IEC 60317-21:2013 specifies the requirements of solderable enamelled round copper winding wire of class 155 with a dual coating. The underlying coating is based on polyurethane resin, which may be modified providing it retains the chemical identity of the original resin and meets all specified wire requirements. The superimposed coating is based on polyamide resin. NOTE - A modified resin is a resin that has undergone a chemical change, or contains one or more additives to enhance certain performance or application characteristics. The range of nominal conductor diameters covered by this standard is: - Grade 1: 0,050 mm up to and including 1,600 mm; - Grade 2: 0,050 mm up to and including 1,600 mm. The nominal conductor diameters are specified in Clause 4 of IEC 60317-0-1:2013. This third edition cancels and replaces the second edition published in 1990, Amendment 1:1997 and Amendment 2:1999. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - new 3.2.2 containing general notes on winding wire, formerly a part of the scope; - revision to references to IEC 60317-0-1:2013 to clarify that their application is normative; - consolidation of 17.1 and 17.2 of the solderability requirements; - modification to Clause 19, Dielectric dissipation factor; - new Clause 23, Pin hole test. Keywords: requirements of solderable enamelled round copper winding wire, class 155, dual coating