Thomas J. D'Agostino, P.E., C.I., & Daniel Friedman
What is copper-clad aluminum wire?
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. The photograph of copper-clad aluminum wiring shown above was provided by and used with permission of Roger Hankey, a Minnesota home inspector. Details abuout copper-clad aluminum wiring 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.
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)
How to identify copper-clad aluminum wire
Recognizing that electrical wire is copper clad aluminum is useful for technical reasons.
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).
History of Copper Clad Aluminum Electrical Wiring
Mr. Tom D'Agostino was employed at Underwriters Laboratories from 1969 to 1996 and spent a decade and a half studying and testing the safety of aluminum electrical wiring.
[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.
The patent included provisions to assure that the aluminum surface was free of contaminants as were the copper strips. [Abstracted from the patent.]
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
similar to that of solid copper-only wiring devices (with binding head screw terminals
satisfactory for use in AL-CU pressure wire connectors and
along with copper wire performed poorly, less than adequate in "back-wired push-in" wiring devices.
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.
Don't confuse copper-clad wire with tinned-copper plated wire nor with COALR or CU-AL Devices
Watch out: tin-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.
Watch out: don't confuse references to copper-clad aluminum wire or tin-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
Contact the authors
Thomas J. D’Agostino, P.E, C.I.
T. D’Agostino Home Inspection USA Corp.
(Islandwide Home Inspection Service)
9 Forest Court, Ste. A
Ronkonkoma, New York 11779
Office # 631-467-4663
Fax # 631-585-7048
Cell # 631-831-2076
Thomas Jack D’Agostino, C.I.
Long Island Home Inspector Associates 250 North 2nd. Street, Ste A
Ronkonkoma, New York 11779
Office # 631-585-4269
Cell # 631-831-2077
Daniel Friedman can be reached via InspectApedia at CONTACT US
References for copper clad aluminum wire & related research
Ahmed, N. "Extrusion of copper clad aluminum wire." Journal of Mechanical Working Technology 2, no. 1 (1978): 19-32.
Aronstein, Jesse, and Doug Lee. "Selection Criteria for Residential Aluminum Connections." In Electrical Contacts (Holm), 2012 IEEE 58th Holm Conference on, pp. 1-8. IEEE, 2012.
Aronstein, Jesse. "Analysis of field failures of aluminum-copper pigtail splices made with twist-on connectors." In Electrical Contacts, 1999. Proceedings of the Forty-Fifth IEEE Holm Conference on, pp. 87-93. IEEE, 1999.
Aronstein, J. "Evaluation of receptacle connections and contacts." In Electrical Contacts, 1993., Proceedings of the Thirty-Ninth IEEE Holm Conference on, pp. 253-260. IEEE, 1993.
Aronstein, J. E. S. S. E., and THOMAS K. Hare. "Evaluation and analytical electron microscopy investigation of a plated aluminum wire for branch circuit applications." Components, Hybrids, and Manufacturing Technology, IEEE Transactions on 11, no. 2 (1988): 218-226.
Austin, David, John Cabral, and Joseph Longever. "Copper clad aluminum strips and a process for making copper clad aluminum strips." (2002)
Carlson, Charles L., Rosecrans, Irwin and Stanley A., assignors to Westinghouse Electric Corporation, Pittsburgh PA, Original application 12 Jan. 1956, Patent No. 2,947,069 dated 2 Aug. 1960, divided and this application 9 June 1960. U.S. Patent No. 3,096,577, 9 July 1963.
D’Agostino, Thomas. J. "Recognition of copper-clad aluminum conductor for use in terminals suitable for copper conductor." Underwriters Laboratories, Inc., Melville, NY, Bulletin, Subjects 4, 44,83,486,498 (1971).
D'Agostino, T.J., personal communication with D Friedman by telephone & email, May 2014.
Dion, Paul A., & Carr, Martin W., assignors to Texas Instruments, "Manufacture of Clad Wire and the Like", United States Patent No. 3,455,016, 15 July 1969.
Fan, John CC. "Cermet film selective black absorber." U.S. Patent 4,312,915, issued January 26, 1982.
"Method for producing copper-clad aluminum wire." U.S. Patent RE28,526, issued August 26, 1975.
Kwon, Hyouk Chon, Taek Kyun Jung, Sung Chul Lim, and Mok Soon Kim. "Fabrication of copper clad aluminum wire (CCAW) by indirect extrusion and drawing." In Materials Science Forum, vol. 449, pp. 317-320. 2004.
Lin, Mei-mei. "Manufacturing process for making copper-plated aluminum wire and the product thereof." U.S. Patent 4,919,769, issued April 24, 1990.
National Electrical Code, U.S., For aluminum and copper-clad aluminum conductors, see NEC Section 310.15.
Perrard, Wayne. "TECHNICAL PAPERS-Strategies for optimizing cable design and performance through the use of bimetallic wire-Used separately or in combination, copper-clad aluminum wire and copper-clad steel wire." Wire Journal International 34, no. 7 (2001): 154-159.
Polleys, William V. "Copper Clad Aluminum Wire." Wire Ind., 1974 Yearbook, 188, 191. (1974).
Rhee, K. Y., W. Y. Han, H. J. Park, and S. S. Kim. "Fabrication of aluminum/copper clad composite using hot hydrostatic extrusion process and its material characteristics." Materials Science and Engineering: A 384, no. 1 (2004): 70-76.
Sasaki, T. T., R. A. Morris, G. B. Thompson, Y. Syarif, and D. Fox. "Formation of ultra-fine copper grains in copper-clad aluminum wire." Scripta Materialia 63, no. 5 (2010): 488-491.
Shea, J., and Xin Zhou. "Material effect on glowing contact properties." In Electrical contacts-2007, the 53rd ieee holm conference on, pp. 90-97. IEEE, 2007.
"Equipment Wiring Terminals for Use with Aluminum and/or Copper Conductors -
UL 486E", Underwriter Laboratory Standards, Retrieved 5/4/2014,original source: http://ulstandardsinfonet.ul.com/scopes/0486e.html [Abstract only]
Yamaguchi, Tetsuo, Teruyuki Takayama, and Masao Hiderita. "METHOD OF PRODUCING COPPER CLAD ALUMINUM WIRE." U.S. Patent 3,854,193, issued December 17, 1974.
Ziemek, Gerhard, "Method for Making Copper Plated Aluminum Wires." U.S. Patent 3,648,356, issued March 14, 1972.
Ziemek, Gerhard, assigned to Kabel-und Metallwerke Gutehoffnungshuette AG, Hannover Germany, Issued 5 June 1974, as a reissue of U.S. Patent No. 3,800,405 2 April 1974
Abstract: 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.
The copper tube is reduced to the diameter of the aluminum core. This composite wire is then passed through a plurality of drawing dies which reduce the diameter of the wire, preferably at least 50 percent, care being taken to prevent the copper sheath from tearing.
The drawing operation produces, depending on the reduction rate, an initial or a complete bond between the core and sheath.
Subsequently, the clad wire is either subjected to a limited diffusion heat treatment, conditions of the heat treatment being controlled to produce a complete and flawless bond between the sheath and core but, at the same time, avoiding the formation of any CuAl2, a phase which is brittle or is annealed to get the required grade. Generally, the diffusion layer on either side of the sheath-core interface is limited to about 10 μ, preferably less.
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 J. Aronstein, "Fire Due to Overheating Aluminum Wired Branch Circuit
Connections", Electrical Safety Conference: Electrical Fires; Cause,
Prevention, Investigation. University of Wisconsin, Extension, Madison
WI, April 7, 1981.
 "National Controlled Study of Relative Risk of Overheating of
Aluminum Compared With Copper Wired Electrical Receptacles in Home and
Laboratory", Executive Summary. Prepared for U.S. Consumer Product
Safety Commission. Report #F-C4812-01, Franklin Research Center,
Philadelphia, PA, April 20, 1979.
 R. Newman and W.H. King, Jr., "Pilot Study of Branch Wiring Systems
in Montgomery County, Maryland", U.S. Consumer Product Safety
Commission, Sept., 1977.
 J. Aronstein, "Summary Report, Study of Overheating of Aluminum-Wired
Electrical Receptacles in Scarborough, Toronto, Homes", Wright-Malta
Corp., Ballston Spa, NY, January 11, 1982.
 J. Aronstein, "Test of 'Old Technology' Aluminum Wire With Twist-On
Connectors", Project Report CPSC-C-79-0079, Task II, For U.S. Consumer
Product Safety Commission, Wright-Malta Corp., Ballston Spa, NY, Feb.
 J. Aronstein, "Overheating Failures of Presently-Listed
Aluminum-Wired Connection Combinations Within Rated Service Conditions",
Wright-Malta Corp., Ballston Spa, NY, November 23, 1981.
 "The Trouble With Aluminum Wiring", Consumer Reports, January, 1981,
 R.L. Hicks, "Pigtail Splicing Connections for Baseboard Heaters and
Similar Cyclic Loads", Ontario Hydro Research Division, Report
#78-235-K, May 17, 1978, p. 3, (Table 1).
 "Aluminum Building Wire Installation Manual and Design Guide", The
Aluminum Association, Inc., Washington, DC. (p. 12 in 1978 Edition).
 J. Aronstein and T.K. Hare, "Evaluation and Analytical Electron
Microscopy Investigation of a Plated Aluminum Wire for Branch Circuit
Applications", IEEE Transactions: Components, Hybrids, and Mfg. Tech.,
V. CHMT-11 No. 2, June 1988.
 J. Aronstein, "Evaluation of a Twist-On Connector for Aluminum
Wire", Transactions, 43rd IEEE Holm Conference on Electrical Contacts,
 J. Aronstein, "Analysis of Field Failures of Aluminum-Copper
Pigtail Splices Made With Twist-on Connectors", Transactions, 45th IEEE
Holm Conference on Electrical Contacts, Pittsburgh, PA, 1999
Reducing the Fire Hazard in Aluminum-Wired Homes Sept. 12, 2000 p. 17
6. BIBLIOGRAPHY: TECHNICAL REPORTS, CONNECTOR PERFORMANCE WITH
R. Newman, "Hazard Analysis of Aluminum Wiring", April, 1975, U.S. CPSC,
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,
[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]
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.
The Aluminum Electrical Wiring Hazard Explained (in the document you are presently viewing)ALUMINUM WIRE REPAIR METHODS to reduce risk in buildings with Aluminum Electrical Wiring - Overview of Acceptable Repair Practices (in the document you are presently viewing)Aluminum Wire Repair Method Details - "How to" details, how to identify, COPALUM repair, alternative repairs, history, products, research, source of special AMP TYCO COPALUM connectors & COPALUM Electricians (in the document you are presently viewing)COPALUM Electricians: Sources of TYCO COPALUM -Certified/Trained Aluminum Wire Repair Services (in the document you are presently viewing)
Reducing the Fire Hazards in Aluminum-Wired Homes, Jess Aronstein, Ph.D., This document answers most technical questions about the hazards and remedies of aluminum electrical wiring. Some of the sections of this very thorough document are listed below:
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