Aluminum Wiring
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 led 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 homeowner policy. Homeowners should talk with their insurance agents about whether the presence of aluminum wiring in their home is a problem that requires changes to their policy.
Facts and Figures
- In April 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 outlet.
- 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, when 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 that 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.
- 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.
- 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 loosen.
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…
Options for Correction
Aluminum wiring should be evaluated by a qualified electrician who is experienced in evaluating and correcting aluminum wiring problems. The CPSC recommends the following two methods for correction:
- Rewire the home with copper wire: While this is the most effective method, rewiring is expensive and impractical in most cases.
- 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…
Knob-and-Tube Wiring
Knob-and-tube (K&T) wiring was an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1940s. The system is considered obsolete and can be a safety hazard, although some of the fear associated with it is undeserved.
Facts About Knob-and-Tube Wiring
- It is not inherently dangerous. The dangers from this system arise from its age, improper modifications, and situations where building insulation envelops the wires.
- It has no ground wire and thus cannot service any three-pronged appliances.
- While it is considered obsolete, there is no code that requires its complete removal. It is treated differently in different jurisdictions. In some areas, it must be removed at all accessible locations, while others merely require that it not be installed in new construction.
- It is not permitted in any new construction.
How Knob-and-Tube Wiring Works
K&T wiring consists of insulated copper conductors passing through lumber framing drill holes via protective porcelain insulating tubes. They are supported along their length by nailed-down porcelain knobs. Where wires enter a wiring device, such as a lamp or switch, or were pulled into a wall, they are protected by flexible cloth or rubber insulation called loom.
Advantages of Knob-and-Tube Wiring
- K&T wiring has a higher ampacity than wiring systems of the same gauge. The reason for this is that the hot and neutral wires are separated from one another, usually by 4 to 6 inches, which allows the wires to readily dissipate heat into free air.
- K&T wires are less likely than Romex® cables to be punctured by nails because K&T wires are held away from the framing.
- The porcelain components have an almost unlimited lifespan.
- The original installation of knob-and-tube wiring is often superior to that of modern Romex® wiring. K&T wiring installation requires more skill to install than Romex® and, for this reason, unskilled people rarely ever installed it.
Problems Associated with Knob-and-Tube Wiring
- Unsafe modifications are far more common with K&T wiring than they are with Romex® and other modern wiring systems. Part of the reason for this is that K&T is so old that more opportunity has existed for improper modifications.
- The insulation that envelopes the wiring is a fire hazard.
- It tends to stretch and sag over time.
- It lacks a grounding conductor. Grounding conductors reduce the chance of electrical fire and damage to sensitive equipment.
- In older systems, the wiring is insulated with varnish and fiber materials that are susceptible to deterioration.
- Compared with modern wiring insulation, K&T wiring is less resistant to damage. K&T wiring insulated with cambric and asbestos is not rated for moisture exposure. Older systems contain insulation with additives that may oxidize copper wire. Bending the wires may cause insulation to crack and peel away.
Full pdf document here: Safe_Home_Book-ELECTRICAL-SAFETY