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What is a good way to secure cables to a PCB?

There are some good advice in the following post, but the application is slightly different:

Securing electrical cables to holes in enclosures?

In this case, the strain-relief/securing of the cables will be onto the PCB, not to a casing. (The PCB will be encapsulated or just given a layer of conformal coating, so there isn't any casing.)

I'm considering to run the cables to the edge of the board. Then at the edge, press the cables between the PCB and a metal bar. The metal bar is pressed against the PCB with bolts and nuts (nylock or thread lock).

What might be the problems of this solution and what other methods should I consider?

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    \$\begingroup\$ I find the method from the last image from your linked question is a good one: it's easy to implement, and it serves quite well. The detail to look out for is to have the wires really fit into the holes tightly. We used this method in a 220VAC-6VDC power supply on the mains cord. For that kind of use and strain it seems to work well. The more holes - the better, probably. \$\endgroup\$
    – Gallifreyan
    Commented Oct 29, 2019 at 13:11
  • \$\begingroup\$ @K0ICHI Can you describe your cable a little more? What's the outside diameter of the cable? Are you going to have a connector between the cable and the PCB, or are you going to solder the wires directly to the PCB? Are you going to conformal coat the PCB with cable attached, or separately? \$\endgroup\$
    – Nick Alexeev
    Commented Oct 29, 2019 at 14:07
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    \$\begingroup\$ @Gallifreyan Yeah, that method didn't look to bad. My concern with it though, is how the cable may rub against the edge of the (last) PCB hole. With repeated movement, it could eat through the insulation. Also that way, the cable will come off the PCB perpendicular to the plane of the PCB. I would prefer the cable to be flush with the PCB instead. \$\endgroup\$
    – K0ICHI
    Commented Oct 29, 2019 at 15:04
  • \$\begingroup\$ @ Nick Alexeev. The cables are 2-core 16AWG. They look like this: warmnsafe.com/collections/accessories-cables/products/… No connector, they'll be soldered on to the PCB. Conformal coated with the cables attached. \$\endgroup\$
    – K0ICHI
    Commented Oct 29, 2019 at 15:13
  • \$\begingroup\$ Just as a general principle, everything can/should be attached to anything with hot glue... \$\endgroup\$
    – RadioRaheem
    Commented Oct 30, 2019 at 6:13

3 Answers 3

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Zip ties are a good way to provide strain relief for cables attached to a PCB. You lay out a path for the cable on the PCB, and put adequately large holes on either side of this path for the zip tie.

I've done this many times on custom assemblies in which using a connector would have been counterproductive.

Here's one example. It's a board that functions as a "hub" among several different devices in a cramped aerial photography pod. Each device requires a USB connection, a power connection and/or a control connection. The wiring for one of the devices is shown installed. Adjacent zip ties share the same hole.

top view

side view

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  • \$\begingroup\$ I also like this solution, and already considered it. I would place it at a good 2nd place after using a metal plate and bolts though, in terms of durability. In 1st place in terms of easy of installation though. \$\endgroup\$
    – K0ICHI
    Commented Oct 29, 2019 at 15:10
  • \$\begingroup\$ If you want additional durability, you may pass the individual wires through an additional hole (unplated) before bending them back to be soldered to a plated hole (forming a "C" or a partial "S" curve). This is a form of strain relief, but increases the installation difficulty. The NPTH should be sized slightly larger than the diameter of the insulation, allowing free movement, but "catching" if it is pulled.This looks very similar to this example, but there are two rows of holes (one plated and one not plated) per connection. \$\endgroup\$
    – crasic
    Commented Oct 29, 2019 at 21:50
  • \$\begingroup\$ @crasic: see the link in Gallifreyan's comment. Not really relevant to my answer, though. One or the other of you should write that up as a separate answer. \$\endgroup\$
    – Dave Tweed
    Commented Oct 29, 2019 at 22:08
  • \$\begingroup\$ I'm just suggesting to combine your approach with an extra loop to avoid any chance of pulling on the joint in the case the zip tie loosens or cable slips, the link in the other comment has another additional loop on top of that. \$\endgroup\$
    – crasic
    Commented Oct 29, 2019 at 22:43
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Cable ties are great. Just put two through holes in the PCB away from the connector.

Enter image description here

There are also a variety of flat tie holders that can also facilitate zip ties. These can be pushed in or fastened with fasteners.

Snap-in cable clamps (many different varieties) can be used in PCBs with one through hole.

Enter image description here

Source: Flat Cable Clamp - Snap-In, Low Profile (Essentra Components)

Stick-on cable clamps also work good on most surfaces:

Enter image description here

Source: Cable Clamps (Essentra Components)

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One very simple technique used on spaceflight PCBs (and thus good against vibration) for a small number of cables is to insert the wire through one hole, and solder the stripped end at a distance from that hole corresponding to the minimum bending diameter of the wire (which may be assumed 5 times the outer diameter if you do not know it). A spot of glue (epoxy or hot glue if not available) is then added to relief the solder from mechanical stress.

enter image description here

The minimum bending diameter is not only chosen to reduce the footprint on the PCB, but also to ensure the wire has some curvature inside the glue: if the wire is straight, since wires are often insulated with PTFE which has very low adhesion to most glues, the wires would have very low resistance to pulling.

Note that for larger number of wires, we also use T-wraps (at least the shape of it, most plastics release too much gas in vacuum) such as presented by Dave Tweed in addition to custom clamping parts: it yields very good resistance.

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