The paper deals with the statistical analysis of the impact various parameters (electrode length, soil conductivity and permittivity) can have on the value of transient impedance of the horizontal grounding electrode. Deterministic model for the transient impedance calculation is based on the corresponding Pocklington integro-differential equation in the frequency domain for the calculation of induced current and Generalized Telegrapher’s Equation for the calculation of the scattered voltage. These equations are solved using previously developed analytical techniques, thus obtaining transient impedance directly in the time domain. Stochastic collocation method is applied by taking into account random parameters and performing subsequent sensitivity analysis.