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Insulating Material Property Question

Discussion in 'Electronic Design' started by Rileyesi, Apr 27, 2004.

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  1. Rileyesi

    Rileyesi Guest

    First, thanks to all who replied to my request for sources for insulating
    washers.

    One vendor quoted me PVC washers as opposed to the linen based phenolic washers
    that we have used in the past, but they could not tell me the difference it
    would make in the insulating properties. I hope someone can shed some light on
    this for me.

    The application is in an office environment, so no temperature or humidity
    extremes. The signal that will be insulated is a variable 0-15 VDC at 100 mA
    max. This will be used on the back of an analog panel meter and the function
    of the washers is to isolate the signal from the metal meter case.

    I think the PVC will do just fine, but would like any thoughts the group may
    have.

    Thanks.
     
  2. Tim Wescott

    Tim Wescott Guest

    Electrically it probably won't make a difference, but there may be
    mechanical issues. I know that nylon hardware has a reputation of
    creeping under temperature and vibration, but even there a washer was
    considered OK.
     
  3. John Larkin

    John Larkin Guest

    PVC is not generally used as an insulator under pressure. It's soft,
    melts easily, makes toxics when it burns, and may cold-flow. The
    cheapest insulator is probably "fish paper", a phenolic or something
    laminated fabric that punches well. You can buy sheets of it at most
    auto-parts stores to see what it's like.

    Have you looked for a standard part, Keystone or somebody?

    John
     
  4. Active8

    Active8 Guest

    I think it's HCl
     
  5. R.Legg

    R.Legg Guest

    Normally you'd want something with a recognized temperature or
    flamability index. PVC is for low temperatures.

    Normal plastics query at UL seems to be unavailable through the normal
    web link;
    http://data.ul.com/ULiQ_Link/index.asp

    RL
     
  6. Terry Given

    Terry Given Guest

    humidity

    are you sure? Inside a PC chassis in an office can be pretty hot for
    example, especially when the chassis is in a cupboard - 70 degrees!
    (cupboard to prevent idiots from physically switching server off.
    ventilation added later)

    well put. Not only does it outgas toxic things, but corrosive ones too - I
    used to work for an AC drive manufacturer that made large drives (400kW+)
    with many crimped connections, and they found that crimp reliability was
    greatly improved by changing away from PVC insulation - warming the
    insulation to 60-70 degrees C softens it and increases outgassing of
    chlorine compounds (dont know exact chemistry) which attack the exposed
    copper in the crimp joint, increasing resistance and hence
    temperature.....changed cable to RADOX (x-linked polymer sheathing) which is
    rated at 125C and joint reliability increased significantly (calibrating
    crimpers daily, too)

    (Ultimately this was all replaced with large aluminium plates and a 1mm
    nomex spacer, greatly reducing ESR and ESL, and eliminating almost all
    crimped connections)
     
  7. Terry Given

    Terry Given Guest

    probably. It certainly eats copper!
     
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