By Mike Bacidore, Managing Editor
The electrical characteristics For cable must meet or exceed performance standards set by a variety of organization, including TIA/EIA and ISO/IEC, and Ethernet applications defined by IEEE, as well as safety codes by NEC and NFPA. Increased regulatory requirements rarely improve performance, but for wire and cable, innovation comes in very small lengths.
"With the changes to the NEC in the past 10 years, protective conduit or raceway is no longer required when running an exposed-run (ER) cable from the tray to the equipment or device," explains John Gavilanes, director of engineering, Lapp USA (www.lappusa.com). "With the allowance of unlimited length per NEC Article 336, there's a greater area of cable that is now susceptible to the exposure conditions in the industrial environment after installation. Tests are done to evaluate performance under crushing conditions of 1,000 or 2,500 lb. and an impact force of 10 or 50 lb. To determine flammability, the typical flame test standard is the CSA FT4, where cables are loaded vertically in a tray and subjected to intense flame and heat conditions. When exposed to real-world conditions, cables could begin to deteriorate, split or crack, creating a potentially hazardous condition along with the potential for machine and production down time."
Under NFPA 79, the Electrical Standard for Industrial Machinery, machine-tool wire (MTW) is one of the permitted types of cable, explains Gavilanes. "Under the standard for Machine Tool Wire UL 1063, oil resistance is mandated, as compliance to the Oil Res I test is required and further severe testing such as the Oil Res II is optional," he says. "Environmental resistance tests such as those per UL standards were implemented to standardize oil resistance requirements of cables used in the manufacturing of industrial machinery throughout the world."
Global awareness of environmental issues also affected cable manufacture. "For several years manufacturers have been removing things from the products to make them more environmentally friendly," says Eric Bulington, chief engineer, US Wire & Cable, Anixter Int'l (www.anixter.com). "In many cases, they've moved to higher-performing compounds in order to meet the same requirements without environmentally hazardous materials."
Unshielded twisted-pair (UTP) cable uses metallic conductors twisted in pairs to minimize the electromagnetic interference, known as crosstalk, resulting from adjacent wire pairs and external noise sources, explains Carol Everett Oliver, marketing analyst at Berk-Tek (www.nexans.us). "A greater number of twists/ft increases noise immunity."
"We've seen the transmission capabilities of Ethernet cable more than quadruple," says Brian Shuman, RCDD, senior product development engineer, Belden (www.belden.com). "Impedance stability and reduced pair-to-pair coupling, or crosstalk, have been achieved beyond 500 MHz on unshielded twisted-pair cables. While demand created the need for such enhanced cable, improved manufacturing technology has made this a reality."
Impedance and resistance are factors that can affect the cable's characteristics, such as attenuation. "Attenuation is the measurement of signal loss from one end to the other," explains Oliver. "The more attenuation there is, the poorer the signal will be at the receiver. Attenuation is a problem with UTP cable due to the cable's inherent lack of uniformity caused by differences in twist tension and rate, bends in the cable and other inconsistencies that could occur in manufacturing. UTP cable must follow precise specifications governing how many twists or braids are permitted per meter of cable."
While laser measurement and other production quality-detection devices have allowed increased wire and cable performance, the major improvements have been made in the control technology of the equipment manufacture, says Lou Garriga, senior director, industrial business, Northwire (www.northwire.com). "One example of this control technology advancement would be gearless braiders, which operate with PLC control," he says. "They are capable of preserving electrical performance by managing physical needs through tension control. Though the braiders are set up and run the same, the PLC control allows for a broader use of existing equipment."