Conductor cross-section in terms of power and current for electrical wiring in an apartment. Dependence of cable and wire cross-section on current loads and power Maximum load on cable 1 5
From personal experience I was convinced that the thinner the wires, the worse their use both for devices and for the wiring itself.
First, I’ll touch on the main problems that arise when choosing the wrong wiring:
- Some devices do not have enough current power, this is clearly noticeable on a welding machine; the thinner the wires, the worse their welding. But you can also see the difference in the light of the light bulb; if you connect, say, a 150-watt light bulb to wiring with a cross-section of 0.5 mm and 2.5 mm, then the light at 0.5 mm will be dimmed than at 2.5 mm.
- The thinner the wires and the greater the power of the end device used, the more they heat up, to the point that they can ignite. This depends on the fact (in simple terms) that it is more difficult for the wires to transmit a certain amount of current necessary to consume the device. This is a busy narrow road.
- This point comes out of point 2, but I will touch on it separately. Connections of wires with a smaller cross-section oxidize and burn faster, since larger power flows passing through them than those calculated for the cross-section heat up these places faster, which subsequently leads to poor contact. Well, where the contact is poor, there is a possibility of strong heating, even to the point of igniting the insulation and burning the wires.
You should always use only the cross-section of wires that is suitable for the power of the device!
Now let's get closer to your question.
I would like to warn you right away that wires of the same cross-section from the same material may differ in technical characteristics, at least in the fact that copper wires (which you are asking about in the question) can be of at least two options - single-core and stranded.
The apartment's wiring uses single-core copper wire VVG, which is exactly what I wanted to talk about.
So what are your examples:
Copper wires with a cross section of 1 square
They are practically not used in the apartment, but can be connected to low-power LED lighting, as well as various light indicators.
Copper wires with a cross section of 1.5 square
These wires are used for laying lighting with a total consumer value of no more than 4 kW, i.e. count all the light bulbs by power and the result should not exceed this value. They are also used (I do not recommend placing them on those sockets where many electrical appliances are plugged in) to connect the sockets of one device. For example, separate lamps, a TV, a computer, a vacuum cleaner, chargers, etc., in which the power is not higher than 4 kW. Of course, you can use several devices in one outlet, but combinations such as: computer + vacuum cleaner + hair dryer are quite dangerous.
Copper wires with a cross section of 2 squares
This section is practically not used, I have not even seen it on sale, so it makes no sense to focus on it.
Copper wires with a cross section of 2.5 square
But 2.5 square meters is the recommended wiring in the apartment (except for, as I mentioned above, electric stoves). This cross-section is suitable for connecting several devices to one outlet at once, but the total should not exceed 5.8 kW. Or individual devices, such as:
- Fridge
- Water heater
- Washing machine
- Oven
- Machines operating from an engine no higher than 4.5 - 5.0 kW
In general, if we talk about the distribution of wiring across sections, you will clearly and quickly understand in this figure (by the way, the hood in it was set at 1.5 mm, I would leave it at 2.0 mm):
www.remotvet.ru
What load can aluminum wires with a cross section of 1, 1/5, 2, 2/5 square withstand, what can be connected?
Table of load capacity of electrical wiring made of aluminum wire
Wire diameter, mm 1.6 1.8 2.0 2.3 2.5 2.7 3.2 3.6 4.5 5.6 6.2
Wire cross-section, mm 2.0 2.5 3.0 4.0 5.0 6.0 8.0 10.0 16.0 25.0 30.0
Maximum current under continuous load, A 14 16 18 21 24 26 31 38 55 65 75
Maximum load power, watt (VA) 3000 3500 4000 4600 5300 5700 6800 8400 12000 14000 16000
Table of power and current consumption by household electrical appliances at a supply voltage of 220 V
Household electrical appliance Power consumption depending on the model of the electrical appliance, kW (BA) Current consumption, A Note
Incandescent light bulb 0.06 – 0.25 0.3 – 1.2 Current value constant
Electric kettle 1.0 – 2.0 5 – 9 Continuous operation time up to 5 minutes
Electric stove 1.0 – 6.0 5 – 60 With a power of more than 2 kW, separate wiring is required
Microwave oven 1.5 – 2.2 7 – 10 During operation, the maximum current is consumed intermittently
Electric meat grinder 1.5 – 2.2 7 – 10 During operation, depending on the load, the current consumption changes
Toaster 0.5 – 1.5 2 – 7 Current value constant
Grill 1.2 – 2.0 7 – 9 Current value constant
Coffee grinder 0.5 – 1.5 2 – 8 During operation, depending on the load, the current consumption varies
Coffee maker 0.5 – 1.5 2 – 8 Current value constant
Electric oven 1.0 – 2.0 5 – 9 During operation, the maximum current is consumed periodically
Dishwasher 1.0 – 2.0 5 – 9 Maximum current consumed from switching on until water is heated
Washing machine 1.2 – 2.0 6 – 9 Maximum current consumed from the moment it is turned on until the water is heated
Dryer 2.0 – 3.0 9 – 13 Maximum current consumed during the entire drying time
Iron 1.2 – 2.0 6 – 9 During operation, the maximum current is consumed periodically
Vacuum cleaner 0.8 – 2.0 4 – 9 During operation, depending on the load, the current consumption varies
Heater 0.5 – 3.0 2 – 13 Current value constant
Hair dryer 0.5 – 1.5 2 – 8 Current value constant
Air conditioner 1.0 – 3.0 5 – 13 During operation, the maximum current consumed varies periodically
Desktop computer 0.3 – 0.8 1 – 3 During operation, the maximum current consumed varies periodically
Power tool (drill, jigsaw, etc.) 0.5 – 2.5 2 – 13 During operation, the current consumption varies depending on the load
www.remotvet.ru
Copper wire 4 squares in a single-phase network - what load can it withstand?
There are special tables that are convenient to use when choosing a wire cross-section, taking into account the load on it. 
If we are talking about a 220-volt network, then 4 square copper cores will withstand a load of 8.3 kilowatts (see table above).
This is a very serious indicator.
For socket groups they usually take two and a half squares of copper, for lighting one and a half squares.
That is, for almost (almost) any household appliance, the same 2.5 square meters of wire cross-section is enough (refrigerators, washing machines and dishwashers, electric kettles, irons, vacuum cleaners, TVs, air conditioners, etc.).
4th square, the apartment must have some very powerful household appliance, for example an electric stove (a separate wire runs from the panel), or a high-power instantaneous water heater (for storage and 2.5 squares is enough).
Well, or such a wire is pulled to a socket group, where the total power of the connected electrical appliances is very significant.
www.remotvet.ru
Calculation of wire cross-section for load
When choosing cable and wire products, first of all, you need to pay attention to the material used in manufacturing, as well as the cross-section of a particular conductor. To make the right choice, it is necessary to calculate the cross-section of the wire according to the load. With this calculation, the wires and cables will ensure, in the future, reliable and safe operation of all electrical wiring.
Wire cross-section parameters
The main criteria by which the cross-section is determined are the metal of the current-carrying conductors, the expected voltage, the total power and the value of the current load. If the wires are not properly sized for the load, they will continually heat up and eventually burn out. It is also not worth choosing wires with a cross-section larger than necessary, since this will lead to significant costs and additional difficulties during installation.
Practical definition of section
The cross-section is also determined in relation to their further use. So, in a standard apartment, copper cable is used for sockets, the cross-section of which is 2.5 mm2. For lighting, conductors with a smaller cross-section can be used - only 1.5 mm2. But for electrical devices with high power, from 4 to 6 mm2 are used.
This option is most popular when calculating the cross-section of the wire according to the load. Indeed, this is a very simple method; you just need to know that a 1.5 mm2 copper wire can withstand a power load of over 4 kilowatts and a current of 19 amperes. 2.5 mm - respectively, withstands about 6 kilowatts and 27 amperes. 4 and 6 mm freely transfer power of 8 and 10 kilowatts. If connected correctly, these wires are sufficient for the normal operation of all electrical wiring. Thus, it is possible to create even a certain small reserve in case of connecting additional consumers.
When calculating, operating voltage plays an important role. The power of electrical appliances may be the same, however, the current load arriving at the cores of the cables supplying power may be different. So wires designed to operate at a voltage of 220 volts will carry a higher load than wires designed for 380 volts.
How to choose the right cable for connecting a consumer? This question is not as simple as it might seem at first glance. When choosing, you need to take into account many nuances, know the length of the line and the total power of the devices connected to it, and only after that, using formula for calculating cable cross-section , choose the most suitable option. In this article we will consider in detail all the nuances associated with the selection and type of cables.
A cable is a wire covered with insulation that serves to transmit electricity from a source to a consumer. Today's market is ready to offer customers many types of similar wires: aluminum, copper, single-core, multi-core, single- and double-insulated, with a cross-section from 0.35 mm2 to 25 mm2 or more. But most often, to connect household consumers, cables with a thickness of 0.5 to 6 square meters are used - this is quite enough to power any equipment.
Classic cable for wiring in an apartment
Why is it necessary to select insulated conductors, and not buy the first one you come across? The thing is that the thickness of the conductor determines the current strength it can withstand. Eg,the permissible current for copper wires 1 mm thick is up to 8 Amperes, aluminum - up to 6 Amps.
Why not just buy the thickest wire possible? Because the thicker it is, the more expensive it is. In addition, a thick cable needs to be hidden somewhere, a groove must be cut for it in the ceiling and walls, and holes must be made in the partitions. In a word, there is no point in overpaying, because you won’t be driving a KAMAZ to buy bread.
If you choose a wire with a smaller diameter, it simply cannot withstand the current passing through it and will begin to heat up. This leads to insulation melting, short circuit and fire. Therefore, you should never rush when choosing a high-quality cable for connecting any devices - first think about what exactly will work on the new line, and then choose the thickness and type of cable.
How to calculate the power of devices
First, let's look at the option selection of cable cross-section according to power devices connected to it. How to count correctly?
Think about which devices will be powered by a particular cable. If you pull it into the hall, then a TV, computer, vacuum cleaner, audio system, set-top box, hair dryer, floor lamp, aquarium lighting or other household appliances can simultaneously operate from the outlet in the room. Add up the power of all these devices and multiply the resulting value by 0.8 to get the real figure. Indeed, it is unlikely that you will use them all at the same time, so 0.8 is a reduction factor that will allow you to adequately estimate the total load.
If you are counting for the kitchen, then add up the power of an electric kettle, electric oven and hob, microwave, dishwasher, toaster, bread maker and other available/planned appliances. The kitchen usually consumes the most energy, so it should have either two cables with separate circuit breakers, or one powerful one.
So, to calculate the total power of all devices, you need to use the formula Ptotal = (P1+P2+...+Pn)*0.8, where P is the power of a specific consumer connected to the outlet.
Copper wires are better for wiring and can withstand greater loads Choosing thickness
Once you have determined the power, you can select the cable thickness. Below we provide table of wire cross-sections by power and current for classic copper wire, since aluminum is no longer used to create wiring today.
| Cable cross-section, mm | For 220 V | For 380 V | ||
| current, A | power, kWt | current, A | power, kWt | |
| 1,5 | until 17 | 4 | 16 | 10 |
| 2,5 | 26 | 5,5 | 25 | 16 |
| 4 | 37 | 8,2 | 30 | 20 |
| 6 | 45 | 10 | 40 | 25 |
| 10 | 68 | 15 | 50 | 32 |
| 16 | 85 | 18 | 75 | 48 |
Attention:When choosing, keep in mind that most Russian manufacturers save on material, and a 4 mm2 cable may actually end up being 2.5 mm2. Practice shows that such “savings” can reach 40%, so be sure to either measure the cable diameter yourself or purchase it with a reserve.
Now let's look at an example calculating wire cross-section based on power consumption . So, we have an abstract kitchen, the power of the appliances is 6 kW. We multiply this figure 6*0.8=4.8 kW. The apartment uses one phase, 220 volts. The closest value (you can only take it as a plus) is 5.5 kW, that is, a cable 2.5 square meters thick. Just in case, we have a reserve of 0.7 kW, which “smoothes out” the savings for producers.
It should also be borne in mind that if the wire is working at its limit, it will heat up quickly. Due to heating to 60-80 degrees, the maximum current is reduced by 10-20 percent, which leads to overload and short circuit. Therefore, for critical sections of the chain, an increased coefficient should be used, multiplying the value not by 0.8, but by 1.2-1.3.
Correct calculation of cable thickness is the key to its long service life Most often, copper structures with a thickness of 1.5 squares are used for laying lighting systems, for sockets - 2.5 squares, for powerful consumers - 4 or 6 squares (machines are installed at 16, 25, 35 and 45A, respectively). But this use is only suitable for standard apartments or houses that do not have powerful consumers. If you have an electric boiler, boiler, oven or other appliances that consume more than 4 kW, then you need to calculate the cables for each specific case, and not use general recommendations.
The aboveuses boundary values, so if you get calculated numbers overlapping with encyclopedic ones, then try to take a cable with a reserve. For example, if our kitchen had a power of 7 kW, then 7 * 0.8 = 5.6 kW, which is greater than the value of 5.5 for a 2.5 square cable. Take a cable of 4 squares with a reserve or divide the kitchen into two zones by connecting two 2.5 mm2 cables.
What to do with the length
If you are counting cables in an apartment or small house, then you don’t have to make any adjustments to the cable length at all - it’s unlikely that you will have branches 100 meters or more in length. But if you are laying wiring in a large multi-story cottage or shopping center, then you must take into account possible losses along the length. Usually they are 5 percent, but it is more correct to calculate them using a table and formulas.
So, the load moment is calculated as the product of the length of your wire and the total power consumption. That is, the length of your cable is calculated as the product of the cable length in meters and the power in kilowatts.
In the table below we see how losses depend on the cross-section of the conductor. For example, a cable with a thickness of 2.5 mm2 with a load of up to 3 kW and a length of 30 meters has a loss of 30x3 = 90, that is, 3%. If the loss level exceeds 5%, then it is recommended to choose a thicker cable - there is no need to skimp on your safety.
| U, % | Load moment, kW*m | |||||
| 1,5 | 2,5 | 4 | 6 | 10 | 16 | |
| 1 | 18 | 30 | 48 | 72 | 120 | 192 |
| 2 | 36 | 60 | 96 | 144 | 240 | 384 |
| 3 | 54 | 90 | 144 | 216 | 360 | 575 |
| 4 | 72 | 120 | 192 | 288 | 480 | 768 |
| 5 | 90 | 150 | 240 | 360 | 600 | 960 |
This table of loads for the cable cross-section valid for a single-phase network. Three-phase is characterized by an average increase in load size of six times. The value increases three times due to distribution over three phases, and two times due to the neutral conductor. If the load on the phases is uneven (there are strong distortions), then losses and loads increase greatly.
Correct connection of machines with copper cable You should also consider which consumers will be connected to your wire. If you plan to connect halogen low-voltage lamps, then try to place them as close to the transformers as possible. Why? Because if the voltage drops by 3 volts at 220 volts, we simply won’t notice, and if the voltage drops by the same 3 volts at 12 volts, the lamps simply won’t light up.
If you spend selection of wire cross-section for current for an aluminum cable, keep in mind that the resistance of the material is 1.7 times higher than that of copper. Accordingly, losses in them will be greater by the same 1.7 times.
Types of cables
Now let's look at what kind of cables you can choose to create electrical wiring on site. Remember that according to standards, wires can only be laid in a closed way in boxes or pipes. In this case, the cables are laid freely - they can even be run along the surface, which is often practiced in wooden and log houses.
You already know how to calculate cable cross-sections based on power, Therefore, let's consider the principle of cable selection. For installation in residential premises, the classic VVG is best suited (it is better to choose the one marked NG - non-flammable). NYM is well suited for connecting to a panel or a powerful consumer. Let's look at the types of cables in more detail.
VVG is a cable with copper conductors protected by a polyvinyl chloride “jacket”. The wires are covered with an additional plastic sheath, which prevents possible breakdowns and breaks. This cable can be used even in damp areas, it bends well and protects the surface from fire. For wiring, a flat wire is best suited, in which the wires are located in the same plane - it takes up minimal space.
NYM is a product containing several copper strands covered with non-ferrous metal filled with non-flammable rubber. On top, the cores are packed in polyvinyl chloride insulation (sometimes several layers are used). In most cases, it has non-flammable properties and does not emit harmful gases at critical temperatures. It has excellent flexibility - it is very easy to lay it in corners, display it on various surfaces, etc.The main thing is to do it right selection of wire cross-section according to current, taking it with a small margin.
PUNP is a classic flat-shaped installation wire that is used to connect various consumers. Very often used to create inexpensive wiring in apartments and houses. Has two/three cores covered with polyvinyl chloride. It has a flat shape.
There are many other cables - armored, reinforced, for laying in damp rooms and areas with a high risk of explosion. But the ones listed above are used most often.
Now you know how calculate the wire cross-section for the load and which cables to choose to create a complete electrical wiring. We remind you - always make a power reserve of 20-30 percent to avoid troubles.
In contact with
Technical characteristics can vary significantly depending on what type of wire it is, what marking it has, how many cores it contains, and other parameters. However, it is possible to identify a number of key characteristics that, to one degree or another, apply to each of the power cables of this type.
The VVG cable is manufactured according to OKP code 352100.
Description and technical documentation
The dimensions of the cable largely depend on the number and type of cores that it contains. The minimum diameter of the core gives 1.5 mm 2 in its cross-sectional area. The maximum cross-sectional area of the core is 240 mm 2 in a single-core cable, 95 mm 2 in a two- or four-core cable and up to 50 mm 2 in a five-core cable. The cross-sections of neutral conductors (in the case of a smaller cross-section than the main ones) and grounding conductors, depending on the cross-section of the main conductors up to 50 mm 2, are given below.
Larger options are much less common. The most common among VVG cables with conductors of unequal cross-sections are cables with three main and one neutral conductor (the so-called “three plus”).
The outer diameter of the electrical wire is directly proportional to the number of cores and the nominal cross-section. With an area of 1.5 mm2, the cable diameter starts from a size of 5 mm and can reach up to 53.5 mm in four-core versions. In the same way, the weight of one kilogram of cable increases, starting from 39 kg/km and reaching several tons, so the weight of the wire must be taken into account when designing its installation.
The nominal and minimum values of the radial insulation thickness for VVG cables with a cross-section of up to 50 mm 2 for an operating voltage of 0.66 kV and 1 kV are given in the table.
The thickness of the protective sheath of the VVG electrical wire depends on the twisting diameter of the insulated conductors under the sheath. The nominal and minimum values of the shell thickness are given in the table.
Continuous-permissible current VVG
The continuous-permissible current that a given cable supports varies depending on the number of cores, their cross-section, and also on where the electrical wire runs - in the ground or in the air. The minimum current is 19 A, in any case, it is better to check the specifications of the specific cable that you are purchasing. Permissible load currents for electrical wires with a cross-section of up to 50 mm 2 laid in air are indicated in the table.
| Nominal cross-section of cores, mm2 | Permissible load current, A | ||
| With two main cores | With three main cores | With four main cores | |
| 1,5 | 24 | 21 | 19 |
| 2,5 | 33 | 28 | 26 |
| 4 | 44 | 37 | 34 |
| 6 | 56 | 49 | 45 |
| 10 | 76 | 66 | 61 |
| 16 | 101 | 87 | 81 |
| 25 | 134 | 115 | 107 |
| 35 | 166 | 141 | 131 |
| 50 | 208 | 177 | 165 |
The rated current, in this case, can be 0.66 or 1 kilowatt, and its frequency is 50 hertz. The power with a minimum cross-sectional area of the cable reaches 3.5 kW. As for resistance, it varies depending on the cross-sectional area of the cores. When it is 1.5 mm2, the resistance is 12 MOhm/km, when it is less than 4 mm2 – 10 MOhm/km, when it is 5 mm2 – 9 MOhm/km, and from 10 to 240 mm2 this figure is 7 MOhm/km . It is customary to take into account the resistance at a temperature of +20 degrees Celsius.
Technical characteristics of VVG power cable
The electrical resistance of the current-carrying cable cores up to 50 mm 2 at direct current should be no more than that indicated in the table.
The electrical resistance of the insulation per 1 km of length at a temperature of 20 0 C is at least 7 - 12 MOhm, depending on the cross-section of the conductors.
Finished cables must withstand alternating voltage testing at a frequency of 50 Hz for 10 minutes. The voltage is applied between the cores and is 3 kV for cables with a rated voltage of 0.66 kV and 3.5 kV for cables with a rated voltage of 1 kV.
Power cable storage conditions
Wires are stored under canopies or in closed rooms. It is also permitted to store cables on drums in open areas in a sheathed form. At the same time, the shelf life changes: in closed premises the shelf life will be 10 years, under a canopy in the open air - 5 years, on drums in open areas - only 2 years.
Weight and dimensions: main parameters
Approximate external dimensions and weights of individual cables with a cross-section of up to 50 mm 2 for packaging and transportation purposes are given in the table below. Depending on the manufacturer, these figures may vary with a 10% deviation.
| Cable cross-section | External size value for packaging and transportation purposes, mm | Weight value for packaging and transportation purposes, kg/km |
|---|---|---|
| Flat cables | (a x b) | |
| 2x1.5 | 5 x 7.5 | 70 |
| 2x2.5 | 5.5 x 8 | 90 |
| 2x4 | 6 x 9.5 | 140 |
| 2x6 | 7 x 10.5 | 180 |
| 3x1.5 | 5 x 9.5 | 95 |
| 3x2.5 | 5.5 x 11 | 135 |
| 3x4 | 6 x 13 | 200 |
| Stranded cables | Diameter | |
| 3x1.5 | 8 | 90 |
| 3x2.5 | 9,5 | 135 |
| 3x4 | 11 | 200 |
| 3x6 | 12 | 260 |
| 3x10 | 14,5 | 410 |
| 3x16 | 17 | 590 |
| 3x25 | 20,5 | 810 |
| 3x35 | 23 | 1300 |
| 3x50 | 27 | 1700 |
| 3x4+1x2.5 | 12 | 230 |
| 3x6+1x4 | 14 | 310 |
| 3x10+1x6 | 16 | 480 |
| 3x16+1x10 | 19 | 650 |
| 4x1.5 | 8,5 | 110 |
| 4x2.5 | 10 | 170 |
| 4x4 | 12 | 240 |
| 4x6 | 13 | 320 |
| 4x10 | 16 | 510 |
| 4x16 | 19 | 750 |
| 4x25 | 23 | 1150 |
| 4x35 | 26 | 1550 |
| 4x50 | 31 | 2200 |
| 5x1.5 | 9,5 | 135 |
| 5x2.5 | 11 | 205 |
| 5x4 | 13 | 300 |
| 5x6 | 14 | 405 |
| 5x10 | 17,5 | 630 |
| 5x16 | 21 | 950 |
| 5x25 | 26 | 1450 |
| 5x35 | 29 | 1900 |
| 5x50 | 35 | 2700 |
Temperature and operating conditions
Particular attention should be paid to the temperature conditions for which these cables are adapted. The temperature at which the electrical cable is laid should not be lower than -15 C. Operation is allowed in wider temperature ranges, which start at -50 C and reach +50 C. However, if unusual situations arise, the temperature can rise to + 70 C without any problems, and in an emergency the cable can withstand short-term heating up to +80 C. Humidity should not exceed 98%. The minimum bending radius is at least 7.5 times the cable diameter. Service life - 30 years.
This material will focus on how NOT to choose a cable cross-section.
I often see that the required cable cross-section is chosen based on the number of kilowatts that can be “loaded” on this cable.
Usually the argument goes like this: “A cable with a cross-section of 2.5 mm2 can withstand a current of 27 amperes (sometimes 29 amperes), so we set the machine to 25 A.”
And in practice, sometimes you come across socket groups protected by a 25A circuit breaker, and lighting by a 16A circuit breaker.
This approach when choosing circuit breakers leads to overheating, melting and damage to the insulation, and as a result - to a short circuit and fire.
Let's refer to table 1.3.4. from PUE.
The permissible long-term current for copper wires laid hidden is 25 A. Everything seems to be correct, is it so?
If you install the machine at 25A, which is called “head-on”, and from we remember that the thermal protection of the machine can operate when the rated current is exceeded by 13%, which in our case will be 25x1.13 = 28.25A. And the response time will be more than an hour.
And if there is an overload of 45%, the thermal release will operate in less than 1 hour, i.e. 25Ax1.45=36.25 A. But it can work in an hour.
It is clear that at such currents the cable will simply burn out.
If you install a 16A machine on the lighting, the result will be similar, you can calculate it yourself.
In addition, sockets are produced for a maximum current of 16A, and switches - 10A. If you install overrated circuit breakers on sockets and lighting, this will lead to their melting, destruction of contacts and potentially a fire. I think you've seen melted sockets - the result of connecting a very powerful load that the sockets are not designed to handle.
REMEMBER! In our apartments and houses, socket groups are made with a 2.5 mm2 cable with the installation of a 16A circuit breaker, lighting groups are made with a 1.5 mm2 cable with the installation of a 10A circuit breaker. A lower denomination is possible, but a larger one is not!
A variation of this approach: the machine knocks out, especially for the kitchen outlet group where powerful appliances are connected. As a reserve, a 32A and even 40A machine is installed. And this is with wiring done with a 2.5 mm2 cable!!! The consequences are obvious and discussed above.
There are also situations when a cable with a larger cross-section (for example, 4 mm2) is laid up to the branch box, and then the lines are separated at 2.5 mm2 each and a machine is installed at 25A or 32A.
The circuit breaker current must be selected based on the weakest point in the line, in our example, this is a 2.5 mm2 cable. Therefore, such a group still needs to be protected by a 16A machine.
If you set the machine to 25A, then when a load close to 25A is connected to one of the sockets, the cable to the branch box will burn out, but for a cable with a cross-section of 4 mm2 from the branch box to the circuit breaker, this will be normal mode.
All these points must be taken into account when calculating the cable cross-section.
Watch detailed video:
Calculation of cable cross-section. Errors
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 not known, 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 not known, 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 (kVA) | 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 (motor windings are connected in a delta pattern) is 1.2 A, and at a voltage of 380 V (motor windings are connected in a delta pattern) "star" circuit) is only 0.7 A. Taking the current indicated on the nameplate, according to 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.
