Degradation of TPE Insulation of Low Voltage Cabling

Insulation of cables applied in rolling stock usually has a service life of approximately 40 years. However, in 2015 a European railway company was confronted with severe deterioration of the insulation of low voltage cabling in one of the train types. At numerous locations insulation had become brittle and broke into pieces. It concerned control cabling with a rated voltage of 500 V with insulation of halogen free flame retardant thermoplastic elastomer (TPE), sometimes referred to as thermoplastic rubber (TPR). From inspections in the rolling stock it was found that the most severe degradation was mainly present in humid areas (100%RH) and/or areas of elevated temperature (max. 60°C). The trains were approximately 19 years in service. The expected remaining service life of the trains should be at least 20 years. The cable was also applied in another train type that was in service for approximately 12 years.