Purpose. Definition of the direction for further research to improve accuracy of the calculation of rated parameters of ground grids based on the analysis of statistical databases of electro-physical characteristics of the soil. Methodology. To solve this problem we compiled the statistical base of soil of Ukraine in the location of electrical substation, we performed the statistical analysis for the number of layers of geoelectric structure, and electrical characteristics. In the experiments implemented the comparing of accuracy calculation of the most typical three-layer soil in the Ukraine, by the new three-layer model of ground grids and the equivalent two-layer model, which used previously. Results. On the results of analysis the ranges of the electrical resistivity and statistical distribution for electro-physical characteristics of the soil are determined. The resulting distributions allow to develop criteria for instruments, installations and means of interpretation during the sounding of soil, as well as the requirements for mathematical models of ground grids. It was found that the most typical for places of locations the electrical substations in Ukraine are three-layer geoelectric structures. In the paper the statistical distribution for three-layer soil by type (Q, K, H, A) are described. The results of numerical experiments show that the use of methods to simplify of the multilayers soil does not allow the calculation of grounding grids with high accuracy. In the work recommendations for applicability the method equivalenting depending on the type of geoelectric structure are developed. Originality. For the first time, we obtained the statistical distribution of stratification of the soil in the location of power plant in Ukraine, determined the accuracy of the method to simplify a multi-layer soil in determining the rated parameters of grounding grids. In the paper the necessity to develop a mathematical model of the grounding device located in the three-layer soil is shown, as well as a new installation of soil sounding, which allows to increase the depth of sounding and new means of interpreting the results of sounding Wenner installing a four-layers geoelectric structure. Practical value The resulting recommendations for the applicability of equivalenting of multilayer soil, as well as research in specific work areas would help to reduce costs on materials and labours during the modernization and upgrade of grounding devices, moreover it will increase the electrical safety and reliable operation of electrical substation.