H215A20 H215A20 H215A20 3 in max 6 ft 6 ft 3 in max Figure 4-81.  Spacing of printed identification marks.  the marking should be legible, and the stamping color should  contrast with the color of the wire insulation. For example,  use black stamping with light-colored backgrounds, or white  stamping on dark-colored backgrounds. Most manufacturers mark the wires at intervals of not more  than 15 inches lengthwise and within 3 inches of each  junction or terminating point.  [Figure 4-82]  Coaxial cable and wires at terminal blocks and junction  boxes are often identified by marking or stamping a wiring  sleeve rather than the wire itself. For general purpose wiring,  flexible vinyl sleeving, either clear or white opaque, is  commonly used. For high-temperature applications, silicone  rubber or silicone fiberglass sleeving is recommended.  Where resistance to synthetic hydraulic fluids or other  solvents is necessary, either clear or white opaque nylon  sleeving can be used. While the preferred method is to stamp the identification  marking directly on the wire or on sleeving, other methods  are often employed. One method uses a marked sleeve tied in  4 3  2  1 4 3 2 1 TB - 1 H215B20 H216B20 H217B20 H218B20 H215A20 H216A20 H217A20 H218A20 XYZ 15 XYZ15 Sleeve marker tied in place Pressure-sensitive tape 4-51 Figure 4-83.  Alternate methods of identifying wire bundles. Figure 4-82.  Wire identification at a terminal block.  Wire Groups and Bundles Electrical Wiring Installation place. The other uses a pressure-sensitive tape.  [Figure 4-83]  The following recommended procedures for installing aircraft  electrical wiring are typical of those used on most types  of aircraft. For purposes of this discussion, the following  definitions are applicable: Grouping or bundling certain wires, such as electrically  unprotected power wiring and wiring to duplicate vital  equipment, should be avoided. Wire bundles should generally  be limited in size to a bundle of 75 wires, or 2 inches in  diameter where practicable. When several wires are grouped  at junction boxes, terminal blocks, panels, etc., the identity  of the group within a bundle can be retained.  [Figure 4-84  1.  Open wiring—any wire, wire group, or wire bundle  not enclosed in conduit. 2.  Wire group—two or more wires in the same location,  tied together to identity the group. 3.  Wire bundle—two or more wire groups tied together  because they are going in the same direction at the  point where the tie is located. The bundle facilitates  maintenance. 4.  Electrically protected wiring—wires that include in  the circuit protections against overloading, such as  fuses, circuit breakers, or other limiting devices. 5.  Electrically unprotected wiring—wires, generally  from generators to main bus distribution points, that  do not have protection, such as fuses, circuit breakers,  or other current-limiting devices. Twisting Wires