Since wire and cable products are closely related to consumers’ lives, their quality and safety directly impact their personal and property safety. Therefore, proper installation and use of wire and cable are extremely important.
Recently, we’ve encountered customer feedback regarding oxidative discoloration (blackening) of the copper wire in cable conductors during installation and use. However, we don’t know the cause of this oxidative discoloration. How can we prevent this oxidative discoloration?
Oxidative discoloration (blackening) of cable copper conductors can be caused by factors such as moisture exposure during storage, installation, and use due to overcurrent, as well as environmental pollution. To provide a comprehensive understanding of this phenomenon, Chancheng Cable brought together sixteen professional technicians from across the company’s production, technical, testing, and R&D departments to conduct research and analysis. The results indicate that oxidative discoloration (blackening) of cable copper conductors is often caused by inadequate preventative measures, allowing harmful environmental factors to enter the copper conductor and react with it, causing oxidative discoloration (blackening).
What are the main causes of blackening of cable copper conductors?
In reality, the oxidative discoloration and blackening of cable copper conductors is caused by a variety of factors, including production, transportation, storage, and use, as well as exposure to humidity and temperature. However, the location of oxidative discoloration (blackening) varies depending on the cable: 1. Oxidation and discoloration (blackening) at the cable conductor ends; 2. Oxidation and discoloration (blackening) at the cable conductor ends, while the center conductor remains intact.
Typically, oxidative discoloration (blackening) at the cable conductor ends occurs due to humid conditions or rainwater intrusion during production, transportation, storage, installation, and use, leading to a chemical reaction between the copper conductor and oxygen and water, causing discoloration (blackening). This phenomenon is more common in hot summer months, when the humidity is high and the temperature accelerates the oxidative discoloration (blackening) reaction.
Several factors can cause oxidation and discoloration (blackening) of the copper conductor at the cable end:
Improper cable gland sealing
Blackening can also occur if air intrudes into the copper conductor due to improper sealing of the cable gland. Most cable gland wrappers use insulating tape to seal the ends directly. However, insulating tape is not waterproof and has a layer of adhesive on top, which can cause the cable to turn black over time.
Moisture in the insulation
This is also very common, typically occurring at cable joints in direct burial or conduit installations. For example, poorly manufactured cable joints and joints made in humid climates can allow water or water vapor to enter the joints, causing the cable to turn black over time.
In-use
During installation, if the customer cuts the cable without properly sealing the joints, improper installation procedures can lead to water ingress and oxygen release, which can also easily cause the cable to turn black.
While both ends of the cable conductor are intact, oxidation discoloration (blackening) of the middle conductor can occur due to the following reasons:
Transportation Environment
During transportation, the finished product may be damaged by bumps, collisions, or scratches on the cable insulation. If the damaged copper conductor is exposed to oxygen and moisture in the air for a long time, oxidation discoloration (blackening) may occur.
Copper Rod Drawing Process
Copper rod is made into copper wire of various gauges through the wire drawing process. Drawing emulsion (lubricant) is added to the wire drawing process on large, medium, and fine wire drawing machines. If the emulsion (lubricant) remains on the copper wire surface and is not properly treated, the copper wire surface will oxidize and discolor (blacken) due to prolonged contact with air.
Construction and Installation
Some users do not follow proper procedures when laying and installing cables, which can easily cause mechanical damage. Civil construction work on directly buried cables can also easily damage the cables in operation. If the damaged copper conductor of a cable is exposed to moisture underground for a long time or if the surface is exposed, oxidation discoloration (blackening) may occur.
What causes copper conductors in cables to discolor due to oxidation?
Copper conductors have a protective layer of copper oxide on their surface. If this oxide layer comes into direct contact with air over time, the copper conductor will discolor. Discoloration of copper conductors in cables can occur in the following ways:
Blackening of the conductor
This discoloration is mostly caused by moisture inside the cable during installation, which creates excess moisture.
Purple-red discoloration of the conductor
The main cause of purple-red discoloration is excessively high temperatures:
In the copper rod drawing process, due to the continuous operation of the drawing equipment, insufficient saponified liquid in the coolant in the sealed chamber and excessively high cooling water temperatures can increase friction between the copper wire and the guide pulleys, causing the copper wire temperature to continue to rise, resulting in purple-red oxidation discoloration on the copper wire surface.
The customer’s cable carries excessive current, leading to long-term overload operation. This increases resistance and generates heat, causing the copper conductor in the cable to overheat and discolor to purple-red.
The conductor turns verdigris.
This is because the copper conductor reacts with oxygen, water vapor, and carbon dioxide in the air. Over time, it oxidizes to form basic copper carbonate (Cu2(OH)2CO3), also known as verdigris.
Conclusion: To summarize the above reasons for the blackening and discoloration of cable ends, everyone should have noticed that the main cause of cable discoloration is water ingress, moisture, or air intrusion.
Post time: 2025-09-08
