Wood is an essential building material, and this post explains how electric utilities maintain wood infrastructure for a longer lifespan.
In the earliest days of the power grid, wood provided the main bones of the beast – cross arms, braces, guy guards and molding. Today, while utilities also build with steel, fiberglass and other materials, the unique qualities of wood continue to make it an important building material for electric infrastructure.
If utilities want to get the most out of their investment, they need to know how to buy, deploy, and manage wood throughout its entire lifecycle.
Proper testing: How electric utilities maintain wood infrastructure
While the lifespan of wood infrastructure is considered by some to be 25-40 years, it can last much longer. How can utilities reliably assess the strength and resiliency of older assets?
Visual assessments help, of course. Most utilities schedule regular inspections of wood arms, poles and other assets in the field, which is crucial for correcting loose or missing hardware and doing proper vegetation management. Structures can be tested for vertical and transverse loading, and oftentimes, braces and minor structural modifications are all that is needed to extend service life. This is relatively more affordable than replacing entire structures.
Wood has unique qualities that continue to make it popular. In addition to visual appeal, the lower cost and electrical conductivity of wood give it appeal for safety and value-conscious buyers. Its low-maintenance and significant durability give it staying power.
Where wood works well
Like any product, the key to using wood materials begins with understanding the right circumstance for choosing the material.
If wooden H-frame structures are knocked down during a storm, for example, should they be replaced with wood or steel? This is a common question. Immediacy and material availability often play a part in the decision process. Wood replacements are chosen much of the time because it leads to restoring power more quickly.
On the other hand, if there’s more time to explore other options for this type of structure replacement scenario, a steel product might be the right choice, depending on the circumstances.
Ultimately, wood can be a superior alternative to steel or fiberglass. Wood braces, for example, provide superior mechanical strength while meeting important basic insulation level (BIL) requirements. Similarly, a wooden alley arm brace delivers greater strength than a formed angle iron brace, with less weight.
Douglas fir, the gold standard for solid wood utility infrastructure, is a material with tremendous resistance to sun damage. Its deterioration rate is a mere quarter inch per century, which makes it an ideal product in areas of high ultraviolet radiation. Wood guy markers also work well, significantly outlasting most resin-based, plastic guy guards.
How to evaluate wood quality
Visual grading has long been a key approach to rating wood. Characteristics such as rate of growth, seasoning checks, slope of grain, pitch pockets, rot and knots remain vital to understanding wood quality.
While some say newer wood is of lesser quality than old, it’s important to understand that since grading standards have remained unchanged over the past century, wood of a verified grade is the same quality as ever. Glue-laminated wood is an effective and popular alternative to sawn lumber, offering consistent strength properties and lower moisture content.
Wood standards vary by type of product. Utility cross arms, for example, must be made of thoroughly seasoned timber with a moisture content determined to meet American Wood Protection Association (AWPA) standards.
How it’s made matters
Certain production techniques can further enhance the strength of wood for utility infrastructure.
Treating the exposed fibers of wood has, in some cases, extended the lifespan of components like cross arms to over 50 years. Hughes Brothers, Inc., for example, uses proprietary Hughes P9 oil with pentachlorophenol in pressure treating. The manufacturer has two large “retorts” for pressure treating (40 and 65 feet long each).
Additionally, small incisions made on all faces of cross arms help with preservative penetration, and relieve wood fiber surface tension. Hughes operates its own preserving facility in accordance with Environmental Protection Agency (EPA) guidelines on site.
NOTE: Buyers should always conduct an inspection either at the point of manufacture or upon delivery.
The now iconic X-brace (invented by Hughes Brothers around 1929) is a good example of a product that improves resiliency – its development was an early example of how full-scale testing can be used to this day. Full-scale tests of X-braced frames showed a drop in top deflection from 58 inches to 6 inches, and increased the overall framing strength from 4,060 pounds to 13,600 pounds.
Other examples of quality wood construction include tapping steel-fitting holes to ensure that, even as timber shrinks over time, connections remain tight. Similarly, wood structures built with metal connections allow full drainage of moisture, leaving no place for decay to develop.