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Thread: Using ROMEX® to feed subpanel, do I have to derate from Table 310.15(B)(6)

  1. #1

    Default Using ROMEX® to feed subpanel, do I have to derate from Table 310.15(B)(6)

    I want to put a subpanel in the garage. According to Table 310.15(B)(6), I would need #4 Copper for a 100amp subpanel. Is this table for individual conductors in conduit or can you use ROMEX® to feed the subpanel at 100amp? The reason I ask is I read that when using ROMEX® you had to derate the THHN in ROMEX® to the 60*C rating.

    Thanks,
    Mike
    Last edited by Terry; 12-07-2011 at 10:08 AM.

  2. #2

    Default

    Further research has indicated that I do need to derate when using NM.

  3. #3
    Electrical Contractor/Instructor jwelectric's Avatar
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    Do just a bit more research and you will see that Table 310.16 must be used also

  4. #4
    Licensed Electrical Contractor Speedy Petey's Avatar
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    You are not "derating" anything. NM cable simply must use the 60 deg C column.

    IF you did need to derate the cable you would do so from the actual insulation temperature column which is 90 deg C.

  5. #5
    Electrician Chris75's Avatar
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    Quote Originally Posted by Mr_Magoo View Post
    I want to put a subpanel in the garage. According to Table 310.15(B)(6),

    Thanks,
    Mike

    As already mentioned, you cannot use table 310.15(B)(6).

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