Mingxin School: Is it because the copper wire turns black?

We often find that during the installation and use of wires and cables, there is a problem of conductor copper wire oxidation and discoloration (blackening). Many people think that blackening of copper wire is poor quality. Why is it blackening? What are the reasons for blackening? Below, Mingxin Cable will explain a few of the most easily overlooked reasons for blackening.

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The main reasons for the blackening of copper conductors in wires and cables

The oxidation discoloration (blackening) of copper conductors in general cables is caused by the chemical reaction of copper conductors with oxygen and water during the production, transportation, storage, laying, and use of products due to humid environments or rainwater immersion in the cable conductors, resulting in discoloration (blackening).

The black areas and conditions of copper conductors in wires and cables are also different: the conductor ends of the cable are black or the two ends are intact, and the middle is black.

In summary, there are generally three reasons for the oxidation and discoloration (blackening) of copper conductors in cables: water ingress, moisture exposure, and air immersion.

Several situations that can cause blackening:

01

Improper sealing of cable joints

The sealing of the cable joint was not properly packaged, resulting in air intrusion into the copper conductor and blackening. When packaging cable heads, most technicians use insulating tape to directly seal them. In fact, insulating tape is not waterproof and there is also a layer of adhesive on top, which can cause the cable to turn black over time.

02

Damp insulation

This situation is very common and usually occurs at cable joints in buried or piping systems. If the cable joint is not made up to standard and is made in humid weather conditions, it will cause water or steam to enter the joint, and over time, the cable will turn black. This phenomenon is more common in hot summer because the humidity in the air is relatively high, and temperature accelerates the oxidation reaction of copper conductors.

03

Improper use

During the customer's installation process, cutting the cable without sealing the cable head or non-standard construction operations can lead to water ingress and oxygen generation, which can also easily cause the cable to turn black.

There are several situations where the middle is black and both ends are good:

01

Transportation environment

During transportation, the finished product may experience bumps and damage to the insulation layer of the cable, such as compression, collision, and scratching. When the copper conductor of the cable is partially damaged and comes into long-term contact with oxygen and moisture in the air, it may be oxidized and discolored (blackened).

02

Copper rod drawing process

The production of various specifications of copper wire from copper rods is achieved through a drawing process. For large drawing machines, medium drawing machines, and fine wire machines, it is necessary to add drawing emulsion (lubricant). If the emulsion (lubricant) remains on the surface of the copper wire and is not treated properly, the surface of the copper wire will oxidize and discolor (turn black) after long-term contact with air.

03

Construction and installation

Some users do not follow proper construction standards when laying and installing cables, which can easily cause mechanical damage; Civil construction on buried cables can also easily damage cables during operation. If the copper conductor of the cable is locally damaged and exposed to moisture underground for a long time, oxidation and discoloration (blackening) will occur.

Mingxin Intelligent Optics (Jiangsu) Co., Ltd. was established as a national high-tech enterprise in 2018, and the Mingxin "MX" brand was named a famous trademark in the province in 2015. The company mainly produces various types of weak current monitoring cables, YJV