Discolored insulation on ungrounded conductors

1967 home, Bryant panel, every ungrounded conductor has discoloration that at first looks like overheating, but there are no other signs of melting, or scorching. I am thinking it is just the type of coating they used on these wires? Anyone else seen this? Notice the white insulation is still just as white, but every black wire looks the same, so I wasn’t going to call it out unless someone here has an explanation…

Did the home have sulfur water?
Was pool chemicals close by?

Neither one

Is it near salt water?

Not sure about the discoloration. Could be the jacket material reacting to the salt air. Was the panel inner cover already missing or did you remove it to inspect?

No, it’s a set of row homes, there is a pool across the street for the community, but it is in Clearwater, but still a few miles from ocean

I removed it. Maybe you and Roy are onto it, it’s a few miles from ocean

I’ve seen this happen when pressure washing with bleach.

Actually I just checked on the map and it was only a half mile from water… didn’t realize that when I was there! Haha

I wouldn’t worry about it.

Yeah, its in hurricane territory. Wind driven water can do some crazy things.

Seems like a poor manufacturing process on the coloring of the black conductors but from the photo is doesn’t appear that the insulation is compromised. I agree with Roy not a concern.

Here’s how I wrote up a similar situation I came across.
“ The copper conductors and grounds were observed to become blackened inside the panel but not at the termination sites such as the receptacles. The blackened effect is usually caused by a sulfur compound in the air. There are various sources which could have caused the effect which may be long gone such as fumes from charging a lead-acid battery, fumes from a leaking container of fruit tree spray (contains sulfur), sewer gases, stagnated water contained in the underground electrical conduit etc. Recommend having a Licensed Electrical Contractor strip the effected wires back to clean copper and re-make the connections.”

Just my two cents but I don’t think that is the problem. The ends of the conductors and the bare EGC’s appear to be normal. The white and red conductors and other black conductors also appear to be normal so the issue is with the black conductor insulation in that one type of NM cable. Wouldn’t a problem like the one that you’ve mentioned affect all of the conductors?

Yeah, that’s exactly what I was thinking, just wanted to make sure. I didn’t even mention it in my report.
Thanks guys!

Here are some pics.

That’s what I would do. Yep!

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Chinese drywall surrounding the panel?