 At lower temperatures the service life of the wire is longer (about a factor of 2 for every 10 °C lower temperature).Common temperature classes are 105 °C, 130 °C, 155 °C, 180 °C and 220 °C.In practice maximum current density can vary from 2.5 A/mm2 for a wire isolated from free air to 6 A/mm2 for a wire in free air.