During the last couple of decades, many nuclear power plant operators are seeking the life extension of the operating nuclear power plants. This makes the condition assessment of major components in the plant an important topic. One such component is low voltage power and instrumentation and control cables, which are more than 1000 km in length and makes their replacement a severe cost burden. Since these cables during service are under high thermal and radiation stress, hence making the condition assessment of them inevitable. The thermal stress as compared to other stresses results in the structural change and hence effecting the electrical integrity of the cable insulation. In this work, the complex permittivity of the XLPE/CSPE based low voltage nuclear power cable will be studied under thermal stress. The potential electrical aging markers from the measurement will help in calculating the expected lifetime of the cable for the case of life extension of the nuclear power plants.