Electric Strength of Small Insulating Distances

The capabilities of modern materials and new technologies allow significant size reductions to be achieved particularly in the field of low-voltage equipment. The limits encountered are often due not so much to technical or physical factors, but to widely varying safety requirements determined in many cases by earlier technological capabilities and the limits and specifications based thereon. This paper reports further results obtained from an extensive research project. Exposure of a large number of test specimens to various environmental conditions has proved conclusively that spacings on the surfaces of insulating materials are affected only if contamination is significant. Under heavy contamination these so-called creepage distances form tracks leading sooner or later to failure. Comparatively clean creepage distances however are not affected by tracking and should therefore only be dimensioned on the basis of their short-term electric strength. The results of this extensive series of tests are a statistically verified basis for the dimensioning of rather clean, small creepage distances (>10 mm). They can be incorporated directly into the relevant standards. Other results from the research project will be reported on conclusion of current investigations. However, it is expected that this work will not be completed before 1988.