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Thread: 75°C Ampacity of 200°C Wire

  1. #1
    Join Date
    Mar 2005
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    Hampton, VA
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    75°C Ampacity of 200°C Wire

    I have an application where a user wants to use a high power, water cooled motor for research applications. The motor is feed by high temperature motor wiring having an insulation rating of 200°C to handle the large current and reduce conductor size due to space limitations. This will have to be connected to VFD equipment that will have 75°C terminals.

    My thought is to connect the motor leads to 200°C rated terminals. From the terminals feed (unknown qty) parallel sets of the same size 200°C wire (or larger size (?) 200°C wire) to the VFD such that the ampacity of the 200°C wire connected to the VFD is not greater than the 75°C ampacity of the wire, and thus can be connected to 75°C terminals of the VFD.

    Several questions:
    1. Assuming a 30°C ambient, how do you determine the 75°C ampacity of the 200°C wire?

    2. Is there a better way to connect the high temperature motor conductors to 75°C rated terminals?

  2. #2
    Join Date
    Jul 2006
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    Why not just use the ampacities in the NEC for 75degC based on the AWG size of your 200degC conductor between your 200degC termial block and VFD.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  3. #3
    Join Date
    Mar 2005
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    Good point. This is a high flexibility wire, but could use the ampacity for the same size and stranding 75°C wire as the 200°C wire. Thanks.

  4. #4
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    Derate the 75c wire based on 200c.

  5. #5
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    Dec 2007
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    Is your 200C conductor copper or is it nickel or some other metal/alloy?

    T310.15(16) will be fine if copper or aluminum. 75C column is what you want to use for 75C terminations even if you have more then 75C insulation.

    Add: there is T310.15(18) that has higher temp and nickel conductors in it - but keep in mind the ampacities in that table are for more then 75C so can't apply to a 75C terminal.
    I live for today, I'm just a day behind.

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