The use of these Re and Xe curves in estimating the zero sequence impedance of circuits for which no field data are available obviously is limited to the feeder system on which the experimental data were taken, since even the diameter of a faulted cable is an important factor among the various field conditions that influence the resultant impedance.
So far as earth resistivity is concerned, the number of points available for determining the Re and Xe curves seemed to include data from enough circuits of different lengths and locations to make the curves adequate for estimating purposes without having to take into account the variations in earth resistivity that probably exist.