Shielded wires on step motor

Discussion in 'General Electronics Chat' started by boxjoint, Dec 3, 2010.

  1. boxjoint

    Thread Starter New Member

    Dec 2, 2010
    Hi guys,
    I have a question about shielded wires. I have a cnc setup with stepmotors. The previous installation had unshielded wires. Where should I connect the shield? AC Ground? Circuit Ground? The circuit ground is isolated from the AC Ground.

  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    From all of the stepper controller data sheets I've found/read such as, PacSci, Slo-Syn, Superior, Dragon Driver,etc, the wires should be twisted-pair and shielded. But, the shield is only connected to the drive board/circuit ground, NOT, to the motor.
    boxjoint likes this.
  3. mbxs3

    Active Member

    Oct 14, 2009
    Alberto, why wouldn't the shielded wire be grounded on both sides?
  4. tyblu


    Nov 29, 2010
    It depends on the noise frequency and electrical wavelength along the cable. I can't find a source to explain it, and don't remember the details! Anyway, there are times to connect one side, times for the other, and times for both connections. I think it has something to do with quarter-wavelength transformers at the frequency in question. There are industry precedences (not exactly standards), such as in telecom (CAT5e, coax), for grounding a certain end, but I'm not in telecom so I can't say much about it.
    I know -- huge help. ;)
    I would speculate that if a cable is closer to N/2-wavelengths, it should be grounded at both ends or just the GND end; if it is closer to (2N+1)/4-wavelength, it should be grounded at the noise generator end. If you're not sure, pay attention to ground loops -- if there is a loop, attach to signal end; if not, attach at both ends.
  5. BillO

    Distinguished Member

    Nov 24, 2008
    You do not want to realize the very probable possibilty that a current be induced in the shield. However, this is more of a concern with small signal (millivolt or less) cables

    The sheild should be attached to chassis ground.
    Last edited: Dec 5, 2010