Designing a wire harness is simple, right? Just pick out an appropriate wire for your voltage and environmental requirements, select a connector that meets your needs, decide how long you need it to be, and you are off to the races.
There are a few more things to consider before taking your released design to your wire harness builders. Depending on your application, you will need to design a harness that will be flexible enough to fit into the space needed and robust enough to handle the environmental factors that are brought to bear against it.
In some instances, you may need a very stiff wire bundle.
In others, a simple, flexible assembly may suffice.
Take care to consider how much strain may be placed onto your mated connectors if you design a harness that lacks flexibility. A wire harness that is too stiff and difficult to mate to an adjacent assembly could result in damaging a connector during installation or contribute to a stress-induced field failure in the future.
Many factors can contribute to how flexible your wire harness will be. The following items will help you decide what level of protection you need and how much flexibility you are willing to sacrifice for that protection.
Heat shrink durometer
– Be aware of the Shore Durometer rating of your chosen material. Higher durometer ratings result in a less flexible material. Some heat shrink datasheets will list this as “Hardness,” and the rating is usually in Shore D units. If the datasheet does not list durometer or hardness, check with the manufacturer to see if they can provide that information.
Expandable sleeving vs. heat shrink
– Quite often, engineers will use heat shrink along the entire length of their wire harness assembly as a method to encase the wire bundle. This is appropriate in highly demanding environments, but it is often a better choice to go with an expandable sleeving (Expando). When fuel/oil resistance and extreme abrasion aren’t significant factors, Expando can contain and protect your wire bundle without compromising flexibility and significantly improving manufacturing ease.
Adhesive heat shrink
– Be exceptionally mindful when using an adhesive heat shrink option on your wire harnesses and use sparingly. Although the durometer of the selected adhesive heat shrink may be low enough to support a flexible harness, the adhesion with the wires bundle may cause binding, resulting in an assembly that may be less pliable than intended.
– Some applications benefit from the use of waxed lacing to manage the wire bundle. This is a light-weight option that allows for ease of accessibility for diagnosis and repair. The waxed lacing allows for wire in the bundle to slide independently of each other to support flexibility. This method does not allow for protecting your assembly from environmental concerns such as abrasion but may be perfectly suitable in the right conditions.
– When using connectors with keyways, consider the angle at which it needs to mate. With non-flexible assemblies, torquing them into proper orientation can cause damage to the assembly as well as the mating application. Adding flexibility creates less rotational stress on all components.
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