A test procedure for thermal life testing of polyimide wrapped medium voltage machines has been developed and initial testing has occurred. Polyimide wrapped medium voltage motors, such as those tested by this new procedure, are primarily used in electric submersible pump (ESP) systems. Current thermal life testing standards do not adequately support these ESP machines. The reason for the gap in the standards as currently constituted is the unique design constraints that are imposed on ESP machines by their oilfield applications.ESP motors are used in deep, downhole applications that require wide ranges of horsepower and a supply voltage between 2kV and 7kV. These motors must fit into an oil well casing that imposes a motor frame with an outside diameter between 3 and 9 inches. These design requirements significantly restrict the design of the insulation system. In most cases machine designs are polyimide wrapped (most areas of the machine have less than 10 mils of insulation) polyimide-based systems. The new test procedures are based on existing standards but take into consideration the unique design and the unique application of ESP motors. This paper discusses the distinctive aspects of the machine's application and design, outlines the new testing procedure and reviews initial test results. Further, this paper discusses how this testing procedure fits into the landscape of insulation life testing standards.