Black Copper Conductors

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ssmith9

Member
We are constantly being called to inspect and service electrical panels at the request of home inspectors, prior to many real estate transactions.

We have a fairly common phenomenon in our area, after about two years all of the copper conductors in the panel turn black from some sort of oxidized coating.



Do you know what the cause of this phenomenon is?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Black Copper Conductors

Is "sulfer water" common in your area? The H2S gas given off from this type of water will cause all exposed copper to turn black in a short time.
Don
 

bphgravity

Senior Member
Location
Florida
Re: Black Copper Conductors

This definitely sounds like an environmental issue as oppossed to an electrical condition.

I have experienced this same occurrance with both well-pump systems, and equipment near sea water.

Im am not too sure if this really has any effect on termination or connection quality as oxidation does on aluminum.

The integrity of the copper does not seem to be effected. It just seems to discolor? :confused:
 

charlie

Senior Member
Location
Indianapolis
Re: Black Copper Conductors

This is sorta related but doesn't apply to your situation (I think). I have had to put jumpers around Western Union splices due to the build up of copper oxide (an insulator) over the years. This was an overhead, open wire, span to a barn. One had opened up completely and the other two were of high resistance. :)
 

brian john

Senior Member
Location
Leesburg, VA
Re: Black Copper Conductors

We have completed projects at pumping stations and sewage treatment plants; the black discoloration is a byproduct of the environment.

Micro-ohm readings are taken at all these facilities utilizing either a 100 amp DLRO (digital low resistance ohm meter commonly referred to as a ducter) or 10 amp DLRO. The readings as taken and recorded fell inline with new equipment, and the discoloration did not seem to be a concern. These sites have been inspected numerous times over 20 years.

I think (though not 100% positive) the copper oxidation is conductive. The problem Charlie is talking about may be corrosion.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Re: Black Copper Conductors

I have seen this in a below ground pool equipment room. (high chlorine concentration) The strange part was that the conductors had turned black, yet the copper busses had turned green (as in oxidation) and did have connection problems from breaker to buss. The black conductors and connections at equipment did not have any problems.

Roger
 

charlie

Senior Member
Location
Indianapolis
Re: Black Copper Conductors

The color of the Western Unions were very green and it was a little messy (as I remember, it came off on my hands where the wire was wrapped).
 

bennie

Esteemed Member
Re: Black Copper Conductors

When I attended a cable splicing school, it was stressed that the western union splice was to be mechanically sound without any solder. Many took this to mean no solder. The solder is to prevent oxidation, or at least slow it down.

Copper oxide forms a rectifier. Second order harmonics can be generated by oxidized connections. Connections that are properly torqued, can overheat, when contact surface is decreased by oxidation. The impedance of the system remains the same.

This phenomenom is a big problem that is being overlooked. Many melt downs are caused by this situation and are wrote off as loose connections, or overloads.
 
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