All aluminum conductors are not created equal. Find out what factors, including different constructions and alloys, affect installation the most
Aluminum building wire installation can be an uncertain subject for electricians, engineers, inspectors, and owners. There are many myths, beliefs, and opinions in the industry on why you should or should not use this product in certain applications. This article will address the most commonly asked questions surrounding this controversial issue and, in doing so, bring you up to date on the latest requirements for installing 600V aluminum alloy building wire by providing information on conductor sizing, termination, and maintenance recommendations. For a historical review of aluminum wire used prior to 1972, go to http://magazine.iaei.org/magazine/06_a/hunter.html.
Today, aluminum alloy building wire is generally available in sizes 8 AWG to 1,000kcmil (up to 1,500kcmil in Canada). Although not required by the 2005 National Electrical Code (NEC), aluminum alloy building wire in the United States is compact stranded and generally can be used in the same size conduit as copper. Compact stranding reduces the diameter of the conductor by about 10% (Photo 1).
Aluminum alloys can have significantly different characteristics, depending on their composition. Alloying, the combining of two or more metals, can significantly affect the properties of any metal. The ability to alloy aluminum — and alter its characteristics — is one of the primary reasons aluminum is so widely used. Aluminum conductor alloys have been developed for a range of strengths, conductivities, and characteristics.
Be cautious when reading information published about installing aluminum wire, since most of the recommendations are not specific about which alloy is being discussed. Many of the published instruction guidelines are applicable only to certain types of common utility wire and may have installation techniques based on anecdotal evidence rather than scientific fact.
Various types of aluminum conductors are manufactured for different applications — all with different alloys, constructions, and annealing or stranding. For instance, alloys used in overhead power lines have excellent tensile strength, yet are so stiff they are not suitable for use as building wire. On the other hand, building wire alloys are formulated for connection performance and flexibility but are not used for overhead applications due to a lack of the required mechanical characteristics.
For the purpose of this article, the guidelines and information presented here will be limited to compact stranded 600V cables made with AA-8000 series aluminum alloy and cross-linked polyethylene insulation (XLPE). We will not discuss smaller size branch-circuit connections because manufacturers in the United States generally only provide 8 or 6 AWG to 1,000kcmil aluminum wire and cable. The remainder of this article will refer to AA-8000 series aluminum building wire as “AA-8000” and to copper building wire as “copper.”
- What are the physical characteristics of AA-8000 wire?
AA-8000 is about half the weight of an equal ampacity copper wire. This lower weight translates to a lower pulling tension, which may decrease the likelihood of damaging the insulation of the wire during installation. AA-8000 has a higher strength-to-weight ratio than copper and a slightly larger diameter (based on compact stranding) for equal ampacity conductors. AA-8000 conductors are generally less expensive than equivalent ampacity copper conductors. ASTM B800 contains a table that lists the composition of all AA-8000 series formulas currently registered. ASTM B801 contains the construction requirements for compact stranded AA-8000 series wire.
- Are there any special requirements to address when installing AA-8000?
In short, the answer is no. Most terminal lugs are dual-rated for both copper and AA-8000, and cable installed in them should follow the lug manufacturer's recommended installation procedure. Terminating both AA-8000 and copper wire involves the same steps: Strip the insulation, wire brush the exposed conductor, apply oxide inhibitor, and torque or compress the connector to the recommended value. It is widely believed that using oxide inhibitor is only required for aluminum conductors, but that is untrue. This belief comes from the widespread use of an oxide inhibitor in utility applications where aluminum is the most prevalent conductor, as well as the use of this substance in connecting dissimilar metals, such as aluminum and copper conductors. Review the connector manufacturer's directions (and local code requirements) when installing conductors to determine if an oxide inhibitor is required.
There are too many types of connections (splices, terminations, compression, screw type, etc.) to discuss in detail within this article. However, if you're looking for a good step-by-step instructional reference on how to properly install AA-8000 wire in different applications, refer to the National Electrical Contractors Association's “Recommended Practice for Installing Aluminum Building Wire and Cable.” This standard contains detailed instructions on how to install aluminum wire and cable. More information about the standard is available on its Web site at www.neca-neis.org.
Table 300.19(A) of the NEC contains requirements for supporting conductors in raceway systems in vertical applications. The requirements for AA-8000 and copper conductors are very different.
- What are the recommended termination methods for AA-8000?
AA-8000 wire can be terminated using any connector listed for the application. These include mechanical screw-type connectors (Photo 2), compression connectors (Photo 3), pin connectors, and other specialized connectors. Check with your gear manufacturer or connector manufacturer for specific connectors that fit your application.
Most mechanical screw-type lugs provided with electrical equipment are dual-rated for both AA-8000 and copper in accordance with UL486A-B. Be sure to choose the appropriate size connector for your conductor. Connectors are usually listed with a wire size range, and that range is often the same for both copper and AA-8000. Therefore, if you convert a circuit from copper to AA-8000 or vice versa, you should verify that the connector range includes the new wire size.
- Does AA-8000 require frequent maintenance?
AA-8000 conductors require no more maintenance than copper conductors. As with copper, maintenance considerations should be based on the location and operating characteristics of the electrical connections. One resource for developing a maintenance procedure for electrical connections is NFPA 70B, the “Recommended Practice for Electrical Equipment Maintenance.” This standard does not differentiate between AA-8000 and copper wire.
- What does the NEC require for AA-8000 conductors?
Conductor material — Section 310.14 of the NEC requires that aluminum conductors of most insulation types be made of AA-8000 series conductors. The NEC recognized aluminum alloy conductor materials in 1981 and expanded their use in 1987. The language has remained relatively unchanged since then.
Physical characteristics — Chapter 9, Table 5(A) includes compact aluminum wire dimensions. Chapter 9, Table 8 includes some aluminum conductor electrical properties. More exact information may be available from the conductor manufacturer.
Conduit fill — Conduit fill for compact stranded conductors is based on the “(A)” tables in Annex C. These tables apply to both aluminum and copper compact stranded wire. Software is also available to calculate the NEC minimum conduit size for equivalent circuits.
Terminations — Section 110.14(A) requires that terminals used for aluminum be so identified. Section 250.64(A) requires that aluminum grounding electrode conductors used outdoors shall not be terminated within 18 inches of the earth.
- How should AA-8000 wire be specified?
A specification for aluminum wire should call for UL-listed AA-8000 series conductors, XLPE insulation, and compact-stranded conductors. UL-listed connectors also should be specified, as well as the type of connection.
- What should the contractor look for when purchasing the wire?
The installer should verify that any aluminum wire installed in applications governed by the NEC is UL listed and that its insulation is suitable for the installation location.
For example, XHHW-2 is rated for 90°C in both dry and wet locations. It is sunlight resistant and has a higher short-circuit withstand rating than thermoplastic insulations such as THHN. One other common insulation type available for AA-8000 building wire is USE-2/RHH/RHW-2. With the multiple insulation types, this conductor can be direct buried and used for interior wiring applications.
- What should the inspector look for when inspecting AA-8000 conductor installations?
Inspectors should verify the conductor is UL listed and is sized properly for the load. Table 310.16 in the NEC contains allowable ampacities for AA-8000 wire in most feeder and branch-circuit applications. Inspectors also should verify the lugs are rated for use with aluminum conductors, that mechanical screw-type connectors are torqued properly, and that the proper tool and method is used for compression connectors and pin connectors. If the inspector has any doubts about the proper torquing of a connection, he can ask that the connection's torque value be verified in his presence by a qualified electrician.
AA-8000 series aluminum alloy building wire can be used in branch, feeder, and service applications, as well as for temporary wiring. It offers the advantages of being lightweight, flexible, reliable, and cost-effective. These characteristics make AA-8000 an option to consider on your next project.
Hunter is a senior engineer with Alcan Cable, Atlanta.
Sidebar: Aren't Aluminum Wire Mechanical Screw-Type Connectors Unreliable?
A common belief in the electrical industry is that AA-8000 connections loosen up over time on screw-type connections. However, laboratory tests and field installations have proven otherwise.
One such study was performed in 1995 by the Georgia Power Research Institute (now known as NEETRAC). The study included four different installation methods and five different wire sizes subjected to accelerated life testing more severe than industry standards. Test results revealed that both copper and AA-8030 conductors perform reliably on mechanical screw-type connectors. The full report is available at www.cable.alcan.com.