IEC 60317-20:2013 specifies the requirements of solderable enamelled round copper winding wire of class 155 with a sole coating based on polyurethane resin, which may be modified providing it retains the chemical identity of the original resin and meets all specified wire requirements. 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: 0,018 mm up to and including 0,800 mm; - Grade 2: 0,020 mm up to and including 0,800 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; - modification to Clause 15 to remove specific wire specimen sizes; - consolidation of 17.1 and 17.2 of the solderability requirements; - modification to Clause 19, Dielectric dissipation factor; - new Clause 23, Pin hole test. Key words: requirements of solderable enamelled round copper winding wire, class 155, sole coating based on polyurethane resin