Aluminum Wiring

Aluminum Wire Then and Now:   Aluminum wiring was widely used in residential electrical systems from around the mid-l960’s until its use was significantly limited in the mid-l970’s.  During this period, aluminum wiring was cheaper and more readily available than copper.  However, after a decade or so of use, aluminum was found to be a less than ideal replacement for copper in residential wiring systems.  Aluminum has several characteristics that make it less desirable than copper for many specific residential electrical wiring applications.

Among the more significant characteristics of aluminum wire are;

·         Lower ductility,

·         Pressure sensitivity/flow,

·         Deleterious effects from oxidation,

·         Higher resistance to electrical current flow,

·         Greater vulnerability to mechanical damage,

·         Thermal sensitivity (causing expansion and contraction), and,

·         Incompatibility when placed in contact with certain other metals.

All of these properties, if not clearly understood and respected when working with aluminum wiring, can lead to conditions which may damage the wiring and cause over-heating in the surrounding area.  There are two major potential safety hazards associated with any improper residential electrical wiring condition, regardless of the wiring materials used – excessive heat and electrocution.

RESISTENCE

Aluminum’s inherently high resistance to electrical current flow (lower conductivity) requires larger diameter conductors than would be necessary if copper were installed.  For example; a number 14 gauge copper wire is adequate for a 110 Volt, 15 Amp circuit, but a number 12 gauge aluminum wire is required for the same circuit (the smaller the gauge number the larger the diameter of the wire).

Ductility

Aluminum is less ductile than copper.  It fatigues and breaks more readily than copper when subjected to repeated bending.  Greater care is required when working with aluminum wire.  As the wire fatigues, it breaks down internally, which in turn increases its already higher resistance to electrical current flow.  This results in excessive heat build-up at the area of fatigue.

Compatibility

The incompatibility of certain metals when in contact with other metals causes a reaction known as galvanic corrosion.  Simply put, one metal is eaten away by its contact with another.  Galvanic corrosion occurs when aluminum comes into contact with certain other metals.  This requires that care be taken to determine the component material of any outlet, switch or other electrical device to which aluminum wiring is connected.  If aluminum wiring contacts an incompatible metal, it may be damaged; resulting in increased resistance to electrical current flow and, again, heat build-up.  To insure that any receptacle, switch or other electrical device is compatible with aluminum wiring, the designation “CUAL” or COALR” should be clearly visible on the device, or the device should be clearly specified
by the manufacturer as being compatible with aluminum wiring.

Mechanical Damage

Aluminum’s greater vulnerability to mechanical damage means that greater care is required when working with aluminum wiring to avoid nicking or otherwise damaging the wire. 
When an aluminum wire is nicked, the diameter of the wire is reduced at the nick, and the same thing happens that occurs with fatigue; the resistance to electrical current flow increases, resulting in excessive heat build-up at the nicked area.

Oxidation

Oxidation on the surface of a metal occurs when that metal reacts with oxygen under certain conditions.  Some metal oxides are very electrically conductive and others are not.  Aluminum oxide, which forms as a white powder on the surface of aluminum wiring when moisture is present, is not conductive.  In contrast, Copper oxide is very conductive.  Therefore, greater care must be exercised to ensure that the exposed surfaces of aluminum wiring are free of oxidation and coated with an electrically conductive anti-oxidant compound.  If aluminum oxide is present, it causes an increase in the resistance to electrical current flow, and excessive heat build-up can result.

Temperature Sensitivity

The diameter of both copper and aluminum wire increases as the electrical current flow and/or surrounding air temperature increases, and the diameter decreases as electrical
current flow and/or surrounding air temperature decreases.  However, the diameter of aluminum wire changes significantly more than copper does when subjected to the same variations in electrical current flow or surrounding air temperature.  The significance of this property of aluminum wiring becomes evident at points where the wires are confined at a connection such as a screw terminal on an electrical device.  At such points, movement due to increases and decreases in the size of the wire can cause the wire to become loose at the connection.  A loose connection causes reduced contact between the wire and the device resulting in an increased resistance to electrical current flow and, again, heat build-up.  This
is one reason why aluminum wires should never be inserted into the “push-in”, “bayonet” or “stab” type terminations often found on the back of some receptacles and light switches.

Pressure Sensitivity/Flow

Because aluminum wire is softer or more malleable than copper wire, it will tend to continue to deform or “flow” when compressed under a pressure terminal such as a screw terminal on an electrical device.  This means that if a screw terminal is over tightened on aluminum wiring, the aluminum will continue to deform or “ flow” after the tightening has stopped.  This continued deforming, or flow, leads to a loose connection, which also results in increased resistance to electrical current flow and heat build-up.

Aluminum Wire In Perspective

By now it should be clear that all of the undesirable characteristics of aluminum wiring will tend to increase the potential for excessive heat build-up at the terminations or connections in a wiring system, not along the unexposed sections of the wiring.  This does not mean that the presence and use of aluminum wiring will automatically result in any or all of these conditions.  When aluminum wiring is installed by a competent professional who understands all of the characteristics of the material and who follows the steps necessary for safe installation, it is not considered hazardous.  If modification of aluminum wiring to reduce or eliminate potential hazards at terminations or connections is performed, it is not necessary to remove or replace all of the wiring in the home.