This document describes a recommended procedure for measuring insulation resistance of armature and field windings in rotating machines rated 750 W or greater. It applies to synchronous machines, induction machines, dc machines, and synchronous condensers. It does not apply to fractional-horsepower machines. The document also describes typical insulation resistance characteristics of rotating machine windings and how these characteristics indicate winding condition. It recommends minimum acceptable values of insulation resistance for ac and dc rotating machine windings. Other IEEE standards that include information on insulation resistance measurement are listed in Clause 2.