Word on the Wires

shutterstock / inked pixels. An illustration of wires.
Photo credit: shutterstock / inked pixels
Published On
Oct 15, 2019

at the 2019 NFPA Conference and Expo in San Antonio in June, we had a 17-hour marathon dealing with various code and standards that were up for adoption. I was most interested in the last NFPA document and the adoption of the 2020 National Electrical Code . There were too many issues and potential changes for the 2020 NEC discussed than I have time to include here. However, one potential change that involved copper-clad aluminum was of special interest to me. I remember when aluminum wiring was being used in the early 1970s for residential 15- and 20-ampere (A) branch-circuit wiring. Anyone involved in wiring during the early 1970s also remembers the installation issues of aluminum wire to copper wiring devices that I mentioned in a recent article.

Copper-clad aluminum was first inserted into the 1971 NEC (the Code version I used when I took my test and became an electrical contractor in 1975) as a new addition to Tables 310-14, 310-15 and Table 310-21.

Table 310-14 in the 1971 NEC dealt with allowable ampacities of insulated aluminum and copper-clad aluminum with no more than three current-carrying conductors in a raceway, cable or directly buried in the earth. Table 310-15 in the 1971 Code dealt with allowable ampacities of insulated aluminum and copper-clad aluminum in free air, and Table 310-21 was a simplified wiring table that addressed six or fewer continuous or noncontinuous use, copper, aluminum or copper-clad aluminum conductors in a raceway or cable.

In the 1975 NEC, Table 310-18 covered aluminum and copper-clad insulated conductors with not more than three current-carrying conductors in a raceway, cable or directly buried in the earth. Table 310-19 covered allowable ampacities of insulated aluminum and copper-clad aluminum installed in free air.

In the 1978 NEC, copper, aluminum and copper-clad aluminum were incorporated into all four ampacity tables, Tables 310-16 through 310-19, like the method used in the current NEC style of allowable ampacity tables. A new definition was added to Article 100 in the 1978 NEC dealing with copper-clad conductors and states that “copper-clad aluminum conductors were drawn from a copper-clad rod with the copper metallurgically bonded to the aluminum core. The copper forms a minimum of 10 percent of the cross-sectional area of a solid conductor or of each strand of a stranded conductor.” The reason for this short history lesson is to emphasize how far back in the NEC process copper-clad insulated conductors were recognized as an alternative to copper and aluminum wiring. Based on the 2020 NEC process, No. 12 AWG, No. 10 AWG copper-clad aluminum through 4/0 AWG are still being dealt with for the 2020 NEC.

While most electricians and electrical contractors are very familiar with both copper and aluminum wire, many are not as familiar with copper-clad aluminum. Newly installed and cut copper-clad aluminum conductors will have a shiny aluminum or silver color on the inside of the conductor, but over time the aluminum will start to oxidize and turn to a dull-gray color. Without close examination, an electrician may not recognize the copper-clad conductor and may mistake it for a copper conductor. Often, a wire cutting tool, a side cutter or lineman’s tool will cause the copper cladding to cover the end of the internal aluminum of the conductor by pinching the copper cladding over the aluminum part of the conductor, which helps to further disguise the copper-clad aluminum conductor.

Many ECs often mistake copper-clad aluminum conductors for tinned copper conductors where tinning was applied to copper wires to reduce the harmful effects of rubber insulation. Tinning is a very thin coating of a conductive material on a copper conductor with the coated copper conductor having a different DC resistance than uncoated copper conductors (shown in Table 8 of Chapter 9, covering conductor properties and the direct current resistance at 75°F, or 167°F). Coatedcopper wires with solder or silver are very different from copper-clad aluminum wire since the coated-copper wires are basically a copper wire with an external coating.

One of the main issues with the aluminum- only conductors is the use of aluminum terminations. The key with aluminum, copper-clad aluminum and copper-only terminations is determining if the switch or receptacle is acceptable for these different materials. Terminals of 15- and 20-A receptacles marked CO/ALR are for use with aluminum, copper-clad and copper conductors. If the receptacle or switch is not marked CO/ALR, then copper or copper-clad is acceptable. To ensure safety, always check the manufacturer’s listing and installation instructions as well as the listing requirements by UL.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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