This article documents a high voltage test of a couple of PTFE insulated silver plated copper wires.
In each case, a single wire is tested, one electrode to the wire and another being an alligator clip clipped onto the wire about 30mm from the end. This approximates a knife edge test which subjects the insulation to the highest electric field strength.
At the time of the test, temperature was 21° and relative humidity 65%. Whilst not extreme humidity, it is sufficient to degrade breakdown often giving rise of an arc over the surface of the wire to the cut end. For that reason, about 30mm of insulation is left clear at each end.
The source is 50Hz AC, so peak voltage is 1.414 times the RMS value shown on the instrument.
Above, the orange PTFE insulated wire on essentially a knife edge test at 6.2kV AC, 8.7kVpk. The conductor is stranded and 1.0mm diameter (#18), diameter over the insulation is 1.5mm, so about 0.25mm thickness PTFE.
Above, the red PTFE insulated wire on essentially a knife edge test at 6.2kV AC, 8.7kVpk. The conductor is stranded and 0.9mm diameter (#19), diameter over the insulation is 1.3mm, so about 0.2mm thickness PTFE.
I have used both these wires to wind ‘tuner baluns' where the wire is subjected to quite high voltages. Whilst on the basis of these tests we might expect that the wire to wire withstand is more than 16kV, breakdown of other components like a balun input coax connector will set a practical limit of something less than 5kV. Breakdown is degraded by high humidity, and accumulated dirt on wires, connectors and terminals, so again tests of clean wire in low humidity need to be interpreted sensibly.
These wires can be obtained on eBay or Aliexpress for modest cost.