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#453288 11/22/09 08:13 PM
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On a new building I'm putting in a full rack. I asked the electricians what size of ground wire I should be putting and they were clueless.

I'm thinking 4/0?

Do you guys ground your racks separately from the grounds the equipment uses from its electrical connection?


Jeff
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#453289 11/22/09 10:29 PM
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You should use #6 ground wire, and maybe find a new electrician. You should be able to explain the application to your electrician and trust them to provide the solution. Yeah I know...if only we lived in a perfect world.

Here are a couple of resources to give you some ideas:

https://www.mohawk-cable.com/support/ansi-tia-eia-607.html
https://www.csemag.com/article/190225-Guidelines_for_data_center_grounding_and_bonding.php

The second link explains how they can provide an isolated ground while still satisfying code regarding all building grounds being connected.

If you have very expensive equipment, you should check with the vendor to see what grounding practices they may required to satisfy the warranty.

I hope that helps. I'm in a different country with no knowledge of your NEC, so I'm hesitant to give any specific recommendations.

#453290 11/22/09 11:34 PM
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4/0! :rofl: Are you expecting lightning too hit that rack?

Do you guys ground your racks separately from the grounds the equipment uses from its electrical connection?

Short answer is no. Any equipment you mount in that rack that is powered and has a grounding line cord, like a server, is going to ground the rack as soon as you tighten up the screws. Since this hardly is a "data center" those references are total overkill and I haven't checked them for compliance and accuracy anyway.

So my answer is either to not bother with grounding since it will be automatically grounded anyway or, if you have some compulsion, run a #6 ground to the same point the ground in the electrical receptacle originates from. My reason for doing that is to eliminate the possibility of a difference in potential and a ground loop.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#453291 11/23/09 04:04 AM
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I agree with Hal on individual racks....I always have "sparkie" common the outlet ground to the rack....even on a backboard I have them take it to a mini bus bar to common the ground to the KSU/VM, whatever.

A short aside....one building I worked in had 8 comm rooms and constant problems for the in-house IT people. I had a complete common ground installed and all the racks grounded. The ground originated at the main electrical ground.

The end result was the switches were popping like popcorn. Two lead power cords and an isolated internal ground. Once these switches were replaced all was well and the IT guys got to go back to cruising the internet.


Ken
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#453292 11/23/09 04:23 AM
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Hal, the way our luck is here lately it might just be lightning!! smile

This building replaced the last one that burnt down because an old man left a pan of grease on the fire in the upstairs apartment...burnt down an Dr.'s office that had fairly new equipment in.


Jeff
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#453293 11/23/09 04:41 AM
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#6 would be the BICSI way, as long as the run is less than 100'. Do not use an isolated ground.

I've always felt the same way Hal does on this subject. Most every piece of equipment you put on the rack is grounded, hence the rack will be grounded as well. But, we just do it the way the "experts" tell us to.

#453294 11/23/09 05:08 AM
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A #6 is perfectly adequate. The reason for an external ground wire (as I understand it) is to protect you in case the electrical circuit the equipment is plugged into is ungrounded.

Panduit offers a whole system of grounding for data centers that's pretty intensive:

https://www.panduit.com/Products/ProductOverviews/GroundingSystem/index.htm

They're good for referencing.

Bell and GTE had extensive grounding standards for COs. Bell went as far as to insist on minutae as severe as cloth covered ground wire.

You could also do a search on EIA/TIA 607.

But yes, a #6 will do fine.

Sam


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#453295 11/23/09 08:31 AM
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I think many electricians have a problem understanding the difference between a performance ground and a safety ground. Usually racks would be grounded for performance reasons, especially A/V equipment racks. Ask your favorite bug-eyed hi-end audio/video enthusiast, he'll be happy to talk, and talk, and talk...
But yeah, I don't see how a single rack would have a load that a #6 wire can't cover.

#453296 11/23/09 08:47 AM
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I think many electricians have a problem understanding the difference between a performance ground and a safety ground.

I think many electricians have a problem understanding the difference between a technical ground and a safety ground. A technical ground is what one of those articles above is talking about with those grounding electrodes, copper grids and ufer grounds. I get real nervious when I read things like that because very rarely is going to that extreme even necessary today and the tendency is to not bond it to the building electrical ground which creates a serious safety problem. There have been instances where a manufacturer required a separate grounding system for their equipment and prohibited it from being bonded to the building service ground. If it was it would void their warranty. This was due to their engineers not understanding why bonding is important which led to violations and safety concerns using their equipment.

Those bug-eyed A/V enthusiasts over at the asylum would be the last people to ask about really any issue. Pretty much like IT "professionals", all they know is what they are obsessed with.

Grounding and bonding for commercial installed sound is very different from data racks so you can't compare the two. For consumer A/V equipment, well the operative word there is "consumer" and there are no standards. What seems to work for one manufacturer's equipment and installation isn't necessarily going to work for another.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#453297 11/23/09 10:36 AM
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Maybe I should open a can of worms like this more often! I seem to learn so much more from it than from reading books or articles online smile


Jeff
Lead Field Engineer, MSCNS
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