Aging mechanisms of two polymeric insulation materials that are used widely in nuclear power plant low-voltage cables; cross-linked polyethylene (XLPE) and ethylene propylene rubber/ethylene propylene diene terpolymer (EPR/EPDM), are reviewed. A summary of various nondestructive methods suitable for evaluation of cable insulation is given. A capacitive sensor capable of making local nondestructive measurements of capacitance and dissipation factor on cable polymers, and potentially suitable for in situ cable monitoring, is introduced. Correlating values of elongation-at-break, indenter modulus, capacitance and dissipation factor measured on a set of 47 aged flame-resistant EPR samples shows a higher correlation between indenter modulus and dissipation factor than between indenter modulus and elongation-at-break.