[bodini]

Can the ground wire that runs inside shielding be connected to the cabinet right where it exits the shielding or does it need to all be run to a common star ground? By cabinet, i mean the cabinet that is holding the BOB, drives, power supply, etc.

[harryn]

My understanding is that the shield can be cabinet grounded and should be grounded on only one end. Just keep in mind that RF follows a surface, not the bulk of a conductor, so it might be necessary to use braided wire grounding for the cabinet for it to be effective.

Failure to use a braided wire ground for RF has caused late work hours for many, and few ever forget the experience.

[bodini]

so it might be necessary to use braided wire grounding for the cabinet for it to be effective.

Thanks for the reply. Please describe exactly where braided wire should be used. Do you mean in the shield (I am using belkin 8732 shielded twisted pair), or in the cabinet? And if in the cabinet, between where and where. Currently my cabinet uses an computer style efi filter and plug, and then the ground connects to the cabinet as soon as it gets inside.

I am already chasing a noise issue, which is why I am asking about all this. Late nights indeed.

THANKS!

[wayneb]

Ideally it should be shielded at both end. The easiest way is to solder a "pig tails" to the shielding and slip a bit of heat shrink over it. Keep the pig tail as short as possible and ground it to metal frame. Or you can buy solder sleeve from RS or similar stores, as pictured.

[harryn]

Thanks for the reply. Please describe exactly where braided wire should be used. Do you mean in the shield (I am using belkin 8732 shielded twisted pair), or in the cabinet? And if in the cabinet, between where and where. Currently my cabinet uses an computer style efi filter and plug, and then the ground connects to the cabinet as soon as it gets inside.

I am already chasing a noise issue, which is why I am asking about all this. Late nights indeed.

THANKS!

The ground in your plug is most likely not sufficient to act as an RFI ground. The wire in the wall is likely a solid copper wire attached to a water pipe (if in a house) or industrially, sometimes to a stake pounded into the ground. A solid wire will not ground RF, it only will ground through a braided wire.

If you are having RF noise issues, then try running a braided cable from the wire shield connection point to a copper stake pounded in the ground. Add some water around the stake to make sure the ground is wet around the copper post.

Sometimes, it is necessary to add all kinds of RF ground paths, including connections to doors, etc.

[Al_The_Man]

http://www.automation.siemens.com/do.../emv_r.pdf?p=1
Particularly section 6.
Al.

[brtech]

Ground the shield at the entrance to the chassis. I assume you have a foil shield, and you are talking about the bare wire that is placed in contact with the foil. You ground at the entrance.

The old advice, and still good up to a GHz or so is ground one end of shielded wire. These days, if we have multiGHz components, we need to ground both ends.

If you are in some really noisy environment, like a machine shop, you may external grounds on a chassis, but in most more benign environments, you shouldn't. The chassis may need to be RF tight, which may take some work.

If grounding at the chassis entrance doesn't do it, tell us more about your setup.

And Al's link is a great source of information

[bodini]

OK, thanks all. I have lots to go on here, so I will use it and get to work.