Electrical cable

Copper wires in a cable may be bare, or they may be plated with a thin layer of another metal, most often tin but sometimes gold, silver or some other material.

Tin, gold, and silver are much less prone to oxidation than copper, which may lengthen wire life, and makes soldering easier.

Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords).

Plastic materials are generally used today, except for high-reliability[clarification needed] power cables.

This was invented in 1930, but not available outside military use until after World War 2 during which a telegraph cable using it was laid across the English Channel to support troops following D-Day.

These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction.

In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center.

This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel each other.

This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line.

Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.