by Nick Gromicko, Lon Henderson, Ben Gromicko, and numerous InterNACHI® members who have contributed images and content
The U.S. Consumer Product Safety Commission (CPSC) and other government entities have investigated numerous hazardous incidents and fires involving aluminum branch circuit wiring throughout the United States. This article offers guidance for home inspectors who observe aluminum wiring while conducting a home inspection according to the InterNACHI® Home Inspection Standards of Practice (www.nachi.org/sop). In addition, this article covers solid and stranded wires, inspection tips, reporting, trouble signs, observations, disclaimers, myths, building codes, connections, comparisons, and the history of aluminum wiring.
The inspection image above was provided by InterNACHI® Certified Home Inspector Lon Henderson (https://www.nachi.org/certified-inspectors/lon-henderson-cmi-53115).
Standards of Practice
Home inspectors should conduct inspections in accordance with the InterNACHI® Standards of Practice (SOP). The SOP requires home inspectors to report the presence of solid conductor aluminum branch-circuit wiring observed during the inspection. Inspectors should review the SOP by visiting www.nachi.org/sop at least once a year to read for any changes to the standards.
The InterNACHI® Home Inspection Standards of Practice, Section 3.7 Electrical, states, "The inspector shall report as in need of correction the presence of solid conductor aluminum branch-circuit wiring, if readily visible."
We suggest that the inspector report any observed wiring defects as in need of correction. The presence of solid aluminum conductors should be documented in the inspection report. In addition, solid aluminum wiring confirmed or suspected of being installed before 1972 should be recommended for evaluation by a licensed electrician.
The following inspection image was provided by InterNACHI® Certified Home Inspector Eli Klugmann (https://www.nachi.org/certified-inspectors/eli-klugmann-73256).
Many observed electrical defects that inspectors typically report are related to aluminum wiring. And there are important observations and comments that inspectors should write in their reports about aluminum wiring.
Unfortunately, failing aluminum-wired connections seldom provide easily detected warning signs. Aluminum-wired connections and splices have been reported to fail and overheat without any prior indications or problems. If a home inspector observes any indications of a problem, the inspector should recommend a qualified electrician to further evaluate and determine the cause. Homeowners should never try to fix electrical problems themselves. They could make the electrical problems worse or they could be electrocuted.
Indications of electrical wiring problems may include:
Solid and Stranded
Inspectors may encounter two forms of aluminum wiring during a home inspection: solid and stranded aluminum wiring. A solid wire is a single thick wire. A stranded wire is made of thin wires twisted together inside the plasticized insulation jacket to form the conductor or complete wire. Stranded aluminum wiring rarely has problems and is still in everyday use. Therefore, solid aluminum wire is the primary focus here.
The inspection image above was provided by InterNACHI® Certified Home Inspector Lon Henderson.
Home inspectors usually first observe aluminum wiring when they remove the dead front or cover of the service equipment (electrical service or main panel). Removing the dead front is not required by the SOP, but many inspectors remove it.
It is common to find stranded aluminum wiring inside the main electrical panel. The inspector may see the stranded aluminum wiring as correctly connected or bonded without any apparent looseness, indications of overheating or oxidation, or other major defects.
Identifying Aluminum Wiring
Virtually all aluminum wiring was installed as plastic-sheathed cable (Type NM, often called Romex®) with no readily discernible distinction from a cable with copper conductors. Look at the printed or embossed markings on the outer jacket of the electric cables, which are visible in unfinished basements, attics, garages, or at the electrical panel. Use a flashlight shining on the surface at a low angle to help make the embossed markings readable.
Cable with aluminum conductors has “Al” or “Aluminum” and other information marked on one side of the cable jacket every few feet along its length. Be sure to read as much of the marking as possible because the marking “CU-clad” or “Copper-clad,” in addition to the “Al” or “Aluminum,” means that the cable uses copper-coated aluminum wire.
Inspection Tip: Solid conductor aluminum cable sheathing has “AL” or “Aluminum” printed on the sheathing every few feet along its length.
The following inspection image was provided by InterNACHI® Certified Home Inspector Eli Klugmann (https://www.nachi.org/certified-inspectors/eli-klugmann-73256).
If the inspector cannot identify the type of wire in the home or building by this method but suspects it is aluminum wire, a qualified electrician could make the determination. If the home has aluminum wiring that has not been remediated, a permanent repair of the connections is recommended.
Aluminum Wiring Inside the Panel
Most states, cities, and localities do not allow anyone but licensed electricians and homeowners to touch anything inside the service panel and sub-panels. Therefore, the inspector may remove the dead front but do nothing inside that cover beyond making visual observations. Removing the dead front from the electrical panel is not required by the SOP.
The inspection image above by InterNACHI® Certified Home Inspector Kenton Shepard (https://www.nachi.org/certified-inspectors/kenton-shepard-cmi-3689) is of solid aluminum wiring inside the electrical panel observed during a home inspection.
The following is a list of recommendations for the inspector when solid aluminum wiring is observed during the electrical panel inspection. (Copper-clad aluminum wiring has different observation tips and recommendations than solid aluminum wiring.)
If the inspector observes solid aluminum wiring inside the electrical panel, they should:
The following inspection image is provided by InterNACHI® Certified Home Inspector Ben Gromicko (https://www.nachi.org/certified-inspectors/big-ben-gromicko-163186).
As of the publication of this article, an antioxidant is not required by the National Electrical Code® (NEC®) or the International Residential Code (IRC). There is no specific NEC® or IRC code requirement for antioxidant paste at the lug connections of multi-strand aluminum wires in electrical panels.
Older electrical panels may have antioxidant paste at the lug connections. Home inspectors should look for oxidation at the lug connections at older electrical panels. There should not be any indication of excessive oxidation at the lug connections.
The local authority having jurisdiction (local code inspector) may require that an antioxidant be applied to aluminum wire connections.
Here’s an inspection image provided by InterNACHI® Certified Home Inspector Neil DeGaris (https://www.nachi.org/certified-inspectors/neil-degaris-cmi-ky-license-102167-32458).
Some manufacturers of electrical panels and over-current protection devices (breakers) require using antioxidant compound/grease/paste at connections with aluminum wire. Some manufacturers require antioxidant paste at aluminum wire terminations or splices, while others do not.
Some manufacturers provide instructions for the preliminary preparation of conductors, such as using conductor termination paste (antioxidant). Some connectors are made pre-filled with conductor termination compound. For non-pre-filled connectors, the conductor termination compound may be used if recommended by the connector manufacturer as preliminary preparation of the conductor.
Terminals for aluminum conductors are manufactured so they do not react with the aluminum with or without an antioxidant. If it's required, the manufacturer of the terminal would have pre-filled it or have provided some literature stating that it's required.
Inspection Tip: It's recommended to disclose in the report that some insurance companies have exceptions or special rules concerning the presence of solid aluminum branch circuit wiring.
Main Service Entrance Cables
Regarding stranded aluminum wires commonly used for the main service entrance cables and 240-volt circuits:
Here’s an inspection image provided by InterNACHI® Certified Home Inspector Kevin Leonard (https://www.nachi.org/certified-inspectors/kevin-leonard-cpicmi-156443).
Aluminum Wiring Outside of the Panel
The following is a list of recommendations for the inspector when solid aluminum wiring is observed at locations outside of the electrical panel during the home inspection.
If the inspector suspects or observes solid aluminum wiring in an area of the home outside of the electrical panel, they could:
Non-COPALUM Crimped Connectors
There are many other brands and types of crimp connectors — including those intended to be installed with a pliers-type of hand tool — that are readily available to consumers at common retailers. No other crimp connectors have been evaluated for connecting copper and aluminum conductors. Non-COPALUM crimped connectors are not recommended as a repair method.
One type of temporary repair involves pigtailing with a twist-on connector. The effectiveness of pigtailing using twist-on connectors has been evaluated by the CPSC. A substantial number of these connectors severely overheated. It is possible that some pigtailing “repairs” made with twist-on connectors may be prone to even more failures than the original aluminum wire connectors. Accordingly, this method of repair does not solve the problem of overheating present in aluminum-wired branch circuits.
Inspection Tip: A loose connection may be micro-arcing, which can occasionally be heard as a faint buzzing from a receptacle. Sometimes the slightest touch or jostling of the outlet or switch causes the buzzing to stop or the circuit to lose electrical connection. This should be reported as a defect requiring further evaluation and correction by an electrician.
Inspection Report Disclaimers
The following is a list of disclaimers that may be used by home inspectors in their inspection reports in relation to inspecting aluminum wiring:
Manufacturers of solid aluminum wiring may provide particular installation and connection instructions. This inspection did not verify the solid aluminum wiring was installed in accordance with the manufacturer’s instructions and electrical safety requirements. Pre-1972 aluminum wire has documented problems known to cause circuit failures and fires. Some insurance companies may not insure residences with solid aluminum wiring. Some insurance companies may have special conditions, requirements, and additional costs for insuring homes with solid aluminum wiring. The client is encouraged to investigate the concerns related to aluminum wiring and insurance for homes and buildings with solid aluminum wiring.
Myths and Misconceptions About Aluminum Wiring
One myth is that solid aluminum wiring is illegal. The IRC (International Residential Code) and NEC® (National Electrical Code®) permit the use of solid aluminum wiring. In recent years, some home inspectors have observed several home builders who install aluminum wiring in all of their homes, including new construction.
The 2021 IRC, Section E3406.2, states, “Conductors used to conduct current shall be copper, aluminum, or copper-aluminum except as otherwise provided in Chapters 34 through 43. Where the conductor material is not specified, the material and the sizes given in these chapters shall apply to copper conductors. Where other materials are used, the conductor sizes shall be changed accordingly.”
Copper conductors are used almost exclusively for branch circuits of 15 and 20 amperes. Non-metallic sheathed cable with aluminum conductors was used in the 1970s in some regions for these smaller circuits in residential wiring, but now it is not readily available. Aluminum conductors, even in these smaller sizes, are NOT prohibited by the code. The 2021 Table E3705.1, which lists the allowable ampacities for conductors, begins with size 12 AWG for aluminum conductors. For repair and remodeling work, the ampacities are included for these smaller aluminum conductors. Aluminum is commonly used for larger conductors, such as for services and feeders.
The training required to become an InterNACHI® Certified Home Inspector reflects the most recent building code and standards, including the International Residential Code (IRC). Home inspectors are not code inspectors, but home inspection training is based on code. (InterNACHI® School is a home inspector college accredited by a national accrediting agency of the U.S. Department of Education. Take accredited home inspector training at www.internachi.edu.)
Another myth is that aluminum wiring is inherently inferior to copper wiring, that it's brittle, and that it's a ticking time bomb waiting to cause a fire. While pre-1972 solid aluminum wiring is a weak alloy and prone to structural failure in residential wiring, post-1972 alloys are strong and supple and perform similarly to copper. Most failures with post-1972 aluminum wiring are similar to those of copper and are caused by improper connections.
Adding fuel to this myth is the summary of a 2011 study funded by the CPSC. This study by The Franklin Institute found that "homes built before 1972, and wired with aluminum, are 55 times more likely to have one or more wire connections at outlets reach ‘Fire Hazard Conditions’ than homes wired with copper. However, that survey encompassed only the wire connections at outlets.” The study does not address other types of aluminum wire connections and splices in homes that are also prone to fail. This study is frequently misquoted and used to condemn all aluminum wiring. There are sources that claim aluminum wiring installed correctly is as safe as copper wiring installed correctly.
Concerns about aluminum wiring were elevated with the 1977 Beverly Hills Supper Club fire in Kentucky, where 165 people died and many more were injured by a fire ignited by the sub-standard electrical installation of aluminum wiring.
Another myth is that copper transmits or conducts electricity better than aluminum. By volume, that is true, but by weight, aluminum has twice the conductivity. That's the reason that overhead high-voltage transmission lines are always aluminum.
Commentary and Some History
In the mid-1960s, the price of copper and copper wiring increased sharply. Builders made the economic decision to save money by switching to aluminum wiring, which was substantially cheaper. They used solid aluminum wiring for 120v circuits. The use of aluminum wiring was progressive, and there is no definitive date when the use of it began. The aluminum wiring was installed similarly to how copper wire was installed, except they sized up the aluminum wire. The next size up of aluminum wire is required to get the equivalent electricity flow of electricity compared to copper wire. So, for example, a 15-amp circuit that uses 14-gauge copper wire uses 12-gauge solid aluminum wire, one size larger.
The IRC addresses this size difference. The 2021 IRC, E3406.3, states, “The minimum size of conductors for feeders and branch circuits shall be 14 AWG copper and 12 AWG aluminum or copper-clad aluminum. The minimum size of service conductors shall be as specified in Chapter 36.”
While aluminum had been used for high-voltage overhead electrical transmission since the beginning of the electrical age, it was not widely understood that safe and effective installation of aluminum wiring in residences and buildings requires different practices than with copper wiring.
Although aluminum wiring has been allowed since 1946, copper wire was the standard. It was cheap, strong, and well understood. As a result, aluminum was rarely used in residential wiring. Soon after the widespread use of solid aluminum wiring was implemented, problems like flickering lights, dead circuits, and even fires began. Electricians started to learn that aluminum is not the same as copper.
First, it is much softer. Over-tightening connections can crush or flatten aluminum wire. This creates a weak point at the transition area between the intact round wire and the flattened wire wrapped around the connection screw. This weak point can and does break. In addition, when aggressively stripping the insulation, the wire can be easily nicked, gouged, or scraped, creating a weak area that can break with bending the wire.
Second, aluminum wire expands and contracts far more than copper as electricity flows on and off. This expansion and contraction can loosen connections or cause the wire to creep out of the connection. The common term for this is called “creep.” Aluminum connections and terminations must be tight enough to prevent creep but not so tight that the wire is damaged.
Third, when exposed to air, aluminum quickly oxidizes. Copper also oxidizes, but copper oxide is electrically conductive. However, aluminum oxide does not conduct electricity and effectively insulates the wire. This thin layer of insulation can cause a loss of conductivity at connections. Therefore, oxidation on aluminum is a desirable protective coating except at connections. Some connections, such as wire nuts and open lug connections (follow manufacturer’s instructions) require antioxidant grease or paste to prevent oxidation and maintain conductivity.
Pure aluminum would be water-soluble without this layer of oxidation protecting it. Aluminum wire is an alloy or mix of aluminum with other metals and minerals that still oxidize. The oxidation that we are describing here is a chemistry term for rust. On aluminum, this rust layer is whitish.
Aluminum Wire Connections
In the early 1960s, outlets and switches had steel screws for terminal wire connections. Research revealed that aluminum-to-steel connections formed a highly insulated oxidation layer that reduced electrical conductivity. Steel screws were vulnerable to the creep effect. Flickering lights or a dead circuit could result. This small separation at the connections could start arcing. This micro-arcing is hot, reaching thousands of degrees. Heat can damage the connection, melt away insulation, expose more wire, and sometimes cause a fire.
The following inspection images were provided by InterNACHI® Certified Home Inspector Brian Cawhern (https://www.nachi.org/certified-inspectors/brian-cawhern-cmi-50791).
Rather than abandon solid aluminum wiring, the industry developed aluminum-compatible devices that became required for use. The designations for these outlets and switches are CO/ALR or AL-CU, or CU-AL. The connection screws are brass. (In the late '60s, the first designation was CU/ALR, but these devices proved to be unreliable and were soon replaced by improved CO/ALR outlets and switches.) The CU-AL designation is used for breakers. CU is the periodic table or atomic designation for copper. Aluminum connections have to be tight and secure.
The aluminum wire must be wrapped clockwise around the terminal screw of a receptacle to secure it firmly under the screw head. Push or quick-connections used for copper wire are not allowed for aluminum wire.
Luminaires (light fixtures) and other direct-wired devices do not have to be rated CU-AL, but approved connectors must be used.
Common multi-colored wire nuts are not allowed. There are two problems with common wire nuts. First, antioxidant grease must be used for these connections. At copper/aluminum pigtails, copper and aluminum are dissimilar metals with a galvanic corrosive reaction that can deteriorate the connection without an approved antioxidant grease. Home inspectors cannot know if an antioxidant was applied without removing the wire nut. Therefore, inspectors should never remove the wire nut.
The Ideal No. 65 “Twister AL/CU wire connector,” often called the purple wire nut, is approved for use on solid aluminum wire connections, including splicing or pigtailing copper wire to aluminum wire. These wire nuts have antioxidant compounds inside. Unfortunately, the purple wire nut has a high failure rate. Whether the failure rate is a design problem or an installation error is unimportant to home inspectors. However, inspectors who observe purple wire nut splices on the aluminum wire should disclaim that, while permitted by the IRC, the Consumer Product Safety Commission deems the use of twist-on connectors to be a temporary repair and should not be used for permanent connections and splices.
Connections approved by the code and the CPSC are the AlumiConn and COPALUM connectors. The AlumiConn connectors are purple square plastic connectors. They have holes to insert aluminum wire and screws to secure the wire, which must be tightened with a torque screwdriver to manufacturer specifications. AlumiConn connectors can be used for pigtailing.
AlumiConn can be used by any electrician and is often used by competent laypersons and DIYers. Negatives with AlumiConn are that the person using them must fully insert the wire and torque the screws to the correct settings. In addition, a small junction or receptacle box with many wire ends can become cramped with bulky connectors.
The image below shows an AlumniConn connector repair method.
The COPALUM is a franchised, trademarked, cold-weld method by Tyco Electronics. A special crimp tool fuses aluminum ends or copper pigtails under tremendous pressure. The procedure and connections have proven to be very reliable. Only franchised, trained electricians can use the crimp tool to make COPALUM splices. The splices take up far less space in a junction box than wire nuts and AlumiConn connectors.
The 2021 IRC addresses aluminum and copper connections in Section E3406.8. It reads, “Terminals and splicing connectors shall be identified for the material of the conductors joined. Conductors of dissimilar metals shall not be joined in a terminal or splicing connector where physical contact occurs between dissimilar conductors, such as copper and aluminum, copper and copper-clad aluminum, or aluminum and copper-clad aluminum, except where the device is listed for the purpose and conditions of application. Materials such as inhibitors and compounds shall be suitable for the application and shall be of a type that will not adversely affect the conductors, installation, or equipment.”
Another problem with solid aluminum wiring was recognized by 1970. Pure aluminum is too soft, with low tensile strength, to be practical for the rigors of wiring installations. Aluminum alloys have always been used. The alloy used in the mid-1960s was called the AA-1350 series. It worked fine for overhead transmission wires but was not adequately ductile and flexible enough for residential wiring. It was prone to breaking at stress points like sharp bends. House wiring often involves pulling wire with great stress on the wire and sharp bends to negotiate the framing and small confines of junction boxes.
In 1972, a new alloy called the AA-8000 series was introduced to solve this problem. All the other issues with aluminum wiring stayed the same. There is no exact date when AA-1350 aluminum wire was no longer used and AA-8000 began. Existing stocks of AA-1350 were likely used even after AA-8000 became the new standard.
Note that stranded AA-1350 rarely has failure issues because the individual wire strands are so fine that the conductor can be safely bent. The wide use of solid aluminum wiring ended in the mid-1970s. By 1975, the price of copper eased back down, and the growing stigma of aluminum wiring caused builders to abandon it. As a result, solid aluminum wire is rarely encountered in construction after 1976.
Inspectors will often see solid aluminum wiring in pre-1965 homes. These are usually circuits added between 1965 and 1975, or "the aluminum years." For instance, a basement in a 1950 home was finished in 1970, and the circuits were done with cheaper aluminum wiring. All of the comments and inspection practices mentioned here apply even if only one circuit is solid aluminum wiring.
Inspectors who are aware that the solid aluminum wiring at an home inspection is likely pre-1972 should report that the observed solid aluminum wiring is or may be pre-1972 technology known to have safety issues and should be evaluated by a licensed electrician. Unfortunately, home inspectors have no chemistry test to determine alloy composition.
Clients may ask why aluminum was ever used. There are several positive attributes of aluminum wiring besides being cheaper than copper. First, a pound of aluminum conducts the same electrical current as two pounds of copper. Second, aluminum is 70% lighter than copper. Third, it is the most abundant metal on our planet, so it is readily available.
When installed correctly, its performance is equal to copper. Since it is only 61% as conductive as copper by volume, an aluminum wire has to be sized up to match copper for conductivity.
Is Aluminum as Good as Copper?
Clients often ask what the concerns about aluminum are and how to make corrections. Home inspectors should advise their clients with homes with aluminum wire that stranded aluminum wire is common and not necessarily an immediate material defect or major safety concern. However, solid aluminum wire is the subject of concern. Post-1972 solid aluminum wire installed correctly can perform as well as copper wire. Pre-1972 solid aluminum wire should be recommended for further evaluation and correction by a licensed electrician.
Regarding post-1972 installations, clients should be advised that all aluminum wiring has special installation requirements, and a proper and thorough evaluation is beyond the scope of a home inspection. For post-1972 homes, there is a high probability of unprofessional workmanship and improper work on electrical receptacles and fixtures that may have been completed by the homeowner who did not follow the required and recommended practices regarding aluminum wire connections. Most problems with aluminum wire occur in the last inch of the wire, where it terminates or is connected to something. If no problems were found with aluminum wiring during a home inspection, many inspectors should still recommend further evaluation by a licensed electrician. Many inspectors advise their clients that some insurance companies will not insure homes with solid aluminum wiring.
Aluminum wiring can be replaced or repaired to effectively and permanently reduce the possibility of fire and injury due to failing (overheating) wire connections and splices. It is highly recommended that a qualified electrician perform any corrections. Other than the complete replacement of aluminum wire with copper wire, there may be numerous potential solutions for the permanent repair of hazardous aluminum wire connections and splices.
However, CPSC can recommend repair methods or products only where there is satisfactory, documented evidence that the methods or products meet the following criteria:
Based on these standards, as of the date of this article, CPSC approves of only three methods for a permanent repair:
Corrections can be costly. They may include rewiring the house, or building with copper wire, and pigtailing or splicing all of the solid aluminum wire terminations with copper wire, including every outlet, switch, luminaire, and termination in the service panel and sub-panels. And junction box connections may need to be wired with AlumiConn or COPALUM connectors.
The InterNACHI® Home Inspection Standards of Practice (at www.nachi.org/sop) requires home inspectors to report the presence of solid-conductor aluminum branch-circuit wiring observed during their inspection. There are particular inspection and reporting tips, trouble signs, disclaimers, myths, building codes, connections, comparisons, and general history for aluminum wiring that inspectors should familiarize themselves with, which will be useful especially when inspecting older homes.
Special thanks to InterNACHI® members Lon Henderson, Jim Milby, Robert Meier, Kevin Leonard, Brian Cawhern, Eli Klugmann, Neil DeGaris, Kenton Shepard, and everyone who contributed to the article. If you would like to make recommendations to improve this article, please email Ben Gromicko at firstname.lastname@example.org.