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Joined: Oct 2004
Posts: 72
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Member
Where in the code book can I find reference to a "high-frequency reference grid system" (or signal-reference grid)? I need to know what kind of grounding point I need to provide in order to prevent unwanted noise.

Thanks!

Joined: Mar 2002
Posts: 582
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Ron Offline
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There is nothing in the NEC regarding this design. Check the IEEE colored book series.


Ron
Joined: Oct 2003
Posts: 156
D
Member
This is a design issue, and not NEC related. There are many good sources for a SRG. Best guidline is in MIL-HNBK-495A and FIPS-94. There are also some guidelines in IEEE Emerald Book, ITU-T K.27, and ANSI T1.333-2001.

Joined: Oct 2003
Posts: 156
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Bucketman, FWIW, a SRG isn’t bonded to any particular point per se. They can be constructed of either the raised floor grid structure, #6 AWG copper conductor grid under the raised floor, a wire mesh embedded into the concrete or suspended from the ceiling, or a cable rack grid either under a raised floor or suspended from the ceiling. Lots of variables to work with. The important thing is the size of the grid. It depends on the frequency cut-off of interest. The grid is designed on 1/16 of the wavelength, so for a 30 Mhz grid you are looking at something with 2-feet on center. The higher the frequency the smaller the dimensions

As far as bonding or connecting, it is connected to everything like conduits, water pipes, every AC panel EGC bus in the area, all equipment frames, every XO in transformers, every building steel column it passes by, every ground electrode available, etc. The point is not necessarily low impedance to earth, but rather low impedance between any two points on the system and to the power source.

Edited to correct spelling


[This message has been edited by dereckbc (edited 11-05-2004).]

Joined: Apr 2002
Posts: 2,527
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A general but obsolete/withdrawn NIST document that introduced a lot of terms and concepts for “signal” versus “power” grounding is www.itl.nist.gov/fipspubs/fip94.pdf Early on, authors Lewis and Kalbach were thought to have landed from Mars with some very revolutionary but much-needed discussion on “convergence” of the two widely conflicting systems, and—equally important—the modes of thinking that fostered the original confusion.


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