Wednesday, 8 November 2017

pcb assembly - How to reliably secure stranded wire in terminal block?


My 18AWG stranded wire continues to come out of the terminal block it's screwed into. What are some ways that I can more reliably secure this in an industrial environment?



  • Strip extra wire and loop/fill more of the chamber before fastening down?

  • Twist strays and then tin the ends of each wire tip before fastening down? How much of a solder blob are we talking about?

  • Twist down harder? (I'm worried about cracking the solder and/or ripping off the terminal block)




Answer



(This is info already mentioned in the comments on the question — but nobody wrote an actual answer, so I'm doing that. It does also agree with my small experience.)


Do not use any solder at all. Use a wire ferrule, which is a metal sleeve that slides over the (straight) strands and is crimped in place, making a solid end that can be clamped securely by a screw terminal of the type you are using.


Caveats:




  • Use the proper crimp tool, which will leave a textured surface that is readily gripped by the terminal and resists sliding out more.





  • Adding the ferrule will increase the size of the wire end, possibly too large to fit in the screw terminal. (This should not be a problem if one of the options you have considered is doubling over the wire.)





This picture shows several sizes of ferrules, two ferrules crimped on 22-gauge stranded wire, and the crimp tool I used ($21 when I bought it).


The plastic part of the ferrule guides the strands in, covers any exposed metal, provides some strain relief, and identifies the size of the ferrule. Caution: ferrule makers do not all use the same color scheme!


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