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Asset management strategies are amongst the most important tools to address the economical, reliability, and operational requirements of extensive distribution networks in the environment of increasing deregulation. The key objectives are full utilization (i.e., exploitation of available network reserves), investment for expansion, and maintenance including asset replacement. The paper will focus on the methodology and the results of a condition-based preventive maintenance concept as part of the overall asset management strategy. As an example, the condition of 20-kV XLPE service aged cables of a German distribution grid is evaluated and categorized. The "isothermal relaxation current analysis" (IRC-Analysis), which is a nondestructive and nonpartial discharge diagnostic method, is used to assess the cable conditions. Obtained categories are combined with the impact of one distinct cable on local system reliability in order to optimize replacement strategy. This concept called "reliability centered maintenance" is applied by the author's company Lechwerke AG (LEW AG). As a result, the annual budget to guarantee service quality could be reduced substantially.