Enamel wire, 0.375 mm diameter, under a microscope: left - cut end with a visible copper core (pink metal) and a layer of enamel (darker coating), right - crack in the enamel coating caused by bending the wire over too small a radius (bare copper visible underneath).
This a “grade 2” enamelled wire (double coating of enamel), with the outer diameter (with enamel) of 0.43 mm. Therefore, the thickness of the enamel coating for this particular wire was just 0.0275 mm. The manufacturer-guaranteed breakdown voltage for such grade of wire is 4.35 kV (Elektrisola, Technical Data for Enamelled Copper Wire by Size acc. to IEC 60317, {accessed 2020-11-08})
enamelled_wire_e_magnetica.jpg
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S. Zurek, Encyclopedia Magnetica, CC-BY-4.0
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