Callister - An introduction - 8th edition

732 • Chapter 18 / Electrical Properties
Table 18.2
Tabulation of Compositions, Electrical Conductivities, and Coefficients of Thermal
Expansion for Aluminum and Copper Alloys Used for Electrical Wiring
Electrical
Alloy Alloy Composition Conductivity Coefficient of Thermal
Name Designation (wt%) [(#
m) 1 ] Expansion (C) 1
Aluminum (electrical 1350 99.50 Al, 0.10 Si, 0.05 3.57 10 7 23.8 10 6
conductor grade)
Cu, 0.01 Mn, 0.01 Cr,
0.05 Zn, 0.03 Ga, 0.05 B
Copper (electrolytic C11000 99.90 Cu, 0.04 O 5.88 10 7 17.0 10 6
touch pitch)
are concealed, these materials may smolder or a
fire may spread undetected for an extended period
of time.
Warning signs that suggest possible connection
problems include warm faceplates on switches or
receptacles, the smell of burning plastic in the vicinity
of outlets or switches, lights that flicker or burn
out quickly, unusual static on radio/television, and
circuit breakers that trip for no apparent reason.
Several options are available for making
buildings wired with aluminum safe. 3 The most
obvious (and also most expensive) is to replace all
of the aluminum wires with copper. The next best
option is the installation of a crimp connector repair
unit at each aluminum–copper connection. With
this technique, a piece of copper wire is attached
to the existing aluminum wire branch using a specially
designed metal sleeve and powered crimping
tool; the metal sleeve is called a “COPALUM
parallel splice connector.” The crimping tool
essentially makes a cold weld between the two
wires. Finally, the connection is encased in an insulating
sleeve. A schematic representation of a
COPALUM device is shown in Figure 18.10. Only
qualified and specially trained electricians are allowed
to install these COPALUM connectors.
Two other less-desirable options are CO/ALR
devices and pigtailing. A CO/ALR device is simply
a switch or wall receptacle that is designed to be
used with aluminum wiring. For pigtailing, a twiston
connecting wire nut is used, which employs a
grease that inhibits corrosion while maintaining a
high electrical conductivity at the junction.
Insulated COPALUM
splice assemblies
Typical
receptacle
Aluminum
wire insulation
White aluminum
wire
Black aluminum
wire
Grounding
aluminum wire
Copper wire
pigtails
Aluminum
wire insulation
Figure 18.10 Schematic diagram of a COPALUM
connector device that is used in aluminum wire
electrical circuits. (Reprinted by permission of the U.S.
Consumer Product Safety Commission.)
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.)
3 A discussion of the various repair options may be downloaded from the following Web site:
http://www.cpsc.gov/cpscpub/pubs/516.pdf.