This part of the International Standard series IEC 60099 presents the minimum criteria for the requirements and testing of gapless metal-oxide surge arresters and is applicable to non-linear metal-oxide resistor type surge arresters without spark gaps designed to limit voltage surges on a.c. power circuits with Us above 1 kV. The following modifications have been made with respect to the third edition of DIN EN 60099-4 (VDE 0675-4). Editorial modifications for improvement of the readability of the document have been made. New terms and definitions have been specified. The concept of arrester classification and energy withstand testing was introduced. The line discharge classification was replace by a classification based on repetitive charge transfer rating (Qrs), as well as on thermal energy rating (Wth) and thermal charge transfer rating (Qth), respectively. Requirements depend on the intended arrester application. The new concept clearly differentiates between impulse and thermal energy handling capability, which is reflected in the requirements as well as in the related test procedures. Requirements and tests for UHV arresters for highest system voltages Us >800 kV have been introduced. Power-frequency voltage versus time tests - with and without prior duty - were introduced as type tests. Requirements and tests on disconnectors have been added. Requirements and tests on disconnectors were added. "Test series B: 5 000 h" was removed from the weather ageing test, thus following the new approach of IEC 62217. Former Annexes C, D, E, H, I and J were removed. New annexes for determining the start temperature for tests on thermal stability, for determining the axial temperature distribution along tall arresters, for providing an example of how to determine energy requirements for the operating duty test and for comparing the new classification system with the former line discharge class system were introduced. The responsible committee is Subcommittee DKE/UK 441.1 "Überspannungsableiter" ("Surge arresters") of the DKE (German Commission for Electrical, Electronic and Information Technologies).