radii for rigid conduit are shown in  Figure 9-141 . Kinked or  wrinkled bends in rigid conduits are not recommended and  should be replaced. Tubing bends that have been flattened  into an ellipse and have a minor diameter of less than 75  percent of the nominal tubing diameter should be replaced,  because the tube area has been reduced by at least 10 percent.  Tubing that has been formed and cut to final length should be  deburred to prevent wire insulation damage. When installing  replacement tube sections with fittings at both ends, care  should be taken to eliminate mechanical strain. Flexible aluminum conduit conforming to specification  MIL-C-6136 is available in two types: Type I, bare flexible  conduit, and Type II, rubber-covered flexible conduit. Flexible  brass conduit conforming to specification MIL-C-7931 is  available and normally used instead of flexible aluminum  where necessary to minimize radio interference. Also available  is a plastic flexible tubing. (Reference MIL-T-8191A.) Flexible  conduit may be used where it is impractical to use rigid conduit,  such as areas that have motion between conduit ends or where  complex bends are necessary. The use of transparent adhesive tape is recommended when  cutting flexible tubing with a hacksaw to minimize fraying  of the braid. The tape should be centered over the cutting  reference mark with the saw cutting through the tape. After  cutting the flexible conduit, the transparent tape should be  removed, the frayed braid ends trimmed, burrs removed from  inside the conduit, and coupling nut and ferrule installed.  Minimum acceptable bending radii for flexible conduit are  shown in  Figure  9- 142 . In conventional wiring systems, circuits are shielded  individually, in pairs, triples, or quads depending on  each circuit’s shielding requirement called out for in the  engineering documentation. A wire is normally shielded  when it is anticipated that the circuit can be affected by  another circuit in the wire harness. When the wires come  close together, they can couple enough interference to cause  a detrimental upset to attached circuitry. This effect is often  called crosstalk. Wires must come close enough for their  fields to interact, and they must be in an operating mode  that produces the crosstalk effect. However, the potential for  crosstalk is real, and the only way to prevent crosstalk is to  shield the wire.  [Figure 9-143] One of the more important factors in the design and  maintenance of aircraft electrical systems is proper bonding  and grounding. Inadequate bonding or grounding can lead to  unreliable operation of systems, EMI, electrostatic discharge  damage to sensitive electronics, personnel shock hazard, or  damage from lightning strike. Bonding and Grounding Wire Shielding Flexible Conduit Figure 9-142.  Minimum bending radii for flexible aluminum or  brass conduit.   $^{3}$/$_{16}$  $^{1}$/$_{4}$  $^{3}$/$_{8}$  $^{1}$/$_{2}$  $^{5}$/$_{8}$  $^{3}$/$_{4}$  1  1$^{1}$/$_{4}$  1$^{1}$/$_{2}$  1$^{3}$/$_{4}$  2  2$^{1}$/$_{2}$ 2$^{1}$/$_{4}$ 2$^{3}$/$_{4}$ 3$^{3}$/$_{4}$ 3$^{3}$/$_{4}$ 3$^{3}$/$_{4}$ 4$^{1}$/$_{4}$ 5$^{3}$/$_{4}$ 8  8$^{1}$/$_{4}$ 9 9$^{3}$/$_{4}$ 10  Nominal ID of  conduit (inches) Minimum bending  radius inside (inches)  $^{1}$/$_{8}$  $^{3}$/$_{16}$  $^{1}$/$_{4}$  $^{3}$/$_{8}$  $^{1}$/$_{2}$  $^{5}$/$_{8}$  $^{3}$/$_{4}$  1  1$^{1}$/$_{4}$  1$^{1}$/$_{2}$  1$^{3}$/$_{4}$  2  $^{3}$/$_{8}$  $^{7}$/$_{16}$  $^{9}$/$_{16}$  $^{15}$/$_{16}$  1$^{1}$/$_{4}$  1$^{1}$/$_{2}$  1$^{3}$/$_{4}$  3  3$^{3}$/$_{4}$  5  7  8  Nominal tube OD (inches) Minimum bend radius (inches) Figure 9-141.  Minimum bend radii for rigid conduit. Figure 9-143.  Crosstalk. Two wires in free air may couple capacitively,  resulting in crosstalk. A charge on the 1st wire induces an opposite charge on the 2nd wire. + − 9-85