Probabilistic aspects of harmonic impedances are considered. Attention is devoted to the effects of statistical correlation among currents, impedances and voltages that exist in real cases. The IEEE industrial test system for harmonic modeling and simulation is considered. The system impedance probabilistic model taking into account parameter uncertainty and load and supply configuration variability, already developed in a previous paper, is recalled. Three methods to evaluate harmonic voltages, characterized by different complexity and accuracy, are compared among them.