Oxygen. And maybe a loose connection causing resistance that generates heat to combine with the oxygen. Or maybe there is a source of chemical fumes that is causing the discoloration and is low enough not to be noticed, but has been at it long enough to cause the color change.
Dear Mr. Ninja_Newyork (Mechanical)(OP)17 May 22 06:41 " .... My busbar turns into a black and seems to be oxidised. What might be the issue ? "
1. Indoor Copper busbar surface turned black is very common in sewerage pumping stations. The busbar is exposed to (sulphuric fume) which turned into [sulphuric acid] with the wet surrounding air.
2. In most cases, it does NOT cause problem, besides the cosmetic appearance. There is NO over-heating at any joints or along its length. This is evident when you dismantle a good over-lapping joint, the contact surfaces are still bright, NOT blackened at all. However, if the contact surfaces are blackened or sign of over-heating, remedial action must be taken.
3. FYI: Lookout for corrosion on small fine wires on the relay coils and contacts operating on low voltage and low current. They can be problematic, instead of the heavy busbars.
Che Kuan Yau (Singapore)
Hydrogen sulfide gas (H2S) will react with bare copper to turn it black (Copper sulfide). Actually anything that produces sulfides will do that. H2S is just the most common though because it is in anything that rots or involves yeast fermentation, such as sewage or winemaking, as well as most petroleum based processes. So where is your busbar located?
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