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  1. #1
    Hey everyone,

    Quick sanity check. I know signal wires donít need to be particularly beefy however I'm switching my motors over to JMC servos which have the driver built in, so I wasn't sure if this changes things. I use my setup for video production not CNC hence cables are quite long, 7 metres. I'll be using separate cables for power and signal.

    For signal I was planning to use 6 core cable for; stp, dir, gnd, enable, disable, and then cable ground (grounding shield to star point in control box). Will this cable be ok? Not sure if 25 AWG is too thin.


    These are the motors:




    One other quick question. DC power to these drives is just two cables V+ and V- there's no ground run to the motor, or is that V-? SOrry for the obvious question, it's been ages since I've done this.

    Thanks for the help

  2. #2
    Doddy's Avatar
    Lives in Preston, United Kingdom. Last Activity: 23 Hours Ago Has been a member for 8-9 years. Has a total post count of 1,364. Received thanks 188 times, giving thanks to others 66 times. Referred 1 members to the community.
    Cable is fine for the control signals. For power, yes, two wire +/- supplies - but you should consider a protective earth on the general machine in any case. Screening the power cables (connected to a star-ground) may be useful but depends on the noise exhibited by the drives and cable routing. One good solution would be to provide the DC supplies local to the machine/motors and not export this from the control box.

  3. #3
    I am using simple 8 core shielded tp ethernet cables. Good quality reliable for signals.

    Regarding your question about the grounding, I use this huge PSU now:

    The DC goes to the servo through a separate 1.5 mm≤ pair. The negative of my 50V DC is connected to the protective earth inside my PSU box, so it is on the same potential as the mains protective GND. Don't make any DIY earth connection at the motor end, but your machine should of course be connected to PE, also because you are (I believe) using a VFD powered spindle, and that must definitely have an earth connected. The servo motor does not have a proper earth screw, unless you want to use one of the four screws attaching it to your machine's motor holder.
    Last edited by A_Camera; 03-03-2022 at 09:59 AM.

  4. #4
    Thanks for the replies. Very useful! I thought that cable would be fine but good to have it confirmed.

    A_Camera - Your PSU looks good! I'm using Mean well SDR units to power multiple drives.

    In terms of ground, the case itself is grounded using the mains ground which goes to a star point. All of the signal cables then have the shield grounded to the same star point inside the case. The only difference now is the DC power going to the drives on the motors rather than the stepper drivers inside the control box. I was previously using stepper motors but am now using these integrated servos instead.

    I wasn't going to shield the DC power going to the integrated drives, just the signal cable.

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