Application Purposed Cable & Harness Testing - DIT-MCO

Not all harnesses are created equal

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Cable assemblies and wiring harnesses don’t know whether they are in a plane, train, automobile, or washing machine! All wiring harnesses are basically the same: wires, connectors, ring lugs and terminals, splices, etc. Some are soldered, some are crimped, and some are terminated via IDC. However similar harnesses are, there are significant differences in the manufacturing and testing processes, depending on the intended application.

Industry classifications of wiring harnesses

Although the lines can be blurry, several industry classifications of wiring harnesses correspond with different classes of tester requirements. The Bishop Report* published in identified ten end-use categories: Computer, Business/Office equipment, Medical, Test/Instrumentation, Industrial Equipment, Automotive, Transportation non-automotive, Military/Aerospace, Telecom/Datacom, and Consumer Electronics. The WHMA-IPC A-620 Standard classifies cable assemblies into three distinctive tiers: Class 1, Class 2, and Class 3. Once again, the lines tend to blur between the three, particularly when determining which A-620 tier each of the ten end-use harness classifications falls into. It is the author’s experience that, for electrical testing, the distinction between Class 1, 2, and 3 is uncertain. I would submit the following table represents, in general terms, the matching of industry harness classifications with A-620 testing classes:

Electrical testing requirements per classification or harness type

The A-620 standard primarily focuses on build methods and includes an electrical test requirement section, 19.4. Before the publication of the A-620, there were few electrical testing standards for the cable assembly industry. The most prominent, Mil-Std 202, still is the primary test spec for Mil/Aerospace/Defense cables.

Not all testers are created equal

1. Just as the wiring harness doesn’t know where it is, the cable tester doesn’t know or care. However, there are significant differences in commercially available testers regarding size, price, and capability. When looking for the most suitable cable tester for your needs, the following questions should be considered:
2. How many test points are required?
3. Is high current or High Voltage required? (required for A-620 Class 3 and Mil-Std 202)
4. Besides wires, does anything else need to be tested? This might include resistors, diodes, capacitors, coils, switches etc.
5. Is there a requirement for the tester to supply external power? Sometimes referred to as latching matrix (LM) or external energization (EE) power, this is usually required when there are relays to activate or lamps to light.

Plugging the cable in – test adaptation

One of the biggest challenges in testing harnesses with automatic testers is plugging them into the tester, which requires some kind of adaptation scheme (for a great look at this subject, see Mark Molnar’s article Wire Harness Testing Evolution and the Advent of Test Fixtures in the Sept/Oct issue of Wiring Harness News). Usually referred to as the “test interface,” “test adapter,” or “test fixture,” these can take the form of adapter cards that snap directly into the tester, adapter cables, or test tables with customized test modules. Regardless of the method used, the testing interface must have the requisite number of mating connectors to plug in all of the connectors of the D.U.T. Small, end-to-end cables with only a few connectors are generally the simplest to adapt to. Large, multi-legged harnesses with dozens or even hundreds of connectors are the most difficult. This is where significant differences surface when choosing the correct cable tester for the job based on the nature of the cables, i.e., how large, complex, and accessible. To reiterate, it’s not only the complexity of the testing requirements that defines the difficulty of testing different types of cables but also the difficulty of the adaptation.

“Big” vs. “Small” harnesses

Defining “small” or “big” harnesses can be misleading. It doesn’t always connote physical size. You may have an incredibly dense circuit card assembly or black box that fits on a tabletop with 10,000 interconnection points to be tested or a harness of only a few hundred wires that is hundreds of feet long and weighs hundreds or thousands of pounds.

Small cables are relatively simple to test

End-to-end cables with a few to a few hundred wires are generally tested on the bench with a smaller tester, either plugged directly into the tester or through short adapter cables.

Automobile and White Goods – Very high-volume production

Over 60 million automobiles and around 450 million significant appliances are produced globally each year, so imagine the number of wire harnesses to be tested! It is unfeasible to test these harnesses using the actual mating connector. Automotive and white goods harnesses are mostly tested using dedicated test tables with spring probe test fixtures, commonly with the wiring analyzer buried inside the test table. Although physically larger, automotive harnesses generally range from a few to only a few hundred wires, so while the test table might be sizeable, relatively small testers are all that is required.

Mil/Aero/Defense Harnesses present unique adaptation challenges

Cables in planes, trains, ships, weapons, satellites, and space vehicles tend to be the largest, most complex, and, therefore, most difficult to interface for testing. These harnesses vary greatly from small to large, both in number of wires and physical size. Electrical test specs are generally the most stringent due to A-620 Class 3 and MIL-STD 202 testing requirements. Wiring analyzers that can expand in size, i.e., the number of test points that are modular, are required for most of these large-scale testing applications. Mil/Aero harnesses generally must be tested at the point of fabrication and again after being installed in their final application, be it a missile, vehicle, aircraft, ship, satellite, or rocket. Modular analyzers generally have a central control unit and multiple switching modules that can be distributed around the U.U.T., be it on the building board or in situ, allowing for much shorter adapter cables. The switch modules are connected via single daisy chain cables that carry not only the voltage and current stimulus to each
module, but also the 110 or 220V mains power, eliminating the need to plug each module into its power supply.

Hook-up time vs. test time vs. troubleshooting time

Another critical consideration is the time to plug the harness in vs. the time it takes to do the test vs. the time to troubleshoot failures. In high-volume applications, thruput is critical. If you’re testing hundreds or thousands of cables per day, quick plugging and unplugging and fast tester cycle times are crucial, hence the discussion of adapter-based testers and spring-probe test tables above. In the case of large complex cables, it is not uncommon for the build time to be several days. Likewise, when testing these harnesses in situ, it may take hours or days to position the tester and plug all of the adapter cables into the D.U.T. In this case, the actual test time isn’t critical. A 10 or 20-minute test isn’t too inconvenient compared to 2 days to plug everything in. Providing easy-to-understand error information is essential to help technicians quickly locate and repair failures. Additionally, wiring analyzers that offer “random” or “smart” hook-up capability tremendously speed up the hook-up time. This feature utilizes smart chips embedded into each adapter cable, allowing the adapter cables to be plugged randomly into any switch module. The tester reads the intelligent chip and re-addresses the test program accordingly.

Standard test programs (TPS’s)

Another critical element of Mil/Aero harness testing is the heightened requirement for documented and verified test program sets (TPSs). While proper test programs are essential at all levels of cable testing, it becomes a whole different world when weapon systems and aircraft are involved. Government regulations often require stringent traceability and verification of TPSs. This requirement, in part, usually drives military end-users to require their cable assembly suppliers to use the same test equipment at fabrication that they use for their end-of-use testing. That way, TPS changes required for harness modifications and engineering change orders can be shared with cable vendors, assuring proper testing at all levels of the supply chain.

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In Summary

Cable testers come in many sizes, shapes, and prices like the cables they test. When considering the best solution for your application, be sure to consider all aspects, and remember that one size rarely fits all.

When you start looking for the perfect solution to your unique cable and wire harness needs, it can be a bit daunting trying to decide between different manufacturers. Just looking over websites might only give you a partial picture as to the capabilities of one firm over another. So what do you use to compare different cable and wire harness manufacturers? 

Today’s spotlight is focused on how to find the best manufacturer to meet the specifications your project demands. 

Past Experience in Custom Wire and Cable Harness Manufacturing

There are many off-the-shelf cable and wire harnesses out there but rarely do these products check all of the boxes the end-user needs to ensure safe and reliable function. Simply put, manufacturers with limited experience in custom cable and wire harnesses will lack the expertise needed to adapt during the manufacturing process. 

With decades of experience under our belts as a custom cable and wire harness manufacturer, Meridian is uniquely poised to meet the tough demands of some of the most demanding projects on Planet Earth, and beyond. 

First up, always look at a manufacturer’s track record for producing products of the same nature as your custom build. We are proud to have produced the harnesses necessary to provide critical infrastructure in industries such as the military, medical, industrial, and telecommunications. 

• Military – the military subjects cable and wire harness components to some of the harshest environments on the planet. Building to MILSPEC takes many years of experience and some truly gifted designers, as these products need to be extremely tough. With military men and women counting on the electronic systems our harnesses help make possible, our commitment to integrity, functionality, and safety is paramount.
• Medical – the medical field uses incredibly advanced equipment to save lives, diagnose, and treat patients every day. Some of these electronics require sensitive considerations like a biomedical jack or specialized strain reliefs. Knowing our cable and wire harnesses must perform exactly as required within medical devices and equipment is all the more highlighted when someone’s health and wellbeing are on the line.
• Industrial – industrial control systems help to power the automation behind massive processing and manufacturing facilities. As well, these systems help control utilities and other necessary municipal functions like water treatment facilities. Cable and wire harnesses play an integral role in providing the infrastructure needed to transmit power, data, and signals throughout the system.
• Telecommunications – today’s world has never been more connected, nor have we ever relied so heavily on communications infrastructure to keep the data flowing. With a heavy emphasis on beefing up the world’s telecommunications capabilities in the last few decades, Meridian has been at the forefront by providing the specific harnesses needed in highly-sophisticated and sensitive communications equipment.

While these four industries represent the core of Meridian’s prowess as a cable and wire harness manufacturer, we have also built up an incredible level of expertise in a vast number of other industries, as well. The best manufacturer is one that is familiar with your industry and can anticipate the needs of the project, even before the client may have fully articulated them. 

From the very first concept meeting right through volume production, our gifted designers and engineers have the experience necessary to produce a product that we know will work as intended, under whatever circumstance our client needs them to. This is where having an experienced custom manufacturer pays huge dividends and can save a project both time and money.

Capabilities of the Custom Wiring Harness Manufacturer

Next, as you compare different harness manufacturers, make sure to pay close attention to the capabilities they have. This may seem basic, but in manufacturing there are many companies that offer a very limited scope of capabilities and may be sourcing the majority of components from other manufacturers. 

Meridian is proud to custom create over 70% of the products that come off our assembly line. In addition to a wealth of experience, this has enabled us to build an incredible tooling inventory from which to choose from to complete the task exactly as required. In fact, we have amassed over 5,000 existing tools, connectors, and other components to be available to complete the project. During the design phase, we also employ some of the most sophisticated design software available today to produce a digital blueprint to follow all the way to volume manufacturing. With such a massive “library” of tools and equipment at our disposal, we have some of the highest levels of capability in the industry. 

Having a blend of hand tools, semi-automated, and fully-automated equipment provides a great level of product breadth and depth when it comes to manufacturing harnesses. We are able to produce a wide range of different harnesses and can also produce many different iterations of one particular type. We have found this combination of experience and capability to be crucial to our success as a custom wiring harness manufacturer.

Commitment to Quality

Quality can be overlooked as you compare different manufacturers as everyone says they are committed to it. If everyone is doing it, what does it really matter? Actually, a great deal as one’s definition of what quality is and what requirements it places on every step of the manufacturing process can vary. 

We’ve mentioned that our cable and wire harnesses are used in some pretty exacting industries, where a mistake can mean much more than time, money, or our reputation. With so much at stake, we take quality to extreme levels. 

With Quality Assurance and Quality Assurance (QAQC) engineers whose sole mission is to ensure functionality, integrity, and safety of the product and the process, quality becomes very much data-driven. Testing is a crucial step that is implemented throughout the design and manufacturing process in order to ensure quality. It is indeed quite rare for a product to go from concept to volume manufacturing without a prototyping phase. We are proud to be able to say we test each and every product multiple times throughout the process but especially once complete and before the product ships to our customers worldwide. We want our clients to be absolutely sure the product they receive functions reliably cycle-after-cycle.

Prototyping allows our engineers a chance to test how different variations come together and function together as part of the larger system. We are also able to measure how well we can source the necessary materials to complete the project both on-time and on-budget. Manufacturers that skip prototyping will generally be costing more in the long run as the product undergoes real-world conditions and may even lead to premature failure. 

We even created a means to test our products under real-world conditions in our Advanced Life Testing Lab. Factors like salt spray, water, humidity, heat, friction, and bending all need to be considered and mitigated against within a cable harness’s engineering. The Advanced Life Testing Lab gives our engineers a chance to review how components hold up under the actual conditions they’re likely to face. This also gives a chance to tweak anything that doesn’t meet the exacting standards set forth in the project plan.

What Industry Certifications Matter Most 

Continuing with our discussion of quality is the certifications that a manufacturer possesses. You may not necessarily group a certification with quality; however, Meridian is proud to be certified exactly for our commitment to quality. 

ISO is an internationally recognized certification that has incredibly high standards. We are very proud to have and maintain our certification in this rigorous quality assurance standard. ISO requires a continued commitment not just to quality of the product and the process, but also in customer service. By continuing to focus on making our processes better, we have continually sought to eliminate process waste and fix any issues before they impact a project. 

Another truly crucial certification to look for in your cable harness manufacturer is that of a UL-approved manufacturing facility. The little stamp with the “UL” inside a circle on the bottom of most every electronic product you purchase means that product has met the stringent requirements as set forth by UL, or Underwriters Laboratory. UL is one of only a very small handful of government-approved independent standards creators. As a UL-approved facility, we are able to produce products that meet UL’s strict requirements and can help get our client’s products UL-certified, as well when it’s desired.

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