We study a series array of nonlinear electrical circuit elements that possess negative differential resistance and find that heterogeneity in the element properties leads to the presence of multiple branches in current-voltage curves and a nonuniform distribution of voltages across the elements. An inhomogeneity parameter rmax is introduced to characterize the extent to which the individual element voltages deviate from one another, and it is found to be strongly dependent on the rate of change of applied voltage. Analytical expressions are derived for the dependence of rmax on voltage ramping rate in the limit of fast ramping and are confirmed by direct numerical simulation. © 2010 American Institute of Physics.