The line discharge class system actually was first used for gapped arresters with current-limiting series gaps. At the beginning of the 1980’s – when MO arrester technology was still in its infancy – a testing standard for MO arresters was developed, and the existing system was adopted, since there were no better alternatives. After such a system is introduced, it is difficult to change it again. In the standardization process, new definitions for energy handling capability are, however, being considered, which are more appropriate for stresses associated with today's arrester applications.