This presentation is devoted to the calculation and measurement of DC line power transmission losses caused by the active resistance. Initially, the power of the electricity consumer in question is known, the voltage of the energy source is known and, when selecting specific wires, the resistance of the power transmission line is also known. The remaining parameters of flowing current, voltage drop and consumer’s voltage can be calculated mathematically by deriving quadratic equations with two solutions, only one of which is correct. However, the results of calculations and computer simulations may differ to some extent from the actual situations depending on the equipment used and other circumstances, so it is recommended to perform experimental measurements. To realize this, a test bench was developed for it, where measurements of power lines of different lengths and resistances can be performed.