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Possible EM reduction thru grounding?
Possible EM reduction thru grounding?
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Old 18th May 2019, 10:24 PM   #1
Top Shelf is offline Top Shelf  Canada
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Default Possible EM reduction thru grounding?

Hello folks. I am running a 3/4" em conduit from one side of my garage up the wall interior across the ceiling then down the other wall. The conduit will terminate into plastic double receptical boxes. The conduit will have a ground clamp with 10 gauge single coated wire run to a sub panel which will have an isolated ground termination for all my audio equipment recepticals that that runs to a copper ground plate outside the garage buried >3' deep.

Inside the conduit i will have 2 coax cables for rca ends and some cat 6. Since the ceiling is already insulated and vapour barriered i will have to run the conduit on the warm side which will rest on the resilient channel as it traverses the ceiling.

Question is, will contact between the conduit and resilient channel (which will now be grounded) provide any type of em sheilding from above the garage ceiling,eg radio, satellite? The rc spacing will be 16" on centre. Is this too far apart to block any type of em waves.( I would like it to block something if it can). Or will it pick up interference and inject it into the grounding system causing issues. I am building a sound studio in the garage so every bit of isolation will help. I know nothing of em theory so be gentle please.

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Last edited by Top Shelf; 18th May 2019 at 10:29 PM.
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Old 19th May 2019, 07:04 PM   #2
Top Shelf is offline Top Shelf  Canada
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Ok, so i was hoping that this could turn into an informative thread for anyone else that might do this in the future.
So what i have found is in canada,cell phone service frequencies run between 850-1900 mhz(rural-urban).
Their wavelengths are around 6-12" respectively. Since this is shorter than my current rc spacing i will try to use a metallic mesh with close spacing tied to the regular ground to eliminate these waves from my workspace.
This mesh has a very tight open space so it should take care of most microwave and radio frequencies.
I will use it on the ceiling and north walls as both of those face a cell tower 300 meters away. (Not a big fan of close proximity cell towers,microwave band and all that).
Hopefully someone else has some constructive info to add.? ie: will steel mesh work or is copper the only way to go. Please feel free to chime in.
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Old 20th May 2019, 10:00 AM   #3
davidsrsb is offline davidsrsb  Malaysia
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Steel trays work fine.
This is a good summary of how to earth and how effective
On the EMC Performance of Cable Trays << Electronic Environment
300m is a long way from a cellular base station
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Old 20th May 2019, 01:53 PM   #4
Top Shelf is offline Top Shelf  Canada
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Great article david. Thank you. Looks like i will bond both ends to ground for best results if i understand correctly, i don't want the tray to act as an amplifier.
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Old 20th May 2019, 05:04 PM   #5
Speedskater is offline Speedskater  United States
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Isolated ground rods in Planet Earth are not permitted by rule, are just asking for equipment damage and Oh yes they are dangerous.
Bonding metal objects (like resilient channel) can be a good idea. It might reduce a few radio frequencies, but it's much too open to act as a good shield.
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Old 20th May 2019, 07:33 PM   #6
Top Shelf is offline Top Shelf  Canada
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Thanks for the reply Kevin. I have consulted with a few electricians that i work with and they have confirmed that an isolated ground is permitted under Canadian E- code, so i should be good there. It will be a csa approved flat copper ground plate buried at least 3 feet deep according to code.
My sub panel will have a regular #6 ground going back to the main house panel, this is just an isolated ground for the a/v equipment not contacting the regularily grounded panel.
I have split the two legs of my panel, one side for a/v, other side for lights and regular recepticals.
For the a/v side i have
(1) 20 amp double outlet box for mid /high amps and mixers processors.
(1) L5-30 outlet receptical for bass amp.
(1) 20 amp triple outlet box for computer hardware etc.
The 3/4" em conduit housing the two coax cables and cat6 will run from behind my computer to the sound equipment rack on the other side of the garage. The cat 6 is just for future proofing.
The layout of the garage negated me having everything together.
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Last edited by Top Shelf; 20th May 2019 at 07:42 PM.
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Old 20th May 2019, 08:52 PM   #7
Speedskater is offline Speedskater  United States
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I have consulted with a few electricians that i work with and they have confirmed that an isolated ground is permitted under Canadian E- code,

I don't think so. There must be a misunderstanding somewhere.
All Planet Earth grounding systems (in/to a building) have to be bonded together.
That includes telephone, internet, cable TV and satellite TV grounds.
* * * * * * * * *
Are your sure that they are not talking about Isolated Safety Ground receptacles?
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Last edited by Speedskater; 20th May 2019 at 08:59 PM. Reason: added content
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Old 20th May 2019, 09:00 PM   #8
Monte McGuire is offline Monte McGuire
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Possible EM reduction thru grounding?
What potential you attach to a Faraday cage will have no effect on its shielding. A good thought experiment is to consider an aircraft at 40,000 feet. It's not "grounded" at all, yet RF principles still apply and work well. Use the safety ground for what it's designed for, and realize that it has absolutely nothing to do with properly designed RF shielding - you can and should have both.
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Old 21st May 2019, 04:13 AM   #9
davidsrsb is offline davidsrsb  Malaysia
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In most countries having two earth systems in a single building that are not bonded together, is not allowed unless they are so far apart that you cannot touch both at the same time (minimum distance is set in regulations). Otherwise you may kill people if there is a lightning strike
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Old 21st May 2019, 04:32 AM   #10
googlyone is offline googlyone  Australia
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Possible EM reduction thru grounding?
There seems to be confusion or conflation of screening and earthing here.

They are different.

Connecting two different earths to a system does not sound like an idea with a happy conclusion.

If you have equipment that uses one earth for protective ground then adding a second earth for the cabling means you have two earth in the system.

Unless they are at exactly the same potential then you have a problem with your earthing.

It is conceptually similar to cutting a faraday cage in half and earthing the two pieces.

Best case you have is there is little potential difference across your system, and nothing happens. Most likely you will create a big earth loop, and things will hum like a mongrel. Worst case is in fault conditions where you may see damaging or hazardous potentials between what look like safe earth points.

All this stuff with mobile towers hundreds of metres away is I hope a red herring .... if your gear is sensitive to this then you have built a radio receiver, not a stereo. Or it is seriously in need of repair / redesign! (Or you were being subtly humorous!)

Last edited by googlyone; 21st May 2019 at 04:36 AM.
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