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Suppose I would like to insert data-cables of varying diameters -- e.g., a cable of 5 mm diameter -- into the 6 mm diameter hole of a plastic enclosure. The wires within the cable are terminated via soldering to a PCB inside the enclosure.

What methods are used in the industry to ensure that pulling the cable won't make it slide in and out of the enclosure (thus preventing damage to the wire connections to the PCB inside)?

Cable

Some options that I have considered:

  1. Two small lengths of thick heat shrink tubing placed around the cable, both just inside and just outside the wall of the enclosure. If the tubing is wide enough, then it will block the cable from sliding. This could work but may have to use too many layers of tubing and also the fit just by friction alone may not be strong enough.

  2. Apply a thick layer of rubber-compatible adhesive in a circle around the cable, both just inside and just outside the wall of the enclosure. The glue blob would act as sort of a bolt/washer. This is too messy in practice, and probably not usable professionally.

  3. Use rubber-and-steel-compatible adhesive to place two bolts around the cable, one just inside and one just outside the wall of the enclosure. The problem with this is that it is hard to find an adhesive that bonds well to both rubber and steel.

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There are a few industry approaches to this.

The first is molded cables. The cables themselves have strain reliefs molded to fit a given entry point, either by custom moulding or with off the shelf reliefs that are chemically welded/bonded to the cable. Not just glued, but welded together.

enter image description here

The second is entry points designed to hold the cable. The cable is bent in a z or u shape around posts to hold it in place. The strength of the cable is used to prevent it from being pulled out.

enter image description here

Similarly, but less often seen now in the days of cheap molding or diy kits, is this. The cable is screwed into a holder which is prevented from moving in OR out by the case and screw posts. enter image description here

Both of those options are a bit out of an individual's reach.

The third is through the use of Cord Grips or Cable Glands. Especially is a water tight fit is needed.

enter image description here

They are screwed on, the cable past through, then the grip part is screwed. These prevent the cable from moving in or out, as well as sealing the hole. Most can accommodate cables at least 80% of the size of the opening. Any smaller and they basically won't do the job.

Other options include cable fasteners or holders. These go around the cable and are screwed or bolted down (or use plastic press fits). These can be screwed into a pcb for example.

enter image description here

Cable grommets are a fairly hacky way of doing it, as they are not designed to hold onto the cable. Instead they are designed to prevent the cable from being cut or damaged on a sharp or thin edge. But they can do in a pinch. As can tying a knot, though that mainly prevents pull outs, but might not be ideal for digital signals. Pushing a cable in doesn't happen too often, so you might not worry about that.

Similar to the second method, is using two or three holes in a pcb to push a cable through (up, down, up), then pulling it tight. This moves the point of pressure away from the solder point and onto the cable+jacket. enter image description here

The other industry method is avoiding all this in the first place, by using panel mounted connectors (or board mounted connectors like Dell does for power plugs, yuck).

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    \$\begingroup\$ Nice comparison of the various methods. The cable fasteners seem like a convenient way to do it, as long as the PCB is designed keeping in mind the allocation for the screw. One hurdle being to find one of the exact diameter allowance. For anyone interested: Found a page listing various fasteners: RS Electronics \$\endgroup\$ – OrCa Jul 31 '13 at 4:01
  • \$\begingroup\$ Accepted? 2+ years hahaha \$\endgroup\$ – Passerby Oct 7 '15 at 7:23
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    \$\begingroup\$ The long con! Just kidding... can't believe I didn't accept this until now. \$\endgroup\$ – OrCa Oct 7 '15 at 23:35
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"Strain relief" or "cord grip" is the magic phrase for Google you are seeking. Here's a selection from McMaster-Carr:

strain relief fittings

Cheaper devices might use gobs of glue or knots in the cord, in combination with a simple grommet, depending on the anticipated stress, cost, safety, and regulatory requirements.

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    \$\begingroup\$ Strain Relief isn't the same as a cord grip. Strain Relief is to prevent damage from bending at a sharp angle. \$\endgroup\$ – Passerby Jul 31 '13 at 2:41
  • \$\begingroup\$ The webpage states: "As you tighten these fittings, they compress to grip your cord, preventing pull out." In practice, how strong have you found this fit around the cable to be? Clearly these cord grips seem to be least a flexible solution, given that they would fit cables of various diameters that exist in my case. \$\endgroup\$ – OrCa Jul 31 '13 at 2:42
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    \$\begingroup\$ @OrCa for the good ones, usually the relief is stronger than the insulation to which it attaches. If you anticipate more strain than that, you should really be using a cable or assembly designed with a structural member incorporated like a steel (non-electrical) cable, which you can then bolt to your enclosure using ordinary hardware. \$\endgroup\$ – Phil Frost Jul 31 '13 at 2:45
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    \$\begingroup\$ @PhilFrost You would also notice that all of the results in your search are called "Cord Grips", not strain reliefs. \$\endgroup\$ – Passerby Jul 31 '13 at 2:48
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    \$\begingroup\$ This is a correct answer showing correct stuff (all the way to UL approval). Yet, somebody seems to have downvoted it. \$\endgroup\$ – Nick Alexeev Jul 31 '13 at 3:23
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You want a cable bushing like this:

enter image description here

The bushing wraps around the cable and goes into a hole of a certain size. The hole is slightly undersize for the bushing and cable combination together, which forces the bushing into the cable and forces the bushing into the hole so that it won't slide out.

Many consumer devices use this bushing for power cord entry. But it is available for cables of other sizes as well.

The one pictured is Digi-Key part RP465-ND.

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YOu are looking for a (probably undersized) grommet

enter image description here

once inside the enclosure there are a variety of ways to secure the cable, a cable tie on the inside and outside will keep it secure enough to stop sliding completely what the grommet friction won't do. You can also tie off chasis ground wires or other unused wires to take the stress away from the signal solder joints

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    \$\begingroup\$ No, grommets are to prevent cable damage from pressing against a sharp edge \$\endgroup\$ – Passerby Jul 31 '13 at 2:38
  • \$\begingroup\$ By cable tie, do you mean standard plastic cable ties like these? (One place inside and one just outside the wall of the enclosure). Cable tie image \$\endgroup\$ – OrCa Jul 31 '13 at 2:39
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    \$\begingroup\$ @Passerby surely they are multifunctional? Maybe my grommets just don't conform to stereotypes \$\endgroup\$ – crasic Jul 31 '13 at 2:39
  • \$\begingroup\$ I've seen plenty of devices that get by with a grommet and a knot, cable tie, or gob of glue. This may not be their best use, or the best solution, but it is the cheapest. \$\endgroup\$ – Phil Frost Jul 31 '13 at 2:40
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    \$\begingroup\$ They are certainly easier to find in home depot than dedicated strain relief connectors \$\endgroup\$ – crasic Jul 31 '13 at 2:42

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