by Nick Gromicko, Rob London and
Between approximately 1965 and 1973, single-strand aluminum
wiring was sometimes substituted for copper branch-circuit wiring
in residential electrical systems due to the sudden escalating price of copper.
After a decade of use by homeowners and electricians, inherent
weaknesses were discovered in the metal that lead to its disuse
as a branch wiring material. Although properly maintained
aluminum wiring is acceptable, aluminum will generally become
defective faster than copper due to certain qualities inherent in
the metal. Neglected connections in outlets, switches and light
fixtures containing aluminum wiring become increasingly dangerous
over time. Poor connections cause wiring to overheat, creating a
potential fire hazard. In addition, the presence of single-strand
aluminum wiring may void a home’s insurance policies.
Inspectors may instruct their clients to talk with their
insurance agents about whether the presence of aluminum wiring in
their home is a problem that requires changes to their policy
- On April, 28, 1974, two people were killed in a house fire in
Hampton Bays, New York. Fire officials determined that the fire
was caused by a faulty aluminum wire connection at an
- According to the Consumer Product Safety Commission (CPSC),
"Homes wired with aluminum wire manufactured before 1972
['old technology' aluminum wire] are 55 times more likely
to have one or more connections reach "Fire Hazard
Conditions" than is a home wired with copper."
Aluminum as a Metal
Aluminum possesses certain qualities that, compared with copper,
make it an undesirable material as an electrical conductor. These
qualities all lead to loose connections, where fire hazards
become likely. These qualities are as follows:
- higher electrical resistance. Aluminum has a high resistance
to electrical current flow, which means that, given the same
amperage, aluminum conductors must be of a larger diameter than
would be required by copper conductors.
- less ductile. Aluminum will fatigue and break down more
readily when subjected to bending and other forms of abuse than
copper, which is more ductile. Fatigue will cause the wire to
break down internally and will increasingly resist electrical
current, leading to a buildup of excessive heat.
- galvanic corrosion. In the presence of moisture,
aluminum will undergo galvanic corrosion when it comes into
contact with certain dissimilar metals.
- oxidation. Exposure to oxygen in the air causes deterioration
to the outer surface of the wire. This process is called
oxidation. Aluminum wire is more easily oxidized than copper
wire, and the compound formed by this process – aluminum
oxide – is less conductive than copper oxide. As time
passes, oxidation can deteriorate connections and present a fire
- greater malleability. Aluminum is soft and malleable, meaning
it is highly sensitive to compression. After a screw has been
over-tightened on aluminum wiring, for instance, the wire will
continue to deform or “flow” even after the
tightening has ceased. This deformation will create a loose
connection and increase electrical resistance in that
- greater thermal expansion and contraction. Even more than
copper, aluminum expands and contracts with changes in
temperature. Over time, this process will cause connections
between the wire and the device to degrade. For this reason,
aluminum wires should never be inserted into the
“stab,” “bayonet” or
“push-in” type terminations found on the back of many
light switches and outlets.
- excessive vibration. Electrical current vibrates as it passes
through wiring. This vibration is more extreme in aluminum than
it is in copper, and, as time passes, it can cause connections to
Identifying Aluminum Wiring
- Aluminum wires are the color of aluminum and are easily
discernible from copper and other metals.
- Since the early 1970s, wiring-device binding terminals for
use with aluminum wire have been marked CO/ALR, which stands for
- Look for the word "aluminum" or the initials
"AL" on the plastic wire jacket. Where wiring is
visible, such as in the attic or electrical panel, inspectors can
look for printed or embossed letters on the plastic wire jacket.
Aluminum wire may have the word "aluminum," or a
specific brand name, such as "Kaiser Aluminum," marked
on the wire jacket. Where labels are hard to read, a light can be
shined along the length of the wire.
- When was the house built? Homes built or expanded between
1965 and 1973 are more likely to have aluminum wiring than houses
built before or after those years.
Options for Correction
Aluminum wiring should be evaluated by a qualified electrician
who is experienced in evaluating and correcting aluminum wiring
problems. Not all licensed electricians are properly trained to
deal with defective aluminum wiring. The CPSC recommends the
following two methods for correction for aluminum
- Rewire the home with copper wire. While this is the most
effective method, rewiring is expensive and impractical, in most
- Use copalum crimps. The crimp connector repair consists of
attaching a piece of copper wire to the existing aluminum wire
branch circuit with a specially designed metal sleeve and powered
crimping tool. This special connector can be properly installed
only with the matching AMP tool. An insulating sleeve is placed
around the crimp connector to complete the repair. Although
effective, they are expensive (typically around $50 per outlet,
switch or light fixture).
Although not recommended by the CPSC as methods of permanent
repair for defective aluminum wiring, the following methods may
- application of anti-oxidant paste. This method can be used
for wires that are multi-stranded or wires that are too large to
be effectively crimped.
- pigtailing. This method involves attaching a short piece of
copper wire to the aluminum wire with a twist-on connector. the
copper wire is connected to the switch, wall outlet or other
termination device. This method is only effective if the
connections between the aluminum wires and the copper pigtails
are extremely reliable. Pigtailing with some types of connectors,
even though Underwriters Laboratories might presently list them
for the application, can lead to increasing the hazard. Also,
beware that pigtailing will increase the number of connections,
all of which must be maintained. Aluminum Wiring Repair (AWR),
Inc., of Aurora, Colorado, advises that pigtailing can be useful
as a temporary repair or in isolated applications, such as the
installation of a ceiling fan.
- CO/ALR connections. According to the CPSC, these devices
cannot be used for all parts of the wiring system, such as
ceiling-mounted light fixtures or permanently wired appliances
and, as such, CO/ALR connections cannot constitute a complete
repair. Also, according to AWR, these connections often loosen
- alumiconn. Although AWR believes this method may be an
effective temporary fix, they are wary that it has little
history, and that they are larger than copper crimps and are
often incorrectly applied.
- Replace certain failure-prone types of devices and
connections with others that are more compatible with aluminum
- Remove the ignitable materials from the vicinity of the
In summary, aluminum wiring can be a fire hazard due to
inherent qualities of the metal. Inspectors should be capable of
identifying this type of wiring.