Fundamentals of Wires and Cables
**Definition**
A cable is typically formed by twisting together several individual wires or several groups of wires (each group comprising at least two conductors), resembling a rope. The conductors within each group are insulated from one another and are often twisted around a central core. The entire assembly is covered with a highly insulating outer layer. Cables are primarily used for transmitting and distributing electrical energy or conveying electrical signals.
**Wire and cable mainly consist of the following four components:**
1. **Conductor Core**
Made of high-conductivity materials such as copper or aluminum. Depending on the flexibility required by the installation conditions, each core may consist of a single solid conductor or multiple stranded wires.
2. **Insulation Layer**
The insulating material used in cables must possess high insulation resistance. Common insulating materials include oil-impregnated paper, polyvinyl chloride (PVC), polyethylene (PE), cross-linked polyethylene (XLPE), and rubber.
3. **Sealed Sheath**
Protects the insulated cores from mechanical damage, moisture, humidity, chemicals, light, and other environmental factors. For insulation susceptible to moisture, an extruded lead or aluminum sealed sheath is generally applied.
4. **Protective Covering**
Serves to protect the sealed sheath from mechanical damage. Galvanized steel tape, steel wire, copper tape, or copper wire is typically applied as armor around the sheath (referred to as armored cable). The armor layer also provides electric field shielding and prevents external electromagnetic interference. To prevent corrosion of the steel tape or wire by the surrounding medium, they are usually coated with bitumen, wrapped with an impregnated jute layer, or provided with an extruded polyethylene or PVC jacket.
**II. Wire and Cable Specifications**
A wire and cable specification denotes the number of cores and the nominal cross-sectional area. The complete designation of a wire or cable is often complex; therefore, a simple name (usually a category name) combined with the model specification is often used to replace the full name. For example, "low-voltage cable" refers to all plastic-insulated power cables rated 0.6/1 kV. The cable type spectrum is well-established, meaning that the exact product can be clearly identified by specifying the standard model and specification.
**III. Application Classification**
**(A) By Insulation Material**
Examples include oil-impregnated paper insulated cables, PVC cables, XLPE cables, etc.
**(B) By Application**
Divided into power cables, communication cables, and control cables, respectively applied in power systems, information transmission systems, and mechanical equipment & instrumentation systems.
**1. Power Systems**
Products used in power systems mainly include overhead bare conductors, busbars, power cables (plastic cables, oil-paper insulated cables — largely replaced by plastic power cables —, rubber-sheathed cables, overhead insulated cables), branch cables (replacing some busbars), magnet wire, and electrical wires and cables for power equipment.
**2. Information Transmission Systems**
Cables used for information transmission primarily include local telephone cables, television cables, electronic cables, radio frequency cables, optical fiber cables, data cables, magnet wire, and power communication or other composite cables.
**3. Mechanical Equipment and Instrumentation Systems**
This sector utilizes almost all product types except overhead bare conductors, but mainly power cables, magnet wire, data cables, and instrumentation cables.
**(C) By Product Category — Five Major Categories**
**1. Bare Wires and Bare Conductor Products**
Main features: Pure conductive metal without insulation or sheath layers, such as ACSR (aluminum conductor steel reinforced), copper and aluminum busbars, and electric locomotive wires. Processing mainly involves metal forming processes including smelting, rolling, drawing, and stranding/compact stranding. Products are mainly used in suburban and rural areas, consumer mains, and switchgear.
**2. Power Cables**
Main features: An insulation layer is extruded or wrapped over the conductor, such as overhead insulated cables; or multiple cores are stranded together (corresponding to phase, neutral, and ground conductors), such as overhead insulated cables with two or more cores; or an additional sheath layer is added, forming plastic/rubber-sheathed cables. Key manufacturing processes include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, and sheath extrusion. Products are mainly used for heavy-current power transmission in generation, distribution, transmission, transformation, and supply lines, carrying large currents (tens to thousands of amperes) and high voltages (220 V up to 500 kV and above).
**3. Wires and Cables for Electrical Equipment**
Main features: Extensive variety in types and specifications, broad application scope, mostly used at voltages of 1 kV and below. New products are continuously developed for special applications, such as fire-resistant cables, flame-retardant cables, low-smoke zero-halogen (LSZH) / low-smoke low-halogen cables, anti-termite and anti-rodent cables, oil-resistant/cold-resistant/heat-resistant/abrasion-resistant cables, medical/agricultural/mining cables, and thin-wall wires.
**4. Communication Cables and Optical Fibers**
Evolution has progressed from simple telephone and telegraph cables to multi-thousand-pair telephone cables, coaxial cables, optical fiber cables, data cables, and even composite communication cables. These products typically feature small, uniform dimensions and require high manufacturing precision.
**5. Magnet Wire (Winding Wire)**
Primarily used in various motors, instruments, and meters.
**IV. The Difference Between Wire and Cable**
In practice, there is no strict boundary between "wire" and "cable." Generally, products with fewer cores, smaller diameter, and simpler construction are called wires; uninsulated ones are called bare wires, while the rest are termed cables. Conductors with a cross-sectional area greater than 6 mm² are often referred to as large wires, and those ≤6 mm² as small wires; insulated wires are also known as building wires. However, as application scopes have expanded, many products blur the line between wire and cable, making strict differentiation unnecessary. In common usage, people call household building wires "wires" and refer to power cables simply as "cables." A wire consists of one or several flexible conductors covered with a light, soft sheath; a cable consists of one or more insulated conductors covered with a tough outer layer of metal or rubber. Both cables and wires generally comprise three fundamental parts: the conductor core, the insulation, and the protective outer covering.
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