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I commonly use 30ga Kynar (Polyvinylidene Fluoride, PVDF) wire for PCB <=24 VDC repairs.

But can it be used to repair 120 VAC signal wires?

Strangely, vendors do not seem to publish a voltage rating for Kynar wire:

Researching, PVDF has a Dielectric strength (at 23°C) of 1.4 – 110 kV/mm. That's quite a range.

Assuming the low-end of that range, and given that the insulation dia of one 30ga Kynar wire is about .020 in (0.50 mm), does that imply an insulation resistance of 700 V for this wire?

ocrdu
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rdtsc
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  • This kind of wire is typically used for signals at low voltages only; it looks like standard wire-wrap wire, which is usually rated to no more than 30 V. It may well *work* for higher voltages, but I wouldn't rely on it in the long term. It would also very definitely preclude any standards qualifications, but since this is a repair I assume that's not under consideration. Do bear in mind that the insulation may be thinner (probably not by much) than the diameter suggests; the insulation and wire may not be perfectly concentric, and it only takes one weak spot to ruin things... – Hearth Oct 18 '22 at 20:02
  • Depends on your definition of used. For very short term, it’s probably ok to several kV. For longer term without breakdown due to partial discharge it’s probably hundreds of V. For a general mains use cable, touched every day by children and the like, you need even more margins. – winny Oct 18 '22 at 20:35

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Corona usually begins at over 400 VAC. Corona causes long term degradation for AC insulation. If you use ample air spacing, there won't be a corona problem at any voltage. Kynar is susceptible to impingement when it is pulled against sharp corners: cold flow may cause eventual shorting. Heat can cause immediate thinning, due to the soldering process, and can happen wherever two lines cross. 30 AWG wouldn't conduct much heat, so that shouldn't be an issue at the middle of wires. Inrush surge is a problem in many 120 VAC circuits. 30 AWG is too fragile for charging electrolytic capacitors, or for energizing transformers. Some systems use negative temperature coefficient (NTC) resistors to limit inrush surge current. But NTC resistors require up to two minutes to cool down. Rapid power cycling can cause major inrush surge problems after an NTC is already hot. Limit peak current. Be careful when soldering. Avoid sharp edges. Kynar can handle 120 VAC.

Jeff Reagan
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