Abstract
The mathematical model for calculation of humidity, temperatures and DC in a soil is presented. The model can be used for calculation of the parameters of various direct current installations in which the current becomes through the ground. The model is consisting from the system nonlinear differential equations with variable coefficients. They are determining in the laboratory tests. Numerical results are given for earth electrodes of the transmission line. It is shown, that the neglect phenomena of transfer of humidity can be result the serious mistakes.