Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-12 GTBL042-Callister-v2 August 13, 2007 21:31

12.9 Electrical Characteristics of Commercial Alloys • 473

Table 12.2 Tabulation of Compositions, Electrical Conductivities, and Coefficients of Thermal

Expansion for Aluminum and Copper Alloys Used for Electrical Wiring

Electrical Coefficient of

Alloy Composition Conductivity Thermal

Alloy Name Designation (wt%) [(-m)−^1 ] Expansion(◦C)−^1

Aluminum

(electrical

conductor

grade)

1350 99.50 Al, 0.10 Si,

0.05 Cu, 0.01 Mn,

0.01 Cr, 0.05 Zn,

0.03 Ga, 0.05 B

3.57× 107 23.8× 10 −^6

Copper

(electrolytic

touch pitch)

C11000 99.90 Cu, 0.04 O 5.88× 107 17.0× 10 −^6

of the aluminum wires with copper. The next best

option is the installation of a crimp connector re-

pair unit at each aluminum-copper connection.

With this technique, a piece of copper wire is at-

tached to the existing aluminum wire branch us-

ing a specially designed metal sleeve and pow-

ered crimping tool; the metal sleeve is called a

“COPALUM parallel splice connector.” The

crimping tool essentially makes a cold weld be-

tween the two wires. Finally, the connection is en-

cased in an insulating sleeve. A schematic represen-

tation of a COPALUM device is shown in Figure

12.10. Only qualified and specially trained electri-

cians are allowed to install these COPALUM con-

nectors.

Insulated COPALUM

splice assemblies Aluminumwire insulation

White aluminum

wire

Black aluminum

wire

Grounding

aluminum wire

Aluminum

wire insulation

Typical

receptacle

Copper wire

pigtails

Figure 12.10 Schematic diagram of a COPALUM

connector device that is used in aluminum wire

electrical circuits. (Reprinted by permission of the US

Consumer Product Safety Commission.)

Two other less-desirable options are CO/ALR

devices and pigtailing. A CO/ALR device is sim-

ply a switch or wall receptacle that is designed to be

used with aluminum wiring. For pigtailing, a twist-

on connecting wire nut is used, which employs a

grease that inhibits corrosion while maintaining a

high electrical conductivity at the junction.

Photograph of two copper wire-aluminum wire

junctions (located in a junction box) that experienced

excessive heating. The one on the right (within the

yellow wire nut) failed completely. (Photograph

courtesy of John Fernez.)