Shield Grounding for Bulk Current Injection Should you ground the shield at one end or both? The question often arises, is it better to ground the cable shield at one end or both ends? If the answer is one end, which end should be grounded? If the answer is both ends, why? What happens if neither end of the shield is grounded?
Folklore Abounds If you ask three different engineers, you are likely to get three different answers. Everyone seems to have an opinion about how best to ground the shield, but when pressed, explanations are often based as much on folklore as on physics.
Why the Confusion? Unfortunately, although the grounding question is simple, the answer is not. The best shield ground is the one that results in lowest induced circuit voltage. The answer depends on frequency, circuit impedance, and the reason for having the shield. In this case, the reason for having the shield is to reduce circuit noise voltage when radio frequency signals inductively couple to the cable bundle during bulk current injection (BCI) tests. The control variables are frequency and circuit impedance.
Bulk Current Injection BCI testing simulates current induced on electrical cables when exposed to low-frequency electric fields. BCI tests are more repeatable and more efficient than low frequency radiated susceptibility tests. BCI tests are a standard part of EMC testing for most segments of the electronics industry.
BCI is just one facet There are several reasons for shielding electrical cables. The most common are:
To reduce field radiation (radiated emissions) To protect end circuits from noised induced by RF fields (BCI and radiated susceptibility) To reduce crosstalk between conductors (usually for signal integrity)
http://emisoftware.com
Copyright © 2017 EMI Software LLC
1|Page