Grounding of Shielding of a twisted pair cable at Both ends

Discussion in 'General Electronics Chat' started by tushki.pat, Sep 13, 2012.

  1. tushki.pat

    Thread Starter New Member

    Sep 13, 2012
    In encoder connection we use Twisted pair with shield cable.And in connection we ground the Shield at both the ends(Drive side as well as encoder side). WHY? Want to knw abt it...Because some one telling that we connec the shielding at one end.
  2. Papabravo


    Feb 24, 2006
    PackratKing likes this.
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    Some people connect just one end in an effort to avoid ground loops.

    However, they have never had to deal with EMC. If you connect the shield at only one end, you have just created an antenna which can radiate high frequencies or conduct into your box.
  4. Papabravo


    Feb 24, 2006
    For which frequency range is the shield an efficient antenna is still an open question.
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I deal with shielded Primary Leads on aircraft magnetos, and shielded spark-plug leads. The goal of shielding is to prevent the wire inside the shield from radiating. If you only ground the shield at one end on a magneto P-lead, the open end radiates into the VHF range and clobbers the radios... If a spark-plug lead becomes ungrounded at one end, you hear ignition noise in the VHF receivers.

    In dealing with low-level audio in aircraft, the shielding on the wire is there to prevent capacitive coupling to other wires that carry power. You are better off grounding the shield only at one end (assuming it is not used as a signal return) because if you do ground it at both ends, you will have ground currents that otherwise flow along the airframe (can you say alternator whine) taking a short cut through your audio wiring....
    Bernard likes this.