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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. 

## Routing and Installation 

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: 

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 

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. 

## Protection Against High Temperature 

To prevent insulation deterioration, wires should be kept separate from high-temperature equipment, such as resistors, 

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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 

