In machine design, it’s rare for data processing, actuators, sensors, power sources and the human machine interface to occupy the same space. Wiring harnesses, also called cable assemblies, are the key to reliable communication and control between the subunits of both simple and complex machines.
While simplicity is always a primary goal of efficient machine design, it’s very common for cable assemblies to form some of the last component parts in the design process. The need to keep the part count and assembly costs down means an increasing trend toward all-in-one harnesses, including power, analog and digital communications and not infrequently, all three within one assembly.
Wire harness assembly. Image courtesy Epec Engineered Technologies
Custom assemblies are by definition application-specific, and like the machines themselves, some applications are more extreme than others.
Equipment that operates in moist or corrosive environments, for example, frequently needs sealed connectors, high-performance insulation or external protection. Medical devices are another example, especially where external cables must be subjected to a wash-down environment or potentially caustic cleaning agents. Health and safety related products must frequently be tested and certified for very high reliability, adding costs and extending lead time to the project.
Cable termination is often more important than the conductors themselves. Assemblies that are frequently connected and disconnected require significantly more expensive and durable connectors, while larger harnesses with multiple terminations benefit from color-coded and/or keyed connectors that prevent errors in assembly or service. A frequent mistake made by design engineers is to render the cable assembly in a two-dimensional drawing, when the assembly must fit into a three-dimensional device. Inadequate length or excessive slack can result, requiring a time-consuming and costly redesign.
How to Specify the Right Cable Assembly for the Job
They key is understanding the application and making a plan.
Customers more often than not approach their cable assembly supplier without a clear picture of what they need, said Brian Morissette, cable assembly product manager at Epec Engineered Technologies.
“We’re always the last ones to be thought of [in the design process],” said Morissette. “Often times they look at a connector that’s pretty, but it may not serve their needs.”
Before deciding on a possible assembly it is important to understand what space is available for it. Adequate clearance for ease of assembly and serviceability is crucial, and easy to miss in the design phase.
It is also important to know what environmental protection the assembly may need. Dangers to consider are vibration, moisture, temperature, chemical exposure, dust and even noise generated from the cables themselves.
“A lot of times customers will know what amount of power they’ll need and they know they need to move the signal, but they don’t understand that as you combine the two, it’s like mixing oil with water,” Morissette said.
RF signals, AC or DC power and analog data signals can crosstalk in a poorly designed system. To avoid inductive pickup effects, both power and signal cables must have adequate spacing. Signal cables are frequently shielded to avoid issues with noise and interference.
Additionally, a customer’s trust in expensive name brands doesn’t guarantee the best assembly for a given job.
“People don’t understand how much of a price connectors can make on an assembly,” said Morissette.
“A lot of the time we’ll work with them and we’ll see if there’s a way we could cost down the connectors by looking at an alternate design or an alternate manufacturer. With cable assemblies, it’s usually the last thing that anybody that’s building a system ever thinks about.”
Once an engineer has made a plan, it is vital to bring as much information to the table as possible when dealing with a cable assembly supplier.
Ways to maximize quality and minimize costs of cable assemblies include:
- Provide full-scale drawings and use shrink tube markers or self-laminating labels
- Detail precise dimensions with loose tolerances
- Specify dimensions for tight tolerances accurate to three decimals +/- .030 inches
- Note connector reference plane dimensions
- State special requirements for center and outer conductor material
- Ensure bend radii are designed as large as possible
- Specify cables and connectors or state “or equivalent”
- Clarify electrical properties across desired frequency ranges and
- Avoid female terminations.
“When you start to develop a cable assembly, if you only have half of the critical information, you’re only going to get half of the project correct,” said Morissette. “We totally understand that in the prototype world there’s going to be quite a bit of change, but give us as much as you can upfront and let us work with the best knowledge that you’ve got to come up with a product that’s going to work for you the first time.”
Finding the Right Manufacturer
Finding a cable assembly manufacturer isn’t just a matter of dealing with the first company that turns up in a Google search.
Different providers have different histories, different specialties and most importantly, different price points. It’s always a smart plan to reach out to multiple companies and compare your options.
When looking for a cable assembly don’t just compare prices, but look at how closely each manufacturer is willing to work with their customers. Strong, open communication and a detailed design process are the key to getting the perfect cable assembly.
A wide array of options and products with the experience to back up their claims of quality are also important.
Epec Engineering Technologies have been providing custom, build to print electronics for over 60 years and offer a host of cable assembly solutions.
Multiple connectors add complexity to the cable assembly, but simplifying installation can mistake-proof the end-user assembly process. Image courtesy Epec Engineered Technologies.
Within that time, Morissette and the Epec team solved some extreme design cases.
“We were asked to do a wire harness for an industrial application. This harness had to be 20 feet long and had to have 40 different connectors, with different terminations throughout that 20 feet. The connectors had to be waterproof because they were going to be exposed to multiple contaminants. It was a fun project. We developed it in a couple of weeks.”
Epecworked closely with the customer’s engineers throughout the design, manufacturing and selection processes for the complex job and created a reliable solution on time and on budget.
For more information about Epec Engineering Technologies and their cable assembly services, visit www.epectec.com/cable-assemblies.
Epec Engineered Technologies has sponsored this post. It has no editorial input to this post. All opinions are mine – Jim Anderton