The structural components of wire and cable products can be generally divided into four main structural parts: conductors, insulation layers, shielding layers and sheaths, as well as filling elements and tensile elements, etc. According to the usage requirements and application scenarios of the products, some products have extremely simple structures, with only one structural component, the wire, such as overhead bare wires, catenary wires, copper-aluminum busbars (busbars), etc. The external electrical insulation of these products is ensured by using insulators and spatial distance during installation and laying (that is, by using air insulation).
The vast majority of wire and cable products have exactly the same cross-sectional shape (ignoring manufacturing errors) and are in the form of long strips. This is determined by the feature that they are used to form circuits or coils in systems or equipment. Therefore, when studying and analyzing the structural composition of cable products, it is only necessary to observe and analyze from their cross-sections.
The following is a detailed analysis of the cable structure composition and cable materials:
1. Cable structure composition: Conductor
Wires are the most fundamental and indispensable main components for products to perform the function of transmitting current or electromagnetic wave information. Wire is the abbreviation of conductive core.
What materials are included in cable conductors? The materials of conductors are generally made of non-ferrous metals with excellent electrical conductivity such as copper and aluminum. The optical cables used in the optical communication networks that have developed rapidly in the past three decades or so use optical fibers as conductors.
2. Cable structure composition: Insulation layer
The insulating layer is a component that covers the periphery of the wire and serves as an electrical insulator. That is, it can ensure that the transmitted current or electromagnetic waves, light waves only travel along the wire and do not flow outward. The potential on the conductor (that is, the potential difference formed to the surrounding objects, that is, the voltage) can be isolated. That is, it is necessary to ensure both the normal transmission function of the wire and the safety of external objects and people. Wires and insulation layers are the two basic components that must be present to constitute cable products (except for bare wires).
What are cable insulation materials: In today’s wires and cables, the classification of cable insulation materials mainly falls into two categories: plastics and rubber. Polymer materials are dominant, giving rise to a wide variety of wire and cable products suitable for different uses and environmental requirements. Common insulation materials for wires and cables include polyvinyl chloride (PVC), cross-linked polyethylene (XLPE), fluoroplastics, rubber compounds, ethylene propylene rubber compounds, and silicone rubber insulation materials.
3. Cable structure composition: Sheath
When wire and cable products are installed and operated in various different environments, there must be components that protect the entire product, especially the insulation layer. This is the sheath. Because insulating materials are required to have excellent electrical insulation properties of all kinds, it is necessary to require extremely high purity and extremely low impurity content of the materials. Often, it is impossible to take into account its protective capacity against the outside world. Therefore, various protective structures must be responsible for withstands or resisting various mechanical forces from the outside (i.e., installation, usage site and during use), resistance to atmospheric environment, resistance to chemicals or oils, prevention of biological damage, and reduction of fire hazards. The main functions of cable sheaths are waterproofing, flame retardancy, fire resistance and corrosion prevention. Many cable products specifically designed for good external environments (such as clean, dry, and indoor environments free from mechanical external forces), or those with insulation materials that inherently possess certain mechanical strength and weather resistance, can do without the protective layer component.
What types of cable sheath materials are there? The main cable sheath materials include rubber, plastic, coating, silicone, and various fiber products, etc. The characteristics of the rubber and plastic protective layer are softness and lightness, and it is widely used in mobile cables. However, since both rubber and plastic materials have a certain degree of water permeability, they can only be applied when high polymer materials with high moisture resistance are used as cable insulation. Then some users may ask why plastic is used as the protective layer in the market? Compared with the characteristics of plastic sheaths, rubber sheaths have higher elasticity and flexibility, are more resistant to aging, but their manufacturing process is relatively more complex. Plastic sheaths have better mechanical properties and water resistance, and are abundant in resources, low in price and easy to process. Therefore, they are more widely used in the market. It should be noted by industry peers that there is another type of metal sheath. Metal sheaths not only have mechanical protection functions but also the shielding function mentioned below. They also possess properties such as corrosion resistance, compressive and tensile strength, and water resistance, which can prevent moisture and other harmful substances from entering the interior of the cable insulation. Therefore, they are widely used as sheaths for oil-impregnated paper insulated power cables with poor moisture resistance.
4. Cable structure composition: Shielding layer
The shielding layer is a key component in cable products for achieving electromagnetic field isolation. It can not only prevent internal electromagnetic signals from leaking out and interfering with external instruments, meters or other lines, but also block external electromagnetic waves from entering the cable system through coupling. Structurally, the shielding layer is not only set on the outside of the cable but also exists between the pairs or groups of wires in multi-core cables, forming multi-level “electromagnetic isolation screens”. In recent years, with the increasing requirements for high-frequency communication cables and anti-interference, shielding materials have evolved from traditional metallized paper and semiconductor paper tapes to more advanced composite materials such as aluminum foil mylar tapes, copper foil mylar tapes, and copper tapes. Common shielding structures include inner shielding layers made of conductive polymers or semiconductive tapes, as well as outer shielding layers such as copper tape longitudinal wrapping and braided copper mesh. Among them, the braided layer mostly uses tin-plated copper to enhance corrosion resistance. For special application scenarios, such as variable-frequency cables using copper tape + copper wire composite shielding, data cables employing aluminum foil longitudinal wrapping + streamline design, and medical cables requiring high-coverage silver-plated copper braided layers. With the advent of the 5G era, the hybrid shielding structure of aluminum-plastic composite tape and tin-plated copper wire weaving has become the mainstream solution for high-frequency cables. Industry practice shows that the shielding layer has evolved from an accessory structure to an independent core component of the cable. The selection of materials for it needs to comprehensively consider frequency characteristics, bending performance and cost factors to meet the electromagnetic compatibility requirements of different application scenarios.
5. Cable structure composition: Filled structure
Many wire and cable products are multi-core. For instance, most low-voltage power cables are four-core or five-core cables (suitable for three-phase systems), and urban telephone cables come in 800 pairs, 1200 pairs, 2400 pairs to 3600 pairs. After these insulated wire cores or pairs are cabled (or cabled in groups multiple times), there are two problems: one is that the shape is not round, and the other is that there are large gaps between the insulated wire cores. Therefore, a filling structure must be added during cabling. The filling structure is to make the outer diameter of the cabling relatively round, which is conducive to the wrapping and extrusion of the sheath, and also to make the cable structure stable and the interior strong. During use (when stretching, compressing and bending during manufacturing and laying), the force is evenly applied without damaging the internal structure of the cable. Therefore, although the filling structure is an auxiliary structure, it is also necessary, and there are detailed regulations on its material selection and shape design.
Cable filling materials: Generally, the fillers for cables include polypropylene tape, non-woven PP rope, hemp rope, or relatively inexpensive materials made from recycled rubber. To be used as a cable filling material, it must have the characteristics of not causing adverse effects on the insulated cable core, not being hygroscopic by itself, not being prone to shrinkage and not corroding.
6. Cable structure composition: Tensile elements
Traditional wire and cable products rely on the armor layer of the sheath to withstand external tensile forces or tensile forces caused by their own weight. The typical structures are steel tape armoring and steel wire armoring (for example, for submarine cables, thick steel wires with a diameter of 8mm are used and twisted to form the armoring layer). However, in order to protect the optical fibers from minor tensile forces and prevent slight deformation of the fibers that could affect the transmission performance, the optical fiber cable structure is equipped with primary and secondary cladding as well as dedicated tensile force components. In addition, if the headphone cable of a mobile phone adopts a structure where fine copper wire or thin copper tape is wound around synthetic fiber filaments and an insulating layer is extruded on the outside, this synthetic fiber filament is the tensile element. In conclusion, in the special, small and flexible products developed in recent years that require multiple bending and twisting uses, tensile elements play a major role.
What materials are included for cable tensile components: steel strips, steel wires, and stainless steel foils
Post time: Apr-25-2025