I need to solder together some wires which will eventually run at about five kV, and I'm trying to figure out the best way to insulate the exposed leads. Heat shrink (my usual go-to) is apparently not rated above about 600 V. Kapton seems to be rated much higher (100's of kV/mm), so I am thinking of wrapping the leads in several layers of this. Given the high voltage hazard, I'm looking for advice: Would this be a good solution, or is there a better way?
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\$\begingroup\$ At that level, partial discharge due to your voltage division between the insulator material and surrounding air will most likley dominate anyway. Is the high voltage continuous? \$\endgroup\$– winnyJul 3, 2019 at 21:02
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3 Answers
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Kapton is not appropriate to wrap cables: it's relatively stiff, and thus won't be conformal to the cable, which leaves air gaps, which have lower insulation per mm.
So, even multiple layers of heat shrink would be better.
At 5 kV, I'd start by trying to keep cables mechanically separated far enough that the air distance ensures sufficient isolation, even in the absence of any dedicated isolating material.
Use high-voltage cables, which come with the necessary isolation. Don't connect them at the same distance – cut one conductor shorter than the other, so that you don't break isolation in close vicinity.
There's isolating potting that you can use to fixate a solder joint.
answered Jul 3, 2019 at 18:22
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KAPTON (tm) is excellent (Polyamide) But must be sealed from humidity to prevent creepage.
Rubber insulated wire is best.
Exposed terminations can be somewhat sealed if dry when applied with RTV Silicone to 25kV/cm safely from high impedance sources.
Ignition wiring uses Rubber insulation but now is all carbon, but you can still get copper wire. Rated for spark plugs.
You MUST be aware of ARC FLASH protection gear if high energy source is being tested.
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\$\begingroup\$ silicone surface to target leakage is why bathtub caulking turns black inside on the wall. Same thing for ionic flow \$\endgroup\$ Jul 3, 2019 at 21:00
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\$\begingroup\$ I don't understand your comment about bathtub caulking. That turns black because of mold growth. \$\endgroup\$ Jul 4, 2019 at 12:24
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\$\begingroup\$ Moisture and organic molecules + heat= mould. this grows under caulking because it creeps along inner surface not always by penetrating thru it. so contact area is the weak link not the silicone , per se but if too thin, them it could be. Moisture creepage is affected by vapour pressure and this may contaminate creepage inner layer surface. Ionic content and organic content follow the same paths. \$\endgroup\$ Jul 4, 2019 at 16:33
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\$\begingroup\$ This is why EE’s take chemistry \$\endgroup\$ Jul 4, 2019 at 16:34
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Kapton is a really good insulative medium and aircraft cable use to be wrapped in it. However... Kapton is susceptible to embrittlement over time
https://www.mitrecaasd.org/atsrac/intrusive/Chapter_6.pdf
https://www.faa.gov/documentLibrary/media/Advisory_Circular/ac25-16.pdf
If it is to encapsulate the solder connections then yes you could rely on Kapton or go for some form of potting to encapsulate the joint