• Rubber beading on high voltage cable insulation

    From Mike Mocha@21:1/5 to All on Wed Jul 20 06:53:17 2022
    XPost: sci.electronics.misc, sci.electronics.repair

    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

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  • From TTman@21:1/5 to Mike Mocha on Wed Jul 20 11:02:01 2022
    XPost: sci.electronics.misc, sci.electronics.repair

    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...



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  • From Dan Purgert@21:1/5 to Mike Mocha on Wed Jul 20 11:10:33 2022
    XPost: sci.electronics.misc, sci.electronics.repair

    -----BEGIN PGP SIGNED MESSAGE-----
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    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).


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  • From chrisnd@privacy.net@21:1/5 to Mike Mocha on Wed Jul 20 15:40:37 2022
    XPost: sci.electronics.misc, sci.electronics.repair

    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

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  • From Joe Gwinn@21:1/5 to All on Wed Jul 20 11:14:26 2022
    On Wed, 20 Jul 2022 06:53:17 GMT, Mike Mocha <mocha@mailexcite.com>
    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>

    The old wire was insulated with tar-soaked woven jute fiber, perhaps
    over gutta percha. The tar is melting and seeping out somewhat.

    Joe Gwinn

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  • From Mike Mocha@21:1/5 to All on Fri Jul 22 06:21:29 2022
    XPost: sci.electronics.misc, sci.electronics.repair

    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

    Thanks for all the responses. I guess that makes sense about it being tar
    over some kind of fiber wrap. Maybe it's time for us to upgrade to
    something more NFPA 130 compliant!!

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