How the wire cross section and power are connected to each other

Any person whose work is related to the maintenance of electrical engineering, simply need to know how to calculate the cross-section of the cable in terms of power. Without this, you can face an unpleasant situation, when recently the line stretched to the consumer breaks down due to the thermal damage of the current-carrying vein. To avoid this, one should not only always remember that the wire cross section and power are interconnected, but also, if necessary, perform calculations. The ability to choose the right diameter of 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 permissible current

Since most of the electrical formulas are rather complicated, many people, having hardly heard about the need to perform any calculations, decide that without the help of a specialist in the field of energy, it will not work out. In fact, the wire cross section and power are connected by a pair of simplest formulas. The task is to determine the maximum current and further selection of the conductor with public reference data.

Theory

It is known from the school course of physics that the current passing through the conducting material causes its heating, the value of which depends on the cross-sectional area and the conductor configuration (it is obvious that the thin conductive veins of the vein will heat up higher than the 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 from known voltage and resistance. It is derived from the classical Ohm's law and looks like I = U / R, where U is the voltage in Volts, R is the resistance in Ohms.

However, how is the wire cross section and power related to this? Directly! It is more correct in this case to use the concept of not power, but current (their connection will be shown below, giving the formula).

The electric power of the consumer is interconnected with the value 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 amperage current. We do not take into account the power characteristic (active or reactive component), however, the given data is quite sufficient for the selection of wire across the section. The last stage 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

From the core of the cable, it is necessary to remove the insulation, exposing the metal, and measure the diameter. Then the obtained value should be substituted into the formula S = (3,14 * (d * d)) / 4, where d is the diameter in millimeters.

It remains to take the reference book (PUE), find the table of correspondences of current and section and select the required cable. The material and method of laying the line are also taken into account.

An example from life

Suppose that you need to connect a 2 kW boiler to the 220 V network. Using the above formula for "P", we get a current of 9 amperes. In the store, the cheapest two-core cable with copper conductors is presented with a cross-section of 0.75 and 1 mm square. Open the directory, we find "open posting". Two-core with a cross-section of 1 mm.kv. Withstands 16 amperes (GOST-80!), And for 0.75 corresponds to 15 A. Almost twice the stock. Thus, in this example, the use of cables with the specified copper cores is perfectly permissible. This is how the wire cross section and power are connected.