Part 3 of IEC 62561 specifies the requirements and tests for isolating spark gaps (ISG) for lightning protection systems. ISGs can be used to indirectly bond a lightning protection system to other nearby metalwork where a direct bond is not permissible for functional reasons. Typical applications include the connection to " earth-termination systems of power installations, " earth-termination systems of telecommunication systems, " auxiliary earth electrodes of voltage-operated, earth fault circuit breakers, " rail earth electrode of power and DC railways, " measuring earth electrodes for laboratories, " installations with cathodic protection and stray current systems, " service entry masts for low-voltage overhead cables, " bypassing insulated flanges and insulated couplings of pipelines. This does not cover applications where follow currents occur. NOTE Testing of components for an explosive atmosphere (as defined in IEC 60079-10) is not covered by this document.