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When laying electrical wiring, you need to know what kind of cable with conductors you will need to lay. The choice of cable section can be done either by power consumption or by current consumption. You also need to take into account the length of the cable and the method of installation.
We select the cable cross-section by power
You can select the cross section of the wire according to the power of the devices that will be connected. These devices are called load and the method can also be called “by load”. Its essence does not change from this.
Collecting data
To begin with, find the power consumption in the passport data of household appliances, write it out on a piece of paper. If it’s easier, you can look at the nameplates – metal plates or stickers fixed on the body of equipment and equipment. There is basic information and, most often, there is power. The easiest way to identify it is by units of measurement. If the product is manufactured in Russia, Belarus, Ukraine, the designation is usually W or kW, on equipment from Europe, Asia or America, the English designation of watts is usually W, and the power consumption (it is needed) is indicated by the abbreviation “TOT” or TOT MAX.
If this source is not available either (the information has been lost, for example, or you are just planning to purchase equipment, but have not yet decided on the model), you can take the average statistical data. For convenience, they are summarized in a table.
Find the equipment that you plan to install, write out the power. It is sometimes given with a wide spread, so it is sometimes difficult to understand which figure to take. In this case, it is better to take the maximum. As a result, when calculating, you will have a slightly overestimated power of the equipment and you will need a cable with a larger cross section. But for calculating the cable section, this is good. Only cables with a smaller cross-section than necessary are lit. Routes with a large cross section work for a long time, as they heat up less.
The essence of the method
To select the wire cross-section according to the load, add up the power of the devices that will be connected to this conductor. At the same time, it is important that all powers are expressed in the same units of measurement – either in watts (W) or in kilowatts (kW). If there are different values, we bring them to a single result. To convert, kilowatts are multiplied by 1000 to get watts. For example, let’s convert 1,5 kW to watts. This will be 1,5 kW * 1000 = 1500 watts.
If necessary, you can carry out the reverse conversion – convert watts to kilowatts. For this, we divide the figure in watts by 1000, we get kW. For example, 500 W / 1000 = 0,5 kW.
Next, in fact, the choice of cable section begins. Everything is very simple – we use the table.
| Cable section, mm2 | Conductor diameter, mm | Copper wire | aluminum wire | ||||
| Current, A | power, kWt | Current, A | power, kWt | ||||
| In 220 | In 380 | In 220 | In 380 | ||||
| 0,5 mm2 | 0,80 mm | A 6 | 1,3 кВт | 2,3 кВт | |||
| 0,75 mm2 | 0,98 mm | A 10 | 2,2 кВт | 3,8 кВт | |||
| 1,0 mm2 | 1,13 mm | A 14 | 3,1 кВт | 5,3 кВт | |||
| 1,5 mm2 | 1,38 mm | A 15 | 3,3 кВт | 5,7 кВт | A 10 | 2,2 кВт | 3,8 кВт |
| 2,0 mm2 | 1,60 mm | A 19 | 4,2 кВт | 7,2 кВт | A 14 | 3,1 кВт | 5,3 кВт |
| 2,5 mm2 | 1,78 mm | A 21 | 4,6 кВт | 8,0 кВт | A 16 | 3,5 кВт | 6,1 кВт |
| 4,0 mm2 | 2,26 mm | A 27 | 5,9 кВт | 10,3 кВт | A 21 | 4,6 кВт | 8,0 кВт |
| 6,0 mm2 | 2,76 mm | A 34 | 7,5 кВт | 12,9 кВт | A 26 | 5,7 кВт | 9,9 кВт |
| 10,0 mm2 | 3,57 mm | A 50 | 11,0 кВт | 19,0 кВт | A 38 | 8,4 кВт | 14,4 кВт |
| 16,0 mm2 | 4,51 mm | A 80 | 17,6 кВт | 30,4 кВт | A 55 | 12,1 кВт | 20,9 кВт |
| 25,0 mm2 | 5,64 mm | A 100 | 22,0 кВт | 38,0 кВт | A 65 | 14,3 кВт | 24,7 кВт |
To find the required cable section in the corresponding column – 220 V or 380 V – we find a figure that is equal to or slightly more than the power we calculated earlier. We select the column based on how many phases there are in your network. Single-phase – 220 V, three-phase 380 V.
In the found line, we look at the value in the first column. This will be the required cable cross-section for a given load (power consumption of devices). A cable with conductors of such a cross section will have to be looked for.
A little about whether to use copper wire or aluminum. In most cases, when laying wiring in a house or apartment, cables with copper conductors are used. Such cables are more expensive than aluminum ones, but they are more flexible, have a smaller section, and are easier to work with. But, copper cables with a large cross section are no more flexible than aluminum ones. And at high loads – at the input to the house, to the apartment with a large planned power (from 10 kW and more), it is more expedient to use a cable with aluminum conductors – you can save a little.
How to calculate the cable cross-section by current
You can choose the cable cross-section for current. In this case, we carry out the same work – we collect data on the connected load, but we are looking for the maximum current consumption in the characteristics. Having collected all the values, we summarize them. Then we use the same table. We are only looking for the nearest higher value in the column labeled “Current”. In the same line, we look at the cross section of the wire.
For example, you need to connect a hob with a peak current consumption of 16 A. We will lay a copper cable, so we look in the corresponding column – the third from the left. Since there is no value of exactly 16 A, we look in line 19 A – this is the nearest larger one. Suitable section 2,0 mm2. This will be the minimum value of the cable cross-section for this case.
It is impossible to pay attention to a line with a slightly lower value. In this case, at maximum load, the conductor will be very hot, which can lead to the fact that the insulation will melt. What could be next? The circuit breaker may trip if installed. This is the most favorable option. Household appliances may fail or a fire may start. Therefore, always make the choice of cable section by a larger value. In this case, it will be possible to later install equipment even a little more in terms of power or current consumption without rewiring.
Cable calculation by power and length
If the power line is long – several tens or even hundreds of meters – in addition to the load or current consumption, it is necessary to take into account the losses in the cable itself. Usually long distances of power lines when entering electricity from the pole into the house. Although all data must be specified in the project, you can play it safe and check. To do this, you need to know the allocated power to the house and the distance from the pole to the house. Further, according to the table, you can select the wire cross-section, taking into account the losses along the length.
In general, when laying electrical wiring, it is always better to take some margin over the cross section of the wires. Firstly, with a larger cross section, the conductor will heat up less, and hence the insulation. Secondly, more and more devices powered by electricity appear in our lives. And no one can guarantee that in a few years you will not need to install a couple of new devices in addition to the old ones. If a stock exists, they can simply be turned on. If it is not there, you will have to be smart – either change the wiring (again) or make sure that powerful electrical appliances do not turn on at the same time.
Open and closed wiring
As we all know, when current passes through a conductor, it heats up. The more current, the more heat is generated. But, when the same current passes through conductors with different cross sections, the amount of heat generated changes: the smaller the cross section, the more heat is released.
In this regard, with an open laying of conductors, its cross section may be smaller – it cools faster, since heat is transferred to the air. In this case, the conductor cools faster, the insulation will not deteriorate. With a closed gasket, the situation is worse – heat is removed more slowly. Therefore, for closed laying – in cable channels, pipes, in the wall – it is recommended to take a cable of a larger cross section.
The choice of cable cross-section, taking into account the type of its laying, can also be carried out using the table. The principle was described earlier, nothing changes. There is just one more factor to consider.
And finally, a few practical tips. Going to the market for a cable, take a caliper with you. Too often, the claimed cross section does not match reality. The difference can be 30-40%, and this is a lot. What threatens you? Burnout wiring with all the ensuing consequences. Therefore, it is better to check right on the spot whether this cable has the required core cross-section (diameters and corresponding cable cross-sections are in the table above). And more about the definition of the section cable by its diameter can be read here.