Insulated copper wire turned into gray powder

[ZG1K]

The powder is CuCl. PVC is 60% chlorine which provides the catalyst for the change, and the location of the wire provided the environment. The copper wire at some point heated to over 450C and reacted with the chlorine in the PVC. This is much more likely to happen in stranded wire, especially improperly protected stranded wire, as a pinch point or other mechanical force exerted on the wire can cause strands to break inside the sheathing, increasing the wire's resistance and decreasing its heat dissipation.

Interestingly enough, the combination of copper wire and PVC sheathing makes for an effective yet presumably unintentional fail safe. In the event of a runaway overload, the chlorine will react with the copper, opening the circuit before the copper can melt and the other layers of pvc reach its melting point.

 

[Majorana]

The powder is CuCl. PVC is 60% chlorine which provides the catalyst for the change, and the location of the wire provided the environment. The copper wire at some point heated to over 450C and reacted with the chlorine in the PVC. This is much more likely to happen in stranded wire, especially improperly protected stranded wire, as a pinch point or other mechanical force exerted on the wire can cause strands to break inside the sheathing, increasing the wire's resistance and decreasing its heat dissipation.

Interestingly enough, the combination of copper wire and PVC sheathing makes for an effective yet presumably unintentional fail safe. In the event of a runaway overload, the chlorine will react with the copper, opening the circuit before the copper can melt and the other layers of pvc reach its melting point.

Interesting possibility, provided that such heating of the copper wire could occur. But the cable was used to connect a SMALL loudspeaker to a SMALL amplifier, to provide background music (i.e. low volume) in a small reception office. The amplifier was not defective (or the loudspeaker coil would have burned loooong before the cable!), both the amplifier and the loudspeaker worked fine after the cable was replaced. No other wires in the vicinity, the loudspeaker cable was the only cable running in that conduit under the floor. Absolutely zero chances that the cable could heat above 40°C.

 

[Tom.G]

Any chance that the PVC was incompletely polymerized leaving som readily available Chlorine? If so, could the CuCl reaction take place at room temp?

 

[Borek]

Any chance that the PVC was incompletely polymerized leaving som readily available Chlorine? If so, could the CuCl reaction take place at room temp?

Doesn't make much sense chemically. No chlorine in the production of PVC. It it used in an earlier step, during production of a monomer, vinylium chloride - but any excess chlorine left before the monomer is used in polymerization would react with the double bond present, converting the vinylium chloride to just a trichloroethane and rendering it useless for the PVC production.

 

[ZG1K]

Doesn't make much sense chemically. No chlorine in the production of PVC. It it used in an earlier step, during production of a monomer, vinylium chloride - but any excess chlorine left before the monomer is used in polymerization would react with the double bond present, converting the vinylium chloride to just a trichloroethane and rendering it useless for the PVC production.

PVC (PolyVinylChloride) is C2H3Cl. There is certainly chlorine in it.

 

[sysprog]

PVC (PolyVinylChloride) is C2H3Cl. There is certainly chlorine in it.

Please re-read what @Borek said. He well knows that there's chlorine in PVC and didn't say that there wasn't. He was in an overviewing manner explaining some things about the PVC production process that were relevant to the question.

 

[David Lewis]

In the 1960s this was called black wire corrosion because the copper wire that disintegrated was more prevalent in wires with black plastic insulation. A tentative hypothesis put forward was corrosion caused by outgassing from the PVC insulation. It was never corroborated, however.

 

[tech99]

I am wondering if it is an attack by rodents. The copper was then exposed to atmospheric corrosion, maybe from ozone created by photocopiers.

 

[Tom.G]

I am wondering if it is an attack by rodents.

...cable was the only cable running in that conduit

I'm not sure I would even like to know there IS a rodent that big!

 

[tech99]

I'm not sure I would even like to know there IS a rodent that big!

Yes, I suppose the rodent is implausible - I had not previously realize Copper is attacked by Ozone. The biggest rodent is the Capybaras, by the way, which is a lovely animal.

 

[Majorana]

@tech99 @Tom.G jokes apart, it's not a matter of conduit size. The PVC insulation on the affected wire was INTACT, as I explained in the opening post. It was just a little "bulging" (swelling) at the spots where the copper got pulverized, but wasn't chewed nor broken before I cut it longitudinally to extract the powder.

 

[Carol]

Dear all,
thank you so much for all your contributions.

Going backwards:

@Klystron the floor is not a raised floor with plenum, ducts etc. It's an ordinary, old concrete floor, with plastic tubing for electrical wires embedded in it.

@Guineafowl I'm really unable to see your point in sticking with the aluminium idea, despite all the contrary evidence. Until now, I did not want to mention the fact that I am an experienced electronics designer, that I also designed electronics for military aircraft in service nowadays, and that I have handled, stripped and soldered electrical wires of any sort for almost 50 years now, but now I feel obliged. Any scientist knows that trying to shape evidences in order to match a theory leads to faulty results. I know very well that an aluminium wire would explain this phenomenon much easily than a copper wire, but unfortunately this is not the case. I might borrow a camera with macro lens just to post a picture of the cross-section of the copper strands, but I feel that this thing has gone too far.

@anorlunda yes, it's perfectly possible, and in addition the colour of that powder was not perfectly homogeneous. The next step I wish to take would be to have that powder analyzed. It's not so easy to find a lab willing to do the job for a private citizen. In case I find one, I would certainly post the results here, be sure of that.

@Borek as I mentioned a couple of times in my above posts, the two external sections of the cable that did not lie under the floor (they went vertically from the floor to a junction box on the wall on one side, and to the loudspeaker on the other side) are completely normal and unaffected, as well as a length of excess cable left over after installation and stored in a drawer in the same office.

Something similar happened to me with a cable, It turned into grey power, but it hadn't been in use for a long time. The cable remained in a house that is on the beach, so there is high humidity and salinity that accelerate corrosion. In my case it was as @Guineafowl mentioned. The sections that still had wires, at first sight seemed like copper, however, when I scratched them, the silver color came out. Perhaps the humidity and salinity affected the alloy of copper with aluminum.

 

[Tom.G]

In a very similar vein, yesterday I was using some very old clip leads (25-30 yrs.) when a clip came off of one. Didn't think to bother with photos but it reminded me that I had seen the bright green wire corrosion before but couldn't place it (oily and the color of Copper Sulfate).

Cutting off a couple inches and stripping the wire back disclosed the same corrosion, again reminding me I had seen it before.

Conclusion/speculation is that the vinyl insulation had something in it that reacted with the Copper. Other clip leads stored in the same box did not show any corrosion.

Cheers,
Tom

 

[Majorana]

Something similar happened to me with a cable, It turned into grey power, but it hadn't been in use for a long time. The cable remained in a house that is on the beach, so there is high humidity and salinity that accelerate corrosion. In my case it was as @Guineafowl mentioned. The sections that still had wires, at first sight seemed like copper, however, when I scratched them, the silver color came out. Perhaps the humidity and salinity affected the alloy of copper with aluminum.

Carol, you got it! My wires look exactly the same way (although corrosion was perhaps more "complete" in my case, but I guess it's just a question of time...)
In my case, the environment is completely different from that of a beach house: large city, hundreds of kilometers from the sea, no construction works in the vicinity. But yes, the climate is generally damp, although not saline.

 

[Larry 202]

I installed after market power door locks on my chevy 1500.
Wound up a year later with same problem All colors red blue green brown white purple black orange all did it.
Thanks for finally finding somewhere to explain.

 

[Rx7man]

I had a set of jumper cables that appeared to be copper (they were copper plated alumimum), I had a lot of problems with them and the conductors corroding off the clamps

 

[rhk01]

FWIW, I'll mention this. Another person on the debian-user@debian.org mail list found this web page, which is relevant to some discussions on that list. I'll cite one post as an example: https://lists.debian.org/debian-user/2023/06/msg00081.html.

The gist is that one debian user in particular (the author of that message) has found, over a long period of time, lots of similar problems with cables that he describes as cables with "hot red" (magenta) cable insulation, extending back from the days when there was typically a red lead leading to a microphone (I'm not clear if that was in CB sets, or more like TV (or radio) broadcast sets), and extending to SATA cables up to almost today. (Users who are cognizant of the problem make it a practice to use SATA cables that are some color other than red.) (Maybe the problem is gone in SATA 3 cables?)

If I was less lazy, I'd try to dig out more of the relevant posts, but I am old and lazy :-(

I decided to just present this as a data point and maybe a hint that might lead to collaboration / further investigation / understanding of the problem.

Oh, he describes it as a rust colored powder, I don't know if that might be also seen as sort of a dark gray...

 

[Tom.G]

See also:
https://www.physicsforums.com/posts/4146172

 

[Majorana]

FWIW, I'll mention this. Another person on the debian-user@debian.org mail list found this web page, which is relevant to some discussions on that list. I'll cite one post as an example: https://lists.debian.org/debian-user/2023/06/msg00081.html.

The gist is that one debian user in particular (the author of that message) has found, over a long period of time, lots of similar problems with cables that he describes as cables with "hot red" (magenta) cable insulation, extending back from the days when there was typically a red lead leading to a microphone (I'm not clear if that was in CB sets, or more like TV (or radio) broadcast sets), and extending to SATA cables up to almost today. (Users who are cognizant of the problem make it a practice to use SATA cables that are some color other than red.) (Maybe the problem is gone in SATA 3 cables?)

If I was less lazy, I'd try to dig out more of the relevant posts, but I am old and lazy :-(

I decided to just present this as a data point and maybe a hint that might lead to collaboration / further investigation / understanding of the problem.

Oh, he describes it as a rust colored powder, I don't know if that might be also seen as sort of a dark gray...

Thank you so much, that is *VERY* interesting!

"replace any "hot red" aka "magenta" sata cable with some other color. I am a CET and known to me since the 1970's, that color of insulation dye will in time, convert the copper of the conductor into a rust colored powder, and that is a poor conductor"

It definitely looks like the same deterioration I observed on my cable in 2019!

 

[rhk01]

If I was less lazy, I'd try to dig out more of the relevant posts, but I am old and lazy :-(

I should mention that that person (Gene Heskett) has reported on that problem on that list over a long period of time -- if someone goes looking for his posts on that subject, you may have to look back as far as 10 years or more. (He is a prolific poster, and you will also find a lot of posts not relevant to the problem.)

The only thing I can think of off the top of my head that might be gained by looking for his old posts might be to clarify what kind of microphone sets he found the problem in (CB, or TV (or radio) broadcast sets, or maybe both), and other red cables he might have found the problem in.

Oh, and I might add, the other lead(s) to the microphone (in other colored insulation) were not affected by the problem.

 

[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