Re: Rubber beading on high voltage cable insulation

[TTman]

On 20/07/2022 07:53, Mike Mocha wrote:
>
> Hey all,
>
> Just curious what you think about this. The photos at the link are
> showing large gauge wire used on a vintage 600 VDC rail vehicle. We're
> talking 1930's electric streetcar technology. Basically 600 VDC connected
> to a knife switch, then to a rotating manual controller which you
> partially see in the photo. The rotation of it sets up the series and
> parallel stages to the traction motors.
>
> We see this weird rubber beading occurring on the outside of the older
> wire insulation. I'm not sure what that insulation is made of or how old
> it is. This only seems to occur on the older wires. The newer NFPA
> compliant wires don't have this symptom.
>
> What is it and what causes it? Any theories? Thanks.
>
> https://imgur.com/a/OqHQV8U
>
Bits of melted tar maybe...



--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[Dan Purgert]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

Mike Mocha wrote:
> Hey all,
>

>[...]

> We see this weird rubber beading occurring on the outside of the older
> wire insulation. I'm not sure what that insulation is made of or how old
> it is. This only seems to occur on the older wires. The newer NFPA
> compliant wires don't have this symptom.
>
> What is it and what causes it? Any theories? Thanks.
>
> https://imgur.com/a/OqHQV8U

If it's anything like the HV wiring in 1940s/50s era locomotives that
I've worked on restoring, the insulation is essentially some kind of
cloth dipped in tar (pitch, whatever).


-----BEGIN PGP SIGNATURE-----
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=V/lA
-----END PGP SIGNATURE-----

--
|_|O|_|
|_|_|O| Github: https://github.com/dpurgert
|O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1 E067 6D65 70E5 4CE7 2860

[chr...@privacy.net]

On 20/07/2022 07:53, Mike Mocha wrote:
>
> Hey all,
>

> Just curious what you think about this. The photos at the link are
> showing large gauge wire used on a vintage 600 VDC rail vehicle. We're
> talking 1930's electric streetcar technology. Basically 600 VDC connected
> to a knife switch, then to a rotating manual controller which you
> partially see in the photo. The rotation of it sets up the series and
> parallel stages to the traction motors.
>

> We see this weird rubber beading occurring on the outside of the older
> wire insulation. I'm not sure what that insulation is made of or how old
> it is. This only seems to occur on the older wires. The newer NFPA
> compliant wires don't have this symptom.
>
> What is it and what causes it? Any theories? Thanks.
>
> https://imgur.com/a/OqHQV8U
>

Looks like heat damage to me!
Possibly caused by resistance heating in a tarnished/corroded
connection? I would disassemble, clean, grease and remake the
connections.
Replace any damaged cable along the way: If I am right, there will be
some. If I am wrong, there may not be :-)

HTH, Chris