Discolored busbar - InspectionNews

#1 (**permalink**) 12-29-2008, 01:42 PM

Any idea why this busbar is discolored? Its is a 7 year old GE 200 amp panel. No signs of overheating of the plastic around the busbar.

Rich

Jim Luttrall · #2 (**permalink**) 12-29-2008, 02:57 PM

That looks like moisture related corrosion, not from heat.

Jerry Peck · #3 (**permalink**) 12-29-2008, 03:10 PM

I'm guessing it is from heat.

That is an aluminum conductor ... note the color of the terminal set screw - it is darker, as though it has been overheated, now look at the bus bar, the darker triangular area is at the corner where the terminal lug connects to ... I'm guessing that the conductor is not properly torqued in the terminal, making for a loose (poor) connection, causing heating, and overheating.

Kevin Barre · #4 (**permalink**) 12-29-2008, 05:21 PM

I'd hate to argue with JP (again), especially on an electrical matter, (there's always a first time) but I'd be suspicious about the heat theory. The coloration on the set screw does not look like heat discoloration to me. And there's no melting on the plastic nib sticking through the bar below the set screw -- or anywhere else on the standoff. I could be wrong, but I seem to remember seeing a reddish factory coloration on some GE set screws. Almost a semi-transparent look, like someone wiped a magic marker over it.

As for the bar itself, even brand new, sometimes the plating on the bars is a bit multicolored. I think at most all you're seeing is a reaction between the plating on the bar and the environment.

Jerry Peck · #5 (**permalink**) 12-29-2008, 05:50 PM

Quote:

Originally Posted by Kevin Barre

As for the bar itself, even brand new, sometimes the plating on the bars is a bit multicolored.

"even brand new, sometimes the plating on the bars is a bit multicolored"

Yes they are, but ... that corner, and only that corner ... is darker ... and looks like it was overheated.

Jim Luttrall · #6 (**permalink**) 12-29-2008, 06:27 PM

Look at the retaining bolt/stud at the bottom left of the photo. That looks like rust on the tip, similar to what is on the bus bar above.
I still think moisture related corrosion.

Kevin Barre · #7 (**permalink**) 12-29-2008, 06:44 PM

Just to play devil's advocate...if we look at the overheating theory, it would seem that the interior of the set screw -- in other words, the recessed part of it closest to the wire -- would be the first to overheat. Right?
If so, why would it not be natural color with no signs of overheating? Why would any overheating discoloration be present only on the top surfaces of the screw -- furthest from the point of contact/arcing? The thickness of the screw at the end contacting the wire is not much, if any, greater than that of the sides of the screw. It would seem to me that any overheating would start at the contact end of the screw and radiate out from there. Any discoloration should do so also.

Jerry Peck · #8 (**permalink**) 12-29-2008, 07:02 PM

Kevin,

Because the rest of the screw is in the heat sink-acting terminal and that top thread or two is not?

Kevin Barre · #9 (**permalink**) 12-29-2008, 07:34 PM

Quote:

Originally Posted by Jerry Peck

Kevin,

Because the rest of the screw is in the heat sink-acting terminal and that top thread or two is not?

I understand the principle of a heat sink. That's exactly why I would expect to see discoloration at the base of the screw as the heat originates and radiates through the screw -- before the heat sink effect occurs. If the heat originated at the base, and there is minimal heat sink effect happening there, wouldn't the discoloration be there also?

So, Mr. Richard Roshak...
It's up to you now. You must go to the job, disconnect the power by yanking the meter, and remove the set screw in question. At that point, you must carefully photograph it and look for any signs of poor contact or anything else that looks odd. After that, you must carefully retorque the screw to the mfr's stated requirements (with new anti-ox goo), restore the meter to it's rightful position, and sneak back out of there.

Then let us all know what you found. Got it?

We're all counting on you.*

* Just kidding.

Tony Mount · #10 (**permalink**) 12-29-2008, 07:57 PM

I would not think it to be a problem unless it is humming. I' am with Kevin it looks like the discoloration is from a reaction between the plating on the bar the anti-ox goo (that you can see on the wire under the screw) and the environment.

Ron Bibler · #11 (**permalink**) 12-29-2008, 10:39 PM

The AU lug has some of the wire strans sticking out. that may support what Jerry P was pointing out... Bad conection.

Best

Ron

Roland Miller · #12 (**permalink**) 12-30-2008, 08:14 AM

Maybe a better option would be to turn all the loads on in this place, wait 30 minutes, and do an IR temperature reading. Of course you will have to do the other phase to compare it with.

If you take it apart you will have to trim the conductor back and re-terminate it to get the proper torque.

Ron Bibler · #13 (**permalink**) 12-30-2008, 05:26 PM

It look to me that there is a lot of corrosion in that panel due to the open wire strands at that lug.

Best

Ron