What is the difference between a wire and cable? This is one of the most basic questions that still needs to be answered. Wire is a single conductor and cable is a group of two or more insulated conductors. If there was not any insulation on the two conductors then it would not be a cable, it would still be a single conductor which would classify as a wire. There are four basic categories of wire and cable. These categories consist of single-conductor, multi-conductor, twisted pairs, and coaxial cable.
There are two types of wire. These are solid wire and stranded wire. Both types have different uses depending on the level of resistance and flexibility required. Solid wire is a single solid conductor that may be bare or insulated. This type of wire offers a little lower resistance. Solid conductors are the key to better performance at higher frequencies. Stranded wire is wire that is made up of several strands of bare conductor to form a single conductor when all strands are put together. This type of wire has more flexibility and a longer flex life before becoming unusable.
There are four basic cable types. These types are twisted pairs cable, multi-conductor cable, coaxial cable, and fiber optics cable.
Multi-conductor cable is cable that is made up of many insulated conductors. This type of cable is common in control applications but is almost never used in signal applications.
Twisted pairs cable consists of pairs of conductors that are twisted together. This cable is specifically intended for signal carrying. This type of cable was invented in the 1880's for the specific intent of wiring up early telephone systems. Twisting the pairs of conductors gives the cable some immunity to interference.
Cable types listed above are considered balanced line configurations. This means that two conductors are kept very close together, normally by twisting them. Conductors must be the same length, size, and have a constant distance between them.
Coaxial cable is the other popular configuration for cable. The signal on the two conductors in coaxial cable is not the same because the shield carries the ground and the signal. Since the signal is not the same on both conductors this configuration is an unbalanced line. Coaxial cable does not have the immunity to interference that twisted pairs cable does, but the performance may be far stabler with coaxial cable then with twisted pairs cable because of the fact that various parts of the cable are “knitted' together.
There are six configurations of shields involved in cable. These are Unshielded, Braid Shields, Serve/Spiral shields, French Braid Shields, Foil Shields, and Combination Shields. Shields are added to prevent noise interference and radiation.
Unshielded cable may be used where there is no crosstalk or noise present. This configuration can also be used if noise is not important or will not substantially affect the cable signal. These cables are used prevalently for the data world where conductor pairs have extremely tight twists or use conductors that have been bonded together. These high performance pairs of conductors have great immunity to interference and radiation.
Serve/Spiral Shields are manufactured to be extremely flexible. Serve Shield effectiveness are compromised by the fact that every time the Serve Shield is flexed it opens up. A Spiral Shield has an affect on the inductance of the shield and so these shield configurations are normally not used for video, only audio. People who choose this type of cable usually are trading performance in exchange for flexibility.
Braid Shields are manufactured by spinning conductors or groups of wires around a center core. The braiding process is very labor intensive and slow to produce, which makes it the most expensive step of the cable making process. The braiding can be single or double braid, with double braiding being more effective. Since there are always holes where the wires cross, braiding is never 100% effective. The higher the frequency the less effective a Braid Shield is.
French Braid Shields are a combination of a Serve Shield and a Braid Shield. This shield consists of two Serve Shields braided along a single axis. This shield gives excellent flexibility and RF performance. The French Braid Shield takes the same effort and material as a Braid Shield so the manufacturing process costs roughly the same for both.
Foil Shields are the cheapest and easiest shield to apply. They consist of two different layers. One layer is metal and the other layer is a polyester substrate. This shield can be applied just as quick as the cable can be run. These shields show performance for low-frequency to be poor but performance for high-frequency to be excellent. Since Foil Shields are made with foil that has no holes, they can be 100% effective.
Combination Shields are shields that use a combination of braiding and foil. Sometimes there are multiple layers of each. Combination Shields are the most expensive of all shields. These shields give the best broadband coverage because the foil works for high frequencies and the braiding works for low frequencies.
Fiber optic cable is divided into three kinds: Plastic Fiber, Multi mode Fiber, and single mode Fiber. Plastic fiber is the largest fiber in fiber optic cable, is made of plastic, and is usually used in high end audio signals. Multi mode fiber is made of glass, ranges in diameter, and is used in the data world. Single mode fiber is considered the king, or the best, because the fiber is too small to see without a microscope. This fiber gives the best performance but is very difficult to connectorize because of fiber size and hardness.