Aluminum has been safely and effectively used in electrical applications in the United States for more than 100 years. It takes only one pound of aluminum to equal the current-carrying capacity of two pounds of copper making it an extremely attractive material for utilities, builders and others. Following are some basic FAQs on aluminum in the electrical sector as well as more detailed background material in this sector. You may also find the installation procedures and design considerations for aluminum building wire and cable in residential, commercial, institutional and industrial applications in NECA/AA 104-2012, an American National Standard publication.
FAQs and Answers For Aluminum Alloy Building Wire
Q1) What are the relative conductivities of aluminum and copper?
Aluminum has 61% the conductivity of copper on a volume basis and 200% the conductivity of copper on a weight basis.
Q2) How do I size aluminum and copper conductors?
Conductor sizing is based on the load to be carried and applicable rules in the National Electrical Code (NEC). The NEC contains Tables to size either copper or aluminum conductors with a variety of insulations. Table 310.16 is the most commonly used, and includes up to three current-carrying conductors in raceway, cable or earth.
Q3) Why is copper used more often for smaller wire sizes?
Copper, having been available to mankind for thousands of years, was readily available at the beginning of the electrical industry in 1882. At that time, aluminum was only available in very small quantities, so it was a precious metal more valuable than gold or silver. Ninety-five percent of all the aluminum ever produced was made after WWII; and by then, the electrical industry had developed using copper. Over the past few decades, aluminum has increasingly replaced copper for electrical applications. The transformation started on the utility grid thru transmission, distribution, and has continued down to service drop, service entrance and building wire feeders.
In the United States today, copper is typically the only choice available for branch circuit wiring. Receptacles and switches are usually rated only for copper, and are less expensive than CO/ALR devices.
Q4) Is there a certain kind of aluminum that must be used for building wire?
Yes. In most cases, you must use an AA-8000 series aluminum alloy building wire as required in NEC 310.14. There are some exceptions, notably underground service entrance conductors that terminate outside a building.
Q5) What are the physical differences between copper and aluminum alloy building wire?
1. Copper and aluminum wire of equal ampacity sizes have equivalent thermal and mechanical performance.
2. Aluminum conductors are larger in size than equal ampacity copper conductors.
3. Aluminum weighs half of the equivalent ampacity copper, which is advantageous for pulling or supporting.
4. The endurance fatigue (the ability to be bent back and forth repeatedly without breaking) of aluminum alloy building wire is generally greater than equivalent ampacity copper.
Q6) Are there considerations other than ampacity when using aluminum or copper?
Conduits: Copper conductors may allow the use of a smaller conduit size. However, with the compact conductors normally used for aluminum alloy building wire, conduit sizing is generally the same for equal ampacity copper and aluminum.
Connections: Connector sizing must match the AWG or kcmil size of the conductor, whether copper or aluminum.
Physical characteristics: Aluminum conductors are lighter and easier to pull and/or support. Aluminum alloy building wire requires less force to bend, and once bent, exhibits less springback.
Cost: Aluminum conductors are usually more economical than equal ampacity copper conductors.
Specifications: Job specifications may require a certain type of conductor. They may or may not permit an alternate.
Local codes: Municipal or state electrical code amendments may restrict the use of conductors beyond the requirements of the National Electrical Code.
Q7) Do you need to use special connectors with aluminum?
All connectors are tested and listed for use with specific conductor type(s). For aluminum, connectors marked “AL” must be used. In most cases, the same connectors can be used for both copper and aluminum provided they are marked: AL9CU or AL7CU. Never use a connector marked CU only with aluminum, just as you shouldn’t use AL only marked connectors with copper.
For all connectors, only those that have been tested for specific conductor types should be used, and you must follow the manufacturers’ installation instructions. Most mechanical screw-type lugs are dual-rated and accept either aluminum or copper conductors.
Q8) Are compression type connectors required for aluminum conductors?
No, both mechanical set-screw and compression connectors marked “AL” can be used with aluminum installed according to manufacturers’ instructions. Both types of connectors have passed the same performance tests. Testing has shown that aluminum and copper building wire perform equally on mechanical screw-type lugs.
Q9) Is joint compound required to be used on aluminum to prevent corrosion?
Only if the connector manufacturer or local codes specifically require it. The NEC does not require oxide inhibitor for either aluminum or copper, but it does require that you follow manufacturers’ installation instructions for listed products.
However, even if oxide inhibitor is not specifically required, it is recommended for both aluminum and copper conductors to prevent ingress of moisture and the possibility of subsequent corrosion. Both copper and aluminum conductors will corrode if installed in corrosive environments. Proper installation and choice of connector help to prevent corrosion at connections.
Oxide inhibitors are also tested for specific uses. Be sure to follow manufacturers recommendations and use only inhibitors specifically listed for the conductor type and voltage class you are installing.
Q10) Do aluminum connections need to be periodically tightened to maintain a good electrical connection?
No. Connections on either aluminum or copper should not be retightened after installation following manufacturers’ installation instructions. Connector test performance requirements are based upon no retightening. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, does not call for retightening aluminum conductors. Connections should only be tightened if there is evidence of a loose connection. Both over-tightening and under-tightening can cause failure of aluminum or copper connections. Unwarranted re-tightening of screw-type connectors can lead to failure of the connection with either aluminum or copper conductors.
Aluminum Electrical Conductor Handbook
This comprehensive guidebook provides detailed technical information on using aluminum for electrical applications.