For roughly a century, electrical contractors (ECs) have used copper or aluminum wiring. Their coexistence at times has been competitive. The nature of the application and, in some cases, price have dictated the choice between the metals. 


Since we live in a cost-conscious world, let’s discuss the price issue first. Earlier this year, copper was selling for $2.90 per pound, while aluminum was going for 76 cents, making it about 75 percent cheaper. But futures-market gurus who have made careers of tracking the price performance of both metals generally agree that they exhibit sharply different patterns of activity.


Aluminum pricing remains considerably less expensive, despite slow incremental increases; its pricing is much more stable. On the other hand, the price of copper has historically fluctuated significantly. In February of this year, it was selling for $3.25 per pound, before dropping close to 11 percent in one month.


The sticker price of the two types of wire isn’t the only matter that contractors have to consider.


On one hand, there is the argument that, when a contractor gets into a lot of larger feeders, the total job price is going to relate to the amount of labor and not just the cost of material. It takes less effort to install aluminum because it is approximately 50 percent lighter than copper and easier to pull.


On the other hand, it can be argued that aluminum wire requires a larger wire gauge than copper to carry the same current, so conduit has to be larger than it is for copper, which in turn entails higher steel and labor costs.


Proponents of this view add that aluminum has more exacting requirements for installation, so the cheaper price of materials up front can prove to be a false economy. As with all endeavors that allow for alternative procedures, there is no one solution.


Code considerations


The National Electrical Code (NEC) covers the usage and installation of both types of wiring.


“Even though the NEC doesn’t specify this, industry practices indicate that copper is used across the whole spectrum of installations, including small branch circuits and all the way up to large feeders,” said Michael Johnston, the National Electrical Contractors Association’s (NECA) executive director of standards and safety. “Aluminum conductors are not used that often for smaller branch circuits up to about 30 amperes; but, above that, they are regularly used for services, branch circuits and feeders. The relatively new AA-8000 alloy of aluminum is a much better conductor than aluminum conductors used in the past, so aluminum today is very competitive.”


Contractors must keep two issues in mind: ampacity and installation processes.


“The ampacity, or current-carrying capacity, of aluminum is often less than that of copper,” Johnston said. “So obviously, if you’re installing aluminum, it typically has to be larger in order to have the equivalent or greater ampacity of copper. Also, there are more specific requirements and techniques for terminating aluminum wiring than for copper.”


Two extra steps are involved in the installation of aluminum wiring. When it is stripped, it has to be wire-brushed, and then an antioxidant compound has to be applied prior to termination. This step is necessary because aluminum oxidizes quickly, and the resulting corrosion is nonconductive. 


Corroded copper retains conductivity. With copper wiring, as long as there is a copper lug or terminal on the equipment, a simple termination is all that is required.


Some passages in the NEC might prove confusing to ECs.


“Many contractors and inspectors don’t realize that, in 110.5, the Code specifies that, unless otherwise provided, everything is based on copper,” said David Brender, national program manager, the Copper Development Association. “There has been a slight change in terminology in the 2014 Code’s Section 545.7, which deals with agricultural use. In the 2011 edition, it specified that, where a grounding equipment conductor is installed, ‘it shall be copper.’ For whatever reason, that phrase was dropped in the 2014 NEC. Maybe the assumption is that the earlier Section 110.5 covers this, but this could mislead contractors.”


Another point of possible confusion has to do with grounding aluminum wire in exterior as opposed to interior locations.


“There are a number of restrictions in the NEC dealing specifically with aluminum wire that electrical contractors should be aware of,” said Christel Hunter, director of field application engineering, General Cable, and chair of the Electrical Division, Aluminum Association. “For example, when an aluminum grounding electrode conductor or equipment grounding conductor is used outside, terminations should be kept at least 18 inches above bare earth. Sometimes contractors or inspectors confuse this and try to apply this rule within an electrical room, keeping the installation 18 inches off the floor. This is unnecessary. The rule only applies to outside, exposed installations.


“There are a few other NEC provisions that contractors should keep in mind,” Hunter said. “They should never directly bury bare aluminum, and it should not be in direct contact with masonry or concrete. It should also be noted that AA-8000 series aluminum alloy conductors are specifically required for most installations using aluminum wire. There are a few exceptions, like USE-2, which may use AA-1350, but AA-8000 series aluminum has been required for interior wiring since the 1987 NEC.”


In short, strict Code compliance is the name of the game.


“Both aluminum and copper wiring are safe installations if they’re done in accordance with the NEC,” Johnston said. “There are pros and cons, depending on specific applications, and appropriate uses for both.”


Applications and installations


Over the last century, some general delineation of wire choices and locations has developed largely on the basis of common sense and experience in the field.


“Aluminum has become widely used by utilities for overhead cabling where weight is obviously an issue,” Brender said. “But copper is the choice in inner-city downtown underground situations, where duct capacity is the major consideration and you have to get the maximum amps through a given amount of duct without digging up the street.”


Over time, engineers have generally specified copper for applications such as data centers, broadcasting, hospitals, military bases and airports, Brender said.


About 50 years ago, aluminum wiring acquired the unfortunate reputation of being a potential fire hazard, which most observers now agree was a result of the use of unsuitable alloys coupled with improper installation. Nevertheless, traces of this prejudicial mindset still linger in some regulatory districts and insurance underwriting circles.


“Contractors should verify that there are no local regulations that restrict the use of aluminum wiring,” Hunter said. “Some local jurisdictions still have outdated 1970s-era Code amendments that restrict aluminum wiring to larger sizes only, even though new alloy conductors are used widely for building wire and connectors have been designed specifically for aluminum conductors. And usually, insurance coverage has restrictions only on branch wiring of the old 10- and 12-gauge wiring installed in the ’60s and ’70s.


“While the old pejorative attitude is still somewhat of a problem, aluminum conductors have experienced a significant increase in use for building wire over the last 10 years,” she said. “Contractors, engineers and owners have gained confidence based on the fact that AA-8000 series aluminum alloy conductors have been installed and operating reliably for over 40 years.”


The torque test


Whenever any system or product fails, the conventional response is to blame the key components involved—in this case, the copper or the aluminum. Perhaps we should recall what Cassius said to Brutus: “The fault, dear Brutus, is not in our stars, but in ourselves.” In this case, the fault may not be in the wiring but in how it’s torqued.


“Torquing between connector and connection is critically important,” Brender said. “Copper is more forgiving, and torquing of the connector is generally not as critical as with aluminum. For example, copper, being a harder material, is not prone to cold-flow out of the joint if over-torqued. Connections stay tight and do not usually need retightening periodically, thus saving maintenance expenses. But regardless of the type of wire being installed, the real question here is: how many electricians carry a torque wrench and know how to use it?”


Brender also noted that engineers generally tend to specify copper for applications such as data centers, broadcasting, hospitals, military bases and airports, where reliability is vital.


A few years ago, the same torque test was conducted at four electrical industry conferences: one each by NECA and the National Joint Apprenticeship and Training Committee and two by the International Association of Electrical Inspectors (IAEI).


“The results were quite revealing,” Hunter said (she also reported on the findings in the IAEI magazine). “The participants, not all of whom were electricians, were given a choice of using either a 12-inch ratchet drive or a folding Allen set. Disappointingly, test results showed that people who had never made an electrical connection before were just as capable of getting within 20 percent of recommended torque as electricians with decades of experience—that is, 25 percent of both groups, both professionals and laymen.


“This indicated that achieving recommended torque is apparently independent of training and experience and requires the use of a torque wrench to properly tighten a connection,” he said. “The findings are disturbing and might explain many of the connection failures that occur a few years after installation.”


The electricians who participated said they were more likely to use a torque wrench on larger conductors (such as those on transformers or switchboards) but not on branch-circuit connections. Only 36 percent said they always use a torque wrench or torque screwdriver to make electrical connections.


“Even though most electricians appear to be using the wrong tools, the reason there aren’t more failed connections is that most electrical systems have built-in safety features, and circuits are rarely fully loaded,” Hunter said. “But this is no justification to ignore the basics of proper installation, especially when a torque wrench is a simple and inexpensive way to improve the reliability and safety of an electrical system.”


Perhaps we should recall what Cassius said to Brutus: 
“The fault, dear Brutus, is not in our stars, but in ourselves.” 


In this case, the fault may not be in the wiring but in how it’s torqued.