Before proceeding with the design of electricians in your home, you need to draw up a calculation chart indicating all the expected loads in the rooms and the length of individual sections of the cable. To draw up such a circuit, it will be necessary to calculate the current “by power”. A correctly compiled map of the electrical system of the house will allow you to choose the cables of the necessary sections, which will protect your wiring from overheating and, accordingly, from the possibility of fire. Let's figure it out, and what is the calculation of the current "power".
The correct selection of switching devices, as well as the cross-section of the cable , largely depends on various values of the parameters of the electrical networks. The most important among them is considered an electric current. And at the design stage, these values can only be determined by the calculated mathematical method. It is considered very important to calculate the current “by power” in three-phase networks, where the load must be placed evenly among the phases in order to prevent distortions. However, in urban household networks, these calculations must be carried out when designing not only switchboards, but also residential premises.
Calculation of the current "by power" is carried out subject to the known values of the power of electrical appliances, the nature of the loads and mains voltage. For a single-phase supply network, the following formula is used: I = P / (U × cosφ), where:
- U is the value of the actual voltage of the network, measured in volts;
- cosφ is the corresponding power factor.
Depending on the nature of the load, a power factor is selected. So, for active loads (heating elements, incandescent lamps), it will be approximately equal to unity. However, if we take into account that the reactive component is always present in the active load, then it is customary to use the value of cosφ equal to 0.95 for calculations. When calculating the load, which is characterized by a large reactive power (lighting chokes, electric motors, induction furnaces, welding transformers , etc.), an average cosφ value of 0.8 is taken.
For a three-phase supply network, the current power formula will have the following form: I = P / (1.73 × U × cosφ).
For three-phase networks , the power factor values for active and reactive loads are completely identical to single-phase networks.
Thus, using these formulas, it is necessary to calculate all the values of the electric current from the load power that will be used in a particular area.
The next step in our calculations will be the choice of cable cross-section. Although in the technical literature you can often find such a thing as “calculation of cable by power”, in fact, this is not a calculation, but still a “choice”. By calculation is meant the above formulas for determining the current load. In the presence of certain values of current and voltage, the
cable section is selected from the reference tables. These tables are very visual and do not require a detailed description. You first select the material of the wire: copper or aluminum, and then determine the cable cross-section by the voltage of the supply network and the current value.
So, in fact, we examined how the electric load is calculated and the cable cross section for electrification of objects is selected.