What Are Cables?

Cables are assemblies of one or more electrical conductors or optical fibers, bound together and enclosed in protective coverings, used to transmit electrical power, signals, or data between two or more points. A cable differs from bare wiring in that it incorporates insulation, shielding, and jacketing layers that protect the conductors from mechanical damage, environmental exposure, and electromagnetic interference, while also maintaining safe electrical separation between the conductor and its surroundings. Cables are fundamental components in power distribution networks, telecommunications infrastructure, industrial automation, transportation systems, and consumer electronics.

The engineering of cables spans multiple disciplines: materials science governs the selection of conductor metals and polymer insulations, electromagnetic theory informs shield design and impedance control, and mechanical engineering addresses the flexibility, bending radius, and tensile strength required for specific installation conditions.

Conductors and Construction

The conductor is the electrically active core of a cable, typically made of copper or aluminum. Copper is preferred for most signal and power cables because of its high electrical conductivity (approximately 5.96 × 10^7 siemens per meter) and ductility, which allows it to be drawn into fine wire and stranded into flexible bundles. Aluminum is used in high-voltage overhead and underground transmission cables where weight and cost are primary constraints, accepting the tradeoff of lower conductivity and greater susceptibility to oxidation at terminations. Conductors are configured as solid wire for rigid applications or as stranded wire for flexible cables, with the stranding pattern (concentric, rope-lay, or bunch-stranded) chosen to optimize flexibility, resistance, and packing density. Multi-conductor cables group several insulated conductors in a single jacket, with pair twisting used in data cables to control crosstalk between adjacent conductors.

Insulation and Shielding

Each conductor in a cable is surrounded by an insulation layer that sets the voltage rating and determines operating temperature limits. Common insulation materials include crosslinked polyethylene (XLPE) for medium- and high-voltage power cables, polyvinyl chloride (PVC) for building wiring and low-voltage control cables, and polytetrafluoroethylene (PTFE) for high-temperature aerospace applications. Above the insulation, shielded cables incorporate a conductive foil or braid layer that attenuates electromagnetic interference: the shield prevents external fields from coupling into the signal conductors and contains radiation emitted by the cable's own current. The IEEE 1143 Guide on Shielding Practice for Low Voltage Cables provides the technical framework for selecting and grounding shields in instrumentation, control, and communications cable installations.

Types and Classification

Cables are classified by their intended application, voltage rating, and construction. Power cables carry electrical energy at voltages ranging from low-voltage (up to 1 kV) distribution wiring to extra-high-voltage (above 220 kV) transmission cables. Coaxial cables enclose a center conductor within a tubular shield separated by a dielectric, maintaining a controlled characteristic impedance for RF and video signal transmission. Twisted-pair cables, used throughout telecommunications and data networking, balance differential signal pairs to achieve high common-mode rejection of interference. Fiber-optic cables replace copper conductors with glass or polymer optical fibers, transmitting signals as light pulses for applications requiring immunity to electromagnetic interference and very high bandwidth over long distances. The National Academies' handbook on frequency allocations for scientific uses illustrates how cable type selection intersects with broader electromagnetic compatibility considerations in mixed-media installations.

Fault Location and Testing

Locating faults in buried or inaccessible cables is a specialized discipline within cable engineering. Time-domain reflectometry (TDR) measures the round-trip travel time of an electrical pulse to a fault or impedance discontinuity, allowing precise location without excavation. For high-voltage power cables, dissipation factor (tan delta) testing and partial discharge measurement characterize insulation degradation before a fault develops. Research on insulation resistance measurement for medium-voltage XLPE cables illustrates how diagnostic testing extends cable service life by identifying degradation early.

Applications

Cables have applications in a range of fields, including:

• Electrical power transmission and distribution at all voltage levels
• Telecommunications and data networking via twisted-pair and fiber-optic cables
• Industrial automation and process control wiring
• Subsea installations connecting offshore platforms, islands, and continents
• Automotive and aerospace wiring harnesses linking sensors, actuators, and control systems
• Winch and tether applications where cables carry mechanical loads alongside electrical signals