This paper presents some preliminary results of mechanical and electrical tests carried out on CSPE/EPDM polymer insulation used in low-voltage nuclear power plant cables. The whole cables were exposed to operation stresses for 30 years, then the inner low-voltage insulations have been aged further in the lab under thermal and radiation stresses. Electrical measurements are performed on aged cable specimens using dielectric spectroscopy. Mechanical properties are investigated through tensile testing, i.e. elongation at break and Young's modulus. These properties are aging markers commonly used to assess the conditions of low-voltage cables operating inside nuclear power plants containment area. First results have shown a significant increase of the real and imaginary parts of dielectric permittivity, especially at low frequencies, which can be correlated to bulk insulation aging. This paper represents only a part of a more extended work, which aims at identifying electrical aging markers able to correlate electrical and mechanical properties with aging.