International development in insulation system characterization

A large part of the present international standards regarding insulation classification, for particular equipment is based on the temperature classification of the International Electrotechnical Commission (IEC) in publication 85. This document, reflecting the occurrence of the plastics revolution, represented a transition from the traditional philosophy, "Tell me what insulation material you have and I shall tell you its temperature class," towards a novel one which emphasized experimental verification as the basis for insulation rating. However, IEC 85 is now widely considered to be obsolete and its withdrawal, rather than a mere revision, has been officially proposed for the following reasons: Experimental verification is recommended in principle but no concrete directions were given. It is used indiscriminately for rating both insulating materials, insulation systems and insulated apparatus. An appendix with examples intended for guidance of designers is commonly being wrongly applied as a materials classification system in the traditional style.