InterNACHI Home Inspection Glossary
by Nick Gromicko and Kenton Shepard
Between approximately 1965 and 1973, single-strand aluminum wiring was sometimes substituted for copper branch-circuit wiring in residential electrical systemsAluminum and copper wiring, with each metal clearly identifiable by its color 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 language.
Facts and Figures
•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 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, 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 hazard.
•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 location.
•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 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 marked CO/ALR, which stands for “copper/aluminum revised."
•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 wiring:
•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 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 be considered:
•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 over time.
•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 wire.
•Remove the ignitable materials from the vicinity of the connections.
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.
by Nick Gromicko and Kenton Shepard
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.
InterNACHI inspectors should always disclaim knob-and-tube wiring during their inspections.
Facts About Knob-and-Tube Wiring: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 K&T 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, 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 contained insulation with additives that may oxidize copper wire. Bending the wires may cause insulation to crack and peel away.
K&T wiring is often spliced with modern wiring incorrectly by amateurs. This is perhaps due to the ease by which K&T wiring is accessed.
K&T wiring is designed to dissipate heat into free air, and insulation will disturb this process. Insulation around K&T wires will cause heat to build up, and this creates a fire hazard. The 2008 National Electrical Code (NEC) requires that this wiring system not be covered by insulation. Specifically, it states that this wiring system should not be in…
hollow spaces of walls, ceilings and attics where such spaces are insulated by loose, rolled or foamed-in-place insulating material that envelops the conductors.
Local jurisdictions may or may not adopt the NEC’s requirement. The California Electrical Code, for instance, allows insulation to be in contact with knob-and-tube wiring, provided that certain conditions are met, such as, but not limited to, the following:
•A licensed electrical contractor must certify that the system is safe.
•The certification must be filed with the local building department.
•Accessible areas where insulation covers the wiring must be posted with a warning sign. In some areas, this sign must be in Spanish and English.
•The insulation must be non-combustible and non-conductive.
•Normal requirements for insulation must be met.
Modifications:Knob and Tube Wiring on thermal insulation
When K&T wiring was first introduced, common household electrical appliances were limited to little more than toasters, tea kettles, coffee percolators and
clothes irons. The electrical requirements of mid- to late-20th century homes
could not have been foreseen during the late 18th century, a time during which electricity, to many, was seen as a passing fad. Existing K&T systems are notorious for modifications made in an attempt to match the increasing amperage loads required by televisions, refrigerators, and a plethora of other electric appliances. Many of these attempts were made by insufficiently trained handymen, rather than experienced electricians, whose work made the wiring system vulnerable to overloading.
•Many homeowners adapted to the inadequate amperage of K&T wiring by installing fuses with resistances that were too high for the wiring. The result of this modification is that the fuses would not blow as often and the wiring would suffer heat damage due to excessive amperage loads.
•It is not uncommon for inspectors to find connections wrapped with masking tape or Scotch tape instead of electrical tape.
K&T Wiring and Insurance:
Many insurance companies refuse to insure houses that have knob-and-tube wiring due to the risk of fire. Exceptions are sometimes made for houses where an electrical contractor has deemed the system to be safe.
Advice for those with K&T wiring:
•Have the system evaluated by a qualified electrician. Only an expert can confirm that the system was installed and modified correctly.
•Do not run an excessive amount of appliances in the home, as this can cause a fire.
•Where the wiring is brittle or cracked, it should be replaced. Proper maintenance is crucial.
•K&T wiring should not be used in kitchens, bathrooms, laundry rooms or outdoors. Wiring must be grounded in order to be used safely in these locations.
•Rewiring a house can take weeks and cost thousands of dollars, but unsafe wiring can cause fires, complicate estate transactions, and make insurers skittish.
•Homeowners should carefully consider their options before deciding whether to rewire their house.
•The homeowner or an electrician should carefully remove any insulation that is found surrounding K&T wires.
•Prospective home buyers should get an estimate of the cost of replacing K&T wiring. They can use this amount to negotiate a cheaper price for the house.
In summary, knob-and-tube wiring is likely to be a safety hazard due to improper modifications and the addition of building insulation. Inspectors need to be wary of this old system and be prepared to inform their clients about its potential dangers.