IEC 62631-3-3:2015 covers methods of test for the determination of the insulation resistance of electrical insulating materials or insulating systems by applying DC voltage. This first edition cancels and replaces the first edition of IEC 60167, published in 1964, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the first edition of IEC 60167: a) IEC 60167 has been completely revised, both editorially and technically, and incorporated into the new IEC 62631 series; b) test methods have been updated to current day state of the art.