To limit the spread and hence cost of cathodic protection current to those pipes that need to be effectively and economically protected by the main cathodic protection system. To electrically split up long pipelines into very distinctive cathodic protection system. To isolate a pipeline and to ensure that cathodic protection or stray electricity currents do not cause increased corrosion. To provide protection against earthing currents at domestic and industrial premises where the PME system is in use.