Brown marks on Romex®

Discussion in 'Electrical Forum discussion & Blog' started by Mlang2000, Jan 24, 2021.

  1. Mlang2000

    Mlang2000 New Member

    Joined:
    Apr 10, 2019
    Location:
    Midwest
    I saw brown marks on some Romex® in my basement. It was also on some spots where it touched insulation. I nearly freaked out until I Googled and saw similar stuff like this or this and people said it could be just warm enough to pull the tar from the insulation or could be sap from running through studs or even condensation.

    It was easy to access so I replaced it and spliced it open to confirm it was on the outside of the jacket but not the inside.

    Have any of you seen stuff like this?

    IMG_3983.jpg
    IMG_3985.jpg
     
    Last edited: Jan 24, 2021
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    First pix looks like it came in contact with some steel which rusted.

    My first thought on the second was some kind of mold, black in color, but I hesitate to say those words.
     
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  4. Mlang2000

    Mlang2000 New Member

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    Apr 10, 2019
    Location:
    Midwest
    See the two links in my first post with similar pics from others. It's apparently not uncommon. The color matches the adhesive tar on the backside of the insulation.
     
  5. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
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    It was just my first thought. A bleach solution would not affect tar.
     
  6. wwhitney

    wwhitney Well-Known Member

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    Mar 17, 2019
    Location:
    Berkeley, CA
    Just an idea without any evidence, but it could also be that plasticizers from the Romex outer jacket can interact with the tar in the insulation vapor barrier and cause it to migrate through the paper.

    Cheers, Wayne
     
  7. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
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    I had missed that the two pictures were related. So my rust theory doesn't work.
     
  8. aaroninnh

    aaroninnh Member

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    Apr 14, 2014
    Location:
    NH
    Could be getting a little warm and causing the tar to bleed through. There is a reason the NEC makes you derate multiple NM-B cables when in contact with insulation.

    I wouldn't worry about it.
     
  9. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    The facing on kraft-faced insulation is made of kraft paper with an asphalt coating that makes the paper impermeable to water vapor. The paper creates a vapor barrier that helps keep the water vapor in the warm, moist, heated indoor air from migrating outward into the wall or other structure.
     
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