IEC 60505:2011 establishes the basis for estimating the ageing of electrical insulation systems (EIS) under conditions of either electrical, thermal, mechanical, environmental stresses or combinations of these (multifactor stresses). It specifies the principles and procedures that shall be followed, during the development of EIS functional test and evaluation procedures, to establish the estimated service life for a specific EIS. This standard should be used by all IEC technical committees responsible for equipment having an EIS. The main change with respect to the previous edition is that Annex A: Glossary is now available in an Internet version as well as a hardcopy version. The internet version contains an abridged text version and a multimedia supplement. The contents of the corrigendum of March 2017 have been included in this copy.