Odd Conductor Insulation

[Gunnar Alquist]

This is not necessarily a problem, but I have not run into anything that looks like this before. This is located in a distribution panel at the circuit breakers. The last fraction of an inch of some of the conductor insulation is clear. It does not look to be added-on, but I didn't actually try to separate. I suppose it could be the outer sheath of THHN


Unfortunately, I did not get the brand of the cable.


I was just curious. Has anyone noticed anything like this in the past?34453

[Jerry Peck]

What that first looked like to me was the outer clear plastic of THHN/THWN insulation.

My first guess was that the wire was stripped back and, somehow, the outer covering 'stretched out' over the inner insulation.

But ... when I was zoomed in on it to see it better, the jagged cut end of the clear covering matches the nicks in the copper conductor - which is not to be nicked like that (the conductor is susceptible to cracking and breaking if nicked).

Any other ideas about what is shown?

[Gunnar Alquist]

What that first looked like to me was the outer clear plastic of THHN/THWN insulation.
My first guess was that the wire was stripped back and, somehow, the outer covering 'stretched out' over the inner insulation.
But ... when I was zoomed in on it to see it better, the jagged cut end of the clear covering matches the nicks in the copper conductor - which is not to be nicked like that (the conductor is susceptible to cracking and breaking if nicked).
Any other ideas about what is shown?

Thanks Jerry,

I guess I didn't post the really close-up image. I thought I did. And the real close-up doesn't show the nick.

Someone else guessed that it was a dull wire stripper that didn't cut through the outer clear nylon but managed to pinch-off/separate the inner PVC.

[Jim Luttrall]

Yep, I have found clear outer covering many times.

[Bill Kriegh]

I missed this in my intermittent browsing and picked it up in Brian's e-mail.

It has been my experience that some types of older insulation will turn clear after repeatedly being very warm or hot. It seems that the required temp to start this process is very specific and hence the almost immediate change from color to clear. The color to clear appears not to be exactly a straight line toward the top of the picture and this is what I typically see.

While the nick in the copper is a bad practice it doesn't appear to have caused this. I'd be all for checking the terminal screw on the breakers to see if they are snug. It's almost a sure bet they're not torqued. It does look to me like the exposed copper has been heated a bit but the picture makes it hard to tell for sure.

I had a job once where the homeowner had run a #14 NM to a dryer using the ground as a neutral and the neutral as a second hot wire. Then he added a washing machine to the circuit using the ground wire and the white wire. The cable had been so hot that the insulation on both the black and white conductors AND THE SHEATH was clear and you could see the copper through the sheath. There was a bit of color in the sheath and conductors near the few staples present. Amazing stuff. The insulation was drooping in only one place and wasn't charred anywhere, or brittle.

All fed from a 50 AMP 2 pole breaker BTW.

[THOMAS HORNE]

The problem that I see is that the insulation is stripped too far back on the conductor. Best practice is that it be stripped no longer than needed for the conductor to be completely in the terminal without any insulation under the terminal pressure plates nor inside the connector itself. I would bet a pretty penny that those terminations were not made in accordance with instructions included in the listing or labeling.

--
Tom Horne

[gibbon]

This is not necessarily a problem, but I have not run into anything that looks like this before. This is located in a distribution panel at the circuit breakers. The last fraction of an inch of some of the conductor insulation is clear. It does not look to be added-on, but I didn't actually try to separate. I suppose it could be the outer sheath of THHN


Unfortunately, I did not get the brand of the cable.


I was just curious. Has anyone noticed anything like this in the past?34453

I ran into that stuff when I used to do industrial controls. The clear coating is Teflon. It's chemical resistant and makes it easy to pull through long runs of conduit.