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

Discussion in 'Electrical Forum discussion & Blog' started by Mr_Magoo, Sep 23, 2008.

  1. Mr_Magoo

    Mr_Magoo New Member

    Mar 8, 2008
    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.

    Last edited by a moderator: Dec 7, 2011
  2. Mr_Magoo

    Mr_Magoo New Member

    Mar 8, 2008
    Further research has indicated that I do need to derate when using NM.
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  4. jwelectric

    jwelectric Electrical Contractor/Instructor

    Jun 14, 2007
    North Carolina
    Do just a bit more research and you will see that Table 310.16 must be used also
  5. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Jun 16, 2007
    Licensed Electrical Contractor
    NY State, USA
    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.
  6. Chris75

    Chris75 Electrician

    Aug 12, 2007
    Litchfield, CT

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