Any person whose work is connected with the maintenance of electrical engineering is simply obliged to know how the calculation of the cable cross-section by power is performed. Without this, one may encounter an unpleasant situation when the line recently extended to the consumer fails due to temperature damage to the conductive core. To avoid this, one should not only always remember that the cross-section of the wire and power are interconnected, but also, if necessary, perform calculations. The ability to choose the right diameter of conductive conductors depending on the power consumption can be useful in everyday life: for example, to choose a cable for a self-mounted electric boiler.
Wire cross section, power and current rating
Since most electrical formulas are quite complex, many people, having barely heard of the need to perform any calculations, decide that without the help of an energy specialist, this will not work out. In fact, the cross section of the wire and power are connected by just a couple of simple formulas. The task boils down to determining the maximum current and further selecting a conductive core using publicly available reference data.
Theory
It is known from the school physics course that the current passing through the conductive material causes it to heat, the value of which depends on the cross-sectional area and the conductor configuration (it is obvious that the thin conductive hair of the core will heat higher than a metal plate). The current value of the current also has an effect, that is, with its increase, the heating processes become more intense. Let's recall the formula for calculating the current according to known voltage and resistance. It is derived from Ohm's classical law and looks like I = U / R, where U is the voltage in Volts, R is the resistance in Ohms.
However, how are wire cross-sections and power related to this? Directly! It is more correct in this case to use the notion of power, but of current (we will show their connection below, giving the formula).
The electrical power of the consumer is interconnected with the magnitude of the current flowing through the conductor. In the general case, it can be determined by the formula P = I * U, where I is the current in amperes. We do not take into account the power characteristic (active or reactive component), however, the data given is quite sufficient for selecting a wire over the cross section. The last step remains - to determine the cross-sectional area of the cable core. Experienced electricians determine this parameter “by eye”, but we recommend using a simple formula that will avoid possible errors.
Practice
It is necessary to remove the insulation from the cable core by exposing the metal and measure the diameter. Next, the obtained value must be substituted into the formula S = (3,14 * (d * d)) / 4, where d is the diameter in millimeters.
It remains to take the directory (PUE), find the table of correspondence of current and cross-section and select the desired cable. The material and method of laying the line are also taken into account.
Life example
Suppose you want to connect a 2 kW boiler to a 220 V network. Using the above formula for "P", we get a current of 9 Amps. In the store, the cheapest two-core cable with copper conductors is presented with a cross section of 0.75 and 1 mm.kv. We open the directory, we find "open wiring." Two-core with a section of 1 mm.kv. withstands 16 Amps (GOST-80!), and for 0.75 corresponds to 15 A. Almost a double supply. Thus, in this example, the use of cables with the indicated copper conductors is quite acceptable. This is how the wire cross section and power are related.