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I've been using unshielded "communication and security system cable" (https://www.mcmaster.com/8280T32-8280T321/) for running cable to connect stepper motors to motor controllers. I haven't had any problems with this approach, but I was curious what "best practice" would be for connecting to stepper motor leads?

This question (Nema 17 stepper external wiring) somewhat addresses this topic, but is about an off-the-shelf product and not about best practice.

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  • \$\begingroup\$ “Best practice” would be wires that are the same size or larger so reduce voltage drop. \$\endgroup\$
    – Solar Mike
    Jun 28, 2021 at 6:42
  • \$\begingroup\$ Not much concern in terms of shielding, or maybe twisted pairs? \$\endgroup\$
    – William
    Jun 28, 2021 at 6:43
  • \$\begingroup\$ Define “best practice”... \$\endgroup\$
    – Solar Mike
    Jun 28, 2021 at 6:52
  • \$\begingroup\$ I'm open to different interpretations. I guess I'm wondering what solution a professional with training would do, or maybe how a company would approach this, like maybe Brother printers, what would they do for the steppers in their device? \$\endgroup\$
    – William
    Jun 28, 2021 at 6:54
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    \$\begingroup\$ Best practise for EMC is minimize the cable length. In other words, don't extend the cables; bring the controllers to the motors. \$\endgroup\$
    – Andy aka
    Jun 28, 2021 at 8:24

1 Answer 1

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Determine how much current your stepper motor draws under load. Then Google: Voltage drop calculator.

Pick a gauge where you'll have something like 90-95% of the source voltage at your motor for the length of your wire runs.

There isn't an exact number that works best in every situation. If the motor isn't doing anything strenuous, you can afford a bit more voltage drop.

You can find the minimum voltage that works by using a variable power supply and dropping the voltage until the stepper starts failing to do its job in the worst conditions its likely to encounter. Pick a gauge that keeps you safely above that value.

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  • \$\begingroup\$ Thank you for your answer! Based on your answer and the other comments, I'm starting to think that the best practice here is really about wire gauge. I was thinking more about cable type (shielded vs unshielded, twisted pair vs not), but it seems maybe my noise concerns are not top priority here. \$\endgroup\$
    – William
    Jun 30, 2021 at 21:37
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    \$\begingroup\$ Correct, noise concerns probably aren't really a factor for the stepper motors. Noise is still potentially an issue if you have some really sensitive components in the path of the power lines. Slamming the power on and off for the stepper could cause trouble for those other components. Unlikely, but possible. The hypothetical trained professionals you mentioned would usually be able to anticipate that kind of problem by understanding the whole system. If something like that slipped through the cracks, it should get caught by QA, who would punt it back. \$\endgroup\$
    – Naptha
    Jul 1, 2021 at 2:17
  • \$\begingroup\$ Interesting, thanks for the feedback! Yes I was thinking about the potential effects of the noise from the stepper motor lines affecting other electronics nearby. But like you said then you have to take a whole system approach. It makes sense that "best practice" would vary a lot in this case based on context. \$\endgroup\$
    – William
    Jul 1, 2021 at 20:57

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