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Melting point of silicone cable insulation?

Discussion in 'Electrical Engineering' started by Lars, May 10, 2005.

  1. Lars

    Lars Guest

    I am in the UK.

    What is the temperature of the melting point of insulation on mains
    flex which is made of silicone?

    Does anyone have a comparable figure for PVC insulation?
     
  2. You're premise is wrong. Silicone insulation doesn't melt- it chars.
    Operating temperature ratings are typically around 200-250°C, IIRC.
    Ratings typically run from around 80°C to a bit over 100°C. Burning
    moderate quantities PVC can be hazardous.


    Best regards,
    Spehro Pefhany
     
  3. ^^^^^
    As is the above apostrophe ;-)


    Best regards,
    Spehro Pefhany
     
  4. The immersion heater cable you can buy is, I believe, 180C max
    operating temperature, but it's rubber (and I don't think silicone).
    I'm not sure these have a 'melting' point, as the rubber is
    thermosetting insulation, which will probably jusy go hard, and
    eventually char or burn.
    There are different types of PVC. The Twin and earth normally
    used for wiring is derated to zero current at 70C ambiant, or
    designed to operate at 70C at max current (whichever way you
    want to look at it). IIRC, this allows for fault currents to
    raise the temperature another 90C to 160C (in the time it takes
    the protective device to trip), which is regarded as the max
    momentary conductor temperature allowed before the cable sustains
    instant permanent damage. So I presume it's above 160C but cable
    is not designed to operate that hot other than in occasional
    fault conditions.

    Temperature affects the life in years of wiring too. At 70C,
    you can expect PVC wiring to last around 23 years, whereas at
    40C the life is (calculated) at 1,498 years. See:
    http://www.iee.org/Publish/WireRegs/Commentary-UpdateApr04.pdf
     
  5. Hal Murray

    Hal Murray Guest

    What is the temperature of the melting point of insulation on mains
    Two stories from ages ago... (60s)

    My father was OEM sales manager for Pass and Seymour. They used to make
    things like big ceramic sockets for street lights. Some of his customers
    wanted high temperature pig tail wires on those sockets. For silicon rubber,
    the limit was not the insulation. The copper wire (fine strands) inside
    corroded too fast at temperatures which were fine for the insulation.

    I spent a summer/co-op at GE's Engineering Standards Lab. They
    used to test parts coming in from vendors. Standard procedure was
    to give a sample part and the spec to a technician. Technician would
    read the specs and do all the the tests. My boss told me the story of
    a spec that (essintially) called for silicon rubber on flexible
    waveguide. Spec said roughly: bake at x C for 1 hour. No problems
    sould be visble on the furface of the insulation. x was big.

    The technician turned on the oven, cut a couple of lengths of heavy
    wire off the spool, bent them into hooks and suspended the sample
    (2 ft long?) from the screw holes in the end bells to the rack in
    the oven. Then he set the timer for an hour and went to lunch.
    A short time later there was smoke all over the place. The solder
    holding the end bells on had melted. (I said x was big.)
    The silicon rubber had fallen on to the way-hot floor.
    Other than a bit of scorching where it had hit the floor, the
    insulation was fine.
     
  6. Lars

    Lars Guest


    Does anyone know how much temperature the mains leads with a woven
    cotton outer can withstand?

    Is a woven cotton outer better or worse than silicone insulation?
     
  7. The cable is silicone. Nowadays, the woven cotten is just retained
    to stop it snagging on the cloths you are ironing, so the cable
    easily slides over the cloths and the edge of the iorning board.
     
  8. Lars

    Lars Guest

    On Sat 14 May 2005 15:20:36, Andrew Gabriel wrote:
    I thought a side benefit of the cotton covering was that it did not
    kink so easily. Mind you, when it does kink then it really does
    kink.

    However I figured from a "side comment" which I read in an electrical
    catalogue that the cotton probably had good heat-resistent properties
    too. I just don't know how the heat-resistent property might be
    quanitified.
     
  9. If you go back to days of old rubber insulation, cotten was
    used on any appliance which got hot, such as toasters, heaters,
    etc to help protect the old rubber which would burn. I think
    it's only still used on irons nowadays as the solicone
    insulation doesn't require any additional heat protection,
    but has a rather high friction coefficient with fabrics.
     
  10. With me, it's normally some part inside the iron which fails
    before the cord. Actually, I have a couple of cords I cut off
    irons when the rust was being chucked out.
     
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