[Steve D]

The gauge of the copper wire, which is proportional to the wire diameter, determines the current carrying rating which has nothing to do with voltage rating.. The wire insulation determines the voltage withstand rating. For a given gauge copper wire overall diameter of the insulated wire is determined by the insulation thickness. Different insulation materials have different voltage breakdown ratings so the voltage withstand rating of the insulation is not directly proportional to overall wire diameter. For example, for a given voltage rating, PVC insulated wire is thicker and thus larger in overall diameter than Teflon insulated wire of the same gauge.

Steve D