EMC Question of the Week: September 12, 2022

illustration of shielded cable showing the option of grounding or floating the shield at each end

To reduce electric-field coupling to an electrically short cable, the cable shield must be

  1. grounded on at least one end
  2. grounded on both ends
  3. floated on both ends
  4. rigid and continuously grounded


The best answer is “a.” Electric field protection is provided by grounding the shield at one or both ends. This effectively keeps the shield at the same potential as the ground as long as the cable length is short relative to a quarter-wavelength at the shielding frequencies. Grounding at both ends is required for magnetic field shielding. Grounding at both ends is also required to reduce coupling at frequencies where the length of the cable is not short relative to a quarter wavelength.

Cable shields should always be bonded to the product's EMC ground structure (usually the frame ground). In the case of a coaxial cable where the shield is carrying signal current, it must also be connected to the signal's current return conductor (usually the circuit ground). 

Have a comment or question regarding this solution? We'd like to hear from you. Email us at This email address is being protected from spambots. You need JavaScript enabled to view it..