at each end of the bend, a minimum radius of three times  the outside diameter of the wire, or wire bundle, is usually  acceptable. There are exceptions to these guidelines in the  case of certain types of cable; for example, coaxial cable  should never be bent to a smaller radius than six times the  outside diameter. All wiring should be installed so that it is mechanically  and electrically sound and neat in appearance. Whenever  practicable, wires and bundles should be routed parallel with,  or at right angles to, the stringers or ribs of the area involved.  An exception to this general rule is the coaxial cables, which  are routed as directly as possible. The wiring must be adequately supported throughout its  length. A sufficient number of supports must be provided  to prevent undue vibration of the unsupported lengths. All  wires and wire groups should be routed and installed to  protect them from: Wires and wire groups should be installed so that they are  protected against chafing or abrasion in those locations where  contact with sharp surfaces or other wires would damage the  insulation. Damage to the insulation can cause short circuits,  malfunctions, or inadvertent operation of equipment. Cable  clamps should be used to support wire bundles at each hole  through a bulkhead.  [Figure 4-88]  If wires come closer than  ¼ inch to the edge of the hole, a suitable grommet is used in  the hole.  [Figure 4-89] Sometimes, it is necessary to cut nylon or rubber grommets  to facilitate installation. In these instances, after insertion,  the grommet can be secured in place with general purpose  cement. The slot should be at the top of the hole, and the  cut should be made at an angle of 45° to the axis of the wire  bundle hole. exhaust stacks, heating ducts. The amount of separation is  usually specified by engineering drawings. Some wires must  be run through hot areas. These wires must be insulated with  high-temperature rated material, such as asbestos, fiberglass,  or Teflon. Additional protection is also often required in the  form of conduits. A low-temperature insulated wire should  never be used to replace a high-temperature insulated wire. Many coaxial cables have soft plastic insulation, such as  polyethylene, that is especially subject to deformation and  To prevent insulation deterioration, wires should be kept  separate from high-temperature equipment, such as resistors,  4-53 Protection Against High Temperature Figure 4-89.  Cable clamp and grommet at bulkhead hole.  Figure 4-88.  Cable clamp at bulkhead hole. 1.  Chafing or abrasion; 2.  High temperature; 3.  Being used as handholds, or as support for personal  belongings and equipment; 4.  Damage by personnel moving within the aircraft; 5.  Damage from cargo stowage or shifting; 6. Damage from battery acid fumes, spray, or  spillage; and 7.  Damage from solvents and fluids. Protection Against Chafing Routing and Installation Cable clamp $^{1}$/4" minimum clearance  Angle bracket with two point fastening Approved grommet Wires less than $^{1}$/4" from hole edge