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Shielding components from EMI/RFI... Help please

A recent experiment with a product designed to reduce EMI/RFI left me curious about other ways to reduce EMI/RFI in my system. In the past ten days, I've stepped onto a slippery slope, at the bottom of which is surely some kind of insanity...

I've been experimenting with copper plates in an effort to absorb, deflect, diffract, and block EMI/RFI. I've tried copper plates under components, on top of components, and inside components.

This is the point where you tell me I don't know what I'm doing and I'm likely to short circuit something and/or electrocute myself. Consider me duly warned. This is also the point where you tell me to get some balanced interconnects, or at least to get some shielded interconnects for Chrissake. Consider me duly informed. Moving on...

I'm hoping you can help me make the most of this experiment, and help me avoid killing a component or myself. My strategy so far has been to:

1. Place copper plates at locations that generate a lot of EMI/RFI, e.g., components with switching mode power supplies or high frequency clocks. The system has a total of 3 SMPS and 3 clocks.

2. Place copper plates at locations that are vulnerable to EMI/RFI, e.g., under the amp, near the transformer.

3. Place copper plates inside noisy components -- in particular, my Meridian G68 preamp/processor. I've begun to build 2 partial Faraday cages, one for the SMPS, and one for the analog output stage.

4. Ground the copper plates either to the component chassis (when plates are used inside a component) or to an independent ground point (when plates are used above/below a component).

Has anyone tried this sort of thing?

Bryon
bryoncunningham
jea48
4,301 posts
 
Neither of those scenarios seems applicable to what Bryon was doing with the second ground rod, assuming that the means of insulation between the Reclocker and the Sonos and their grounded enclosures is sufficient to withstand the voltage that would appear across it during the lightning strike scenario.

Al,

You hit the nail on the head. The insulation would possibly have to withstand hundreds of thousands of volts. Though quicker than the blink of an eye, still long enough to damage solid state devices.
Odds? No idea.... But if the connection to the rod made no difference in sound why take the chance.

If memory serves me right a lightning strike can travel through the earth for 5 miles.
>>>

I can say with some degree of confidence that (1) and (2) sound better than (3), but I cannot say with much confidence whether (1) sounded different from (2). So maybe the ground rod is adding nothing other than additional risk.
02-13-12: Bryoncunningham
A Faraday cage does not have to be earth grounded to work.

Though usually, say in the case of a 2 wire cord and plug piece of electronic equipment such as a CDP, the Faraday cage (metal enclosure) is connected to the signal ground.

Electronics RFI shielding/Faraday cages of a Stealth Bomber are not connected to the earth.
almarg's avatar
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almarg
9,670 posts
 
Thanks Jim!

Best regards,
-- Al
sarcher30
596 posts
 
Almarg, I've always wondered about the code to use only one ground rod as well. I have never heard an explanation. Usually people say you can't do it but never explain why. I will have to read that paper you linked to.
sarcher30
596 posts
 
Well I read the Whitlock paper and it explains it quite nicely. Thanks for the link.
jea48
4,301 posts
 
Almarg, I've always wondered about the code to use only one ground rod as well. I have never heard an explanation.
02-14-12: Sarcher30


Sarcher30,

There is no limit of the maximum number of grounding electrodes (ground rods), only the minimum required.

What NEC does require is that they must all be tied electrically together. When all tied together they are considered by NEC as one grounding electrode.

Several 8ft ground rods is not necessary better than one 30ft deep driven ground rod. What matters is the rod/earth resistivity...... The lower the earth soil resistance the better. 3 ohms or less is considered very good.

I would bet very few houses even come close. NEC code says if the earth resistance is greater than 25 ohms the ground rod shall be augmented by one additional ground rod. The earth resistance could be 60 ohms but all NEC calls for is one additional rod. The earth resistance still could end up higher than 25 ohms...... NEC code is satisfied with the one addition rod.....

At least in my area, I have never heard of a residential electrical contractor ever checking the earth ground resistance. I have only seen it checked on industrial facilities. Special equipment is required for the test.

http://www.cpccorp.com/deep.htm

http://www.erico.com/public/library/fep/strike/LT0540.pdf
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