Peter,

Sorry I missed your question. This is a standard test of the dielectric strength of the insulation. Magnet wire is generally designated by it's cut through value. These values range from a low of 105 C to 220C. The higher the value the more complex the chemical makeup of the enamel. In turn the dielectric values are also higher. For shaped wire you strip insulation off one end and then x inches away you wrap the foil tape around the wire. An alligator clip is connected to the bare place on the wire and another on the foil tape. You increase the voltage/current into the sample until the insulation fails. Different enamel grades and different thicknesses have different standards.