Observation and help with 4GA wire to sub panel issue

[Kingsrule]

I decided to clean the contacts on the 4GA from the main panel to the sub panel. The main is in the garage and the sub is in the basement. 10years old, never been touched. Basement is dry, 58 degrees, 50% humidity.
All 4 ends in the main were perfect, bright copper. ProGold all 4 and move to the basement sub panel. To my surprise, the 3 R-W-B legs were corroded! The G was perfect as were all the rest of the ends in the sub. I cut back an inch or so of insulation and the wire was still visually corroded.
Can the experts here please suggest what is going on??

Here are 2 pictures, one showing the R leg with insulation cut back and the other showing the perfect G wire from the 4GA cable

 

[Kingsrule]

Roger...read my post
I know its oxidation. The point being it doesn't occur on the ground wire in the sub panel (just the 3 primaries) and not on any of the legs in the main panel and is still there when I peel back more insulation....

 

[RogerD]

Do you have a sump system in your basement? Looks like that is the only copper that has oxidized. have you talked to a electrician yet? It's hard to tell from the photo...any pitting?

https://www.nachi.org/forum/f19/black-film-copper-wiring-main-panel-75479/

https://www.nachi.org/forum/f19/oxidation-copper-wiring-97312/

 

[Kingsrule]

Roger

Thank you for trying but your attachments are irrelevant to my issue and questions. And yes it is the only oxidation as I stated in my OP. U keep trying to tell us what I already have stated.

To be clear, no other copper anywhere in the house has any oxidation other than the sub panel end of the 4GA cable, still showing even when I cut back the insulation and inch or so.....something I hope the electric guys on the forum can comment and advise on. Also in talking to the electrician who wired the entire house, he has no explanation at the moment that he is willing to offer.

My

 

[RogerD]

Roger

Thank you for trying but your attachments are irrelevant to my issue and questions. And yes it is the only oxidation as I stated in my OP. U keep trying to tell us what I already have stated.

To be clear, no other copper anywhere in the house has any oxidation other than the sub panel end of the 4GA cable, still showing even when I cut back the insulation and inch or so.....something I hope the electric guys on the forum can comment and advise on. Also in talking to the electrician who wired the entire house, he has no explanation at the moment that he is willing to offer.

My

One of those mysteries...I hope you can find out,good luck.

 

[Kingsrule]

Thank you Roger

Hopefully someone will be able to explain this.....

 

[DaveC]

That's pretty normal for 10 yr old copper wire. The corrosion will proceed up the wire as the thick stranding provides a good bit of airspace. In cars, I've seen entire lengths of thick starter wire completely corroded. However, notice the area under the set-screw is still not corroded, this is good. Usually copper wire like this is sealed with a corrosion-inhibiting substance when the panel is installed, looks like it was never used in this panel.

 

[Kingsrule]

But why on one end and not the other? Neither end had any corrosion-inhibiting substance on them with I took apart the connections. And no other wires in the sub panel exhibit corrosion?

 

[CGabriel]

Roger

Thank you for trying but your attachments are irrelevant to my issue and questions. And yes it is the only oxidation as I stated in my OP. U keep trying to tell us what I already have stated.

To be clear, no other copper anywhere in the house has any oxidation other than the sub panel end of the 4GA cable, still showing even when I cut back the insulation and inch or so.....something I hope the electric guys on the forum can comment and advise on. Also in talking to the electrician who wired the entire house, he has no explanation at the moment that he is willing to offer.

My

The current carrying conductors heat up when power is drawn and cool when the power is turned off. This cycle of heating and cooling cause a chemical reaction with pollutants (and moisture) in the air and the copper. Additionally, the energized conductors exert an electric charge that in the presence of pollutants act very similar to the electroplating process. The ground wires are not affected because they have virtually no electric charge and do not carry current and don't heat up.

This is fairly common with wires that carry high currents.

 

[DaveC]

But why on one end and not the other? Neither end had any corrosion-inhibiting substance on them with I took apart the connections. And no other wires in the sub panel exhibit corrosion?

Why is a tough one, the only thing I can come up with is it's related to either it's connections, how much current it's carrying, or both. I've seen this in car electrical systems, a failed fuel pump that's 20 ft of wire away (Chevy Suburban) from the battery has battery acid corrosion all over the connection right at the fuel pump but it's totally clean at the fuse panel.

I'd just clean it up, if the wire is extremely corroded it might be best to replace it, that doesn't look horrible but corroded wires can heat up, which could cause a fire, etc... so it might be safest to replace the wire if you strip off a bit more wire and it continues. I think the issue could be mitigated by use of dielectric grease that would seal both the set-screw connection and the wire/insulation interface area.

 

[DaveC]

The current carrying conductors heat up when power is drawn and cool when the power is turned off. This cycle of heating and cooling cause a chemical reaction with pollutants (and moisture) in the air and the copper. Additionally, the energized conductors exert an electric charge that in the presence of pollutants act very similar to the electroplating process. The ground wires are not affected because they have virtually no electric charge and do not carry current and don't heat up.

This is fairly common with wires that carry high currents.

Thanks for the explanation, that makes sense!

 

[Kingsrule]

The current carrying conductors heat up when power is drawn and cool when the power is turned off. This cycle of heating and cooling cause a chemical reaction with pollutants (and moisture) in the air and the copper. Additionally, the energized conductors exert an electric charge that in the presence of pollutants act very similar to the electroplating process. The ground wires are not affected because they have virtually no electric charge and do not carry current and don't heat up.

This is fairly common with wires that carry high currents.

Thank you Caelin This is what we came up with this afternoon. It has to be heat causing this. The thought is also to replace the 100amp breaker in the main panel to the sub panel as there has been some moisture observed on the breaker during extreme cold temps (even though the wire ends are perfect on this side)
So, should I be concerned regarding any sonic implications here? I cleaned and treated with ProGold the and things definitely sound better....

 

[CGabriel]

Thank you Caelin This is what we came up with this afternoon. It has to be heat causing this. The thought is also to replace the 100amp breaker in the main panel to the sub panel as there has been some moisture observed on the breaker during extreme cold temps (even though the wire ends are perfect on this side)
So, should I be concerned regarding any sonic implications here? I cleaned and treated with ProGold the and things definitely sound better....

After cleaning the wiring and re-terminating - get some of the car battery terminal spray protectant. I can't remember the name off hand but it is hard and almost a clear red color when dry. It will put up a protective barrier on the wiring and terminals and it was designed to be a hot environment.

 

[Kingsrule]

After all was cleaned at the sub panel, things actually seem better. Clearer and a more dynamic.
After hearing this improvement I had a thought that things could get even better.
So I replaced the 100amp, 10 year old breaker feeding the sub panel. Best $60 I have ever spent. I'm hearing little details and spaces like never before.

I think someone commented here that breakers should be replaced periodically.....a bigtime recommendation!

 

[DaveC]

After all was cleaned at the sub panel, things actually seem better. Clearer and a more dynamic.
After hearing this improvement I had a thought that things could get even better.
So I replaced the 100amp, 10 year old breaker feeding the sub panel. Best $60 I have ever spent. I'm hearing little details and spaces like never before.

I think someone commented here that breakers should be replaced periodically.....a bigtime recommendation!

Good observation, my house is getting older and the breakers are at least 10 years old. I'll grab a new main and branch breaker and see what happens. I also have a couple of filters from Folsom to try out, it's been waaaaay to long... It is amazing how much of a difference AC power makes!