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Fiberglass Crossarms: An Overview

Fiberglass crossarms, as a key structural component in power transmission and distribution systems, are gradually replacing traditional wood and steel crossarms due to their unique material advantages and high performance. Compared to wooden crossarms, fiberglass crossarms are widely used in various demanding situations due to their excellent durability and fire resistance.
This article will delve into the definition, manufacturing process, different types, and applications of fiberglass crossarms in power systems, providing engineers and industry experts with a comprehensive understanding and reference.

What Are Fiberglass Crossarms?

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Fiberglass crossarms are structural components used in transmission and distribution systems. Made from Fiber Reinforced Polymers (FRP), a composite material consisting of a polymer matrix reinforced by fibers, typically glass fibers in an unsaturated resin. This combination enhances the strength and rigidity of the crossarms while the polymer matrix protects the fibers and distributes the load. They are used to support the conductors of power lines and serve as an alternative to traditional materials like wood or steel.

What Is the Other Term for Fiberglass Crossarms?

Another term for fiberglass crossarms is “composite crossarms.” This terminology is used because these crossarms are made from composite materials, particularly glass fiber-reinforced polymer (FRP), which combines the polymer matrix with glass fibers to enhance strength and durability.

How Are Fiberglass Crossarms Made?

The manufacturing process for fiberglass crossarms is known as pultrusion, a continuous process to create composite profiles with consistent cross-sections. Here’s a step-by-step overview of the pultrusion process for fiberglass crossarms:

  1. Resin Impregnation: Glass fiber rovings or mats are pulled through a resin bath to ensure complete saturation with thermosetting resins like polyester or vinyl ester, often including additives like UV inhibitors and flame retardants.
  2. Preforming: The saturated fibers are then pulled through a preforming guide to start shaping the composite material into the desired cross-sectional profile.
  3. Heating Mold: The resin-saturated fibers are pulled through a heated mold, causing the resin to cure and solidify into a rigid profile matching the mold’s shape.
  4. Cutting: After exiting the mold, the cured fiberglass profiles are cut to specified lengths to produce individual crossarms.
  5. Finishing: Additional processes such as drilling for hardware attachment points, applying protective coatings, installing end caps, or embedding inserts may be performed to enhance durability and performance.
  6. Quality Control: Throughout the manufacturing process, quality control measures are taken to ensure the crossarms meet industry standards and specifications, like the National Electrical Safety Code (NESC) and ASTM standards.

What Are Different Types of Fiberglass Crossarms?

There are various types of fiberglass crossarms designed to meet specific structural and functional requirements of transmission and distribution systems. The straight crossarm is the most common type, featuring a simple horizontal structure used to support insulators and conductors, widely utilized in both transmission and distribution lines.

What Are the Advantages of Fiberglass Crossarms?

The benefits of fiberglass crossarms include:

  1. UV Resistance: Typically made with UV-stabilized polyester resin, these crossarms possess excellent resistance to UV degradation, enhancing their lifespan and durability in outdoor environments.
  2. Non-conductive: As a non-conductive material, fiberglass reduces the risk of conductivity, adding an extra layer of safety in critical utility areas.
  3. Low Maintenance Costs: Compared to traditional materials, fiberglass crossarms require minimal maintenance. They do not rot, rust, or corrode, making them ideal for use in various environmental conditions, including areas with salt air, high temperatures, or acid rain.
  4. Lightweight: The composite materials used in fiberglass crossarms are much lighter than traditional materials like wood or steel, which facilitates easier transportation and installation, and offers cost-effectiveness.
  5. High Strength: Despite their lightweight, fiberglass crossarms possess high strength and durability, capable of withstanding heavy loads and harsh weather conditions.
  6. Long Lifespan: With features like UV resistance and thermal bonding, fiberglass crossarms often exceed a 60-year lifespan, reducing the need for frequent replacements and lowering lifecycle costs.
  7. Environmental Resistance: Capable of withstanding various levels of humidity and climates, making them suitable for different geographical regions.
  8. Fire Resistance: They exhibit low flammability and will not sustain combustion, significantly reducing the risk of fires on electrical poles.
  9. Customizability: Fiberglass crossarms can be manufactured in various lengths and shapes to meet specific utility needs, providing flexibility in design and application.

What Is the Color of Fiberglass Crossarms?

The color of fiberglass crossarms typically includes shades of gray and brown, selected to blend with landscapes and meet aesthetic requirements for various applications.

What Are the Materials Used in Fiberglass Crossarms?

Materials used in the manufacture of fiberglass crossarms include:

  1. Glass Fiber: The primary reinforcement material, providing strength and stiffness.
  2. Polymer Resin: Usually thermosetting resins like polyester or vinyl ester that bond the glass fibers together and offer environmental resistance.
  3. Coatings: UV-resistant coatings are applied to fiberglass crossarms to prevent UV degradation and extend their lifespan.
  4. Fillers: Materials like silica and calcium carbonate may be added to the resin to adjust the performance of the composite, such as increasing flexural strength or reducing costs.
  5. Bushings These are used to reinforce holes on the crossarms where hardware is attached, providing torque resistance and preventing damage during hardware installation.
  6. Closed-cell Polyurethane Foam: Used to fill some crossarms, providing additional stability and preventing moisture and contaminants from entering.
  7. Structural Aluminum or Galvanized Steel: These materials are used at the support ends of fiberglass crossarms to provide a robust and durable connection point.

What Are the Applications of Fiberglass Crossarms?

Fiberglass crossarms are primarily used in the transmission and distribution sectors.

  1. High Voltage Applications: Their high dielectric strength makes them suitable for high voltage applications where electrical insulation is crucial. They help prevent discharge and maintain the safety and integrity of power systems.
  2. Harsh Environmental Conditions: Fiberglass crossarms are particularly important in areas with challenging environments, such as coastal regions, high humidity areas, or places susceptible to chemicals and salts. Their corrosion resistance, UV resistance, and temperature tolerance make them highly suitable for these conditions.
  3. Grid Hardening and Reliability Enhancement: In areas prone to severe weather impacts or where grid reliability is a major concern, fiberglass crossarms help reinforce the grid. Their strength and durability enhance the overall resilience of the power network.
  4. Replacement for Traditional Materials: Fiberglass crossarms can also replace traditional materials like wood and steel, which may suffer from issues like rot, pest infestation, and corrosion. This substitution helps utility companies reduce maintenance costs and extend the lifespan of their infrastructure.

What Are the Factors That Affect a Fiberglass Crossarms’s Performance?

Factors influencing the performance of fiberglass crossarms include:

  1. Material Composition: The type of resin and glass fibers used, as well as the inclusion of UV inhibitors and other additives, significantly impact the durability and lifespan of the crossarms.
  2. Environmental Conditions: Exposure to UV light, moisture, temperature fluctuations, and other environmental factors affect the performance and lifespan of fiberglass crossarms. Over time, these conditions can cause material degradation.
  3. Mechanical Loads: The ability of fiberglass crossarms to withstand mechanical loads, including the weight of cables and the tension produced by support structures, is crucial. Mishandling can lead to structural failure.
  4. Creep Characteristics: Over time, materials may deform under constant stress, affecting the applicability and reliability of the crossarms.
  5. Electrical Insulation: Since fiberglass crossarms are used in electrical applications, their insulation and ability to prevent electrical conduction are critical. These properties are influenced by the material characteristics and environmental resistance of the composite.
  6. Manufacturing Process: The pultrusion process used to manufacture fiberglass crossarms must be precisely controlled to avoid defects such as voids and ensure uniformity of the composite material.
  7. Design and Installation Practices: The specific design of the crossarms and the methods used for installation also impact performance. This includes the integration of features like metal mounting brackets and the correct alignment and securing of the crossarms on utility poles.


Fiberglass crossarms play a critical role in modern electrical infrastructure, offering significant advantages over traditional materials. With their impressive array of properties, these components ensure safety, durability, and cost-effectiveness in a variety of applications, making them a preferred choice in the power distribution industry.

If you want to know more about Fiberglass Crossarms, please contact us.

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