load indicators of all electrical appliances used);
- select the rated voltage (most often single-phase, 220 V, but sometimes three-phase - 380 V);
- indicate the number of phases;
- core material (technical characteristics of the wire, there are two compositions - copper and aluminum);
- line length and type.
Be sure to include all values. After that, click on the “calculate” button and get the finished result.
This value ensures that when calculating the cable cross-section by online power, the wire will not overheat under operating load. Ultimately, it is important to take into account the factor of voltage drop on the wire cores, while selecting parameters for a particular line.
Table for selecting wire cross-section depending on power (W)
How to independently calculate the cable cross-section along the length?
In domestic conditions, such data is necessary when making extension cords over long distances. However, even with accurately obtained results, you need to leave 10-15 cm in reserve for connecting wires (using welding, soldering or crimping).
In industry, the formula for calculating cable cross-section by power and length is used at the network design stage. It is important to accurately determine such data if the cable will have additional and significant loads.
Example of calculation in everyday life: I = P/U cosφ, where
I – current strength, (A);
P – power, (W);
U – network voltage, (V);
cosφ – coefficient equal to 1.
Using this calculation formula, you can find the correct wiring length, and cable cross-section indicators can be obtained using an online calculator, or manually. To convert Watts to Amps - .
Program for calculating cable cross-section by power
To find out the power of an equipment or device, you need to look at the tag, which indicates its main characteristics. After adding up the data, for example, 20,000 W, this is 20 kW. This indicator indicates how much energy all electrical appliances consume. If their percentage is used at a time about 80%, then the coefficient will be equal to 0.8. Calculation of cable cross-section by power: 20 x 0.8 = 16 kW. This is the core cross-section for a copper wire measuring 10 mm. For a three-phase circuit - 2.5 mm at a voltage of 380 V.
It is better to choose a wire of the largest cross-section in advance, in case of connecting unplanned equipment or devices. It’s better to add money today and do everything efficiently than to change the cable and buy a new kettle tomorrow.
A more detailed calculator that takes into account different coefficients.
Standard apartment wiring is designed for a maximum current consumption under continuous load of 25 amperes (copper wire with a cross-section of 5 mm and a diameter of 2.5 mm is used). The greater the planned current consumption, the more cores there should be in the cable. If the wire has a diameter of 2 mm, then its cross-section can be easily determined using the following formula: 2 mm × 2 mm × 0.785 = 3.14 mm 2. If you round the value, it turns out to be 3 mm squared.
To select a cable cross-section based on power, you need to independently determine the total current of all electrical appliances, add the result and divide by 220.
The choice for laying the cable depends on its shape; it is better to lay round wiring through walls, and for interior work, a flat cable is better suited, which is easy to install and does not create obstacles in operation. Their technical characteristics are the same.
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.
The correct choice of electrical cable to power electrical equipment is the key to long-term and stable operation of installations. Using the wrong wire has serious negative consequences.
The physics of the process of damage to an electrical line due to the use of an unsuitable wire is as follows: due to the lack of space in the cable core for the free movement of electrons, the current density increases; this leads to excess energy release and an increase in the temperature of the metal. When the temperature gets too high, the line's insulating sheath melts, which can cause a fire.
To avoid trouble, you must use a cable with cores of suitable thickness. One way to determine the cross-sectional area of a cable is to start from the diameter of its cores.
Calculator for calculating cross-section by diameter
To simplify calculations, a calculator has been developed for calculating the cable cross-section by diameter. It is based on formulas that can be used to find the cross-sectional area of single-core and stranded wires.
You need to measure the cross-section by measuring the core without insulation, otherwise nothing will work.
When it comes to calculating tens and hundreds of values, an online calculator can significantly simplify the life of electricians and electrical network designers due to convenience and increased speed of calculations. It is enough to enter the value of the core diameter, and, if necessary, indicate the number of wires if the cable is multi-core, and the service will show the required wire cross-section.
Calculation formula
You can calculate the cross-sectional area of an electrical wire in different ways, depending on its type. For all cases, a single formula is used to calculate the cable cross-section by diameter. It looks like this:
D – core diameter.
The core diameter is usually indicated on the wire sheath or on a general label with other technical characteristics. If necessary, this value can be determined in two ways: using a caliper and manually.
The first way to measure the core diameter is very simple. To do this, it must be cleared of the insulating shell, and then use a caliper. The value that it will show is the diameter of the core.
If the wire is stranded, you need to unravel the bundle, count the wires and measure only one of them with a caliper. There is no point in determining the entire diameter of the beam - such a result will be incorrect due to the presence of voids. In this case, the formula for calculating the cross section will look like:
D – core diameter;
a is the number of wires in the core.
If a caliper is not available, the core diameter can be determined manually. To do this, a small section of it must be freed from the insulating shell and wound around a thin cylindrical object, for example, a pencil. The coils should fit snugly against each other. In this case, the formula for calculating the diameter of the wire core looks like this:
L – wire winding length;
N is the number of complete turns.
The longer the core is wound, the more accurate the result.
Selection by table
Knowing the diameter of the wire, you can determine its cross-section using a ready-made dependence table. The table for calculating the cable cross-section by core diameter looks like this:
| Conductor diameter, mm | Conductor cross-section, mm2 |
| 0.8 | 0.5 |
| 1 | 0.75 |
| 1.1 | 1 |
| 1.2 | 1.2 |
| 1.4 | 1.5 |
| 1.6 | 2 |
| 1.8 | 2.5 |
| 2 | 3 |
| 2.3 | 4 |
| 2.5 | 5 |
| 2.8 | 6 |
| 3.2 | 8 |
| 3.6 | 10 |
| 4.5 | 16 |
When the cross-section is known, it is possible to determine the permissible power and current values for copper or aluminum wire. In this way, it will be possible to find out what load parameters the current-carrying core is designed for. To do this, you will need a table of the dependence of the cross section on the maximum current and power.
| In the air (trays, boxes, voids, channels) | Section, sq. mm | In the ground | |||||||||
| Copper conductors | Aluminum conductors | Copper conductors | Aluminum conductors | ||||||||
| Current. A | power, kWt | Tone. A | power, kWt | Current, A | power, kWt | Current. A | Power, kWt | ||||
| 220 (V) | 380(V) | 220(V) | 380(V) | 220(V) | 380(V) | 220(V) | |||||
| 19 | 4.1 | 17.5 | 1,5 | 77 | 5.9 | 17.7 | |||||
| 35 | 5.5 | 16.4 | 19 | 4.1 | 17.5 | 7,5 | 38 | 8.3 | 75 | 79 | 6.3 |
| 35 | 7.7 | 73 | 77 | 5.9 | 17.7 | 4 | 49 | 10.7 | 33.S | 38 | 8.4 |
| *2 | 9.7 | 77.6 | 37 | 7 | 71 | 6 | 60 | 13.3 | 39.5 | 46 | 10.1 |
| 55 | 17.1 | 36.7 | 47 | 9.7 | 77.6 | 10 | 90 | 19.8 | S9.7 | 70 | 15.4 |
| 75 | 16.5 | 49.3 | 60 | 13.7 | 39.5 | 16 | 115 | 753 | 75.7 | 90 | 19,8 |
| 95 | 70,9 | 67.5 | 75 | 16.5 | 49.3 | 75 | 150 | 33 | 98.7 | 115 | 75.3 |
| 170 | 76.4 | 78.9 | 90 | 19.8 | 59.7 | 35 | 180 | 39.6 | 118.5 | 140 | 30.8 |
| 145 | 31.9 | 95.4 | 110 | 74.7 | 77.4 | 50 | 775 | 493 | 148 | 175 | 38.5 |
| ISO | 39.6 | 118.4 | 140 | 30.8 | 97.1 | 70 | 775 | 60.5 | 181 | 710 | 46.7 |
| 770 | 48.4 | 144.8 | 170 | 37.4 | 111.9 | 95 | 310 | 77.6 | 717.7 | 755 | 56.1 |
| 760 | 57,7 | 171.1 | 700 | 44 | 131,6 | 170 | 385 | 84.7 | 753.4 | 795 | 6S |
| 305 | 67.1 | 700.7 | 735 | 51.7 | 154.6 | 150 | 435 | 95.7 | 786.3 | 335 | 73.7 |
| 350 | 77 | 730.3 | 770 | 59.4 | 177.7 | 185 | 500 | 110 | 379 | 385 | 84.7 |
Converting watts to kilowatts
In order to correctly use the table of wire cross-section versus power, it is important to correctly convert watts to kilowatts.
1 kilowatt = 1000 watts. Accordingly, to obtain the value in kilowatts, the power in watts must be divided by 1000. For example, 4300 W = 4.3 kW.
Examples
Example 1. It is necessary to determine the permissible current and power values for a copper wire with a core diameter of 2.3 mm. Supply voltage – 220 V.
First of all, you should determine the cross-sectional area of the core. This can be done using a table or a formula. In the first case, the value is 4 mm 2, in the second - 4.15 mm 2.
The calculated value is always more accurate than the tabulated value.
Using a table of the dependence of cable cross-section on power and current, you can find out that for a cross-section of a copper core with an area of 4.15 mm 2, a power of 7.7 kW and a current of 35 A are permissible.
Example 2. It is necessary to calculate the current and power values for an aluminum stranded wire. Core diameter – 0.2 mm, number of wires – 36, voltage – 220 V.
In the case of a stranded wire, it is not advisable to use tabular values; it is better to use the formula for calculating the cross-sectional area:
Now you can determine the power and current values for a stranded aluminum wire with a cross section of 2.26 mm 2. Power – 4.1 kW, current – 19 A.
Of the cross-sections of current-carrying conductors of a copper wire indicated in the question, a wire with a cross-section of 1 square millimeter is perhaps the most rarely used. This wire can be used to make internal switching of a chandelier or lamp; for each light bulb in the chandelier it will be more than enough, because individually they rarely exceed 500 Watts. With a wire of 1 square millimeter, today you can also install a lighting line for internal electrical wiring in which energy-saving or LED lamps will be used; their power is low and a wire of one square is enough. Why in a private house? Yes, because the wiring of apartments is still done according to the PUE and must have a cross-section of at least 1.5 square meters. The total power that the wire cross-section will withstand 1 square millimeter - 2200 Watts (2.2 Kilowatts) (10 Amps) You can connect any device whose power does not exceed this value. For example, it is not critical to connect a hair dryer, computer, TV, video set-top box, power supply for video surveillance systems, mixer... When determining the power characteristics of a device, you must first of all refer to its passport data indicated in the passport plate (usually stuck on the device in an inconspicuous place)
Wire with a cross-section of 1.5 is usually used in lighting, although the power reserve in the lighting line is not very bad. By the way, the maximum permissible load on the wire should not be taken as standard; there should always be a reserve of power, about 10 percent. In this case, your wire will never heat up even if all consumers are turned on for a long time, especially the connection points, which are the weakest link in any electrical circuit.
Below is a table of the ratios of the cross-sectional area of the core, permissible current and power. So these are the peak values, subtract 10 percent from them and your wiring will not overheat with any installation method - closed or open wiring.
As you noticed, the value of current and power for different voltages is also different. The question does not indicate the voltage, so I give it for both a 220 Volt network and a 380 Volt network.
So what can we connect in a 220 Volt household network to the wire in -
- 1.5 square- 3500 Watt. This can be at the same time an electric kettle of 2 Kilowatts + a Hairdryer of 250 Watts + a mixer of 250 Watts + an iron of 1 Kilowatt.
- 2.5 square- 5500 Watt. This can be at the same time, all the same, a 2 Kilowatt electric kettle + a 250 Watt hair dryer + a 250 Watt mixer + a 1 Kilowatt iron + a 500 Watt TV + a 1400 Watt vacuum cleaner.
This is just a calculation of power with a margin based on the capabilities of the wire.
You may ask why I didn’t give the number of consumers and their power for a wire with a cross-section of 2 squares? Yes, because the main cross-section of copper wires is 0.75; 1; 1.5; 2.5; 4; 6; 10 squares. I do not exclude that for a narrow purpose a copper wire with a cross-section of 2 square meters. mm. and there is, but not in retail sale.
The question emphasizes “..in my own words..” but nevertheless, for educational purposes, I will give a table of the ratios of the power of electrical appliances to the current consumed, so it will be easier to correlate the existing device, its power (or the total power of several devices) and the current consumed by them and the corresponding cross-section of the copper core.
Seeing this sign and knowing that 1 square millimeter of wire can withstand a current of 10 Amps, we can easily calculate the maximum possible power for our wire.
For example, an electric kettle with a power of 1500 Watt consumes a current of 6.8 Amperes. It turns out that for a wire with a cross-section of 1 square, powering such a kettle will not be critical, even with a good power reserve. But for a kettle with a power of 2000 Watts, a wire of the same cross-section will already lie in the “red zone” of the permissible load, and its constant use for this purpose is unacceptable; you need to take a larger cross-section.