Brown marks on Romex®

[Mlang2000]

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?

 

[Reach4]

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.

 

[Sponsor]

 

[Mlang2000]

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.

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.

 

[Reach4]

It was just my first thought. A bleach solution would not affect tar.

 

[wwhitney]

people said it could be just warm enough to pull the tar from the insulation

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

 

[Reach4]

I had missed that the two pictures were related. So my rust theory doesn't work.

 

[Aaroninnh]

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.

 

[WorthFlorida]

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.