content_image/578893.jpg content_image/578896.jpg content_image/578894.jpg
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: 

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). 

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. 

<img src='content_image/578893.jpg'>

<img src='content_image/578896.jpg'>

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. 

## Conductor 

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 . 

<img src='content_image/578894.jpg'>

