Thread: Deep Rainbow Color at Top of Bus Bar

I see light rainbowing from time to time and have been told by seveal electricians that it's not a concern. This was a much deeper color than I've seen and it was only on one leg. The other side was bright silver.

I wrote it up as a possible loose breaker to bus bar connection and to have it looked into further. The panel is from a 1978 house - GE split bus.

Do you guys call the rainbow color when it's really deep like this?

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According to the National Fire Protection Assoc. (NFPA), fuse terminals and fuse clips should also be examined for discoloration caused by heat from poor contact or corrosion. Early detection of overheating is possible through the use of infrared examination. If evidence of overheating exists, the cause should be determined.

I use an IR thermometer to evaluate for heat and also check for stored chemicals.

I note what's observed and move on...

Originally Posted by BARRY ADAIR

I note what's observed and move on...

Just curious.... we have to make a recommendation so what do you say?

Also, with an IR thermometer isn't just testing the day you're there pretty limiting?

There were some other things in the panel (double taps) so I just told them to investigate the cause, particularly a loose breaker to bus connection.

I have seen that on a LOT of panels, with no ill effects.
I will honestly admit I don't know what causes it, but I truly don't think it is overheating.

I don't see what you are describing in those photos, but if it what I have seen, it is the plating on the bus bars during manufacture, nothing wrong though, just the way it turned out.

Here's a picture with the area circled... the pictures really didn't come out good. The one pictured is a deep rainbow color while the other side is completely bright silver. That difference is what got me thinking. I've seen rainbowing many times but never anything close to this deep and rich a color.

Originally Posted by Matt Fellman

Here's a picture with the area circled... the pictures really didn't come out good. The one pictured is a deep rainbow color while the other side is completely bright silver. That difference is what got me thinking. I've seen rainbowing many times but never anything close to this deep and rich a color.

That could be from overheating as that is directly below where that bus bar is tapped off the main breakers, could be a loose or poor connection at the breaker terminals or at the bolted connection at the bus.

Now that I see what you were referring to, if you look at the first photo at 400x zoom you will see what looks to be overheating around that bolt at the bus bar.

Yep.... around the bolt is the first thing that caught my eye but the picture didn't really come out, hence the one from the side.

I talked it through with the buyer and he seemed to grasp the problem. I told him the first thing I'd do (or have an electrician do) is pull the breakers and check the connections and go from there.

Originally Posted by Matt Fellman

Just curious.... we have to make a recommendation so what do you say?
The inspector observed XXXX (pic of perceived problem) and observed/didn't observe a temperature rise (pic of IR temp at perceived problem at time of inspection, all we can do) I advise further investigation by a qualified electrician to assure proper function or make any necessary repairs/replacements required.

Also, with an IR thermometer isn't just testing the day you're there pretty limiting? No more limited than the rest of our inspection. I've not found an electrical defect that repairs itself and anything that is questionable would have to be further evaluated by the qualified electrician for a conclusive answer as to the cause.

There were some other things in the panel (double taps) so I just told them to investigate the cause, particularly a loose breaker to bus connection.
Good call!

i try to keep it simple

Anytime you see a discoloration as described always know it is excessive heat on the buss bar. The source of the heat can be a variety of different things from a breaker not making up properly to the buss to a loose connection of the buss or over amping the buss. It should always be investigated. Ever heat up a piece of metal with a torch or solder a copper plumbing joint, same thing it changes color.
Tony Dolce
Meade Electric
Phoenix electrician affordable repairs and installations electrical service in Phoenix

Originally Posted by Tony Dolce

Anytime you see a discoloration as described always know it is excessive heat on the buss bar.

This is not at all true. I have seen similar discoloration in relatively new equipment and it was NOT from heat.

Just replace the word "always" above with "sometimes".

Originally Posted by Tony Dolce

Anytime you see a discoloration as described always know it is excessive heat on the buss bar.

Originally Posted by Speedy Petey

This is not at all true. I have seen similar discoloration in relatively new equipment and it was NOT from heat.

Just replace the work "always" above with "sometimes".

Peter,

I agree with you. I have seen what could be described as a rainbow effect on brand new equipment which has NEVER been energized. Even out-of-the-box.

I think that statement is mis-leading in that it could likely cause a false determination of the cause.

I would re-word that statement to this: 'Anytime you see a discoloration as described always LOOK FOR EVIDENCE OF excessive heat on the buss bar.'

In the photo shown, that evidence is the darker, much darker, area right at and right around the bolted connection.

Absent other signs - damaged breaker connection, a measured high temperature, etc., I wouldn't worry about it.

I have two reasons. Firse, many panels have those colorings fresh from the box. It seems that there is heat generated at different points of the manufacturing process. Also, the metal may have some corrosion-resistant treatment (such as 'clear irridite' or others) that show such a rainbow effect when there are variations in the thickness of the coating. I have seen differences of even a millionth of an inch result in a dramatically different appearance.