Cable Harness

A cable harness is a group of wires or cables bound together. The individual wires or cables of a harness may also be contained with a protective covering.

Custom Cable Assembly Design may also need to account for cable dressing and/or vibration issues, here are a few more design considerations to make note of.

Cable Binding; Normally individual wires or cable groups need to be secured together or secured to the chassis wall.

Cable Sleeving
Spiral Wrap Cable Sleeving

Harness Ties

A tie or stitch shall be placed immediately before and immediately after any breakout of the wire or cable from the harness

Installed straps shall be locked to prevent them from loosening or opening. Straps shall be placed on both sides of a breakout; otherwise, spacing between straps shall be as required by the Table below. The "ribbed" side of a strap shall always be placed against the wires. Straps shall be tightened so that they do not slide back and forth on the assembly; however, they shall not be so tight as to cause noticeable indentation or distortion of the wires in the harness.

The table below provides the Maximum Distance between Cable Ties on a cable assembly. The cable ties could be a Spot Tie, Plastic Strap, rope stitch or some other method of securing the wire bundle together.

Cable Tie Wrap
Maximum Distance between Cable Ties

An additional consideration is to install a cable tie within some minimum distance off its terminating end. The table below provides the Minimum Distance from the cable termination or connector and the first Cable Tie on a cable assembly. The cable ties could be a Spot Tie, Plastic Strap, rope stitch or some other method of securing the wire bundle together.

Cable Ties Distance
Minimum Distance between Connector Cable Ties

Be sure to specify cable Strain Relief if there might be a requirement or issue with an operator applying to much force on a connector.

Cable Stitching
Single Tape Cable Stitching

Harness Braid Sleeving

Prewoven fabric (unvarnished) braid sleeving to be installed over the wire harness shall be slightly oversized so that it can be slid over the bundle (Requirement). Braided sleeving shall be snugly dressed down over the wire bundle (Requirement). Continuous braid sleeving shall be secured at the ends by plastic cable straps, spot ties, clamps, heat shrinkable sleeving, or a potting material (Requirement). When secured, the covering shall not slide freely.

Braided sleeving may be secured by a spot tie or plastic cable strap. The end of the braid shall be tucked under and secured with a spot tie or plastic strap.

The end of the braid may be secured by connector clamps, other hardware, or potting.

Heat Shrink Sleeving

Heat Shrink Tubing could also be used to secure individual wires or cables together to form a wiring harness.

Harness Splices

The use of splices in a harness design should be minimized as much as possible. The simplest and most reliable wiring design is one that results in the routing of a dedicated, continuous, and unbroken conductor from point to point.

A lap splice is where the conductor ends are laid parallel to, and overlap each other, and are terminated with a solder joint.

A lash splice is a soldered splice identical to the lap splice except for the addition of a single strand wire winding (overlash) that binds the conductors together.

cable assemblies. Cable Derating Guide Lines

Cable Data Rates, next chassis design topic

Cable Considerations

Cable Insulation; Be sure to specify the cable insulation if it's important to the finished design. A military spec chassis may preclude the use of PVC because of the amount of smoke PVC produces when it catches fire. Changes from PVC to Teflon insulation could add cost to the system at the last minute.

Navy; A cable using PVC material is not to be used in enclosed environments or shipboard applications.
Air Force; The Air Force has restricted use of PVC in aerospace and ground support applications.

Cable Color Coding; If the individual wires need a particular color code, or if a wire bundle need to be a certain wire color code than call that out in the chassis specification. Some MIL Specs require Cable Bundle jacket color coding; individual cable bundle jackets shall be color coded for identification in accordance with EIA/TIA-598. EIA-598 will also apply to Ribbon fiber color coding and fiber Binders. In many cases the cable jacket will be Black.
See also Wire Selection

Cable Labeling; Don't forget to call out any printed labels required on the cable. In most cases the source and destination will need to be called out on either side of the cable:
Fiber optic cables shall be identified in such a way to distinguish these cables from wire or coaxial cables.
Cable connectors shall be permanently marked with mating connector designation within 15 cm (6 in) of connector body, or as stated in the engineering documentation.

Do the cables require a particular Back Shell, will the back shell and cable bend radius fit within the chassis.

Cable Ferrites Manufacturers
Connector Environmental Protection Ratings
How To Specify a Equipment Chassis; Index page

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