This part of IEC 317 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 a bonding layer based on a thermoplastic resin. Class 155 is a thermal class that requires a minimum temperature index of 155 and a heat shock temperature of at least 175 °C.