Solid Conductor Aluminum Wiring
Small, solid conductor aluminum wiring,
such as 10 gauge, rated 20 amps and 12 gauge rated 15 amps, was used
from 1965 to 1974. In 1975, the NEC prohibited the use of single
conductor aluminum wiring.
The main concern with small gauge, single
conductor aluminum wiring is its expansion characteristics when it is
heated. If the wire is in a situation where the amount of current that
is being drawn does not heat the wire, there will be no typical aluminum
wire related concerns (i.e., if an aluminum wire circuit only serves a
lamp and a TV, it will not draw enough current to cause expansion
problems). A 15-amp circuit that is serving a lamp and a TV will have a
maximum load of only about 3 or 4 amps. This is not nearly enough to
cause aluminum wire concerns due to heat.
To determine how much current a circuit
is drawing, divide the wattage rating of the lighting and or appliances
on the circuit and divide by the voltage. Watts = Amps X Volts so a 100
watt light bulb divided by 120 volts equals .8 amps.
When almost anything is heated, expansion
will occur. Materials of different densities will expand at different
rates. When an aluminum wire is attached to a steel alloy contact with a
similar steel screw, and the contact, screw and wire is heated by the
current moving through the circuit, everything expands. During this
process, the density of the steel will tend to distort the aluminum
wire. When the contact cools, the steel alloy will return to its
original size, while the aluminum, because it was distorted, will not.
When aluminum is exposed to air, a film
of aluminum oxide forms on the metal’s surface. The oxide formation
causes the wire to loosen under the mounting screws. When the screws are
worked loose, the oxidation of the aluminum wire under the screws heat
and create a fire hazard.
Return to Top
When there is enough distortion, the
aluminum wire will become loose at the contact. It may not appear loose,
because it may not come off, as you would expect from a loose wire. The
loose aluminum wire may function with micro arcing, which will cause
more heat at the contact and make the problem worse. The additional heat
causes stress on the wire, and may cause a slight fracture in the run of
the wire about 1/8 inch from the contact. This fracture causes
additional micro arcing and even more heat. Fractures occur at this
point because this is the point of maximum temperature difference or
change. When multiple arcing occurs, the potential for excessive heat
and possibly a fire may be present.
The apparent solution to the problem
would be to remove the aluminum wire from the steel alloy contacts. The
original suggestion was to pigtail the aluminum wire with a piece of
copper wire and to attach the copper wire onto the steel contact. This
would have been acceptable, except for the fact that the aluminum and
copper, being dissimilar, corrode due to oxidation when they are in
contact with each other.
To help eliminate the problems and
concerns, device manufacturers developed switches and outlets designed
to receive copper or aluminum. These devices were called co/al devices,
however, they were not as effective as the manufacturers had
anticipated, and were revised. The revised devices are called co/alr,
the “r” meaning revised.
With the co/alr devices, the switch and
outlet concerns were addressed, however, there is still a concern with
fixtures that are wired directly, such as a chandelier. In most cases,
and assuming they are wired correctly and the loads are properly
calculated, there should be no problems, because the amount of heat
generated by these fixtures is not enough to stress or overload the
wire. The concerns are related to situations that are unknown or where
the wiring or calculations are incorrect.
Return to Top
AMP Corporation designed a wire crimping
tool and system that will provide dependable results with aluminum to
copper connections. The crimp is designed to ensure that air does not
come between the aluminum and copper. After the connection is crimped,
it is covered with a sleeve, which is shrunk around the connection. This
process minimizes oxidation at the contact. This is the only system that
the Consumer Product Safety Commission (CPSC) has accepted. 1. The CPSC
does not recognize any other system or correction as acceptable. This
creates legal concerns for anyone who may recommend a different
solution. 2. AMP Corporation does not sell the crimping tool; they have
patents pending and only allow users to lease the equipment. This limits
access for residential or small work, because it is difficult to justify
leasing costs for one house. 3. The number of “qualified” electricians
that have gone through the AMP training creates further limitations.
There are very few electricians in the country that have gone through
the training, and most are commercial electricians. Based on this
situation, we as home inspectors cannot recommend this as a solution,
because most of our clients will not be able to find a qualified
electrician in their area. 4. Our posture is to explain the aluminum
wire situation so that our client understands the concerns, and
recommend a licensed electrician to determine the best action.
The NEC and most jurisdictions recognize
twister wire nuts and co-alr device usage. The CPSC has not required the
removal of the other two methods from the marketplace. This would
suggest that there is insufficient research to ban the use of these
products.
ASHI standards require us to report the
presence of single conductor aluminum wire.
Return to Top
