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Manufacture and Installation of Wiring - Specific Tying Recommendations
Optical Fiber Cable and Harness
Figure 006
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Manufacture and Installation of Wiring - Specific Tying Recommendations
Coaxial Cable and Breakouts at Terminal Blocks
Figure 007
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(5) Breakouts for terminal blocks (Ref. Fig. 007) At wiring breakouts to terminal blocks, group wires leading to 3 or 4 modules or terminals together in order to reduce the number of ties.
R R R R R R R (6) Quad/quadrax cables: (Ref. Fig. 008) This type of cable must be installed in harnesses in a specific direction. The correct direction is identified on the cable sheath by the marking "A-B", and on the installation drawing. Correct direction is important during the connection of the contact in the connector to prevent damage to the contact positioning key and prevent twisting of the ends. The "A" side corresponds to the end where the red conductor is on the right. At the "A" end the conductor colors are, in a clockwise direction: red, green, blue and yellow. Colour continuity must be preserved on either side of the cut-off connectors (if any) so the wire is always in the same direction in a connection.
R (7) For twisted cables (Ref. Fig. 009)
(a) General Pre-twisted cables (2, 3, 4... wires) manufactured to design specifications are installed on the aircraft. Cables are twisted to eliminate the voltages induced by electrical and magnetic fields. Such measures are specified in the design documents. Cables are twisted manually or with a machine at the moment of cable manufacture.
(b) Cable lay Cable lay is determined by the number of pitches over a given length (1 meter). The pitch of the cable is the distance between two similar adjacent points on any one wire in the formed wrap.
(c) Lay forming process
____NOTE : This process is only used for cables twisted during manufacture and untwisted too much for connection.
____NOTE : It is important to make sure that the cables are not damaged. Damaged cables must be replaced completely.
- Wires must be twisted in such a way that they fit snugly to one another.
R Manufacture/Installation of Wiring - Wiring Continuity and Identification R Quadrax Wire R Figure 008
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Manufacture and Installation of Wiring - Specific Recommendations Twisted Cables R Figure 009
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- Wires must be twisted in the same direction as at initial
manufacture.
- The lay forming method depends on the number of cables to be twisted:
- 2, 3 and 4 wires can be twisted directly. - If 5 wires are to be twisted, 4 wires are twisted around 1 wire with the final pitch. - If 6 wires are to be twisted, 4 wires are twisted around 2 wires already twisted together, with the final pitch.
R (8) Installation of in-line standard electrical items (Ref. Fig. 010)
(a) Standard electrical items (diodes, butt or parallel splices, resistors, etc.) installed in-line on wires shall be positioned on the outside of the harnesses for easy access, identification, inspection or replacement. They must not be located: - In a section of harness that can move.
- In harness routing with a curve (small bend radius). - In conduits or other types of wire protection in which the item does not remain visible.
- Inside connector backshells.
- Under clamps or other types of cable support. - Under cable ties.
- Under galleys and/or toilet areas.
(b) When they are located in the same area, they shall, whenever possible, be staggered in families along the harness. There must be a minimum distance of 10 mm (0.3937 in.) between each item or family. Any in-line standard electrical items shall be located at a minimum distance of 100 mm (3.9370 in.) from the cable end.
(c) Shielding termination must be positioned approximately 70 mm (2.7559 in.) behind the connector (to facilitate removal and possible repairs of the contact).
R (9) Spare conduits and spare wires in overbraided conduits
R R R (a) To allow additional cables to pass modification and maintenance operations, a spare convoluted type conduit (PTFE or equivalent) can be associated with the harness.
Manufacture and Installation of Wiring - Specific Recommendations Installation of In-line Standard Items R Figure 010
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R (b) Sometimes, provisions shall be made for additional spare wires
R inside the protection.
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