Foot soldiers in our modern Army now are “walking computers.” Night visiongoggles, GPS receivers, computers and radios are becoming commonplace. The interconnecting military cable must be lightweight and strong, but still contain all of the circuit conductors to carry out their mission. The military wire can be snagged on environmental hazards such as bushes or protrusions from vehicles. Increased strength demand means that the addition of
strength members, such as Kevlar or PPO fibers, are now the “norm.” Satellite custom cable need to have lightweight shields while still maintaining the same or higher shield effectiveness. Aracon, which is nickel- or silver-plated Kevlar, can assist in these applications. As a plated fiber that will spread across the cable core, it can easily give greater shield coverage than can be obtained with flat or round copper wires. Ground support equipment, while relying more and more on radio communications, still has the need for robust cables between communication huts. Fiber optics can pass large amounts of data, but there is still the need for power to the equipment. Composite cables can do both. The need for high tensile-strength members to keep the cables from pulling apart as well as crush-resistant materials to protect the fibers calls for tougher materials.
The design process starts with a source control drawing (SCD), as most harsh environment cables do not conform to the old MIL-spec system. Many military and medical cable designs use the material and physical properties and testing requirements from existing MIL-specs as a starting point and then delineate the additional requirements on the SCD granted waivers from the RoHS by the European Union (EU). When the conductor size gets smaller than 30 AWG, consideration
of moving to stainless steel as a conductor material needs to be reviewed. Often, for short conductor lengths, the increased resistance of stainless steel can be tolerated. If not, gold or silver plating can be done on the individual strands of a conductor to bring the resistance down to acceptable levels. For terminations, soldering to stainless
steel is difficult, whereas the gold or silver-plated wire can easily be soldered. Crimp contacts can easily be attached to stainless steel. Table 1 lists the strength and conductivity of alloys that can be considered when copper is not strong enough. After the conductor has been determined, the insulation must be chosen. The environmental considerations determine the temperature rating, solvent resistance and physical characteristics. Many programs
now prohibit the use of PVC. Thermoplastic elastomer’s (TPEs) have taken the place of many PVC materials. Also, to replace PVC, companies such as GE Plastics have created flexible versions of NORYL that can be extruded to ground support equipment, while relying more and more on radio communications.
