When grounding the shield of shielded cables, you should ground at which points?

• A. Never ground.
• B. Always ground at both ends.
• C. Ground the shield at one end or both ends as EMI conditions require.
• D. Ground at the device only.

Answer: (C)

Grounding the shield of shielded cables is about giving EMI a defined path to ground and preventing interference from riding on or into the signal conductors. The best approach is to ground the shield at one end or at both ends as EMI conditions require.

Grounding at one end is common when you want to avoid creating a ground loop along long cable runs that share a single earth reference. It keeps the shield tied to ground at just one point, so circulating currents are minimized while still providing shielding where the cable enters the equipment.

Grounding at both ends can improve shielding in environments with significant EMI or when the shield encloses a run that spans equipment with similar ground potentials, as it provides a lower impedance path to drain interference. However, this can create ground loops if the two grounds are at different potentials, potentially introducing currents and noise if not managed carefully.

Ground at the device only or never grounding the shield both fail to provide a reliable shielding path across the full length of the run or leave the shield without a defined reference, reducing EMI control.

So the guideline is to ground the shield where it best manages EMI and ground-loop risks for the specific installation, following equipment and site standards.