Enamelled Wires Oxygen free copper complies with international standards of 99.99% purity is the right choice for wire production. Oxidized impurities often cause weaknesses in the wire. Removing oxygen eliminates the potential for the chemically caused weaknesses. Class of insulation (120, 130, 150, 180, 200 or 220) or the required thickness (Grade 1, 2, or 3). Wide range from 1.5mm up to 4.5mm, depending on the application.