Why the wires inside your cables are twisted, braided, tinned and wrapped
Take a pair of wires, clamp one end in a hand drill and spin it while keeping the line taut. The result is a twisted pair, one of the simplest defences against electrical interference. Neighbouring stretches of the twist pick up opposite voltages from a passing disturbance, and those voltages largely cancel out.
Every conductor carrying current sends out an electromagnetic field, and every conductor soaks up energy from fields around it. The first effect can disturb nearby equipment; the second adds noise that swamps a signal or corrupts supply voltages badly enough to cause malfunctions. Both scale roughly with length, so the cheapest cures are keeping runs short and routing them away from trouble. Beyond that, engineers rely on three designs: twisting, shielding and coaxial geometry.
Shielding borrows the Faraday cage. Foil or wire mesh wraps the whole length, cutting the wires inside off from outside electric fields, especially when the shield is tied to earth. It does little against low-frequency magnetic hum from a transformer, which is where coaxial layout helps: with the conductor placed exactly at the centre of a round shield, the voltages a magnetic field induces come in two nearly equal halves that cancel. On cables running at 2.5 kilovolts or more, a grounded shield also collects leakage current, guarding people against shock and evening out stress on the insulation.
Flexibility comes from stranding, twisting or braiding many fine wires into a thicker one; bunching the fine wires first gives the most bend. Copper strands are often plated with tin, sometimes gold or silver, since those metals oxidise far less and make soldering easier. Tinning also lubricates the strands and once helped strip away rubber insulation. Winding the strands very tightly produces the stretchy coil of an old telephone handset cord.
Insulation has its own history. Early cables used cloth, rubber or paper, and gutta-percha, a natural latex, proved its worth under water in the 19th century. Polyethylene, invented in 1930, stayed a military material until after the Second World War; one wartime exception was a telegraph line under the English Channel, insulated with it, that served the forces landing after D-Day. Because most jacket plastics burn, bundled cables can be a serious fire risk, handled with special jackets, retardant coatings or non-combustible enclosures.
Source: Electrical cable
