The North American auto industry is converting to a metric wire standard, as it produces more and more global vehicle platforms. Chrysler, Ford and General Motors will begin converting to ISO 6722 wire on new product lines. However, all carryover vehicles will continue to use SAE J1128 wire.

The North American auto industry is converting to a metric wire standard, as it produces more and more global vehicle platforms. I attended a panel discussion at last week’s National Electrical Wire Processing Technology Expo in Milwaukee, where automotive engineers from the Big 3 discussed the transition from SAE-type wire to ISO-type wire.

Chrysler, Ford and General Motors will begin converting to ISO 6722 wire on new product lines. However, all carryover vehicles will continue to use SAE J1128 wire.

The Electrical Wiring Component Application Partnership (EWCAP), a noncompetitive industry standards organization, is overseeing the conversion process. EWCAP focuses on developing common electrical interfaces and is part of the United States Council for Automotive Research (USCAR), which provides a common voice to the supply base.

The “Wiring the Next Generation of North American Automobiles” session in Milwaukee was moderated by EWCAP administrator Jim Roberts. He was joined on the panel by Matt Marzec, connectors and components engineer at Chrysler Group LLC; Don Price, connectors and components technical specialist at Ford Motor Co.; Tim Simko, wiring and connectors technical specialist at GM Powertrain; and Bernie Slovan, connection systems technical specialist at General Motors Co.

“Reduced outer diameter of wire is one of the benefits of moving to the ISO material,” says Roberts. “However, many issues must be resolved to migrate from SAE J1128-style wire to ISO 6722-style wire.” For instance, the move to metric will affect how wire is stripped and crimped.

The conversion to metric wire is already underway at Ford. All new Chrysler programs, such as the Nassau sedan, and Fiat-based compact cars, such as the 500, and will use ISO wire. All new GM vehicle programs will also use ISO wire specifications.

The entire transition process will take several years to implement. “As the older car lines are replaced and the component parts are modified to be compatible with the ISO wire, the SAE-type wire will become obsolete for the North American auto market,” says Roberts. “If a current car line continues for 10 years, the SAE wire will also continue.”

The EWCAP standards were developed with input from several leading suppliers, such as Champlain Cable Corp., C&S Technologies, Delphi Automotive, FCI, Prestolite Wire and Yazaki Corp.

During the Milwaukee presentation, Roberts outlined several key differences between SAE J1128 and ISO 6722 that will affect automakers and suppliers. “Switching from one wire type to another will affect circuit performance, such as voltage drop and fuse protection, which should be considered during the harness design process,” he explains.

There also is a distinct wire core difference between SAE J1128 and ISO 6722. “It is important to recognize that wire can have the same name, but based on the specification, will mean a different size,” Roberts points out. “Depending on the wire size, there could be as much as a 17 percent difference in cross-sectional area between ISO and SAE.”

According to Roberts, SAE minimum conductor size is controlled by core cross-sectional area, while ISO minimum conductor size is controlled by the resistance of the wire core. As a result, the core size changes as the conductivity of the core material changes.

“For instance, 0.5 millimeter wire per SAE J1128 thin-wall specifications has a minimum core area of 0.508 millimeters,” adds Roberts. “The same wire per ISO 6722 has a minimum core area of 0.465 millimeters.”

Stranding construction will also be affected by the move to metric wire. For instance, the new ISO specification allows both symmetric and asymmetric core construction.

In addition, the new wire types will create several assembly challenges to automakers and suppliers. “Stripping, core crimp, insulation crimp and seal compatibility must be considered when switching from SAE to ISO wire types,” warns Roberts, who expects the changeover to spur demand for smaller components in the future.

“Adopting wire with a reduced outer diameter allows terminals to be packaged tighter,” says Roberts. “Smaller wire, such as 0.13 or 0.08 millimeter, will also be used to reduce package sizes.