A few simple guidelines to follow during the handling, routing and installation of cable harnesses will extend their life, ensure peak performance, facilitate installation and repairs, and provide a visible sign of quality workmanship.  Damage to wires shortens the life of the connection and can possibly impact the function of associated circuits.

Dressing the wires and cables entering and exiting the bundle presents a neat appearance and makes it easier to work on the cable in the future.  Strain relief on all terminated ends of a cable or harness will make it easier to install and facilitate an easier repair, if needed.  The proper routing and shielding of the harness will ensure that all signlas will reach their destination free of interference and cross talk.

Damaged cable (like birdcaging, Figure 6-1), can be prevented by twisting the insulation from the end of the wire in the same direction and the same rate as the manufacturer’s twist.  This will make soldering into a cup or on a terminal much easier and will prevent shorts.  Wires cannot exceed the minimum bend radius as outlined by the manufacturer in the IPC-A-610 standard for “Acceptability of Electronic Assemblies”.  Cut or nicked conductors may degrade the signal performance of higher frequency applications, as well as compromise the mechanical strength.  To prevent nicking or cutting conductors, the use of a thermal insulation stripper, or correctly sized mechanical strippers, and appropriate hand tools is required.

Dressing the cable is the process in which all of the insulated wires in a wire bundle or harness are arranged so that there are no crossed, folded, strained, or loose conductors.  Crossed conductors, when tied into a bundle or harness, can lead to crushed insulation in coax cables or split insulation on stranded wire.  Many times the crossed conductors are easily loosened and can be pulled and broken. 

When breaking a wire or conductor out of a harness or bundle, a minimum bend radius of the conductor and required strain relief must be observed (Figure 6-2).  The location of the termination and the break out point should allow the wire to curve gradually to the termination.  This prevents over bending and provides enough wire for strain relief.

Strain relief is not only important when breaking out of a harness, but is essential at all terminations: post, terminal, screw, or multi pin connectors.  If a radio is mobile, or an electrical cabinet can be moved, the strain relief on the conductors and connectors will allow for flexing without any breakage.  Temperature extremes can also put stress on connections, as the wires contract in the cold and expand in the heat.  Strain relief, in most cases, can be accomplished by either excess wire between a fixed mounting point and the connector, or a mechanical grip in the conductor.  When terminating a wiring harness, strain relief is achieved by adding a maintenance loop before the termination point.  A commercially available, gripping grommet relief can be used if the conductor is going through a bulk head or electrical cabinet.

The routing of cable assemblies and wiring harnesses can accomplish three goals: neat appearance, signal isolation and integrity, and material savings.  When designing the routing of wiring harnesses, the engineer or technician should not run low voltage or low data rate busses next to RF or high voltage alternating current (AC) cables unless the cables have been properly shielded.  Even shielded data cables can pick up AC and RF interference when run in the same bundle for long runs.  Also, a well thought out route for cables and conductors can minimize the cable lengths and increase the material savings when multiplied by the number of products manufactured.

Quality workmanship is the keystone to a long service life for harnesses and cables as well as the associated electronics. IPC-A-610 and IPC-A-620 provide the industry standard for cable, harness and connector assembly workmanship.