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Thread: Derating

  1. #1
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    Derating

    I have (4)-20 amp double pole breakers feeding lights that doesn’t have a neutral. Can I use the 8 #12 current carrying conductors in a 3/4 conduit or do need to go to #10s to derate?

  2. #2
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    Yes derating is required because you have more than 3 CCC in a single raceway. Good news is that you can still use #12 AWG conductors.

    #12 THHN = 30 amps @90 degrees C
    30 amps*70% = 21 amps adjusted ampacity.

    Welcome to the forum.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    To follow Robs reasoning, depending on the insulation type of the conductors see article sections 110.14(C), 310.15(B)(3)(a), and 310.15(B)(16).

    Roger
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  4. #4
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    Yes, I did make some assumptions with the 90 degree C conductor. A 75 degree C conductor might also work if you can apply the next size up rule.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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