Rubber beading on high voltage cable insulation...

[Mike Mocha]

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

 

[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...

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[Peter W.]

> Bits of melted tar maybe...

That was (is) a potting material commonly used \'back in the day\' over taped connectors. Now, my electrical experience \'in the field\' goes back to 1972, and the electrician I worked for had a metal pot with a screw-lid & brush cap that he used when we ran cables to stubs in a conduit where there might be water involved. The cables would be bugged to the stubs, taped, then tarred, then taped again.

Peter Wieck
Melrose Park, PA

 

[Dan Purgert]

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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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[ChrisND@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

 

[Mike Mocha]

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!!