Field-assembled cables vs overmoulded

Cable assemblies are the core components for the most critical connections. In many instances, there is an option of choosing between field-assembled cables or overmoulded cables. For some designs, the choice is clear cut, for others not so much. This article explores the design differences between moulded cable assemblies and field-terminated cables.

With field-assembled cables, the connectors are manually assembled to the cables. For many designs field-assembled cables will work just fine, and in certain instances they will be your only option.

For example:

• For specific or custom installations that require a specific length or varied lengths of cable, depending on the install.
• You have to route a cable through a channel or piece of conduit and the design dictates a connector size. We see this, for example, in some vehicle-related installations.
• Your cable will be in a protected environment and once connected it will seldom be disconnected and reattached, ie, no repetitive use.
• For prototype installations where the quantity required is small.

A number of factors such as cost, quality, market, product/application and end-user requirements also need to considered when deciding between field-assembled cables and overmoulded cables. How qualified, how experienced, how good is the personnel assembling your cables? We’re taking it on fact that your cable and connector suppliers are providing you with top-quality, highly functioning components. The field-assembled cable connections are only as good as the people in the field doing the assembling. So, if you’re highly confident about the experience and skills of your employees - or those of your contract manufacturer - and this confidence is borne out by product performance, then overmoulded cables would not seem necessary.

But assembly personnel - in-house and outsourced - can and do make mistakes. For example, we once worked with a manufacturer that had a problem with its contacts opening up. When we researched the problem we determined that during the cable assembly process the contractor overheated the contacts when applying solder. And that resulted in melted plastic and open contacts. The customer switched to overmoulded cable assemblies and the problem was resolved. In another instance, the contract manufacturer used a sealed IP-rated connector in a cable assembly for a refrigerator ice maker - but left out the O ring. This mistake rendered the connector’s IP rating meaningless and severely degraded the performance of the connector and the ice maker.

By no means is the above information intended to be an across-the-board slam against contractors. There are many outstanding contract manufacturers and we’re familiar with most of them. Here’s a bit of common-sense advice: before you commit to using the services of a contract manufacturer, make sure you ask how they will - and how often they will - test your cable assemblies. And be sure you’re comfortable with and confident in the answers you get. This is especially important if your cable assemblies are being used in critical-functioning applications such as bomb suits, commercial pilot headsets or mission-critical industrial applications.

Comparing the cost of field-assembled cables to overmoulded cables is, for the most part, like comparing apples with oranges. The product costs for field-installable cable assemblies are obviously less expensive. But add in the cost of labour and the costs associated with higher error rates for field-installable cables and you may well come to the conclusion that overmoulded cables offer you a lower total cost of ownership.

An overmoulded cable seamlessly combines the cable and connector into a single part. In overmoulding, molten material is injected into a mould cavity and the cooled material conforms to the shape of the mould.

The resulting mould cavity can be plain and simple or quite elaborate, replete with your company name, logo, flanges, an extended strain relief area and more. Overmoulded cable assemblies give you ease of installation and a commonality among installs that you won’t get with field installs.

There are many applications and products for which an overmoulded cable assembly is your only choice or clearly your preferred choice. Key factors that commonly drive the specification of overmoulded cable assemblies are:

Environmental concerns: Unlike with a field-installable cable that’s subject to human error, there’s little or no chance that the sealing on the overmoulded cable assembly will be compromised. The rear of the connector area is sealed and, barring extraordinary circumstances, will forever remain sealed. Additionally, you can be confident that the connector part of the overmoulded cable will perform as rated in harsh weather. This is particularly important for equipment that is continually exposed to moisture or machinery and devices that get regular high-pressure washdowns - such as those used in food preparation and health care. For solar applications, you most likely want a harsh environment seal and some UV protection. You can get that with overmoulded cable assemblies.

Strength and security of connection: Overmoulded cable assemblies have integrated strain relief, giving them the ability to absorb up to 32 kg of pull-out force. Getting this strength of connection in a field-installable cable is typically more difficult.

Aesthetics: If you want to enhance the aesthetic appeal of your medical equipment; high-end, high-tech hardware; any expensive, sleek, high-performance machinery or equipment - overmoulded assemblies are your preferred choice.

For example, a customer and manufacturer of an expensive communications device we work with had been using field-installable cables and electrical tape to form a Y junction on its cables. As you can imagine, the look didn’t exactly scream quality and prestige. We suggested an overmoulded Y junction cable assembly; the customer implemented our suggestion and loved the new, more professional look.

Flex relief: Overmoulded cable assemblies offer the option of a secure flex relief, which will help limit the cable bend radius at the exit of the connector - you’ll always get consistent flex relief and higher, longer fatigue. That’s not often the case with a field-installable cable.

In addition, overmoulded cable assemblies can be used for EMI shielding applications and can be custom designed for right-angle exits or any exit configuration you might require. Plus, overmoulded cable assemblies can be colour coded to foolproof equipment installation or usage.

Example: A manufacturer of auto-diagnostic equipment we work with colour codes its cables and receptacles. This way when the shop guys hook things up it’s always quick, easy and, most importantly, accurate.

Summary

To succinctly sum up the gist of this article: in a controlled environment, for volume installations of equipment and for devices with a limited number of mating cycles and with competent field-assembly personnel, field-assembled cables will usually serve your purposes just fine. In all other instances, give strong consideration to using an overmoulded cable assembly.

Three points should be considered when choosing overmoulded cable assembly manufacturers.

• Is the manufacturer overmoulding its own product or somebody else’s? The supplier that manufactures and overmoulds its own connectors controls every aspect of its production. It stands to reason then that the manufacturing and overmoulding process will involve a higher degree of precision and uniformity and result in a higher quality component. In addition, by utilising the connector supplier manufacturer to mould your cable assembly, you are ensured that the connector interface you specified is utilised in the assembly. Not some cheap knock-off sometimes supplied by contract manufacturers to increase their profits and typically not found out about until it’s too late, after the product has failed.
• Is the manufacturer local to your continent? Simply put, shipping cable is expensive. So whether your operations are in the US, Europe or Asia, you’re almost always better off sourcing local product.
• Does the overmoulding supplier have its own equipment and is the overmoulding done in-house? As with number one, this question speaks to precision, uniformity, quality - and quality control. It’s highly unlikely that you’ll get the same level of attention to detail and quality control if the entity you’re dealing with is farming out your product. From design and production of your connector and overmould to precision-assembly of the finished unit - there are stringent quality control checks every step of the way.