The global assessment system for medium voltage power cable systems has been developed The minimum purpose of diagnostic activity is the economic discrimination and maintenance of bad cables which is likely to cause cable system failure. I have adapted the Aging Time Constant Method to construct the power cable assessment system for the diagnostic purpose. From the field application test and breakdown test results, it could be concluded that the diagnostic system was successful art convenient for the discrimination and maintenance of the bad cables, which is likely to fail sooner or later, economically.