Electrical wiring is one of the most important parts of a large communication system that supplies the house with electricity. From the long and highquality operation of electrical wiring depends on the quality of work of lamps and electrical household appliances, which today is becoming more and more in every home. Therefore, it is increasingly possible to meet on building forums issues relating specifically to wiring problems. And one of these frequent questions is how to correctly calculate the cable crosssection by length and power, that is, by its load.
Professional electricians "by eye" determine approximately this figure. Engineers use special tables or online calculator. But we will reason sensibly. In any house a certain amount of electrical household appliances is installed, and these devices have different power. This is the first. Secondly  the number of office space or rooms in the house can vary significantly in any building. And this will affect the power consumption for lighting. At the same time, some in the house are installed multibeam chandeliers, and some cost and spot lighting. Plus a variety of different lamps.
Thirdly  this is, again, the power of household electrical appliances, which is calculated from actual data. So to say, they practically consider it on their fingers, which electrical appliances and with what power the house owners use. And most importantly, during the calculation of the total power there is no need to take into account the factor influencing how the lighting or electrical appliances work: periodically or permanently. It is necessary to determine the total power per cable.
Content

1 The formula for calculating the cable power over the cross section
 1.1 List of power appliances and an example of cable calculation
 1.2 Calculation of the wire size by room

2 Which cable to choose: aluminum or copper?
 2.1 Video: Calculate cable section
The formula for calculating the cable power over the cross section
So, there is a formula for calculating the power of the cross section of an electrical wire or cable. Here she is:
I = PxK / Uхcos φ  this formula is used for singlephase mains with alternating current of 220 volts. Where:
 K is a coefficient of simultaneity, it is he who equalizes the power index with a temporary value. Since not all the time we use electrical appliances or lighting. This is a constant value and it is 0.75.
 P is the total power of all lighting and household appliances.
 U  alternating current 220 Volts.
 cos φ is also a constant indicator, which is equal to one.
In this formula, almost all values, in addition to the total power, are constant. Therefore, the calculation is based on precisely those loads that have lamps and household appliances. That is, the amount of current will depend on the power used. These indicators are usually specified in the technical passport, which is included with the appliance. Also often manufacturers indicate it on the labels. But here are only certain indicators of power of main electrical appliances, are used more often than others.
List of power appliances and an example of cable calculation
Power of some electrical household appliances:
 Refrigerator 350850 watts.
 TV 150310 watts. This is the power of modern TVs.
 Lighting 3201600 watts. As mentioned above, it depends on the type and number of lamps.
 Iron 12002200 watts. This is one of the most powerconsuming devices.
 This category includes an electric kettle: 12002600 watts.
 Add in this category dishwasher and washing machine  2600 watts.
 Computer 320650 watts.
 Microwave approx 1500 watts.
Other electrical appliances could be added to this list, for example, a stereo system, a hairdryer, a water heater, a vacuum cleaner, etc. That is, to calculate the cable crosssection by power, you must first determine which number of electrical appliances is in the house. Summing up their power, the total power consumption is determined, which affects the wiring.
So, all the data is substituted into the formula to determine the strength of the current. Let's calculate the power of all the above electrical appliances for the minimum indicator. And find out what cable we need. The total power is  6550 watts or 6.55 kW. We substitute it into the formula:
I = 6550х0.75 / 220 = 22.4 Ampere.
Then, in order to determine the cable sections, we will need a table where the ratio of two quantities is given.
Important! The value of the current in the tables, as a rule, is indicated by whole numbers. Therefore, we need to round our result to the greatest value. This will give some safety margin. In our example, this would be 27 Amps over copper cables, and 28 Amps over aluminum. Thus, the wire cross section will be 2.6 mm. sq. on copper and 4.1 mm. sq. for aluminum.
So, you learned how to calculate the cross section of the wire.
Calculation of the wire size by room
The above calculation with the formula is used for the input wire to the house. But you need to consider the internal layout of the rooms and rooms. It’s just that the lighting is more or less clear. Throw at him in all rooms 1.6 mm wire cross section square. and do not worry that all of you have done right. Neither the circuit, nor overheating, you will not happen.
With sockets everything is much more complicated. In the house there are rooms in which the presence of household appliances rolls over. This is a bathroom and a kitchen. In the first, as a rule, the washing machine and the hair dryer usually work. By the way, it has a fairly high power of 12002600 watts. Therefore, the load such a small device creates a rather high.
Therefore, it is necessary to solve one rather important task  correctly distribute the power of the outlet groups along the length. For example, in the kitchen. Initially, the current strength is calculated using the formula described above, where, in the role of power consumption, the power of all household electrical appliances in the kitchen is added, not forgetting the lighting. Done wire gauge selectionthat will fit into this room. But on the outlets stretch the wiring for all household appliances with a smaller section. For tea and coffee makers separately, for the refrigerator separately, for the dishwasher separately. And to every point.
Some may say, is it not too much outlets for one small room? There is an alternative to connect a larger wire to the socket strip (triple or double). It will be necessary to make one more calculation. Thus, there can be a huge number of ways to wiring the electrical circuits. But in any case, you will need to use a table, a calculator and a formula for determining the cable crosssection by power and length. Although experts say that the best option is for each electrical appliance a separate outlet.
And another important point that concerns the length of the wire and its current loss. According to physical laws, the longer the cable, the greater the voltage loss. Therefore, electricians do the calculation of the cable crosssection along its length. However, internal wiring is not subject to this calculation. Very, minimal losses.
Which cable to choose: aluminum or copper?
We will not delve into this issue. Just spend brief comparative analysis.
 Although copper is prone to oxidation, it is not as active as aluminum. Because contacts are operated longer.
 Copper wire is more flexible and durable. With frequent bending, it will not break.
 Aluminum cable is almost five times cheaper than copper.
 The degree of conductivity of copper wires is almost two times higher than that of aluminum. That is, the higher power that the copper wire can withstand.
There are modern electrical rules. And they are recommended to make the internal wiring copper cable, and the outer aluminum.
Thus, summing up all of the above, we can conclude that the calculation of the power of electrical appliances and the crosssection of the wire for the load is a responsible and very important process. An error in calculations can be very expensive. Therefore, care and accuracy are needed here.