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"Semiconductor" sheath on cable?

Discussion in 'Electronic Basics' started by Bob Masta, Aug 11, 2005.

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  1. Bob Masta

    Bob Masta Guest


    A friend is an electrician who works
    mainly on intallations at factories, etc.
    He has a beverage coaster made from a
    thin cross-section of a "primary" cable,
    the kind that brings power into the plant.
    It has a central conductor area of many
    strands of heavy-gage wire, then an
    insulating sheath of something rubbery
    that looks sorta like that red HV silicone
    rubber, then a very thin metallic layer
    which he called a "semiconductor shield"
    before the final insulating jacket.

    I tried to find out exactly what he meant
    by "semiconductor" in this context because
    I couldn't picture silicon or germanium, for
    example, being made into a flexible foil.
    (Well, maybe not *too* flexible, since the
    cable was several inches across!) He said
    he really didn't know about such things,
    but that the layer was supposed to reduce
    the magnetic fields from around the cable,
    which otherwise were a problem at the
    high voltages and currents involved. (Which
    he also didn't know the levels of.)

    Anyone familiar with this technology?


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  2. No, but I think he means "partially conducting" rather than
    semiconductor as in solid state devices.

    Decades ago, I was given a bit of that stuff, I think it
    was left over from a TV transmitter installation. It did indeed
    have some conductivity, but not all that much. I played around
    with it at the time, because I was interested in electronic music
    at the time and there were various controllers based on that sort of
    thing. But memory says I didn't find that there was a good relationship
    between length and resistance. It just seemed to have some conductivity,

    The thing I had was rubber, and it most definitely came from a power
    line cable. If I heard a reason for its purpose at the time, I've
    long forgotten.

  3. Rich Grise

    Rich Grise Guest

    From what Michael Black said, it's "partially-conductive" material,
    probably a lot like that foam that they used to ship chips in.

    I'm guessing that it would "suppress" the magnetic field around
    the big conductor by eddy currents/back EMF. And of course, since
    it's resistive, it has a Q of squat, so instead of a big magnetic
    field around the conductor, you have a hot cable.

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