Connecting with aluminum

Copper is the natural first choice for electrical connections, but there are times when aluminum can be better

by Jacqueline Sylvia and Richard Brooks

When you’re deciding what type of connector material works best in an electrical application, you may instinctively assume copper is the best choice. And indeed, it may be. But there are some applications for which aluminum poses a cost-effective, easier and longer lasting alternative. In order to ensure that you’re specifying the best possible solution for your application, it is important to understand not only when it may be best to specify an aluminum connector, but also what specific traits to look for in each connector as well as your connector-supplier.

Some material history
Copper has earned its solid reputation in the electrical connector industry, having proven particularly useful in residential installations. It should come as no surprise that performance levels with copper is high, as copper is, in fact, one of the oldest known metals. First used in about 8700 BC in what is now Iraq, and extremely popular in Ancient Egypt, copper owned 100 percent of the metals market for about 5,000 years until the arrival of gold.

Copper has had innumerable uses during this period, from early utensils, to ornaments and weapons, through the Bronze Age when it was alloyed with arsenic and tin.

All this being said, copper may be an omnipresent element, but it is far from the only choice for electrical connectors — a good thing considering its escalating cost in recent years. Aluminum is actually a better fit for some customers who have more industrial or commercial applications.

Aluminum as a youngster
Aluminum is relatively “young” compared to copper. In 1787, Antoine Lavoisier identified bauxite as the oxide of a still undiscovered metal, and in 1825 Hans Christian Oersted was credited with preparing the first metallic aluminum from bauxite, a claylike rock found in the earth.

With its high electrical conductivity, ductility and low atomic mass, aluminum is frequently used in everything from electric transmission lines to the coating on telescope mirrors to aluminum foils used in food preparation and storage.

Making the connection
Aluminum is also being specified more frequently in recent years as a great option for electrical connectors, including mechanical and compression terminals, splices and taps. In industrial and commercial installations, such as substations and utility distribution and transmission lines, aluminum connectors are particularly well-suited for these applications due to their lightweight composition, high conductivity and ease of installation.

Mechanical vs. compression
If you’ve selected aluminum for your installation, the next step is to select not only the proper aluminum connectors, but the most competent and knowledgeable connector supplier. Aluminum terminals, splices and taps are offered in both mechanical and compression types, and there are advantages to each.

Mechanical connectors are easy to install, requiring no special installation tooling. Though mechanical connectors may be individually more expensive than compression connectors, the capital investment incurred with the purchase of installation tooling for the compression process is substantial.

Aluminum mechanical connectors are also reusable, have the flexibility to accommodate a wide range of cable, run cooler than conductors being joined, and have high mechanical strength.

Compression connectors have their advantages however, and are typically the chosen method with larger organizations responsible for bigger installations. Compression installations are made to last — they are irreversible and offer an extremely high holding strength. Aluminum compression connectors deliver high quality connections at a low installed cost after the initial investment in special tooling has been made.

Determining whether to go with mechanical or compression connectors is usually an installation-driven decision, with cost a fairly consistent underlying factor. After this decision has been made, there are still other variables to consider.

Choosing the right aluminum products
Whether opting for aluminum mechanical or compression connectors, you should select a manufacturer that offers features such as:

• Dual-rated products for use on both aluminum and copper conductors.
• Connector sections that are heavy enough to carry full electrical loads of conductors and withstand the forces applied during installation.
• Contact surfaces that are finished and protected to prevent reformation of non-conducting oxides.
• Contact paths that are as short and direct as possible.
• Connector designs that prevent moisture and corrosive media penetration into contact areas from causing potential corrosion.
• Ensure that pressure applied from bolts as well as from compression tools is well-distributed over the contact surface and does not weaken the conductor.
• Electro-tin plated contact surfaces that provide for durable, long-lasting, corrosion-resistant connections, if required.

Also, make sure that your manufacturer produces a wide enough range of aluminum products with the right materials and properties to exactly meet your application needs. For example, for bolted mechanical connectors, look for heat-treatable alloys that deliver the right combination of conductivity and strength.

For compression connectors, you’ll want a high-conductivity, malleable grade aluminum that supplies the right level of ductility.

Also, with all your aluminum connectors, you should make sure the required hardware has high strength and provides resistance to both corrosion and galling. Some companies offer hardware that is coated with a lubricant that not only prevents galling, but also results in optimum performance for recommended installation torques.

The oxide issue
Oxide film is an environmental product of aluminum that, if not properly addressed, can be problematic. To offset the effects of oxide film, which is present on all aluminum surfaces and can cause high contact resistance, seek out a connector that incorporates a material designed to inhibit oxide and minimize galvanic corrosion during the service life of a connection.

Up to spec
Of course, specifiers should always ensure that their aluminum connectors meet all the necessary standards. All compression connectors should conform to applicable sections of the National Electric Code.

If you require third party testing and approval, you’ll need products that meet the UL486A-486B Standard, and you may also require a product that has CSA 22.2 No. 65 certification.

To offset future problems, look for a manufacturer with products that meet all of these standards.

Proper installation
Selecting the appropriate aluminum connector for the conductor and application is step one in ensuring a successful aluminum-based connection. After you’ve chosen the right connector, you need to:

• Measure and mark the recommended insulation strip length — carefully cut and remove the insulation to avoid nicking strands
• Wire brush the stripped length of wire and unplated aluminum contact pad thoroughly to remove surface oxides
• Apply an oxide inhibiting compound to any exposed conductor surface before inserting the conductor into the connector
• For compression connectors, select the appropriate installation tool and die — then complete the process with the required number of crimps
• For mechanical connectors, all hardware must be torqued to recommended values according to hardware material and size

The right connection
Aluminum connectors are by no means right for every application. There are certainly many installations, including those on the residential side, where copper makes the most sense. But in order to ensure you are specifying connections that work best for a given application and budget, you should consider all your options, including the connector material and connection type before making sure you follow the proper installation guidelines. By connecting with the right information up front, you’re much more likely to make successful connections on the job.

Jacqueline Sylvia has over 25 years experience in the electrical and electronics industry. She is currently senior product manager at FCI Burndy. Richard Brooks has been with FCI Burndy for the past 15 years, most recently as product manager. With operations in 30 countries and 2005 sales of 1.28 billion euros, FCI is a leading manufacturer of connectors. Its 13,500 employees provide high-quality, innovative products for a wide range of consumer and industrial applications. For more information, visit www.fciconnect.com.