IEC 60099-4:2014 applies 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. This third edition cancels and replaces the second edition published in 2009. This edition constitutes a technical revision. The numerous changes between the second and third editions are listed in the Foreward of the document. Keywords: testing of gapless metal-oxide surge arresters for a.c.power systems