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Rubber beading on high voltage cable insulation

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.

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Reply to
Mike Mocha
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Bits of melted tar maybe...

Reply to
TTman

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

Reply to
ChrisND

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

Reply to
Joe Gwinn

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!!

Reply to
Mike Mocha

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