Armor for Cables
What are armors? Armors are metallic outer covering that protects the cable from mechanical or physical damage. The difference between shielding and armor is that shielding is used as noise protection while armor is used for physical protection. Below are two common forms of armor.
Longitudinal: A relatively thick (6 to 12 mils) “tape” is longitudinally formed and wrapped around the cable and covered by a jacket. The tape may be made of steel, aluminum, bronze or copper. The choice of material is a function of the frequency range of the signal that is being kept in or kept out of the cable as well as the degree of mechanical protection that is desired for the cable. This type of shield may be applied smooth or corrugated if somewhat improved flexibility is desired. The aluminum and steel materials may be coated with a thin plastic coating that thermally bonds to the jacket, improving the mechanical characteristics of the sheath and also improving chemical resistance. The seam may simply be overlapped or continuously corrugated and welded (CCW).
Interlock: This armor is the most common amongst cable. A heavy steel, copper or aluminum strip (20 to 25 mils) is spirally wrapped around the cable core. As it is wrapped, the edges are formed and shaped so that each wrap is interlocked with the preceding wrap. The result is a very strong and robust product. For this reason, interlocking is most often thought of as an armoring rather than a shielding, though it does both. Copper strips provide excellent low frequency noise mitigation.