Basics like strain relief are critical to the long-term reliability of cables and connectors: Neglect it and you could have an unpleasant surprise; anticipate it and you could be a happy user.
I have a lot of respect for cables and connectors. These interconnects are asked to do a lot and take considerable physical abuse in many cases. After all, even though there is so much "wireless" out there for many good reasons, we often go "wired" because it's a power cable, or we prefer the signal integrity and interference resistance of wired, or it's just a personal preference. So, if we are going wired, it's important to ensure that this potentially reliable form of interconnect is given the consideration it needs to do its job. Hard failures — especially intermittent failures — are very frustrating and counterproductive, of course.
I had a clear reminder of this situation when I wanted a mini-mouse with a short interconnect cable for my laptop PC. I have a wireless mouse but kept misplacing the little USB-port plug-in part, so I decided to revert to wired. But I wanted a small mouse and without the usual long (usually about 3 ft/1 m in length) and relatively thick cable.
When I came across a closeout sale on mini-mouses (mice?) with retractable cords (made by I/OMagic), I was thrilled and bought two, just in case (Figure 1). As soon as I started to use one, though, I saw that it had virtues, but it also had a weakness due to the lack of any sort of strain relief (or "strange relief," as a fellow editor told me his spell checker decided it should be) at both the mouse end and the USB-plug end. I was pretty sure that the extremely thin wire bundle wouldn't last long due to both direct pulling and sharp bending of the cable as it exits at each end. The super-thin, rectangular-profile mouse cable was just 1 × 2.5 mm, so the wires inside would be truly thin and impossible to repair if they broke. That's assuming there would even be enough of a "stub" remaining to make a connection.
Figure 1: This retractable mini-mouse seemed like just what I wanted, but the lack of strain relief and its super-thin wires made me doubt how long it would last in use.
Seeing a problem about to happen, I decided to do what most engineers would do: I would try to improve the situation in advance. After all, what wasn't to lose, as these fragile units would not last long in real-world use?
I spent some time looking carefully at the situation and then worked each end with a different tactic (Figure 2). For the USB-connector end, I packed epoxy around the cable's exit from the connector so that the cable insulation would have strain relief to the connector body. This would help to protect against direct pulling, but it did nothing for sharp bends at the exit from the (now) epoxied blob. So I slid an about-an-inch-long piece of large-diameter heat-shrink tubing over the connector body (I do love that tubing!), hit it with the hot-air gun, and it shrank down to allow gentle, but not sharp, bends.
Figure 2: By careful use of epoxy, as well as heat shrink tubing and a piece of a pen refill, I have greatly enhanced the strain relief and, thus, the life of the mini mouse — I hope.
I took a somewhat different approach for the mouse end. Again, I started with a blob of epoxy to relieve the cable as it exits the mouse body, being careful to not get any of the epoxy on the mouse buttons. But that still left the problem of sharp turns and bending. For this, I went to my collection of old ball-point pen bodies and refills (don't we all save some of those just for projects?) and found a refill with an inner diameter of about twice the thickness of the cable. I cut a piece about a half-inch long, made a slit in it from top to bottom, and slid it over the cable. I then slid it down to the mouse body, packed it with epoxy, and also glued it to the mouse body. This arrangement takes the strain off of the cable from those tight-radius bends, which soon cause internal breaks due to repeated bending and flexing.
Right now, I am fairly satisfied with the apparent strain relief results. I have no idea how long it will last, but it will certainly last longer than the original version. And if the cable does break, whether only internally within the insulation or it completely breaks off, I may even have enough of a stub that I can try some micro-surgery soldering to fix it, perhaps with a slightly thicker wire with a better strain-relief design.
Have you ever anticipated a "simple" likely source of failure and taken preemptive steps to hopefully avoid it?