10 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
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
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
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
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
Q7) Do you need to use special connectors with
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
Q8) Are compression type connectors required for
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
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
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.