The process of having a custom harness manufactured often feels like the world’s most high-stakes pioneer game of the telephone game. You have a dream in your mind, technical specifications in paper, and a vendor who is willing to make it come true. However, the point is that, unless the documentation that you submit is absolutely crystal clear, you are preconditioning delays and expensive revisions as well as a significant share of frustration on both ends.
The good news? The appropriate documentation package lets you improve your odds of ending up with what you want on the first try by a significant margin. We will take you on a stroll on what you need to send to your supplier to ensure that your custom harness is constructed right on the first day.
Start With a Detailed Technical Drawing
Consider your technical drawing to be the blueprint that will be used to govern all decisions made by your supplier. It is not a sketch, but a detailed drawing of your harness, which requires no interpretation. Your drawing must contain general dimensions, connector positions, wire routes, and branch points in case your harness has more than one leg.
A variety of points of view are preferred where needed, particularly when your harness requires complicated three-dimensional routing or has strict bend constraints. Label all connectors, wires, and termination points. In case there are certain places where the harness should be adorned around some obstacles or narrow sections, label those specifically.
Also, remember to place a scale on your drawing and also indicate all the measurements using either metric or imperial units throughout. Intermixing is a formula for disaster, and even the most knowledgeable manufacturers might make expensive errors when interchanging between systems.
Provide a Comprehensive Bill of Materials
Your shopping list is your bill of materials, or BOM, that contains a list of the components that your supplier can precisely know that go into your harness. All individual components should be listed in this document such as wire types, connector models, terminals, protective sleeving, labels and any other hardware such as clips, ties or mounting brackets.
You can specify the gauge, the color, and the type of wire, e.g. stranded or solid core, shielded or unshielded. When connector and terminals are available, include manufacturer part numbers. Even such generic descriptions as D-sub connector allow too much variation. Rather, provide something specific such as TE connectivity 1-776231-0 9 position D-sub male connector; solder cup termination.
When dealing with a Cable Assembly Manufacturer particularly one who frequently buys components, he/she might be able to provide an alternative in case of unavailability of certain parts or long lead times. But they can merely do this satisfactorily when they know what it was you had specified, and why in the first place.
Create a Detailed Wiring Schematic
One of your technical drawings is the physical layout and the other is the wiring schematic where the electrical connections are shown. This document lays out the nature of the pin-connections between the wires and the end-termination on the other side of the wires. This is of paramount importance in case of complex harnesses where there are several connectors.
Standard electrical schematic symbols and conventions will be used to ensure that your supplier can easily read your diagram. Label all wires with some sort of identifier that corresponds to your BOM and technical drawing. In case particular wires are powered with power or ground, or carry sensitive signals, make note of that.
In some applications such as Cable assemblies for robots, your schematic may also be required to show the flex life requirements, shielding connections and any special consideration of movement or vibration as well. These facts will assist your manufacturer in choosing the right type of wire as well as construction that will meet the needs of your application.
State Quality and Testing Requirements
Not every harness is considered the same and your supplier must be aware of the standards that your harness must have. Will your harness be continuity tested? Are you required to test hi-pot to make sure the insulation is intact? Does your industry require any industry standards or certifications the harness must meet?
Record any environmental conditions your harness is going to be exposed to. Extreme temperatures, contact with chemicals, UV light, moisture or mechanical stresses all have an effect on material choice and construction techniques. In case you are going to wear a harness in a medical device, aerospace or automotive application, state the standards.
Add tolerable quality levels to such items as pin retention force, insulation resistance and visual defects. In case you need certain paperwork, such as test results, certificates of conformance or material traceability, specify that initially. This is particularly significant when dealing with suppliers who may also deal with PCB manufacturing in Italy or any other area where documentation standards could be different.
Do Not Forget the Functional Requirements Document
Understanding supplier use of these important elements in addition to technical specifications is essential. A functional requirements document will tell you why you need a harness, what medium it is to work in and what limitations it may have that are not immediately apparent in drawings.
This background aids in making better decisions by your supplier in cases where they face ambiguity in the course of manufacturing. It also allows them to introduce improvements onto it, basing it on their experience with similar applications. A manufacturer who has already done Precision Cable Assembly work will have probably seen hundreds of harnesses, and may well have valuable information, but only, of course, when they know what you are doing.
The Bottom Line: Clarity Prevents Costly Mistakes
It is not only the thoroughness of sending your supplier with the comprehensive documentation, but it is also a sign of respect to the manufacturing process and all the people engaged. Through writing precise, elaborate documentation, you are respecting the experience of your supplier and providing them with the means by which they can perform to their utmost ability to meet your specifications precisely.
Admittedly, this documentation preparation is time-consuming at the beginning. But put that investment to the expense of taking a batch of wrongly made harnesses, the time wasted in correcting the errors, and the future frustration of all concerned. The first time is not only possible, it is also fully possible with the proper documentation.