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Conductor ampacity confusion

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  • Dave C
    IÆm trying to find the derating correction values for using copper conductors in high (200 deg C) temperature environments. The conductors are uninsulated so
    Message 1 of 10 , Jun 16, 2014
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      I’m trying to find the derating correction values for using copper conductors in high (200 deg C) temperature environments.

      The conductors are uninsulated so I’m just trying to see what size wire I need.

      The charts I find re. de-rating are using fixed ambient temperature (ie, 30 deg C) and derate for the different rated *insulations*.

      Can anybody point me to a web page that derates for actual ambient temperatures?

      Comments not directly related to answering my question are welcome, but please wait — I want to get the derating question out of the way first.

      Thanks,
      Dave
    • harry jenkins
      Since the conductors have a fixed resistance a lot of your determination may be how much voltage drop can I work with? ... On Mon, 6/16/14, Dave C
      Message 2 of 10 , Jun 16, 2014
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        Since the conductors have a fixed resistance a lot of your determination may
        be 'how much voltage drop can I work with?'
        --------------------------------------------
        On Mon, 6/16/14, Dave C davec2468@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:

        Subject: [Electronics_101] Conductor ampacity confusion
        To: "Electronics101" <Electronics_101@yahoogroups.com>
        Date: Monday, June 16, 2014, 1:37 PM

        I’m trying to find the derating
        correction values for using copper conductors in high (200
        deg C) temperature environments.

        The conductors are uninsulated so I’m just trying to see
        what size wire I need.

        The charts I find re. de-rating are using fixed ambient
        temperature (ie, 30 deg C) and derate for the different
        rated *insulations*.

        Can anybody point me to a web page that derates for actual
        ambient temperatures?

        Comments not directly related to answering my question are
        welcome, but please wait — I want to get the derating
        question out of the way first.

        Thanks,
        Dave

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      • Dave C
        Thanks Harry, I think V drop not critical. The is in a 2KW resistive heater, multiple resistors in parallel, short distance; total cable run = 24 inches (60
        Message 3 of 10 , Jun 16, 2014
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          Thanks Harry,
          I think V drop not critical. The is in a 2KW resistive heater, multiple resistors in parallel, short distance; total cable run = 24 inches (60 cm). I’m just trying to find out what the smallest conductor I can use at 10A and 200 deg C.

          Dave

          -=-=-=-

          On 16 Jun 2014, at 1:48 PM, harry jenkins v8comet2003@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:

          > Since the conductors have a fixed resistance a lot of your determination may
          > be 'how much voltage drop can I work with?’
          > Harry J.

          -=-=-=-

          > I’m trying to find the derating
          > correction values for using copper conductors in high (200
          > deg C) temperature environments.
          >
          > The conductors are uninsulated so I’m just trying to see
          > what size wire I need.
          >
          > The charts I find re. de-rating are using fixed ambient
          > temperature (ie, 30 deg C) and derate for the different
          > rated *insulations*.
          >
          > Can anybody point me to a web page that derates for actual
          > ambient temperatures?
          >
          > Comments not directly related to answering my question are
          > welcome, but please wait — I want to get the derating
          > question out of the way first.
          >
          > Thanks,
          > Dave
        • alienrelics
          The derating is usually made to match the insulation s heat rating. This sounds like an unusual requirement, not something probably taken into account in the
          Message 4 of 10 , Jun 16, 2014
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            The derating is usually made to match the insulation's heat rating.

            This sounds like an unusual requirement, not something probably taken into account in the usual commercial wiring regulations. You will have different things to take into account, different limiting factors like wire sag and annealing of the wire.

            As for derating for ambient temperature, that seems straightforward as a function of the difference between the maximum allowed temperature of the wire and the ambient temperature, applied as a percentage of maximum current.

            Steve Greenfield AE7HD
          • Dave C
            Thanks Steve, May I ask you for an example? Dave -=-=-=-
            Message 5 of 10 , Jun 16, 2014
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              Thanks Steve,
              May I ask you for an example?

              Dave

              -=-=-=-

              On 16 Jun 2014, at 2:13 PM, alienrelics@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:

              As for derating for ambient temperature, that seems straightforward as a function of the difference between the maximum allowed temperature of the wire and the ambient temperature, applied as a percentage of maximum current.




            • harry jenkins
              I seem to recall some high temp applications use other than copper wire, definitely not aluminum though, they used to use that in house wiring and it was a
              Message 6 of 10 , Jun 16, 2014
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                I seem to recall some high temp applications use other than copper wire, definitely
                not aluminum though, they used to use that in house wiring and it was a disaster.
                The connections failed over time from the heat.

                What do they use in a household clothes dryer? Probably doesn't get as hot but it
                has to be safe to pass UL.

                --------------------------------------------
                On Mon, 6/16/14, Dave C davec2468@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:

                Subject: Re: [Electronics_101] Conductor ampacity confusion
                To: "Electronics101" <Electronics_101@yahoogroups.com>
                Date: Monday, June 16, 2014, 2:06 PM

                Thanks Harry,
                I think V drop not critical. The is in a 2KW
                resistive heater, multiple resistors in parallel, short
                distance; total cable run = 24 inches (60 cm). I’m just
                trying to find out what the smallest conductor I can use at
                10A and 200 deg C.

                Dave

                -=-=-=-

                On 16 Jun 2014, at 1:48 PM, harry jenkins v8comet2003@...
                [Electronics_101] <Electronics_101@yahoogroups.com>
                wrote:

                > Since the
                conductors have a fixed resistance a lot of your
                determination may
                > be 'how much
                voltage drop can I work with?’ 
                >
                Harry J.

                -=-=-=-

                > I’m trying to find the
                derating
                > correction values for using
                copper conductors in high (200
                > deg C)
                temperature environments.
                >
                > The conductors are uninsulated so I’m
                just trying to see
                > what size wire I
                need.
                >
                > The charts
                I find re. de-rating are using fixed ambient
                > temperature (ie, 30 deg C) and derate for
                the different
                > rated *insulations*.
                >
                > Can anybody point me
                to a web page that derates for actual
                >
                ambient temperatures?
                >
                > Comments not directly related to answering
                my question are
                > welcome, but please
                wait — I want to get the derating
                >
                question out of the way first.
                >
                > Thanks,
                > Dave





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              • rtstofer
                Google is your friend, I found this by searching for fiberglass covered wire: http://www.awcwire.com/faq-high-temp.aspx
                Message 7 of 10 , Jun 16, 2014
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                  Google is your friend, I found this by searching for fiberglass covered wire:

                  http://www.awcwire.com/faq-high-temp.aspx

                   

                  Then I looked up the specific wire:

                  http://wire.thermalwire.com/viewitems/cable-600v-single-conductor-538-176-c-to-125-176-c/6-f-tggt-apparatus-and-power-cable-600v-heavy-duty

                   

                  For derating I found:

                  http://www.tempco.com/accessories/16-10.pdf

                   

                  As you can see, TGGT can survive in the environment but it can't carry much current.

                   

                  So, redo the search for type MG (450 deg C):

                  High Temperature  Lead Wire

                   

                  Then you'll need #16 AWG Type MG - Mica/Glass.  This is, I believe, what everybody uses for high temp environments.  Grainger's carries it but it is pricey!

                   

                  High Temperature Wire - Wire and Cable - Electrical - Grainger Industrial Supply

                   

                   


                   

                   

                  Richard

                   

                   

                • Stefan Trethan
                  Dave, what you need to know the thermal conductivity wire- ambient (in kelvin/watt) for thin bare wire. I do not know a source for this and would measure it
                  Message 8 of 10 , Jun 16, 2014
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                    Dave, what you need to know the thermal conductivity wire->ambient (in
                    kelvin/watt) for thin bare wire.
                    I do not know a source for this and would measure it myself.

                    However, the classical wire rating tables already have this
                    information used to write them.
                    They already assume a certain amount of heating (from ambient to the
                    maximum insulator temperature).
                    They also assume a certain conductivity. It won't be spot on because
                    of the insulation, but very close.

                    So instead of heating insulated wire from say 30°C to say 70°C you
                    will be heating bare wire from 200°C to 250°C.

                    It won't be exact, but there are huge tolerances and margins anyway
                    (just think differences in installation conditions), so it will be
                    fine.

                    ST


                    On Mon, Jun 16, 2014 at 10:37 PM, Dave C davec2468@...
                    [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
                    > I’m trying to find the derating correction values for using copper conductors in high (200 deg C) temperature environments.
                    >
                    > The conductors are uninsulated so I’m just trying to see what size wire I need.
                    >
                    > The charts I find re. de-rating are using fixed ambient temperature (ie, 30 deg C) and derate for the different rated *insulations*.
                    >
                    > Can anybody point me to a web page that derates for actual ambient temperatures?
                    >
                    > Comments not directly related to answering my question are welcome, but please wait — I want to get the derating question out of the way first.
                    >
                    > Thanks,
                    > Dave
                    >
                    > ------------------------------------
                    >
                    > ------------------------------------
                    >
                    > Please trim excess when replying
                    > ------------------------------------
                    >
                    > Yahoo Groups Links
                    >
                    >
                    >
                  • Dave C
                    Thank you Stefan. Very informative as usual. Dave -=-=-=-
                    Message 9 of 10 , Jun 17, 2014
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                      Thank you Stefan. Very informative as usual.

                      Dave

                      -=-=-=-

                      On 16 Jun 2014, at 10:54 PM, Stefan Trethan stefan_trethan@... [Electronics_101] <Electronics_101@yahoogroups.com> wrote:

                      > Dave, what you need to know the thermal conductivity wire->ambient (in
                      > kelvin/watt) for thin bare wire.
                      > I do not know a source for this and would measure it myself.
                      >
                      > However, the classical wire rating tables already have this
                      > information used to write them.
                      > They already assume a certain amount of heating (from ambient to the
                      > maximum insulator temperature).
                      > They also assume a certain conductivity. It won't be spot on because
                      > of the insulation, but very close.
                      >
                      > So instead of heating insulated wire from say 30°C to say 70°C you
                      > will be heating bare wire from 200°C to 250°C.
                      >
                      > It won't be exact, but there are huge tolerances and margins anyway
                      > (just think differences in installation conditions), so it will be
                      > fine.
                      >
                      > ST
                      >
                      >
                      > On Mon, Jun 16, 2014 at 10:37 PM, Dave C davec2468@...
                      > [Electronics_101] <Electronics_101@yahoogroups.com> wrote:
                      >> I’m trying to find the derating correction values for using copper conductors in high (200 deg C) temperature environments.
                      >>
                      >> The conductors are uninsulated so I’m just trying to see what size wire I need.
                      >>
                      >> The charts I find re. de-rating are using fixed ambient temperature (ie, 30 deg C) and derate for the different rated *insulations*.
                      >>
                      >> Can anybody point me to a web page that derates for actual ambient temperatures?
                      >>
                      >> Comments not directly related to answering my question are welcome, but please wait — I want to get the derating question out of the way first.
                      >>
                      >> Thanks,
                      >> Dave
                      >>
                      >> ------------------------------------
                      >>
                      >> ------------------------------------
                      >>
                      >> Please trim excess when replying
                      >> ------------------------------------
                      >>
                      >> Yahoo Groups Links
                      >>
                      >>
                      >>
                      >
                      >
                      > ------------------------------------
                      > Posted by: Stefan Trethan <stefan_trethan@...>
                      > ------------------------------------
                      >
                      > Please trim excess when replying
                      > ------------------------------------
                      >
                      > Yahoo Groups Links
                      >
                      >
                      >
                    • alienrelics
                      Part of the problem with aluminum wire was electricians and homeowners not following directions. Outlets and wire nuts must be made specifically for aluminum
                      Message 10 of 10 , Jun 17, 2014
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                        Part of the problem with aluminum wire was electricians and homeowners not following directions. Outlets and wire nuts must be made specifically for aluminum wire, due to the much greater thermal expansion.

                        That's my understanding of it.

                        Steve Greenfield AE7HD
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