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Before connecting the load to the network, it is important to make sure that the cores of the supply cable are of sufficient thickness. In the case of a significant excess of the permissible power, the destruction of the insulation and even the core itself is possible due to its overheating.
Before calculating the cable cross-section by power, you should calculate the sum of the powers of the connected electrical appliances. In most modern apartments, the main consumers are:
- Refrigerator 300 W
- Washing machine 2650 W
- Computer 550 W
- Lighting 500 W
- Electric kettle 1150 W
- Microwave oven 700 W
- TV 160 W
- Water heater 1950 W
- Vacuum cleaner 600 W
- Iron 1750 W
- Total 10310 W = 10.3 kW
In sum, most modern apartments consume approximately 10 kW. Depending on the time of day, this parameter can be significantly reduced. However, when choosing a conductor cross section, it is important to focus on a large value.
You need to know the following: the calculation of the cable cross-section for single-phase and three-phase networks is different. But in both cases, three parameters should be taken into account first of all:
- current strength(I)
- Voltage(U)
- Power consumption (P).
There are also several other variables, their meaning differs for each specific case.
Calculation of the wire cross section for a single-phase network
The calculation of the wire cross-section by power is carried out using the following formula:
I = (P × K and) / (U × cos(φ))
Where,
- I- current strength;
- P- power consumption of all electrical appliances in total;
- K and- coefficient of simultaneity, usually a standard value of 0.75 is taken for calculations;
- U- phase voltage, it is 220 (V), but can range from 210 to 240 (V);
- Cos(φ)- for household single-phase appliances, this value is unchanged and equals 1.
If you need to quickly calculate the current, you can omit the value of cos (φ) and even K and. The resulting value will differ downward (by 15%) if a formula of this type is applied:
I=P/U
Having found the current according to the calculation formula, you can safely proceed to the choice of the supply cable. More precisely, its cross-sectional area. There are special tables that provide data that allow you to compare the amount of current, power consumption and cable cross-section.
Data vary greatly for conductors made from different metals. To date, for residential electrical wiring is usually used only rigid copper cable, aluminum is practically not used. Although in many old houses all lines are laid using aluminum.
The cross section of the copper cable is selected according to the following parameters:
Calculation of the wire cross section in the apartment - Table
It often happens that as a result of calculations, a current is obtained that is between the two values \u200b\u200bpresented in the table. In this case, the nearest higher value should be used. If, as a result of calculations, the current value in a single-core wire is 25 (A), it is necessary to select a cross section of 2.5 mm 2 or more.
Calculation of the cable cross-section for a three-phase network
To calculate the cross section of the supply cable used in a three-phase network, you must use the following formula:
I = P / (√3 × U × cos(φ))
Where,
- I- current strength, according to which the cross-sectional area of \u200b\u200bthe cable will be selected;
- U- phase voltage, 220 (V);
- Cos φ- phase shift angle;
- P- an indicator of the total power of all electrical appliances.
Cos φ in this formula is very important. Since it directly affects the strength of the current. For different equipment, it is different, most often this parameter can be found in the technical accompanying documentation, or it is indicated on the case.
The total power of consumers is very simple: all powers are added up, the resulting value is used for calculations.
A distinctive feature of the choice of cable cross-sectional area for use in a three-phase network is that a thinner core can withstand a greater load. The required section is selected according to the standard table.
The choice of cable cross-section for a three-phase network - Table
The calculation of the wire cross-section by power in a three-phase network is performed using a value such as √3 . This value is necessary to simplify the appearance of the formula.
U linear = √3 × U phase
Thus, if necessary, you can replace the product of the root and the phase voltage with a linear voltage. This value is 380 (V) (U linear = 380 V).
When choosing a cable section, both for a three-phase network and for a single-phase network, it is necessary to take into account permissible continuous current . This parameter indicates the amount of current (measured in amperes) that the conductor can withstand for an unlimited amount of time. It is determined according to special tables, they are available in the PUE. For aluminum and copper conductors, the data differ significantly.
Permissible current duration - Table
If the value specified in the table is exceeded, the conductor starts to heat up. The heating temperature is inversely proportional to the current strength.