Abstract :
C. A. Powel (Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa.): This paper by Messrs. Sporn and Gross, dealing with the margin between the levels to be protected and the levels held by the protective devices, is very important, because on these margins depends the entire justification for the basic levels to be submitted for consideration by the joint committee on insulation co-ordination, as proposed in the Sporn-Powel paper. It must be recognized that a proper choice of basic levels is of great economic importance to the industry. The margins shown in the paper are very moderate and might be considered in some cases inadequate except for the fact that other factors, such as rapid decay of the lightning surge and the small probability factor of heavy surges, come into the picture and help the situation.
