This Part of IEC 60317 specifies the requirements of enamelled round copper winding wire of class 120 with a sole coating based on polyvinyl acetal 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. Class 120 is a thermal class that requires a minimum temperature index of 120 and a heat shock temperature of at least 155 °C. The temperature in degrees Celsius corresponding to the temperature index is not necessarily that at which it is recommended that the wire be operated and this will depend on many factors, including the type of equipment involved. The range of nominal conductor diameters covered by this standard is: – Grade 1: 0,040 mm up to and including 2,500 mm; – Grade 2: 0,040 mm up to and including 5,000 mm; – Grade 3: 0,080 mm up to and including 5,000 mm. The nominal conductor diameters are specified in Clause 4 of IEC 60317-0-1