Black copper wire

I did an inspection yesterday and the copper wire in the outside panels ws dark black. At first glance I though the ground wires were insulated. On closer examination, there had all turned black. This was seen in both the service panel and the pool electrical panel. The copper in the inside panel was normal as was the copper on the air conditioner coils.

The home was built in 1997 so before most reports of Chinese drywall and if that were involved, I would have expected the copper inside the home to be affected.

Does anyone have an idea what might cause this and if there is a problem that I should report?

The first photo is the outside panel and the second is the inside panel.

Lightning? That is strange, at first looks like Chinese Drywall issue, but with the inside panel looking clean makes me believe there was an electrical problem with the box. Did you see ANY wiring issues such as melted sheathing or loose wiring? Has the house undergone a major refurb? Maybe it was a Chinese drywall house that has been retrofitted. We did a house built in 1990 with Chinese Drywall issues. Hurricane Charley almost destroyed the house, so it was rebuilt with Chinese Drywall, so the age is not always the tell tale sign. Did you check wiring at outlets, refrig coils, ac coils?

Sulfer, chemical compounds and high moisture environments are possibilities:

Thanks for the replies. When I opened the panel, I thought “OH crap”, Chinese drywall. The home was in good condition and had the original roof so I do not suspect any major renovations. Besides, as was mentioned in the other posts, if it were Chinese drywall, there would most likely be some indication inside.

I didn’t see any indication of overheating or loose wires. I typically check a few wires at random for tightness and all I checked were nice and tight. The only thing I saw was the color of the bare portions of the copper. It seemed to be most prevelant on the neutrals and grounds but there was some on the hot wires also. Inside the house, nice and clean.

BTW Larry, thanks for the link to the other posts. I am impressed with how some of you guys find these things so easily. For some reason when I search for things like this, I have to wade through a lot of unrelated posts and have a hard time finding ones that are relevant.

Was the panel in close proximity to the pool / chemical equipment?


The pool panel was around the corner from the pool and about 20 to 25 feet away. The main panel was about 30 feet down the side wall from the pool panel. I could possibly consider some affect from the pool on the pool panel but I think it would be a stretch to associate that with the main panel.

Just asking. We have chemical plants near here and with the prevailing winds out of the west, I find homes to the East and close by with 3 and 4 yr old air conditioners where the coil fins on the outside units just crumble from corrosion. Something around that area is causing the copper to turn black. If you don’t know the exact cause, best thing to do is report it, recommend an electrician investigate it for any compromise to the system and move on. What about the copper tubing on the HvAC outside?

Please don’t misunderstand me Doug, I am looking for answers and appreciate your response. I was just saying that I could not under the circumstances attribute the discoloration in the service panel to the pool. As to your question about the A/C copper, the copper there was dark, which is what I am accustomed to seeing, but not the same black as I saw in the electrical panel.

It is not unusual to find some minor discoloration on the copper in the exterior panels but this is the first time I have seen this. I don’t even see this on homes that are much older than this house was. I have also done inspections on homes within a few miles of this one but did not see the same thing.

I’m not sure there is a problem but I will report it.

Possiblities include Sulfer, Hydrogen Sulfide, and atmospheric oxygen. Are there any open sewers or other sources of sewer gas close to the panel? In areas of high humidity, it is more likely to be atmospheric oxygen; which is not too great a concern. I would (as an electrician, not as an inspector) coat the conductors with an oxide inhibitor and make sure all the connections are properly torqued. I’d also put a sticker in the box (like an oil change reminder) with a recommendation to service the panel at a future date. Here in Michigan, I would say five years but in Florida, it might be better to make it less than five years.

Possible loose neutral.

I appreciate all the responses. I recommended that they have an electrician inspect the panel and ensure that it would not cause a problem. The sewer is located at the front of the home so I doubt that that is the issue. As to loose connections, I checked a few and every one I checked was good and tight.

Maybe an electrician will find something I didn’t.

Did you check the ground wires at the outlet connections through-out the house? Even though the home was built in 1997 they may have done some repairs with imported drywall. I read it only take 3 boards to cause problem. How did the copper AC high and low pressure lines at the air handler unit connection look? Just a thought.

Ok maybe I am missing something however I am not seeing the other replies here that relate to this topic!!! I have been doing some research on this and of course I am going to list in my report the possibilities and to have further evaluation from electrician. I would still like to know for future reference.

Do the chinese drywall course . Then you will know.

did you do a Google search and did you do a NACHI search ,
What did you find to make you bring up a 5 year old string .
I am sure there is a lot newer information then this

What happened to the Chinese drywall course?