Аннотация
In work the new method of definition of isolation's parameters in a three-phase symmetric electrical network with isolated neutral which is based on measurement of modules sizes of a linear voltage, voltages of phases C and A concerning to ground, after connection of active additional conductivity between phase A of electrical network and ground is shown and the analysis of a blunder of the developed method is made. The analysis of a blunder has shown, that the developed method provides satisfactory accuracy at definition of isolation's parameters, and also simplicity and the safety of operations in working electro installations of up to above 1000 V voltage.