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In Reply to: Are you referring to... posted by Presto on April 2, 2007 at 09:34:06:
"This is done all of the time with instrumentation panels - a separate ground grid (multiple interconnected rods) is used for a ground with less noise on it. The ground conductors are insulated and the ground busses themselves are isolated from all other metal parts normally connected to the system ground."What you stated may be true, but I don't think this is what's done with audiophile "ground isolation." But I could be wrong.
Follow Ups:
Todd:How is it different? They're purposely isolating the ground at that receptacle (note the little "x" on the Romex ground meaning "cap off") and using a separate ground electrode (single rod in this case). The only difference is that a single electrode is one rod or plate, and a grid is comprised of more than one rod or plates.
We (electrical consultants) do this kind of design all of the time for isolated instrument grounds in industrial and institutional applications. The trouble (in a residential installation) would be to find the code rule that permits one to have an isolated ground electrode in the first place. I don't think this would be allowed - I think you would be forced to interconnect multiple electrodes using standardized methods, thus defeating the purpose of having an I.G. in the first place.
One heck of an idea, and it would work for having a ground with a lower noise floor. The question is: is it allowed? And if it IS allowed, would the inspector want a GPR (ground potential rise) test done on that one single electrode? My guess is that if he was open minded enough to allow a separate electrode for an I.G., he'd want to see a GPR test - and the extra testing, the report and the extra time for the additional inspection would all come out of the homeowners pocket, and rightly so.
The diagram shows the concept only. It does not show how to calculate or test for the GPR of the electrode, and it definately does not discuss the ramifications one could encounter when it comes time to have such an installation inspected.
Good information here:http://ecmweb.com/mag/electric_demystifying_isolated_grounding/index.html
Gbeard:Thanks for posting that. Good info.
"For safety purposes, you can't run an IG equipment-grounding conductor in its own conduit or outside the branch circuit or feeder conduit. You also can't terminate the IG equipment-grounding conductor to a lone ground rod. "
Ha ha ha. I need to call a code inspector or two on this one. Some people are saying inspectors will approve the separate rod. Some, including the author of the article you mentioned, say NO WAY!
In any case, we're not just running an I.G. here - we're doing what the article says NOT to... we're talking about having a separate electrode (or grid) for the I.G..
I checked back into some earlier designs where we did separate grids for instrumentation. We used a "ground connection junction box" for the "derived" ground - the isolated conductors from the instrument ground grid, the isolated conductors TO the instrument grounds, AND the bare condcutors from the local ground grid ALL are connected at ONE SINGLE POINT. The junction box is only used for isolating the various grids for TESTING purposes - it is never in service with the grids isolated from one another.
The scheme on page 8 of the referrenced document we have never done and never would do. The two grids need to be TIED TOGETHER to remain at the SAME POTENTIAL. You CANNOT use earth to connect these two grids (or rods) together for the reasons already pointed out. (Potential differences, ground potential rise, etc.).
nt
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