Choosing a Covered Line Wire: Aluminum vs. Copper

Covered line wire is a critical part of an electrical utility's secondary distribution infrastructure. 

In the same way capillaries help deliver oxygen and nutrients in our blood to cells, covered line wire delivers "last mile" electricity from substations to homes and businesses. Often, utility crews use covered line wire for overhead secondary distribution lines and service drops to their final destinations. However, these cables also help deliver larger amounts of power for factories, large facilities, and other power-hungry locations.

But what makes this wire unique is how utility workers handle its installation and maintenance. Covered line wire has a non-electrical covering made from HMWPE or XLPE, meaning workers must treat it like a bare conductor. Though it isn't an electrical insulation, the covering protects the overhead conductors from several types of damage, including: 

• abrasion 

• chemicals 

• oxidation 

• severe weather 

• vibrations 

• sun exposure 

• moisture 

• potential contact with tree branches, wildlife, and other wires

Without its protective covering, the conductor could potentially pick up moisture, dirt, and dust. It would also face mechanical stress, opening the door for corrosion, more resistance, lower conductivity, and potential faults. 

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Copper vs. Aluminum: What's the Difference? 

Copper and aluminum covered line wire may perform the same task, but they aren't one-size-fits-all options. 

Depending on the application and the environment, utilities may choose to use either copper or an aluminum alloy wire. These alloys include ACSR (Aluminum Conductor Steel Reinforced), which uses an aluminized steel core for strength, and AAAC (All-Aluminum Alloy Conductor), which uses a 6201 alloy to perform better in more corrosive locations, like along coastlines. 

And though both wire configurations can safely and reliably deliver electricity to homes and businesses, each has its benefits. 

Conductivity 

Copper conductors are much more conductive than aluminum ones of the same gauge. 

Standard copper is 100% on the International Annealed Copper Standard (IACS) while aluminum is only about 61% IACS. This means workers need a larger aluminum wire gauge (smaller AWG number) to carry the same amount of electricity. General substitution rules suggest an aluminum conductor be two AWG sizes larger than a copper one to match ampacity. 

For example, to get the same amp rating as an #8 AWG copper wire, an installer would need to use a #6 aluminum wire.

Weight and Strength 

Copper wire is heavier than its aluminum counterpart, making it less useful for long runs. 

When utilities choose to use copper covered line wire, it adds stress to utility poles. To fix the issue, workers must place the poles closer together to limit sagging and weight. 

Aluminum is about one-third the weight of copper of the same gauge, which means it carries less weight and stress for utility poles. As a result, workers can space poles out further since there's less stress to worry about. 

Copper might be heavy, but it also has a higher tensile strength and corrosion resistance than aluminum. Unlike copper, which works well by itself, aluminum needs steel or another alloy to perform in harsh environments. 

Cost 

Nothing surprising here; copper wire is way more expensive to buy than aluminum wire. 

Copper is currently trading at around $6.50/lb. at the end of August, while aluminum is only about $2.50/lb. Even with necessary gauge increase to carry the same current, aluminum is still much easier on the wallet. This means utilities can buy and keep more stock on hand in case something damages the lines. 

Aluminum, for its part, is also much less attractive to thieves than copper, thanks to its lower resale value. 

Termination Quality 

Aluminum is a more reactive metal than copper, making quality installations critical. To combat its reactivity, workers use specific antioxidant zinc and grease compounds to prevent reactions. They also focus on using connectors to maintain tight connections at termination points. 

When aluminum reacts with air, it forms aluminum oxide, which protects the metal from further damage. But if water, air, or acids breach the thin oxide layer, it can lead to more damage. Aluminum oxide also increases resistance along the wire and termination points, creating excessive heat. 

Resistance at termination points is especially dangerous for aluminum conductors. If workers don't properly torque connectors or protect the wires with compound, hotpots could form. Over time, those hotpots could become failure points, leading to dangerous situations. 

Beyond its general reactivity, aluminum also suffers from thermal expansion during hot or cold weather. As the wire expands or contracts, it creates looser connections and more resistance. Crews must check aluminum wire termination points to ensure they stay maintained, including tightening connections and removing aluminum oxide. 

Another aluminum-related issue to keep an eye out for is creep. Creep occurs when aluminum undergoes constant mechanical pressure and thermal cycles, causing the conductor to flow away from connectors. The result is a looser connection that affects performance. Preventing creep generally involves consistent maintenance along with an antioxidant grease. 

Copper is less reactive and needs less maintenance than aluminum wiring. In the right situation and when installed correctly, copper wire can perform well for decades. 

When copper conductors encounter air, they form a layer of copper oxide. While the oxide layer creates some conductor resistance, it's semi-conductive, so electricity still passes through safely. 

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Product Applications for Aluminum and Copper Covered Line Wire 

Depending on the situation, either copper or aluminum may be a more economical or safe choice. 

Copper 

Copper is a great conductor choice for short runs where weight isn't an issue. As runs get longer, copper conductors cause sagging and stress, meaning crews must install more poles to handle the weight. 

It also excels in tight areas where space is an issue and larger gauge wires won't perform as well. Copper is a better conductor than aluminum, moving the same amount of electricity with a smaller wire gauge. 

Aluminum 

It might not be as good of a conductor as copper is, but aluminum is much lighter, even at higher gauges. 

Aluminum conductors are great for long runs because it's lighter than copper, requiring fewer utility poles to carry lines. It also works well for applications where space isn't an issue -- aluminum needs larger gauge sizes to match copper's conductivity. 

Finally, aluminum may be the preferred choice for large-scale projects where cost and budgets are critical. Aluminum prices per pound are much less than copper and still incredibly cost-effective with added sizing. The rub here, however, is the added care and maintenance needed to ensure connections are clean and tight. 

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Two Great Options 

Aluminum and copper covered line wires perform the same job but have unique qualities, making them suitable for specific instances. 

Largely, the decision most utilities and work crews will have to make is dependent on several factors, including: 

• overall project cost (large projects tend to lean toward more cost-effective solutions) 

• the length of the run (conductor weight and stress become issues over longer runs) 

• the amount of space available (tighter spaces like conduits may require a smaller wire) 

• the environment (especially in fluctuating temperatures, impacts performance, resistance, and durability)

Regardless of which wire crews choose to use, ALWAYS make sure you install and terminate it properly. Reducing potential risks and mistakes during installation ensures the cable will perform as expected for years to come.