Why do wires and cables age?

I. Introduction

Wires and cables are crucial components in electrical systems. However, over time, they age, which can lead to reduced performance, safety hazards, and increased maintenance costs. Understanding the main chemical and physical factors causing this aging is essential for ensuring the long - term reliability of electrical systems.

II. Chemical Factors

A. Oxidation

• Mechanism: Metals in the cable conductors, such as copper and aluminum, are prone to oxidation when exposed to oxygen in the air. For example, copper reacts with oxygen to form copper oxide. This oxide layer can increase the resistance of the conductor. As resistance increases, more heat is generated during the flow of electricity according to the formula P=I2R (where P is power, I is current, and R is resistance).
• Impact on Cable Performance: Higher heat generation can further accelerate the aging process of the insulation material around the conductor. Over time, the conductor may become brittle, and its conductivity may decrease significantly.

B. Chemical Corrosion

• External Chemicals: Wires and cables may be exposed to various chemicals in their environment. For instance, in industrial areas, they can come into contact with acids, alkalis, and salts. These chemicals can react with the cable materials. If a cable is installed in a sewage treatment plant, the acidic or alkaline substances in the sewage can corrode the cable insulation and conductor.
• Internal Chemical Reactions: Some insulation materials may undergo internal chemical reactions due to factors like temperature and humidity. For example, certain types of plastic insulation may release volatile organic compounds (VOCs) over time, which can cause degradation of the insulation material itself.

C. Cross - Linking Degradation

• Insulation Materials: Many modern cables use cross - linked insulation materials, such as cross - linked polyethylene (XLPE). Over time, the cross - links in these materials can break down. High temperatures, mechanical stress, and exposure to certain chemicals can all contribute to this degradation.
• Effect on Insulation Performance: When the cross - links break, the insulation material loses its mechanical strength and electrical insulation properties. This can lead to increased leakage current and a higher risk of electrical breakdown.

III. Physical Factors

A. Temperature

• Thermal Expansion and Contraction: Wires and cables expand when heated and contract when cooled. Repeated cycles of thermal expansion and contraction can cause mechanical stress on the cable materials. For example, in a power distribution system where cables experience significant temperature variations during daily operation, the insulation and conductor may gradually develop cracks due to this stress.
• Accelerated Chemical Reactions: Higher temperatures also accelerate chemical reactions within the cable. As mentioned earlier, oxidation and cross - linking degradation occur more rapidly at elevated temperatures. A general rule of thumb is that for every 8 - 10°C increase in temperature, the aging rate of the cable insulation can double.

B. Mechanical Stress

• Installation Stress: During the installation process, cables may be bent, stretched, or compressed. If these stresses exceed the limits of the cable materials, it can cause damage. For example, if a cable is bent too sharply during installation, it can damage the internal structure of the insulation and conductor, leading to premature aging.
• Vibration and Movement: In some applications, cables are subject to vibration and movement. For instance, in vehicles or machinery, cables may vibrate continuously. This can cause fatigue in the cable materials, especially in the insulation, leading to cracking and degradation.

C. Ultraviolet (UV) Radiation

• Outdoor Cables: Cables installed outdoors are exposed to UV radiation from the sun. UV rays can break the chemical bonds in the cable insulation materials, especially in polymers. For example, PVC (polyvinyl chloride) insulation can become brittle and crack after long - term exposure to UV radiation.
• Degradation of Protective Layers: UV radiation can also degrade the outermost protective layers of the cable, making the cable more vulnerable to other environmental factors such as moisture and chemical corrosion.

IV. FAQ

• Q: Can proper cable selection prevent aging?
  • A: Yes, choosing cables with appropriate insulation materials and ratings for the specific installation environment can slow down the aging process. For example, using UV - resistant cables for outdoor installations can reduce the impact of UV radiation.
• Q: How can I detect early signs of cable aging?
  • A: Some early signs include changes in cable appearance (such as cracking or discoloration), increased resistance in the conductor, and abnormal temperature rise during operation. Regular inspections and electrical testing can help detect these signs.
• Q: Does humidity affect cable aging?
  • A: Yes, high humidity can promote chemical corrosion and increase the likelihood of electrical breakdown. Moisture can also penetrate the insulation material, causing degradation of its electrical insulation properties.