Let's see how the current is calculated in terms of power

Before you start designing the electricians in your home, you need to draw up a scheme of calculations indicating all the expected loads in the rooms and the length of individual sections of the cable. To compile such a scheme, it will also be necessary to calculate the current "in terms of power." Correctly compiled map of the electrical system of the house will allow you to select the cables of the required cross-sections, which will protect your wiring from overheating and, accordingly, from the possibility of ignition. Let's understand, and what is the calculation of the current "in terms of power."

The correctness of the selection of switching devices, as well as the cross-section of the cable , largely depends on the various values of the parameters of electrical networks. The most important among them is the electric current. And at the design stage, these quantities can be determined only by mathematical calculation. It is very important to calculate the current "in 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 board, but also living quarters.

Calculation of the current "by power" is carried out under the condition of known values of the power of electrical appliances, the nature of the loads and the voltage of the network. For a single-phase supply network, the following formula is used: I = P / (U × cosφ), where:

• U - 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, the power factor is selected. Thus, 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 cosφ equal to 0.95 for the calculations. When calculating the load, which is characterized by high reactive power (chokes lighting fixtures, electric motors, induction furnaces, welding transformers , etc.), an average value of cosφ equal to 0.8 is adopted.

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 section.

The next stage of our calculations will be the choice of cable cross-section. Although in the technical literature it is often possible to find such a concept as "cable power calculation", in fact, this is not a calculation, but still a "choice." By calculation we mean the above formulas for determining the current load. If there are certain values of current and voltage, the cable cross-section is selected from the reference tables. These tables are very illustrative and do not require a detailed description. You first select the wire material: copper or aluminum, and then determine the cable cross-section by the supply voltage and the current value.

Here, in fact, we examined how the electric load is calculated and the cross-section of cables for the electrification of objects is selected.