Proper Grounding of A/V Equipment Racks

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crosen

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I am an A/V contractor and would like to ensure that I am grounding my equipment racks correctly. In most cases, the equipment racks are not in close proximity to the main panel ground bar. So, I am unsure what the racks should be attached to in order to ensure proper grounding.

It appears that a common practice is simply to connect the rack to AC ground via a grounding screw on the rack's UPS. However, I am unsure if this is adequate.

So, on a new construction project where the A/V rack will not be adjacent to the main panel ground bar, exactly what should I ask the electrician to provide to ensure the rack is properly grounded? In other words, what is the correct wording of the grounding infrastructure that I should request, and what exactly is that infrastructure comprised of?

Much appreciate any thoughts.
 
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zbang

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Racks are "grounded" for electrical fault protection by the equipment supply leads, no further grounding is needed for that. Signal grounding is a completely different world and most of what "people say" is wrong (but at a glance, the paper jtinge posted looks sensible; you could also look at Bill Whitlock's papers on the subject).

If you want to request a large conductor from the building's Ground Electrode System (GES, the earth grounding system of a building), there's nothing wrong with that if done properly, but in most cases it will add little-to-nothing to how well properly-connected A/V equipment operates.
 
synchro

synchro

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Chicago, IL
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EE
jtinge said:
I found this to be a useful resource for grounding of A/V systems.
Click to expand...
While browsing through this article it looked very good. But when I saw at the end that Henry Ott is the principle author then that clinched it. He's one of the most recognized experts on noise reduction and EMC. I remember reading his book on noise reduction decades ago and it's excellent. Often I look at write ups like these with some skepticism because they often have some technical errors. But in this case I doubt that there are any.

And the second author listed is the Bill Whitlock zbang mentioned above.
 
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suemarkp

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Kent, WA
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Retired Engineer
Most rack equipment doesn't necessarily bond the rack when installing it because:
  • The ears on the equipment are usually painted.
  • The rack rails may be painted (but the threads should conduct if you've worked the paint out of them and not using cage nuts or speed nuts).
  • The rack mounting screws may have a nylon isolator under its head.
I would ground the power PDU in the rack (hopefully it has one) to the rack chassis. Many rack mount PDUs don't have an external ground screw. In that case, use special rack screws with paint piercing teeth under the head and thread forming screw threads to effectively bond the PDU to the rack rails or rack structure.
 
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