It’s easy to overlook cable, but doing so is unenlightened in relation to the technological accomplishment. Utilized for supporting bridges and controlling elevators, cable cars, and aerial tramways (ski lifts, gondolas, etc.), the helical series of metal wires—whose tensile strength outperforms that of the fibrous counterpart (rope)—are a modern marvel.
So, what exactly is cable? Wire rope consists of three basic components: wires, strands, and a core. The core functions to provide proper support for the strands. Wires wound together concentrically in a helix to form the strands, which in turn also wrap around the core helically. The core does necessarily need to be composed of steel or other metals; instead, it can be a fiber core.
However, these characteristics are what we understand as wire rope. Cable is, in fact, different. Technically, cable is not the same thing as wire rope but a smaller version of the same material—3/8” or less, to be exact. Similarly, the common wire rope construction of 7 x 7, 7 x 19 is known as galvanized cable or aircraft cable.
Regardless, cable and wire rope often are used interchangeably. In fact, in ANSI B77.1-2017, the American National Standard for the safety of passenger ropeways (including aerial tramways, aerial lifts, surface lifts, tows, and conveyors), explicitly uses rope, wire rope, and cable synonymously, with some exceptions.
Therefore, while cable actually does not include wire rope sizes greater than 3/8”, the term’s usage is generally a matter of preference for the industry or application.
The nomenclature for cable or wire rope is structured around describing the number of wires contained within the strands and their relationships to each other in the particular product. For example, 7 x 19 describes seven groups of nineteen wires, and 6 x 25 similarly indicates that the wire rope contains six strands with twenty-five individual wires on each. Wire rope is also classified by the core type, the lay of the strand, and the preforming (the forming of the individual wires of a strand into a helix to enable them to retain their shape as a uniform cylinder after being cut).
As for the attainable tension, it is dependent on numerous factors incorporated into the cable’s design, and certain cables should be used for their intended purposes. Of course, it is a necessity to assure that cables or wire ropes do not break during use. ANSI B77.1-2017 addresses this as the factor of safety, or “the ratio of the nominal breaking strength of the rope and the maximum static design tension of the rope.”
For example, the standard calls for new wire ropes in tension systems to have a minimum factor of safety of 6 and new haul ropes to have a minimum static factor of safety of 4.5.
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