In the previous chaptermodels for probabilistic network analysis were considered assuming, for simplicity sake, the network component impedances remain constant. This assumption can be justified by the complexity of taking into account the time variance of the network configuration and the existing correlations present; the assumption is near to be verified in short-term scenarios. In this chapter, the single node analysis is considered in long-term scenarios so that the dimensions of the problem are reduced and impedance variability cannot be ignored. The probabilistic aspects of harmonic impedances are introduced with reference to a case study. © 2009 John Wiley & Sons, Ltd.