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Corrosion on main breaker


Mark P
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It looks like the entrance cable is aluminum and the corrosion looks like the battery cables in my truck. I'm don't know the cause, but would sure recommend a sparky clean it up and (if aluminum) use some anti-oxidant paste.

Note: I had to put a new battery in the truck...maybe I should look under the hood once in a while.

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Here is another pic showing the label, if you zoom in you can read it and it shows "CU/AL". I stated the wire was not visable due to the corrision, and of course to have it cleaned and evaluated by a qualified electrician.

What exactly does the "CU/AL" stand for. I thought aluminum.

On a side note the realtor kept repeating that it had already passed city inspection.

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Originally posted by AHIS

Here is another pic showing the label, if you zoom in you can read it and it shows "CU/AL". I stated the wire was not visable due to the corrision, and of course to have it cleaned and evaluated by a qualified electrician.

What exactly does the "CU/AL" stand for. I thought aluminum.

On a side note the realtor kept repeating that it had already passed city inspection.

Download Attachment: icon_photo.gif corrision 2.jpg

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Passed city inspection means nothing if this item was missed and obviously it was. The Realtor has a totally different objective than the inspector. I pay no attention to remarks from realtors except to say OK I know what you mean.

Paul B.

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"I was wondering if anyone has a theory on what would cause this type of corrosion."

I always suspect water is entering the service cable. Most of the time I find that to be the cause.

  • No drip loop at connection to OH service.
  • Water in conduit if UG service (capillary action).
  • SEC connection to top of meter box not sealed.
  • No drip loop at SEC connection to side of meter box.
  • Damaged SEC covering.

"...the realtor kept repeating that it had already passed city inspection."

Around these parts, the few municipalities that do a re-sale inspection do not remove the cover, much less note much of anything important.

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The panel was in the attached garage, (along with electric furnace, and water heater) the drip loop to the service mast on the roof was okay. There was no other sign of damage, corrision, or rust anywhere else. The customer was mighty pretty and single, so maybe I'll call in a month or so to see what the electrician had to say.

Thanks all for the input.

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Originally posted by AHIS

Here is another pic showing the label, if you zoom in you can read it and it shows "CU/AL". I stated the wire was not visable due to the corrision, and of course to have it cleaned and evaluated by a qualified electrician.

To me, the corrosion looks like it was caused by some kind of environmental contaminant such as water, water vapor, or any number of corrosive gases. Paul MacLean's battery terminals corrode because of the hydrogen sulfide gas that's vented out the battery during its recharge cycle. There's probably no easy way for you to tell what's caused this. It doesn't really matter. The electrician should take apart the connections and clean the wire. If it's damaged, he should cut away the damage and make new connections. If the wires are too short he should splice on new ones. In any event, he should use antioxidant paste.

What exactly does the "CU/AL" stand for. I thought aluminum.

As the others have said, it means that the breaker specification is for both copper and aluminum wires.

An important side note. The CU/AL specification is fine for breakers, but the 15 & 20 amp switches & receptacles labeled "CU/AL" are obsolete. They were the first attempt at dealing with the problem of fires resulting from aluminum branch circuit wiring and they never worked well. If there's aluminum branch circuit wiring in the 15 & 20 amp ranges, the switches and receptacles should bear the more modern specification of "CO/ALR." It stands for "Copper/Aluminum-Revised." The plating on these connections is better able to protect the aluminum from oxidation and from loosening due to expansion-contraction cycles.

On a side note the realtor kept repeating that it had already passed city inspection.

Everyone's got their own way of dealing with that kind of realtor. How you choose to respond will depend on your goal -- embarrassment, admonishment, education, or physical pain.

- Jim Katen, Oregon

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There don't appear to be any tracks on the cable suggesting a water path along the cable. Could the connection be loose?

Where's the anti-oxidation solution? (Oops, I see now that Mike mentioned that.)

My guess is that a combination of a connection that is not as tight as it should be and oxidation are causing some major resistance and overheating at the connection.

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