IEC 62561-3:2017(E) 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. This second edition cancels and replaces the first edition, published in 2012. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition. - a new classification has been added related to ISGs location installation; - an updated flow chart of tests has been developed.