A wire is described as a single, solid conductor, or as a  stranded conductor covered with an insulating material.  Figure 9-110  illustrates these two definitions of a wire.  Because of in-flight vibration and flexing, conductor round  wire should be stranded to minimize fatigue breakage. The term “cable,” as used in aircraft electrical installations,  includes: The term “wire harness” is used when an array of insulated  conductors are bound together by lacing cord, metal bands,  or other binding in an arrangement suitable for use only in  specific equipment for which the harness was designed; it  may include terminations. Wire harnesses are extensively  used in aircraft to connect all the electrical components.  [Figure 9-111] For many years, the standard wire in light aircraft has been  MIL-W-5086A, which uses a tin-coated copper conductor  rated at 600 volts and temperatures of 105 °C. This basic wire  is then coated with various insulating coatings. Commercial  and military aircraft use wire that is manufactured under  MIL-W-22759 specification, which complies with current  military and FAA requirements.  The most important consideration in the selection of aircraft  wire is properly matching the wire’s construction to the  application environment. Wire construction that is suitable for  the most severe environmental condition to be encountered  should be selected. Wires are typically categorized as being  suitable for either open wiring or protected wiring application.  The wire temperature rating is typically a measure of the  insulation’s ability to withstand the combination of ambient  temperature and current-related conductor temperature rise. The two most generally used conductors are copper and  aluminum. Each has characteristics that make its use  advantageous under certain circumstances. Also, each has  certain disadvantages. Copper has a higher conductivity; is  more ductile; has relatively high tensile strength; and can be  easily soldered. Copper is more expensive and heavier than  aluminum. Although aluminum has only about 60 percent of  the conductivity of copper, it is used extensively. Its lightness  makes possible long spans, and its relatively large diameter  for a given conductivity reduces corona (the discharge of  electricity from the wire when it has a high potential). The  discharge is greater when small diameter wire is used than  when large diameter wire is used. Some bus bars are made of  aluminum instead of copper where there is a greater radiating  surface for the same conductance. The characteristics of  copper and aluminum are compared in  Figure 9-112 . Conductor 1.  Two or more separately insulated conductors in the  same jacket. 2.  Two or more separately insulated conductors twisted  together (twisted pair). 3.  One or more insulated conductors covered with a  metallic braided shield (shielded cable). 4.  A single insulated center conductor with a metallic  braided outer conductor (radio frequency cable).  Figure 9-111.  Shielded wire harness.  Figure 9-110.  Aircraft electrical cable.  Figure 9-112.  Aircraft electrical cable. Conductors Wire single solid conductor Solid conductor Stranded conductor A B  Tensile strength (lb-in) Tensile strength for same conductivity (lb) Weight for same conductivity (lb) Cross section for same conductivity (CM) Specific resistance (ohm/mil ft)  Characteristic Copper Aluminum  55,000  55,000 100 100 10.6 25,000 40,000 48 160 17 9-67