Cable shield grounding guidelines.

[dbaird]

Is there standards/guidelines published for grounding the shield when using shielded cable for EMI? I have heard arguments to ground at one end only; others say to ground both ends and use capacitor to combat ground loop problems; still others say use resistor instead. Which is correct/best method? Is it based upon the signal frequency? I realize that much depends upon the application but some rule-of-thumb guidelines based upon time proven testing/experience would make for easier design decisions.<br> <p>David Baird<br><a href=mailto:dbaird@gemcity.com>dbaird@gemcity.com</a><br><a href= > </a><br>EET degree.<br>
Journeyman Electrician.

 

[xnuke]

I believe the best method is single-point grounding. The others you mentioned rely on components, which can fail. Wiring can fail too, but usually not as often. Also, component specifications can drift over time. All the work that I do with small analog signals on shielded twisted pair cabling uses single-point shield grounds to prevent ground loops. It is the method recommended by major manufacturers, such as Allen-Bradley. A good reference can be found on their website at <A HREF="

http://www.ab.com/manuals/gi/177041.pdf"

TARGET="_new">

http://www.ab.com/manuals/gi/177041.pdf</A>

 

[JoeSmyk]

Single point grounding is THE way to go.&nbsp;&nbsp;Grounding at multiple points leaves you open to a number of problems.&nbsp;&nbsp;The biggest is that if you have a piece of equipment that is leaking current (which is why you ground equipment), it can cause a potential in your ground.&nbsp;&nbsp;It may be small, but it will be there.&nbsp;&nbsp;This will cause current to flow in anything that is multiply grounded.&nbsp;&nbsp;And it may not be small if your are near a power substation!

 

[ambertec]

To simply follow &quot;rules of thumb&quot; is to often end up with burned fingers. Absolutely valid shield grounding arguments can be made for grounding a shield only at the source end, only at the load end or at both ends depending on particular circumstances. It is a problem when someone insists that one and only one grounding approach is valid; their own of course.<br><br>Hewlett Packard and other companies have published some very good application notes about the grounding of shields. If you have a really critical application, research that literature to find descriptions of situations which most closely match your own. Then make your choice.<br><br>If you're interested, e-mail me at <A HREF="mailto:ambertec@ieee.org">ambertec@ieee.org</A> and I can send you a sketch which argues for grounding at the source end only for a case where the &quot;grounds&quot; at the source and load ends are separated by a substantial inter-ground noise voltage.