Black Copper

[ml1936]

When there is black coating on the copper when roving the insulation, what can this mean?

 

[RF Lighting]

Usually means the cable has been damp.

It might indicate overheating / burning.

The black coating will cause a high resistance joint which will quickly fail.

 

[Click-Sure]

Used some prysimian T&E recently that had a reddish brown tint to the copper conductors but never come across black?

New or old cable?

 

[cjard]

Copper's oxidation colour would appear to be an indicator of how fast the oxidation had occurred:
http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA3/MAIN/REDOXCU/PAGE1.HTM

Green: slow oxidation
Black: fast oxidation

THe cable concerned was probably subjected to heat, either external or from load

 

[JohnD]

have seen it black in the presence of green slime

View media item 1631
View media item 1632

 

[ericmark]

There are two copper oxides cupric and cuprous and it combines with other elements in the atmosphere. This can be seen with copper roofs where initially copper oxide forms, replaced by cuprous and cupric sulfide, and finally by copper carbonate. The final carbonate patina is highly resistant to corrosion. Can't remember which is which but one is black and normally means water has got into the cable and it is an insulator so makes terminating the cable hard.
Eric