This guide describes a procedure that may be used to evaluate and compare insulation systems used, or proposed for use, in large ac electric machines. The tests outlined herein are applicable to the groundwall insulation systems applied to form-wound, pre-insulated armature (stator) winding coils and/or bars of generators, motors, and synchronous condensers rated 2300 V or higher. The basic component of these insulation systems is usually mica combined with reinforcing, bonding, and impregnating materials. This guide is based on the experience of the industry with mica-based systems; any evaluation of other insulation systems should, however, consider the requirements of this guide. This document is not intended for use as a manufacturer's quality assurance test plan. Nor should it be used for specifying or procuring armature winding coils/bars.