Rusted lug on exterior electrical panel

Did and inspection today, Exterior electrical panel outside airtemp today was 79F open the dead front and saw the left lug rusted. 4/0 Alum SER wiring and appears to have no anti/oxidation paste. I know it is recommended and I think this is causing the corrosion on the lug.

Second rusted left lug 138F and non rusted right lug 94F Breakers were about 88 to 91F. Is this something I should call out for further evaluation, what causes this, really curious and wanting to make sure this is not a major issue. I’m trying to finish my inspection report.

I would not try to establish a cause and effect relationship between the lack of anti-oxidant on the feeder and corrosion of the steel lug. I would document both as defects individually (in TX we are required to report lack of anti-oxidant as a defect). The corrosion is an issue as it can result in a high resistance connection, which will produce… heat.

The elevated temperature is an issue that warrants correction. I wouldn’t try to go into further detail based on the equipment that you were working with (the actual temperature could be significantly higher), but you have identified a thermal exception that needs attention.

In my opinion the loads in the panel are unbalanced. Having all heavy loads like A/C, Freezers, Appliances, etc… on the same phase will cause an unbalance load. When all the current is on one line (or phase) then the neutral has to carry the full load, and will cause the one conductor to heat up and possibly overheat. But when both conductors evenly carry the current the current on the neutral basically cancel out. I hope that make sense and didn’t confuse ya more!

Please teach me how to tell that from a visible light picture of the line side terminal lugs? How does one place 240v appliances and A/C on just one phase to create an imbalance?

I would have had to see the panel as a whole, measure load on both phases, probably see a thermal image of the full length of the conductors too, before I would have been able to arrive at such a conclusion.

I try to keep defect reporting fact based and minimize the amount of conjecture.

What I could tell from the picture:

  1. There is no anti-oxidant on the aluminum feeders;
  2. There is significant corrosion on the terminal lug;
  3. The observed temperature compared to ambient constitutes a thermal exception

With more information I could: assign a NETA priority; compare the load on the left and right phases; identify if the cause was load or connection related. But I can’t get there from the info available.

Chuck, thank you very much. You are a genius when it comes to the electrical panel. I took this to the report and made it short and sweet to the point. Glad to learn something new. When I first saw it, since it was and exterior panel that it was cause from being outside. But this is making more sense without the oxidation.

Thanks Brother:D

Nice job Shawn

Thanks Mike:D

Any 240 volt circuit is automatically balanced. The neutral is sized of the calculated load so it will not overheat.

Single phase loads in a residential panel are too transient to even attempt to “balance”. It is a waste of time.

Well that is about as far away from the first thing that comes to mind.

What causes excelerated oxide (rust)?

The Andersen Cycle: Heat makes oxidation; Oxidation makes resistance; Resistance makes heat…

But which came first???

I think the rusted panel bolt (uppermost portion of picture) is leaking rain water, which then is falling down onto the service entrance conductor, and then following it down, directly onto the connection. Also, the main throw is beginning to rust, as is a few other non-energized panel bolts.

I know this because I am psyshic. I can prove it. In no less than two posts a surly old man will stop in, add nothing to the discussion, insult someone, and then take his ball and ho home.


I think it’s frigging hot.

Water entry, please enlighten us as to what you see here to substantiate this crap.

There is way to much ADD ADHD on this place…

Wow, my head is spinning.

In the last few months I learned what NETA is, also learned that someone with an IR camera could have quantatively made the call on if the load is unbalanced.
Good example of qualitative and quantitative inspecting.
Inspector visually saw an anomolie, called it out.
With further testing using heat signatures one could report findings.
Either way there is oxidation and no anti-oxident paste.

I may not be describing well but I find it interesting that experienced inspecting with some of the more robust tools can deliver a damn good report.

Nice work.

I think you misspelled psycho - I know because I was out there in the mud :wink:

I should have said this earlier - I though that I had: The OP made a good find and did everything that was necessary to appropriately identify it as a defect.

Here is what you get with an unbalanced thermographer

You are unbalanced, that thread was the best.