JMC servo motor signal cable size

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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 mm² 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.