How bad is this subpanel burnout?

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  #1  
Old 09-17-18, 12:15 PM
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How bad is this subpanel burnout?

It looks like a circuit may have arc'd at one time in one of this panel's (currently unused) breaker slots. Problem?

There are carbon deposits to the left of the red oval and a small piece of metal missing from the blue clamping bar (red oval). The connection to the actual bus bar looks discolored (green oval) - you can see what looks like may be copper under the gray coating. For reference, the blue oval is what the clamping bar should look like and the yellow oval is what the bus bar should look like. In any case, a new breaker still clips in there nice and tight. I'm the new owner of this 1971 house with Aluminum wiring and am wondering if there is any real concern here? Thanks for any advice!

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Last edited by PJmax; 09-17-18 at 01:44 PM. Reason: added second enlarged picture
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Old 09-17-18, 12:51 PM
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At the very least that slot should not be used. Once the bus bar is burned to that extent the corrosive pitting extends through the protective plating and significantly impairs the electrical connection even if it still physically fits tightly.

If I was doing this job at a customer's house, I would remove several breakers around the bad slot and closely inspect the adjacent bus stabs. Often with a problem like that there is significant heat damage extending up and down the bar because the breaker has overheated for a long period of time before it finally burned out. You need to deenergize the main or upstream feeder to do this inspection safely.

Assuming the panel is contemporary to the house (1971) I would lean toward panel replacement unless this damage was obviously limited and contained to only one slot. If the damage continues down into the bus bar or in to adjacent stabs, the panel must be replaced.

That one is a little weird though as if someone might have dropped a loose wire onto the bus bar. Breaker failures alone usually don't blast out like that.
 
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Old 09-17-18, 01:46 PM
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That is a very strange issue. That looks like a heavily loaded breaker and then a short from the bus to ground. Almost like a wire shorted from the bus to ground under the breaker.

It doesn't look like a breaker issue.
 
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Old 09-17-18, 02:44 PM
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Almost like a wire shorted from the bus to ground under the breaker.
That is what it looks like to me as well. This may have occurred when someone worked on the breaker without turning the main breaker off.
I had a similar accident with ground wire before.

The picture is not high-res enough to tell if the tab on bus bar has arc or corrosion mark, but it looks like grease from the breaker and looks to be in good condition.
 
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Old 09-17-18, 03:13 PM
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IMO the green circle shows no damage to to the bus. It looks to me like marks from installing the QO breakers. I suspect if you remove one of the other breakers you will see similar marks.

The red circle appears to be a short that occurred when a wire touched the mounting bar and the bus and caused a short. It is hard to say from the pictures but I might say it is OK. Cleaning the bus with a wire brush (with the panel turned off) might show more.
 
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Old 09-17-18, 03:31 PM
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I pulled the adjacent breakers and kept the pics as high-res as I could for this site. Better?
 
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Old 09-17-18, 03:35 PM
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The adjacent locations are fine. That is a one off issue.,
 
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Old 09-17-18, 03:55 PM
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As suspected what is on the tab (green circled one) is just grease from the breaker.
The bus bar was shorted to breaker mounting bracket at one point, but the bus bar is not damaged enough to worry about. It will be perfectly fine to use as is.
 
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Old 09-17-18, 06:10 PM
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While it is a scar on the bus, (I have a few on my tools ) I also think the panel is OK to keep in service.
 
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Old 09-17-18, 07:41 PM
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No issue or damage to the breaker/bus interface, just grease.
 
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Old 09-19-18, 06:10 AM
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Phew! Thank you so much, PJmax, lambition, Ironhand and pcboss, for all of the helpful insight!
 
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