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Discussion Starter #1 (Edited)
Yesterday, I removed a 12-year old set of In-Wall Speakers to whiten the frame, which had yellowed because of sun exposure. More specifically this was a set of Polk LC65i. Upon removing the speakers, I noticed that the insulation behind the speaker wires was burned. Please see the attached photos. Please note that the photos are sideways because I cannot figure out how to post them in portrait mode.

The Polk speakers are connected to any Onkyo TX-SR605 receiver that is ONLY powered on when it's in use.

What would cause this and how can I correct it?

Thanks!
 

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Are you sure those are burn marks? Perhaps a reaction between the cable jacket and the insulation backing?
 
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Are you sure those are burn marks? Perhaps a reaction between the cable jacket and the insulation backing?
I agree. It doesn't look burned. It looks as though the backing paper has a black coating which the wire has caused to leak through to the wire side. More of a stain than a burn.
 

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I don't think that's a burn. That paper would likely ignite if it were hot enough to char.

But it also looks like the wire is not CL2 rated. Might be wrong, but usually in wall rated wire is thicker than that.

EDIT: Never mind. I see CL3 rating on the wire.
 

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Yesterday, I removed a 12-year old set of In-Wall Speakers to whiten the frame, which had yellowed because of sun exposure. More specifically this was a set of Polk LC65i. Upon removing the speakers, I noticed that the insulation behind the speaker wires was burned. Please see the attached photos. Please note that the photos are sideways because I cannot figure out how to post them in portrait mode.

The Polk speakers are connected to any Onkyo TX-SR605 receiver that is ONLY powered on when it's in use.

What would cause this and how can I correct it?

Thanks!
If it had burned, the damage would be far more extensive. The wire coating would be charred and paper would be burned through along with the rest of the house.
 

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Discussion Starter #6
I agree. It doesn't look burned. It looks as though the backing paper has a black coating which the wire has caused to leak through to the wire side. More of a stain than a burn.
Thanks for all of your responses.

I reinspected the black marks and I believe @kjfalls is right. There is some kind of a black substance on the back of the insulation paper that seems like it has bled through. If you touch the black marks they have a slightly oily feel.

Is it possible that radiated heat from the speaker wires triggered some kind of a chemical reaction? I have never seen anything like this before, but then again I don't know anything about home insulation. :)
 

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Is it possible that radiated heat from the speaker wires triggered some kind of a chemical reaction? I have never seen anything like this before, but then again I don't know anything about home insulation. :)
Not likely. The wires should be near room temperature so wouldn't radiate anything to cause that. More likely a chemical reaction between the wire coating and the paper.
 
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