Insulated copper wire turned into gray powder

[TonyStewart]

I have seen many of my low voltage outdoor soft PVC wires oxidize to grey (e.g. AWG 16 stranded speak wire) from moisture creepage at exposure to solder joints for some distance under the insulation. I have always attributed this to some moisture and heat induced and since then used silicon RTV (low acidic) or better, Polyurethane from my sub-floor adhesive tube applicator to slow down the process and switched to solid wire which has worked better. Then I found just now they make an antioxidant filler for copper insulation. https://omnexus.specialchem.com/product/t-shakun-polymers-htp-02-li

 

[rrrandr]

The speaker wire in my car door also turned to a white powder at the point where it connected to another wire. I stripped it down and reconnected the copper and it works fine. Never seen anything like it before.

 

[Woody363]

I've had EXACTLY the same problem as this. Red/black speaker wire with only the red part corroding at irregular intervals to the point of failure with a greyish powder inside.
I bet this was the same batch of cable, bought about 5/6 years ago I think.
Was terrible to solder to too, I think theory or copper coated aluminium is correct, strands are too thin to be sure, but I can convince myself that it's more silvery when scraped.

Really weird! Never seen anything like this before, no obvious defect in the insulation except for swelling at the corrosion points