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A local ISP is installing fiber optic cable for gigabit internet in my neighborhood. Their construction crews have buried runs of empty conduit which I presume is meant to be filled with fiber or Ethernet cables. They have also been running another, much thinner cable alongside the conduit. I was curious what this was so I picked up a scrap of it they left behind.

Orange coaxial cable with outer insulation stripped off. There is only fabric sheathing and no outer conductor.

It looks like a coaxial cable, but there is no outer conductor (I checked the insulation after I stripped it and there was definitely nothing there. There is outer insulation surrounding what appears to be a thick layer of fabric sheathing. Inside the fabric is a single insulated 24-gauge wire.

Cable interior with inner conductor exposed and stripped. The wire is silver-colored on the outside and copper on the inside.

The wire itself appears to be copper, with a silver-colored foil or plating on the outside. I have only seen them running one of these cables at a time, so there is no second cable for a return path. The thinness of the wire and insulation suggests that it's meant for data transmission, but I can't imagine how this would be useful without a shield or second wire. There are no markings on the outside of the cable indicating what kind of cable it might be. Can anyone tell me what this cable might be used for?

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2 Answers 2

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Technically, if it doesn't have a shield, it's not a coax cable, or wire.

That aside, it may be a tracer wire (not sure if this is the proper name or not).

Utilities bury these alongside non-metallic cables, gas or water pipes, etc, so that they can be located with a metal or RF detector after they have been buried.

See this link for more information- https://www.performancewire.com/tracer-wire/

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    \$\begingroup\$ I used to work pipelines and I’ve seen tracer wires that look like that. I concur \$\endgroup\$
    – Bryan
    Commented Jan 18, 2023 at 5:02
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SteveSh's answer appears correct, but there's an additional piece of evidence he didn't mention that also indicates that this is a tracer wire.

The American Public Works Association (APWA) defines standard colours for the outer insulation of tracer wire, which are described here. The insulation on your wire is orange, which is used for fibre-optic and telecommunications cable, and so matches the installation you described.

The full colour list from the reference is:

Yellow: natural gas lines
Green: sewer lines
Blue: potable water Purple: relcaimed water, irrigation or slurry lines
Orange: fibre-optic or telecommunications
Black: pet containment wire or other uses.

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