This part of IEC 60404 is applicable to surface insulation coatings on electrical steel strip and sheet classified in IEC 60404-1-1. The purpose of this document is to define the general principles and technical details of the tests for the assessment of the thermal endurance of surface insulation coatings on electrical steel strip and sheet. The assessment is made by evaluating the change of a specified property of the surface insulation coating due to a heat treatment at a specified temperature up to 850 °C and a specified duration time up to 2 500 h. The specified property is measured at an ambient temperature of (23 ± 5) °C both without heat treatment and after heat treatment. This document is applicable to the following properties of surface insulation coatings: adhesion; surface insulation resistance; stacking factor. This document is not applicable to other properties of surface insulation coatings, e.g. welding properties, or to other effects e.g. discoloration and off-gassing, which can be caused by exposure to elevated temperatures. NOTE Some of the tests take a very long time to perform and therefore they may not be suitable for acceptance tests of material supplied on a specific order.