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Are there things we do simply because that’s the way we’ve always done them? Even in some of the most innovative industries – industries known for driving technology forward in a huge range of applications – engineers are using techniques that are decades old.
There are plenty of excellent reasons for pursuing the tried and trusted approach. There is a feeling of security that comes with using technology that is long-established. Products with a long track record of safety and performance make for an excellent reputation for reliability. However, just because the product has performed well in the past does not mean that it is the solution for the future. And so, I would like to ask a question.
Is the way we’ve always done it costing us money?
The Cost of Termination
Let’s look at how wires are terminated. For decades, when a wire needs to be fixed to the rear of a switch, relay or connector, there has been a range of solutions.
Solder has been a staple of industry for decades. The solder itself is usually an alloy of tin and lead, although modern lead-free solder uses other elements such as antimony and silver. The solder is melted and flows around the wire and terminal, cooling to form a solid metallic joint. Solder is a firm favourite amongst engineers as it feels very secure and has the advantage of being reworkable – the solder can be remelted and the wire adjusted before it cools and solidifies again. However, solder brings with it a certain number of issues.
It may seem obvious, but using solder requires the application of heat. Many terminals are housed in plastic to provide suitable insulation. With a few exceptions, plastic is vulnerable to heat, and the careless handling of soldering iron has the potential to cause irreparable damage to wires and expensive components. In addition, there are installations in which it may be downright dangerous to be handling tools that have a tip temperature in excess of 200°C. As a result, creating a good solder joint whilst working safely requires an experienced operator, which adds considerable expense to any installation.
There is a further metallurgical issue that needs to be addressed, especially in connections that use traditional tin-lead solder. Many terminals are gold plated, a well-established practise that provides excellent conductivity and protection for the base metal. However, gold dissolves easily in solder, which means that it is possible for the tin of the solder and the gold of the plating to combine, forming an intermetallic layer around the lump of solder – which is now little more than a blob of lead.
This intermetallic layer weakens the bond between the terminal and the wire, reducing the reliability of the electrical termination. If subject to shock and vibration, it is possible for this flawed termination to weaken and fail. This is why NASA and other organisations dictate that the gold should be stripped from a terminal before the wire is fixed. This can be done by scrubbing with an abrasive material or with the application of solder which is then removed before the termination itself is completed. Either method adds considerable expense to the cost of terminating a wire.
Crimping As An Alternative
Crimping offers a reliable alternative to solder. Crimping requires the metal of the wire to be compressed to form a gas-tight seal. The exact force required will vary according to the wire construction and the terminal design, but there is a balance to be maintained between too little compression, which results in a weak mechanical joint, and too much which risks damaging the wire. The good news is that a crimp tool, once set correctly for the combination of wire and terminal, produces repeatable and reliable joints with little skill required from the operator. The bad news is that crimp tools are generally not cheap.
Most crimp terminals are fitted to the wire before insertion into a connector. This too has pros and cons. Loose terminals are small and can easily be dropped and lost if the work is being performed in an awkward space. It is sometimes better for crimping to be done in advance in a more suitable environment, which does generate considerable time saving when completing an installation on-site. However, there is still a relatively high up-front cost associated with crimping equipment.
Wouldn’t it be great if there was a method that did not need expensive tooling or training, that didn’t require handling of fiddly terminals which can get lost or hot solder with its safety issues? There is – it is called screw termination.
The Simple Alternative?
For larger devices such as switches and relays, it is possible to choose this termination method that requires nothing more than a screwdriver. With this choice, we do away with all the inconvenience of soldering or the cost of crimping by simply using a screw clamp. Our problem is solved.
Unfortunately, one problem is replaced by others. Screwing a wire into a terminal can be a slow process. A few seconds per terminal may not seem like much but, over the course of an entire installation, it will add up to a significant amount of time with its associated cost.
There is also the question of convenience and reliability. Installing a wire into a screw terminal is usually a two-handed task - one hand is used to hold the wire in place and the other will turn the screwdriver until the wire is secure. And this still does not solve the question of how far to tighten the screw. Should it be just tight enough to resist a gentle tug, or should the installer keep turning the screwdriver until it squeaks? Most manufacturers will publish a recommended torque value to which the screw should be tightened, but how many installers follow these instructions to the letter? Just how repeatable are screw terminations?
We have seen that the termination techniques we’ve always used bring with them limitations. Some require specialist training and may even present safety issues, others need significant investment in tooling. Even the technique that uses simple hand tools offers a mixed bag of benefits and challenges.
Push-In Technology – Terminations without Tools
We have not yet discussed push-in technology. For many years, manufacturers have sought to design the perfect tool-free installation method. The goal is to create a solution that is quick to install, requires little prior preparation, and can be performed without specialist tools, all while creating a reliable, repeatable, and repairable wire termination. Push-in termination technology offers all of these benefits.
It offers so many advantages over crimp, solder, and screw-in techniques. Even if the price is a little higher – which is not always the case – the reduced cost of installation provides far more value. By reducing the installation time required, push-in terminals liberate skilled operators from repetitive tasks and allow them to be used for those specialist tasks that offer the most benefit.
So why has push-in technology not taken over the industry? It must be said that push-in terminals tend to be a little larger than some other types, but for large machine-building applications, this may be of little consequence.
My answer is that the lack of penetration of push-in technology into the industry so far is a matter of perception. Some engineers may not trust a termination that they haven’t screwed down or crimped. Because they lack the physical feedback that they get from the “turn the screw until it squeaks” technique, they may feel that a push-in joint is not particularly secure.
In fact, the design of modern push-in terminals like the new S3 from IDEC makes them ideally suited to the harsh environments frequently encountered on the factory floor. The spring contacts used within push-in terminals provide positive contact and excellent resistance to vibration, and the speed of the installation process speaks for itself – take a look at this video to see just how quick the task can become.
The way we’ve always done something, although familiar and trusted, may be holding us back. The next time you need to complete an installation, take a step back and consider whether the old way is still the best.
Maybe it’s time for a change.