Aluminum building wiring is a type of electrical wiring for residential construction or homes that uses aluminum electrical conductors . Aluminum offers a better conductivity to weight ratio than copper, and is therefore also used for electrical grids , including overhead power transmission lines and local power distribution lines , as well as for the power cables of some airplanes . also includes . [1] [2] Utility companies have used aluminum wire for power transmission in power grids from the late 1800s to the early 1900s. It has cost and weight advantages over copper wires. Aluminum wire is still the preferred material today in power transmission and distribution applications. [3]
In North American residential construction, aluminum wire was used for wiring throughout homes from the 1960s to the mid-1970s during a period of high copper prices. Electrical equipment at the time (outlets, switches, lighting, fans, etc.) was not designed with the special properties of aluminum wire in mind, and there were some issues related to the properties of the wire, making the installation. Susceptible to problems with aluminum wire. Revised manufacturing standards for both wire and equipment were developed to reduce problems. There is a potential fire hazard in existing homes with this old aluminum wiring used in branch circuits.
material
Aluminum wire has been used as an electrical conductor for a considerable period of time by electric utilities concerned with power transmission lines in use shortly after the introduction of modern power distribution systems beginning in the late 1880s . Aluminum wire requires a larger wire gauge than copper wire to conduct the same current , but it is still less expensive than copper wire for a particular application.
Aluminum alloys used for electrical conductors are only about 61% as conductive as copper of similar cross-section, but the density of aluminum is 30.5% that of copper. Accordingly, one pound of aluminum has the same current carrying capacity as two pounds of copper. [3] Since the cost of copper is nearly three times that of aluminum by weight (about USD $3/lb [4] versus USD $1/lb [5] as of 2017 ), aluminum wire is about the same conductivity as copper wire. one-sixth of the cost. Especially the low weight of aluminum wires makes these electrical conductors easy to use in power distribution systems by electric utilities.This makes it suitable for use in the field, as supporting towers or structures only need to support half the weight of the wires to carry the same current.
In the early 1960s when housing construction boomed in North America and the price of copper increased, utility grade AA-1350 aluminum alloys were used in the shape used for low load branch circuits in homes. The aluminum construction wire was fabricated using . [6] Problems and failures related to branch circuit connections began to emerge in the late 1960s for the manufacture of wire made from utility grade AA-1350 alloy aluminum, resulting in a re-evaluation of the use of that alloy for wire making and identification. Happened. The need for new alloys for the production of aluminum building wire. The first 8000 series electric conductor alloy, still widely used in some applications, was produced in 1972 by the Aluminum Company of America ( Alcoa ).) was developed and patented. [7] This alloy, with AA-8030 (patented in 1973 by Olin) and AA-8176 (patented by Southwire in 1975 and 1980), mechanically performs like copper.
Unlike the older AA-1350 alloys used earlier, these AA-8000 series alloys maintain their tensile strength even after standard current-cycle testing or current-cycle submersion testing (CCST), as specified in ANSI C119.4:2004 is described in. Depending on the annealing grade, AA-8176 can increase up to 30% with low springback effect and possesses a high yield strength ( 19.8 kSi or 137 MPa for a cold worked AA-8076 wire).
A home with aluminum wiring installed before the mid-1970s (as aluminum wire stocks prior to 1972 were allowed to be used) is likely to have wires made from older AA-1350 alloys that were used for power transmission. was developed. AA-1350 aluminum alloy was more prone to problems related to branch circuit wiring in homes due to mechanical properties, which combined with poor workmanship at the time made it more vulnerable to failures as a result of the electrical equipment being used .
A notable event was the 1977 Beverly Hills Supper Club fire , which was caused by poorly installed aluminum wiring.
modern building construction
Aluminum building wiring for modern construction is manufactured with AA-8000 series aluminum alloys (sometimes referred to as “new technology” aluminum wiring), as specified by industry standards such as the National Electrical Code (NEC). has been done . Large gauge stranded aluminum wire (#8) is used in most parts of North America for modern residential construction. Larger than AWG) is quite common. Aluminum wire is used for low voltage service feeders in residential applications from utility to building. It is installed with specified materials and methods by local electric utility companies. In addition, large aluminum stranded building wire made from the AA-8000 series alloy of aluminum is used for electrical services (eg service entrance conductors from utility connections to service breaker panels) and large branch circuits such as sub- For panels, categories, clothes dryers and air conditioning units.
In the United States, the National Electrical Code permits solid aluminum wires made of AA-8000 series aluminum alloys for 15-A or 20-A branch circuit wiring. [8]Terminations must be rated for aluminum wire, which can be problematic. This is especially a problem with wire to wire connections made with twist-on connectors. As of 2017 most twist-on connectors for typical small branch circuit wire sizes, even those designed to connect copper to aluminum wires, are not rated for aluminum-to-aluminum connections. With one exception, Marette #63 or #65 is used in Canada but is not approved by UL for use in the United States. In addition, the aluminum wire must be larger in size than the copper wire used for the same circuit due to the increased resistance of aluminum alloys. For example, #14 AWG copper building wire or #12 according to the NEC A 15-A branch circuit supplying standard lighting fixtures can be installed with AWG aluminum building wire. However, small solid aluminum branch circuit wires are almost never used for residential construction in North America. [3]
old house
When utility grade AA-1350 alloy aluminum wire was first used in branch circuit wiring in the early 1960s, solid aluminum wire was installed in the same way as copper wire installed with the same electrical equipment. went.
Typical connections of electrical equipment to electrical wiring for small branch circuits with solid wires (15-/20-A circuits) are usually made by wrapping the wire around a screw on the device, also called a terminal, and then The screw is made by tightening. , Around the same time, steel screws became more common than brass screws for electrical equipment.
Over time, many of these terminations with solid aluminum wire began to fail due to improper connection techniques and the different resistances of the different metals and significantly different coefficients of thermal expansion, as well as problems with the properties of solid wires. These connection failures generate heat under electrical load and cause overheating connections.
Large-sized stranded aluminum wires do not have historical problems like solid aluminum wires, and the common terminations for oversized wires are dual-rated terminations called lugs. These lugs are typically made with a coated aluminum alloy, which can accommodate either aluminum wire or copper wire. Large stranded aluminum wiring with proper termination is generally considered safe, as long-term installations have proven its reliability.
Problem
The use of old solid aluminum wiring in residential construction has resulted in connection failures in electrical equipment, home fires according to the U.S. Consumer Product Safety Commission (CPSC), and can be difficult to obtain homeowners insurance in some areas. For a house with old aluminum wires. [9] [10] There are several possible reasons for these connections to fail. The two main reasons were improper installation (poor workmanship) and the difference in coefficient of expansion between aluminum wire used from the 1960s to the mid-1970s, and termination, especially when the termination was a steel screw on an electrical appliance. [11] [12] Reported hazards are associated with large solid aluminum branch circuit wiring ( not smaller than. 8 AWG )
improper installation
Many of the aluminum wire terminations installed in the 1960s and 1970s that were properly installed continue to operate without any problems. However, problems may develop in the future, especially if the connections were not established properly initially.
Improper installation, or poor workmanship include: not destroying wires, not applying corrosion inhibitor, not wrapping wires around terminal screws, incorrectly wrapping wires around terminal screws, and insufficient on connection screws Torque. There can also be problems with connections made with too much torque on the connection screw as it damages the wire, especially with soft aluminum wire.
coefficient of expansion and creep
Most problems related to aluminum wire are usually associated with older (pre-1972) AA-1350 alloy solid aluminum wire, sometimes referred to as “old technology” aluminum wires, because of the properties of that wire. This results in significantly greater expansion and contraction. Compared to copper wire or modern day AA-8000 series aluminum wire. Older solid aluminum wire also had some problems with a property called creep , which results in the wire being permanently deformed or at rest over time under load.
Aluminum wire used prior to the mid-1970s had a somewhat higher creep rate, but a more significant issue was that aluminum wire had a critically high coefficient of expansion, which was usually higher than that of brass for this time period. The screws used in lieu of steel were quite different from the screws. Appliances such as outlets and switches. Aluminum and steel expand and contract at significantly different rates under thermal load, so a connection can become loose, especially for older terminations initially installed with insufficient torque of the screws combined with creep of aluminum over time. to be done. Loose connections get progressively worse over time.
This cycle results in a slight loosening of the connection, leads to overheating with a reduced contact area at the connection, and allows intermetallic steel/aluminum compounds to form between the conductor and the terminal screw. This resulted in the formation of a high resistance junction, leading to additional overheating. Although many believe that oxidation was the issue, studies have shown that oxidation was not significant in these cases. [13]
electrical equipment rating
Many electrical equipment used in the 1960s had small plain steel terminal screws, which made the aluminum wires in use at the time more vulnerable to problems with these devices. In the late 1960s, an equipment specification known as CU/AL (meaning copper-aluminum) was created which specified the standard for equipment intended for use with aluminum wire. Some of these devices used large undercut screw terminals to hold the wire more securely.
Unfortunately, Cu/AL switches and receptacles failed to function adequately with aluminum wire, and a new specification called CO/ALR (meaning copper-aluminum, modified) was created. These tools employ brass screw terminals that are designed to act as a metal similar to aluminum and to expand at a similar rate, and have even deeper undercuts in the screw. The CO/ALR rating is only available for standard light switches and receptacles; CU/AL is the standard connection marking for circuit breakers and large appliances.
oxidation
Most metals (with a few exceptions, such as gold) oxidize freely when exposed to air. Aluminum oxide is not an electrical conductor, but an electrical insulator. As a result, the flow of electrons through the oxide layer can be greatly hindered. However, since the oxide layer is only a few nanometers thick, the additional resistance is not noticeable in most situations. When aluminum wire is properly terminated, the mechanical connection breaks down the thin, brittle layer of oxide to make an excellent electrical connection. Unless this connection is loosened, there is no way for oxygen to enter the connection point to form further oxides.
If insufficient torque is applied to the electrical appliance termination screw or if the equipment is not CO/ALR rated (or at least CU/AL-rated for breakers and larger equipment) this may result in insufficient connection of the aluminum wire. In addition, due to the significant difference in thermal expansion rates of older aluminum wire and steel termination screw connections may allow the formation of some additional oxides on the wire over time. However, oxidation was not found to be a significant factor in aluminum wire termination failures.
connecting aluminum and copper wires
Another issue is connecting the aluminum wire to the copper wire. Aside from the oxidation that occurs on the surface of aluminum wires, which can lead to poor connections, aluminum and copper are different metals. As a result, galvanic corrosion can occur in the presence of an electrolyte, making these connections unstable over time.
Upgrades and Repairs
There are several upgrades or repairs available for homes with aluminum branch circuit wiring before the 1970s:
- Completely retrofitting the house with copper wiring (usually cost prohibitive)
- “Pig-tailing” involves connecting a short length of copper wire (pigtail) to the original aluminum wire and then connecting the copper wire to an existing electrical appliance. Splice of copper pigtail to existing aluminum wire can be accomplished with special crimp connectors, special short lug-type connectors, or approved twist-on connectors (with special installation procedures). Pig-tailing generally saves time and money, and it is possible as long as the wiring itself is not damaged.
However, the US Consumer Product Safety Commission (CPSC) currently recommends only two options for “permanent repair” using the pig-tailing method. The more widely tested method uses special crimp-on connectors called copalum connectors. As of April 2011, CPSC also recognized miniature lug-type connectors called Alumicon connectors. [9] [15] The CPSC considers the use of pigtails with wire nuts a temporary repair , and even recommends special installation procedures as a temporary repair, and notes that in attempting to repair There may still be dangers.
COPALUM connectors use a special crimping system that creates a cold weld between the copper and aluminum wire, and is considered a permanent, maintenance-free repair. However, enclosures may not have sufficient length of wires to allow the use of a specialized crimping tool, and the resulting connections are sometimes too large to install in existing enclosures due to limited space (or “box fill”). grow up. Installing an enclosure extender for unfinished surfaces, replacing the enclosure with a larger one, or installing an additional adjacent enclosure can be done to increase the available space. In addition, copalm connectors are expensive to install, require specialized equipment that cannot be easily purchased and require a certified electrician by the manufacturer to use them,
The AlumiConn Miniature Lug Connector can also be used for permanent repairs. [9] The only special tool an electrician needs to install them is a special torque screwdriver that should be readily available to qualified electrical contractors. Proper torque on the connectors set screw is critical for acceptable repair. However, the use of aluminium connectors is a relatively new repair option for older aluminum wiring than other methods, and the use of these connectors may have some of the same or similar problems with limited enclosure space as copalm connectors.
Special twist-on connectors (or “wire nuts”) are available to join aluminum to copper wire, which are composed of an antioxidant compound already filled with zinc-dusted silicon with a polybutene base [16] Dioxide compound added to dismantle wire As of 2014 there was only one twist-on connector rated or “UL Listed” for connecting aluminum and copper branch circuit wires in the US, which is the ideal number. 65″ Twister Al/Cu Wire Connector”. These special twist-on connectors have a distinctive purple color, have been UL listed for aluminum to copper branch circuit wire connections since 1995, and according to the manufacturer’s current literature “pig copper conductors on aluminum branch circuit wires”. -The tail is perfect for “retrofit applications”. [17]CPSC still considers the use of twist-on connectors, including the ideal number. 65 “Twister Al/Cu Wire Connector”, for a temporary repair .
According to the CPSC, using (listed) twist-on connectors to connect copper pigtails to older aluminum wires as temporary repairs requires special installation procedures , including abrading and pre-twisting the wires . However, the manufacturer’s instructions for ideal numbers. 65 Twister [18] recommends only pre-twisting the wires, and does not state that it is required. In addition, the instructions do not mention physically dismantling the wires as recommended by the CPSC, although the manufacturer’s current literature states “compound cut aluminum oxide” pre-filled. Some researchers have criticized the UL listing/tests for this wire connector, and problems with tests (without pre-winding) and installations have been reported.[19] However, it is unknown whether the reported installation problems are associated with unqualified individuals attempting these repairs, or not using the special installation procedures recommended (such as the wiring recommended by the CPSC for older aluminum wire). dismantle and pre-twist, or at least pre-twist the wires recommended by Ideal for your connectors).
Newer CO/ALR rated appliances (switches and receptacles) can be used to replace older equipment that did not have the proper rating in homes with aluminum branch circuit wiring to reduce hazards. [19] These devices are reportedly tested and listed for both AA-1350 and AA-8000 series aluminum wire, and are acceptable in accordance with the National Electrical Code. [8] However, some manufacturers of CO/ALR equipment recommend periodically checking/tightening the terminal screws on these devices which may be dangerous for unqualified individuals to attempt, and some CO/ALR equipment as There is criticism of their use as a permanent repair. Have failed the test when connected with “old technology” aluminum wire. [9]Furthermore, installing only CO/ALR devices (switches and receptacles) does not address potential hazards associated with other connections, such as ceiling fans, lights, and appliances.
