There is a mistake that repeats itself too often in industrial projects: requesting the wiring prototype when the design is already closed, the equipment is in validation and the launch deadline allows no changes. At that point, the prototype stops being a development tool and becomes a source of pressure.<\/p>\n\n
A wiring prototype exists to validate before committing. To detect design, material or integration problems when there is still room to correct them without cost or delay. But it only serves that purpose if it is requested at the right moment in the project.<\/p>\n\n
In this article we explain what a wiring prototype is, what can be validated with it, when it makes sense to request one and when it is already too late.<\/p>\n\n
A wiring prototype is one unit or a small set of units manufactured according to the customer’s specifications \u2014 or according to a preliminary version of them \u2014 with the aim of validating the design before committing to series production.<\/p>\n\n
It is not a finished product. It is a development tool.<\/p>\n\n
What is manufactured in a prototype can vary greatly depending on the project phase:<\/p>\n\n
In all cases, the objective is the same: to obtain real information on how the wiring behaves in the usage environment before manufacturing in volume.<\/p>\n\n
A well-designed wiring prototype allows simultaneous validation of several aspects that are difficult to anticipate on paper \u2014 or in CAD:<\/p>\n\n
Physical integration<\/strong>: does the harness fit in the available space? Are the lengths correct? Are the bending radii achievable with the specified materials? Do the connectors reach their connection points without mechanical tension?<\/p>\n\n Connector compatibility<\/strong>: do the connectors fit correctly in the equipment receptacles? Is the insertion force adequate? Does the polarisation work as expected?<\/p>\n\n Electrical behaviour<\/strong>: is the continuity correct? Are there short circuits or crossed signals in the design? Is the contact resistance within the expected values?<\/p>\n\n Material suitability<\/strong>: does the cable insulation withstand the ambient temperature? Are the mechanical protections sufficient for the expected level of vibration or abrasion? Do the identification colours match the equipment scheme?<\/p>\n\n Mountability<\/strong>: is the harness easy to install in the equipment under real assembly conditions? Can operators access the connectors without difficulty? Is the installation sequence correct? An industrial product development project typically goes through these phases:<\/p>\n\n Concept phase<\/strong>: the product is in functional definition. There is no electrical drawing, no BOM, no final geometry. At this stage it makes no sense to request a wiring prototype because there is nothing precise enough to validate.<\/p>\n\n Preliminary design phase<\/strong>: there is an electrical schematic, an approximate equipment geometry and a first component selection. This is the ideal time to request a functional prototype. The materials may not be the final ones, but the prototype allows physical integration to be validated and design problems to be detected with enough margin to correct them.<\/p>\n\n Detailed design phase<\/strong>: the electrical drawing is closed, the connectors are defined and the equipment geometry is stable. This is the time to request a prototype faithful to the final specifications, which will be used for the validation tests of the complete equipment: functional, EMC, environmental.<\/p>\n\n Validation phase<\/strong>: the equipment is undergoing homologation or certification tests. If the wiring has not been prototyped before, any change at this stage has a high cost: it delays certification, may require repeating tests and compromises the launch deadline.<\/p>\n\n Series production phase<\/strong>: the design is closed and validated. Requesting a “prototype” at this stage is in fact requesting a production sample, which has a different purpose: verifying that the series manufacturing process faithfully reproduces what was validated.<\/p>\n\n Not all prototypes are the same or have the same level of fidelity. Depending on the project phase and what needs to be validated, the appropriate prototype differs:<\/p>\n\n Requesting a validation prototype in the preliminary design phase is a mistake: time and money are invested in manufacturing something with specifications that are still going to change. Requesting a basic functional prototype in the validation phase is another mistake: it does not have sufficient fidelity to detect the problems that matter at that point.<\/p>\n\n One of the most common obstacles to requesting a prototype on time is the belief that all documentation needs to be complete and final. That is not the case.<\/p>\n\n What the manufacturer needs depends on the type of prototype:<\/p>\n\n For a basic functional prototype<\/strong>: a provisional electrical schematic, a signal list with approximate lengths and the type of connectors planned. A final mechanical drawing or closed BOM is not needed.<\/p>\n\n For an engineering prototype<\/strong>: electrical schematic with defined connectors, estimated lengths with \u00b110% tolerance and specification of the intended cable type or insulation.<\/p>\n\n For a validation prototype<\/strong>: complete electrical drawing, BOM with final references, material specification and any applicable certification or regulatory requirement.<\/p>\n\n Requesting the prototype without an electrical drawing<\/strong>: the manufacturer cannot guess the wiring scheme. A prototype manufactured on verbal descriptions or approximate references does not validate anything reliably.<\/p>\n\n Not defining what needs to be validated<\/strong>: if it is not known what is being looked for in the prototype, it is also not known what to review when it arrives. The prototype must be accompanied by a minimum review protocol: what is verified, how and by whom.<\/p>\n\n Changing the design between the prototype and the series without notifying the manufacturer<\/strong>: a change of connector, length or material between the validated prototype and series production invalidates the validation. Any change after the prototype must be treated as a new prototype, even if partial.<\/p>\n\n Requesting a single prototype for everything<\/strong>: in projects with several wiring variants \u2014 for example, different lengths for different versions of the equipment \u2014 requesting a single prototype does not validate the variants that have not been manufactured. Each variant with significant differences needs its own validation.<\/p>\n\n Not keeping the validated prototype as a reference<\/strong>: the approved prototype is the physical reference for the design. If it is not kept or properly documented, there is no way to verify that series production is faithful to what was validated.<\/p>\n\n Beyond technical validation, the prototype serves another function that is often overlooked: it is the meeting point between the customer’s design team and the supplier’s manufacturing team.<\/p>\n\n When the customer reviews a physical prototype with the manufacturer, conversations arise that do not emerge from a drawing: “this bending radius is too tight for the specified cable”, “the connector does not have enough clearance for assembly on the line”, “the length of the secondary branch does not reach the connection point with the equipment assembled”. Those conversations are what align the design with the reality of manufacturing and installation. And they are much more productive when held with the prototype in hand than when held with the equipment already in production.<\/p>\n\nProject phases and when the prototype fits<\/h3>\n\n
Prototype types according to phase and objective<\/h3>\n\n
Prototype type<\/th> Fidelity<\/th> Main objective<\/th> Recommended phase<\/th><\/tr><\/thead> Basic functional prototype<\/td> Low<\/td> Validate physical integration and lengths<\/td> Preliminary design<\/td><\/tr> Engineering prototype<\/td> Medium<\/td> Validate electrical design and connector compatibility<\/td> Preliminary \/ detailed design<\/td><\/tr> Validation prototype<\/td> High<\/td> Functional, EMC and environmental equipment tests<\/td> Detailed design<\/td><\/tr> Production sample<\/td> Maximum<\/td> Verify series manufacturing process<\/td> Prior to launch<\/td><\/tr><\/tbody><\/table><\/figure>\n\n What information does the manufacturer need to make a prototype<\/h3>\n\n
Most common mistakes when managing wiring prototypes<\/h3>\n\n
The prototype as a communication tool between design and manufacturing<\/h3>\n\n