However, the inclusion of arresters modifies the voltage stress across the insulation. This modification is analyzed by considering the equivalent effect to the surge response curve. Consider the surge response curve shown in Fig. 7, which is the result without arresters in the vicinity of the stroke terminating point. Arresters at each grounding point adjacent to the stroke point reduce the volts-per-ampere magnitude, starting at a time dependent upon the length of line to the arresters, the arrester characteristics, and the relative velocities of propagation. If the arrester has not sparked over, the surge voltage rate-of-rise becomes important and adds another variable to the problem. This results in a trial-and- error process converging on the maximumn allowable surge voltage rate-of-rise corresponding to Vk, which is also dependent upon the point on the surge response curve where messenger ground c 0 20 30 40 50 the arrester effect is realized. The crest stroke current then leads required to cause flashover is