Copper-Clad Aluminum Elecrical Wiring: this article describes the history of copper-clad aluminum electrical wiring and its safe use in homes in the United States.
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Thomas J. D'Agostino, P.E., C.I., & Daniel Friedman
Copper-clad aluminum wire is made of a solid aluminum core covered with a copper skin in order to improve its performance in the field. This produc was installed in homes in the United States between 1972 and 1975. Details are provided by Tom D'Agostino:
Copper clad aluminum electrical wire is comprised of a solid aluminum core covered with a thin clad of copper. Approximately 10 percent of the cross-sectional area of the conductor is copper clad, thickness is not specified.
This product (only wire size Nos. 12-10 AWG), was designed by Texas Instruments for use with standard copper-only wiring devicves, ie. switches, receptacles (binding head screw, back-wired, and pressure plate thpe termionals) and was treated as "aluminum" conductor for use in AL-CU pressure wire connectors in response to field failures of solid aluminum conductor branch circuit wiring. - D'Agostino (2014)
I would not assume that copper-clad AL wire might not appear in an older home in which electrical wiring was added or changed during that same interval, and it's also possible, though less likely, that copper clad aluminum wire might appear in new home built after 1975 if an electrician had and wished to use up old copper-clad aluminum wire stock.
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Yes. Copper-clad aluminum electrical wire is described in REDUCE THE AL WIRE RISK: DETAILS, as well as in Aronstein (2011). There Aronstein states
Copper-clad aluminum wire (Nos. 12-10 AWG) has a thin copper outer skin and a core of aluminum. Therefore when installed and where visible in the main electrical service panel, it looks like "fat" copper wire (i.e., 10-12 AWG v. 12-14 AWG) and on the cut end, the copper skin looks to be "smeared" over the aluminum core. Markings on the cable jacket would include "Al" or "Aluminum". There is no known history of connection overheating problems associated with copper-clad aluminum wire. No corrective actions are required for copper-clad aluminum wire. - Aronstein (2011), D'Agostino (2014)
Recognizing that electrical wire is copper clad aluminum is useful for technical reasons.
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Externally, if we eschew noticing printed labels and marking that may be present on copper clad aluminum wire, and if we simply look at the wire itself, stripped of insulation, the wire looks like a copper. However if we can take a closer look at a relatively square-cut end of the wire we should see an aluminum core surrounded by a copper skin. Without disassembly and possibly even careful cutting of the end of the wire this detail may not be easily visible, since typical wire nippers compress the end of the wire when making a cut.
Scraping copper clad aluminum wire may not be adquate to identify its silver-colored aluminum core unless the scrape is vigorous enough to cut completely through the copper cladding.
Below is a cross-section cut of a solid aluminum electrical wire (with white insulation) and a solid copper aluminum conductor (with black insulation).
[Click to enlarge any image]
Early work by Carlson (shown at left) described a process "inside-out" of the later copper-clad aluminum wire. That is, Carlson's patent described applying an an aluminum sheath as the exterior of a copper core. Significant was that the metallic sheath was "metallurgically bonded to the inner core".
Illustrated at above left is the production method for cladding one metal with another to produce a wire of one metal with a cladding of another metal. - Carlson et als. (1963).
Dion (1966) and Dion and Thompson (1967) first described the successful manufacture of copper clad aluminum wire. Rolled aluminum wire is pulled through a lubricated draw to eliminate flat spots and to prepare the wire surface for a solid-bonding phase in which two copper cladding strips are added tothe wire exterior.
Illustrated at left is Dion's method of cladding aluminum wire with a layer of copper. It is significant to note that the copper thickness in this method is much greater than the typical thickness imparted by plating one metal on another. It is likely that it's that thickness that prevents a device connector srcew from cutting through the copper, possibly leading to connector failures in field use.
Continuing by quotation:
When the aluminum wire and the strips enter the rolls from the plenum chamber, heat flows from the copper strips mostly to the aluminum core and some to the rolls. This rapidly brings the aluminum-copper composite to equilibrium temperature as the composite is being bonded by reduction in the solid phase.
Roll geometry copper thickness and aluminum diameter is such as to produce clad composites in the usually demanded three precentages of copper by volume, i.e. 10%, 15%, and 20%. ... The field of the invention is the manufacture of clad wire and the like as exemplified in U.S. Patents 3,220,106 and 3,220,106. - Dion (1969) This patent cites earlier work and patents by Dion (1966) and Thompson (1966, 1967).
Later work described by Ziemek (1974) reversed this process, placing the copper as the outer sheath and solid aluminum as the interior or main body of the wire.
Quoting from a later description of this process, a copper band is formed around an aluminum core wire and the single seam in the sheath material is welded without bonding of the sheath and core, care being taken that all surfaces are clean and maintained free of oxides. - Ziemek (1974)
Mr. D'Agostino relates that in 1971 as project engineer at UL, he conducted tests evaluating the performance of copper-clad aluminum conductor wiring using a number of types of copper-only receptacles (i.e. binding head screw terminals, back-wired terminals, pressure plate screw terminals) and a number of types of AL-CU pressure wire connectors. That research, conducted under the auspices of U.L., demonstrated that performance of copper-clad wire was
The findings of this research was published in a 1971 UL bulletin that was distributed / reviewed by industry and government (i.e. David Rabinov of theU.S. National Bureau of Standards).
The copper clad aluminum wire product produced by Texas Instruments is attributed by D'Agostino to John Fan (see patent citations below). Following successful testing by D'Agostino at U.L., copper-clad alulminum wiring was reognize by UL/Industry and soon thereafter UL Listed NM Sheathed Cable with Nos. 10-12 AWG solid copper-clad aluminum conductor was distributed and installed in homes in the United States (and possibly Canada) between 1972 and 1975.
Original patents on the production of copper-clad aluminum wire were awarded to a variety of parties (cited below) with early patent applications in 1956 (Carlson) and key patents (Carlson, Roserans, Westinghouse Electric) dating from 1963.
Research into the production and use of copper-clad aluminu wire continues to the present, with work by Kwon (2004) and Rhee (2004) and others on fabrication methods and by Sasaki (2010) on the metallurgy of copper-clad aluminum.
- Special thanks to Tom D'Agostino for recapping the history of aluminum electrical wiring and copper clad aluminum electrical wiring. Personal communication 5/3/2014. Mr. D'Agostino presently lives on Long Island, NY. and continues to write and research electrical hazards. He has also worked as a professional home inspector and is a member of ASHI, the Amerian Society of Home Inspectors.
At above left, even without any disassembly we can see a solid conductor aluminum wire (center breaker connection) double-tapped (two wires under one connector) into a circuit breaker along with a silver-colored solid conductor electrical wire that is probably aluminum wire. (The large multi-strand red-insulated wire is a multi-strand aluminum conductor.)
Double-tapping electrical wire connections is improper and unsafe unless the connector is specifically designed for that purpose and is so-indicated by its manufacturer.
But from just this photograph alone one cannot be sure if the silver colored wire is aluminum or plated copper.
Note: Tin plated copper wire was generally a practice used before 1965 on small-sized 14-12 copper wire. On second look, the size of the silver-colored black insulated wire shown above is likely to be a size 10 or 12 AWG aluminum. Further, tin-plated copper presents a "dirty silver" look. - D'Agostino (2014)
A closer look will be needed to confirm the opinions of our note above. Notice that the circuit breaker is marked CU-AL indicating that the manufacturer represented that the breaker could be used with either aluminum or copper wire, notwithstanding that this is not an accepted nor recommened repair for aluminum electrical wiring.
Watch out: In addition to the improper double-tapping in the center circuit breaker shown above, copper wire in contact with an aluminum conductor in an AL-CU rated circuit breaker is not covered by the UL-listing. The device is listed for use with either copper-only or aluminum only.
Details are at ALUMINUM WIRING REPAIR COALR & CU-AL.
We can see silver-colored (soft) metal that is aluminum at three locations:
Watch out: plated copper wire is a completely different product that, because its conductors sport a thin plated silver colored surface, might be mistaken for unsafe alumium wire. It is not aluminum and it is safe unless, as with any electrical wiring, it has been damaged in some manner.
Not all rubber insulated copper wire is plated, but if you suspect that the silvery-colored wire is plated copper, it's easy enough to determine: with the wire disconnected from any power source, scratch the silver colored surface of the rubber-insulated wire and you'll see its red copper interior.
In REDUCE THE AL WIRE RISK: DETAILS, as well as in Aronstein (2011). There Aronstein describes plated-copper wire as:
Plated copper wire is relatively common in older homes, and it looks like aluminum wire. It was commonly used with rubber-based insulation. Identification can be made by careful inspection of a cut end of the wire. In general, plated copper wire would not be present in nonmetallic sheathed cable ("Romex"), it is most generally found in metallic sheathed cable ("BX"). Cable of the "BX" type is not likely to contain aluminum wire. - Aronstein (2011)
Above we show solid aluminum conductor wire and solid copper conductor electrical wire in cross section.
Watch out: don't confuse references to copper-clad aluminum wire or copper-plated electrical wire with devices such as electrical receptacles and switches marked COALR or CU-AL. The latter two are device labels not wire types and are not a recommended repair for aluminum electrical wire. COALR and CU-AL and their field performance and safety warnings are described in more detail at ALUMINUM WIRING REPAIR COALR & CU-AL
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The link just above provides access to Reducing the Fire Hazards in Aluminum-Wired Homes, by Dr. Jess Aronstein, Ph.D., This document answers most technical questions about the hazards and remedies of aluminum electrical wiring.
A current, easy to print form of this guide in PDF form is also provided free at ALUMINUM-WIRED HOMES, REDUCE THE HAZARD [PDF].
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Reducing the Fire Hazard in Aluminum-Wired Homes Sept. 12, 2000 p. 17
R. Newman, "Hazard Analysis of Aluminum Wiring", April, 1975, U.S. CPSC, NIIC-0600-75-H006
M. Leger, "Metallurgical Analysis of Failed CO/ALR Devices", Ontario Hydro, #78-54-K, Ontario, Canada, February, 1978
J. Aronstein and W.E. Campbell, "Failure and Overheating of Aluminum-Wired Twist-on Connections", IEEE Trans. Components, Hybrids, and Mfg. Tech., V. CHMT-5 No.1, March 1982
J. Aronstein, "Tests of 'Old Technology' Aluminum Wire at Special Crimp Type Compression Connectors" (Amp COPALUM), Wright-Malta Corp. Project Report CPSC-C-79-0079 Task III, U.S. Consumer Product Safety Commission, Washington, DC, Feb. 5, 1983
J. Aronstein, "Tests of 'Old Technology' Aluminum Wire", Wright-Malta Corp. Project Report CPSC-C-81-1418, U.S. Consumer Product Safety Commission, Washington, DC, Feb. 10, 1983
J. Aronstein and W.E. Campbell, "Overheating Failures of Aluminum-Wired Special Service Connectors", IEEE Trans. Components, Hybrids, and Mfg. Tech., V. CHMT-6 No. 1, Mar. 1983
J. Aronstein and W.E. Campbell, "The Influence of Corrosion Inhibitor and Surface Abrasion on the Failure of Aluminum-Wired Twist-On Connections", IEEE Trans. Components, Hybrids, and Mfg. Tech., V. CHMT-7 No. 1, Mar. 1984
J. Aronstein and W.E. Campbell, "Evaluation of an Aluminum Conductor Material for Branch Circuit Applications", IEEE Trans. Components, Hybrids, and Mfg. Tech., V. CHMT-8 No. 1, Mar. 1985
R. Schubert, "Erratic Behavior of Al/Al Wire Junctions", Electrical Contacts - 1986, Proceedings of the 32nd IEEE Holm Conference on Electrical Contacts, Boston, 1986.
[Following added 3/5/2003 at Dr. Aronstein's suggestion, not part of original article -- DJF]
J. Aronstein, "Evaluation of a Twist-on Connector for Aluminum Wire", Forty-Third IEEE Holm Conference on Electrical Contacts, Jan 1997, 0-7803-3968-1/97. [This article describes the Ideal Industries Ideal#65 purple "Twister" twist-on connector marketed as a repair/retrofit for residential aluminum wiring .--DJF]
Abstract: A new type of twist-on splicing component for use with aluminum and copper wire combinations is tested to determine initial resistance, performance in a zero-current environment test, performance in a heat-cycle test, and portion of current carried by the connector's steel spring.
The splices tested consist of two aluminum wires and one copper wire. The aluminum wire samples used for the test are of the types actually installed in aluminum-wired homes. Initial resistance is found to be relatively high, and there is a significant sample-to-sample variation.
This reflects failure to consistently establish low-resistance wire-to-wire contact Through the insulating oxide film on the wire. Results of the environmental and heat-cycle tests show deterioration of a significant portion of the samples. The splices made with this connector are also found to be sensitive to mechanical disturbance, such as applied in normal installation when the completed splice is pushed back in to the junction box.
Based on the test results, it is concluded that this connector has not overcome the fundamental deficiency of twist-on connectors for use with aluminum wire applications. Keywords: aluminum wire, connectors, twist-on connectors, environmental test, heat-cycle test.
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