Twisted Component Cable Constructions
Cables composed of twisted components generally have better flexibility characteristics than parallel conductor cables. Required electrical and physical properties can be more easily achieved by varying type, grouping, and position of individual conductors and components within the cable. There are two general classes of twisted cables:
BUNCHED cables consist of a number of conductors twisted together. This construction is created on twinning, quadding and bunching machines.
CONCENTRIC cables, fabricated on rigid bay and planetary cablers, consist of a central component such as a filler, single wire or cable group, surrounded by one or more layers of helically laid wires. If the direction of lay reverses on each layer, the construction is called a "true concentric" construction. If the direction of lay is constant, it is called "unilay concentric".
Additional Considerations
CABLE FLEXIBILITY, in multi-layered cables, is directly related to the lay length of the individual layers. The smaller the lay length, the greater the flexibility and the more expensive, since more wire is required per foot of finished cable. As a rule, lay length is 8 to 16 times the layer diameter.
CABLE FILLERS are included when it is desirable to round out a cable to obtain symmetry or to provide conductor separation. Fillers also provide cushioning in cables subjected to flexing and impact. Common filler include cotton, jute, vinyl and polyethylene.
CABLE BINDERS, also called a serve, is a thread wound with a long lay and low coverage over individual layers of cable to hold the components in place during subsequent processing. Colored binders can also be used to identify and separate groups of conductors.
TAPES are frequently placed beneath the cable sheath as an added protection against mechanical abuse, and between shields and adjacent conductors to prevent physical damage to the insulation. Under a jacket they make it easier to strip, and insure a smooth sheath surface. Cables without tapes may show convolutions of the twisted conductors. There are a variety of tape materials, but polyester is the most frequently used. Polyester tapes reduce cable flexibility to a degree; paper tapes, do not have this disadvantage. Tapes may be applied either spirally or longitudinally.