This bulletin discusses some of the problems associated with the use of aluminum branch
circuit wiring inside buildings and some of the steps the aluminum industry and consumer-
oriented laboratories have taken to control these problems.
Aluminum has been used as an electrical conductor in overhead power transmission lines for
over 80 years. Aluminum conductor was approved by Underwriters Laboratories for use as
building wire in 1946. However, it was not widely used until 1965.
Aluminum conductors were introduced as a substitute for copper conductors during 1965
because of the shortage and escalating costs of copper. It was used extensively for wiring in
homes, apartments and mobile homes. It has been estimated that over two million homes and
condominiums were wired with aluminum conductors between 1965 and 1973.
The use of the aluminum conductors dropped off sharply after 1973 when copper became
more available and less costly than aluminum. Wire manufacturers discontinued
manufacturing aluminum conductors for use in general branch circuit wiring around 1980.
Large size aluminum conductors are still widely used in other applications. Today, virtually
all overhead conductors used by utilities are made of aluminum and roughly 90% of all
residential service entrance conductors are made of aluminum. A high percentage of feeder-
size conductors used inside buildings are aluminum. Larger size aluminum conductors (No. 6
AWG or larger) may be used for electric range applications in residential buildings.
Smaller size aluminum conductors (No. 10 and No. 12 AWG) are no longer in production for
use in branch circuit wiring.
During the years 1968 to 1972, various safety and consumer-oriented organizations received
complaints from homeowners concerning blinking lights, erratic TV set performance, warm
switch plate covers, and fire problems associated with aluminum conductors. The aluminum
wire industry, along with various safety and consumer oriented organizations, including
Underwriters Laboratories, began an investigation to identify the problems and develop
solutions to control the problems. The Consumer Products Safety Commission joined in this
investigative effort when it was organized in 1972.
The investigating parties found that problems experienced with aluminum conductors were
largely limited to the 15 and 20 ampere connections found in home wall receptacles and
switches. They identified the following deficiencies in aluminum conductors
1. Incompatibility with existing wiring devices.
Receptacles, switches, and other wiring devices on the market in the late 60s and early 70s
used copper or steel binding screws, terminals, and other connectors. The aluminum
conductors were not compatible with these wiring devices due to the difference
characteristics of the metals. Aluminum has a much greater coefficient of expansion than
copper and steel. Aluminum also has a greater cold flow rate than copper or steel. Cold flow,
or creep, is defined as the slow deformation of material under stress. When placed into
service in a building wiring system, the aluminum conductors and copper and steel terminals,
binding screws, and connectors are subject to cycles of heating and cooling when the circuits
are energized and de-energized. Because the metals have different characteristics and
respond differently to this stimulus, the connections can become loose resulting in
overheating, arcing, and possible ignition of surrounding combustible materials.
The aluminum conductors produced between 1965 and 1973 were found to be brittle when
compared to copper. Bending of the wire during installation could result in partial fracture
which could result in self-heating and possible failure. Failure was most likely at receptacles
and switches where severe bending was required around binding screws. Failure could also
result anywhere along the circuit where bending was required to pass the conductor through
walls and conduit. Any nicks in the aluminum conductor that occurred during installation
would also cause more self-heating than normally associated with a copper conductor.
Installation of the aluminum conductors required a higher degree of workmanship than
required for copper.
Another characteristic of aluminum conductors is the formation of aluminum oxide on the
surface when exposed to air. This oxide film is of high electrical resistance. Unless the
wiring connection is properly prepared, a high resistance contact is the result and overheating
is likely to occur.
In 1973, new materials and procedures were introduced to control the problems with existing
installations and existing inventories of aluminum conductors and to prevent similar
problems in future installations.
In 1973, the aluminum industry began producing an aluminum conductor with improved
characteristics. The wire is less brittle and has lower creep rates than the original material.
Aluminum produced prior to 1973 is now called “old technology” aluminum and the revised
material “new technology” aluminum. Wiring device manufacturers also began producing
receptacles and switches more compatible with the aluminum conductors.
Three methods were developed for repairing aluminum wiring at receptacles and switches.
1. Pig-tailing (for old technology wiring).
2. CO/ALR devices (for new technology wiring).
3. Pressure connectors.
Pig-tailing is no longer recognized as an
acceptable procedure by Underwriter
Laboratories or the Consumer Product Safety
Commission. This is due to defects uncovered
in laboratory studies. Pig-tailing consists of
disconnecting the aluminum conductor from
the receptacle and joining it to a short length of
copper conductor with a twist type “wire nut”.
The length of copper conductor is then attached
to the receptacle in a normal fashion.
A second method of repairing aluminum wiring involves the use of pressure connectors
instead of the twist type “wire nut” connectors. The aluminum conductor is disconnected
from the receptacle and joined to a short length of copper wiring with a pressure type
connector. The aluminum and copper wires are placed side-by-side and a circular ring is
slipped over them. The assembly is then
inserted into a special crimping tool where
the ring and wires are compressed. The
length of copper conductor is then attached
to the receptacle in a normal fashion. The
compression connectors not only provide a
more secure connection, but also control
the oxidation problem. The pressure
connectors used along with a joint
compound breaks down the aluminum
oxide film and prevents it from reforming
at the connection points. The AMP
Corporation, Valley Forge, PA
manufactures pressure type connectors
under the name of COPALUM, a patented
material that does not require the additional
use of a joint compound. COPALUM along with other type pressure connectors are listed
with Underwriters Laboratories.
A third method of repairing aluminum wiring is by replacing wall receptacles and switches
with hardware designed to be compatible with aluminum conductors. These are called
CO/ALR devices. These products are made of copper hardware and specially plated screws
that match the characteristics of aluminum conductors more closely than older type hardware.
CO/ALR products are listed by Underwriters Laboratories and are generally accepted in the
industry. However, they are not recommended by the Consumer Products
Safety Commission due to failures documented in laboratory tests. The Consumer Products
Safety Commission recommends the repair method using the COPALUM pressure type
Before 1971, switches, receptacles and other devices rated at 15 or 20 amps and intended for
copper only, were not marked. Those intended for copper or aluminum were marked “AL-
CU”. It later became evident that these “AL-CU” devices were not suitable for aluminum
wire in the 15-20 amp ratings. Since September 1971, Underwriters Laboratories required the
use of “CO/ALR” devices. Receptacles or switches were scrawls, quick-wire, push-in
terminals may only be used with copper or copper-clad aluminum wire.
In 1982, the courts rule that the Consumer Products Safety Commission did not have
jurisdiction over aluminum conductors. As a result, the Commission ended their
investigation of this product and their tabulation of losses associated with this product.
However, a preliminary analysis of losses associated with the aluminum conductors, made by
the CPSC in 1975, estimated that at least 500 fires and 12 deaths were recorded. The
Commission retained authority, however, over the products used to make repairs on
The aluminum industry and safety and consumer-oriented organizations recognized the
problems associated with the aluminum wiring produced and installed between 1965 and
1973 and responded by developing better materials and repair methods. Aluminum wiring
systems installed in homes, apartments and mobile homes after 1973 were likely made using
the latest aluminum conductor materials, wiring devices and methods. Some of the old style
existing inventory of aluminum conductor material was likely installed for some period after
1973, however, the hazards associated with using this existing inventory were controlled to
some degree by using the more compatible receptacles and switches and improved wiring
There is no data available to indicate how many aluminum wiring systems installed between
1965 and 1973 have been properly repaired. As a result, the CPSC published document 516
(available on their website: www.CPSC.gov) CPSC provides the following advice for
If you have noticed any of the trouble signs, have a qualified electrician determine
whether the problem is caused by deteriorating connections to aluminum wiring. DO
NOT TRY TO DO IT YOURSELF. You could be electrocuted or you could make the
connections worse by disturbing them. If you are not certain whether your building
has aluminum branch circuit wiring, you may be able to tell by looking at the
markings on the surface of the electrical cables which are visible in unfinished
basements, attics or garages. Aluminum wiring will have "Al" or "Aluminum"
marked every few feet along the length of the cable. (Note – the marking "CU-clad"
or "Copper-clad" in addition to the "Al" or "Aluminum" means that the cable uses
copper-coated aluminum wire and is not covered by this message.)
If you do have aluminum branch circuit wiring, the Commission suggests that you
have a qualified electrician check the system for impending trouble. Remember, you
may not have noticed any of the warning signs, but research shows that trouble may
develop over time and an electrician may spot potential problems before you notice
Underwriters Laboratories, Inc.
American Insurance Services Group, Inc.
Consumer Product Safety Commission
Factory Mutual Engineering Corporation
National Electrical Code
National Fire Protection Association