Single End vs Both End Grounding

[Dave_C]

Over the years there has been a lot of disagreement about how to ground wiring in a control circuit!

If you can grasp the concept of how a TV antenna "induces" the available signal from the air into the antenna, then you are closed to understanding the concept of "single End Grounding".

In the case of a control circuit, you want to "Induce" stray EMI signals into the "antenna" of the wiring so as to drain it to ground and make it of no use.

So to create an "antenna" that will induce these stray signals, you must only ground at one end else the shield is no longer an antenna it is only a shield.

In the case of working with RF signals you have to ground the shield at both ends to maintain the RF signal inside the cable, else you risk RF loss.

Bringing all of these ground points to a central point is called "single point grounding" and known as a "best Practice".

The argument starts when someone says: "If you ground the shield at both ends the EMI can't get into the wiring". Maybe, but where does the EMI go? It floats around on the shields looking for any path to ground or usually a path into a control circuit where you did not want it to be.

My retired friend from NASA who trouble shot issues with Satellite communications said they ran into the same issues as we do. They used single end grounding on all but their RF signals and their problems went away.

Hope this helps,

Dave C.

[tblough]

Just to clarify, when Dave refers to single end grounding, he is referring to the shield only. You still need to connect the equipment grounds at both ends.

[Muzzer]

This is indeed an old chestnut - or possibly a hot potato!

Not sure I'd fully agree with the aerial explanation. And you may be aware that there are some aerials that have the active conductors grounded at both ends.

The more common explanation as to why shields work is the faraday cage, where an electric field can't pass through a conductor. However, the effect of the field on the shield is to generate a current in the shield. This current needs to be returned to something - and generally the electric field has been created relative to ground (a common mode voltage), and so the current path needs to be back to ground.

Connecting both ends of a shield to ground can work to reduce noise interference in many cases but this may inadvertently result in a path (it may be DC) between the circuits at each end (a "ground loop"). In some cases, the conductor grounded at each end can resonate at radio frequencies and cause problems. Equally, it could resonate when only one end is grounded. There's no right or wrong but the default (only connect one end) is probably the safest option.

It's worth noting that some OEMS such as Yaskawa recommend grounding both ends of the cables, while others say only one. As I said, there's no right or wrong, just what works for each individual installation.

[Dave_C]

Well, NASA surely could not be using the best possible methods, so I stand corrected! LOL

Having wired a few recording studios and one vidoe + sound editing studio I know we only grounded shields at one end. Ground loops do come into play when you do it otherwise.

I've never gone wrong just grounding one end of the shield but I have had issue with grounding both ends, thus my conclusion. The 125-year-old Fortune 100 company that I worked at for 20 years would have terminated technicians for grounding at both ends!

I don't know what else to say!

Dave C.