There are over 600 miles of power cable installed in a typical nuclear power plant. Degradation due to thermal and radiation damage of cable insulation has been identified as one of the key factors that contribute to the loss of performance and ultimate failure of the cable. A critical aspect of cable health monitoring is to understand the nature of degradation and develop aging models to predict the service lifetime of the insulation. In this work, thermal degradation in a commercial grade of ethylene propylene rubber (EPR), a cable insulation material used extensively in nuclear power plants, is assessed under accelerated aging conditions. Characterization of thermally aged EPR is performed by measuring macroscopic changes in thermal, electrical and mechanical properties as a function of thermal aging time and temperature. Two kinetic models are developed to estimate the remaining useful life of EPR based on measured changes in thermal and electrical properties, respectively. Finally, the degradation characteristics of EPR when aged in a jacketed cable configuration alongside a chlorinated polyethylene (CPE) jacket is examined and changes in electrical properties as a function of thermal aging as investigated for EPR in the cable geometry by and interdigital capacitive electrode (IDC).