Taking under consideration, that reliable transmission of energy is fundamental to proper operation of national power grid, quality control is essential for newly installed and in-service cable connections. It is known that routine tests (insulation coordination) completely check the quality of a power cable and accessories at the manufacturer. Nevertheless, the risk of problems with the delivery and installation of accessories can affect the quality of a newly installed power cable circuit. Based on international experience gathered on various power grids over the past 20 years, this article focuses on the use of non-destructive testing for after-installation - and diagnostic tests of all types of transmission cables. This document discusses in particular various actual aspects of testing new connections as well as the condition assessment of service aged HV power cables.