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#182786 12/10/08 03:54 PM
Joined: Jul 2004
Posts: 136
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cgw Offline OP
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Owner wants a ground bar in a small server room for bonding racks etc. Fairly typical. I will research it but can you give me a head start by letting me know what is typically done?
Bus bar size?
Bonding wire size? (size based on grounding electrode conductor, circuits serving the room, other?)
Where to bond to bldg ground?

Last edited by cgw; 12/10/08 03:56 PM.
Joined: Jan 2005
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Cat Servant
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The grounding bussbars I've seen have typically been HUGE ... perhaps 1" wide and 3/16" thick, simple copper.

While you don't need this much copper for a ground path, you do need that much for mechanical strength, and for the screws to have a couple threads engage the metal.

Hint: When drilling copper, you want to use drill bits with 135 degree 'split point' tips. When tapping, taps with spiral flutes work better. It's worth a visit to a local machine-shop supply house.

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Usually somebody in their tech staff will want a isolated ground conductor going straight to the equipment bonding bus in the service where the GEC and MBJ land. That might also serve a sub panel for the server room so all the circuits will share the same grounding path.
I think anything beyond standard 250 is usually snake oil. It is good to have a common grounding bus but where the ground comes from is not as important as getting all the equipment in the room bonded to that bus.


The ground bus plates an my radio equipment shelters were more like 4" x 16" and had a bunch of 1/4-20 tapped holes with brass screws in them already. They usually used a #4 cu solid to the ground electrode system, landing in the service disconnect can.


Greg Fretwell
Joined: Mar 2005
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There are a number of ways to do it. Often, I'll see nice thick ground bars under the false floor, way oversized, with big lugs from all the racks. He's concerned about higher frequency ground currents, so the properties are very different than for 60Hz safety grounds. For instance, a metal raised deck that's insulated and not even touching the ground will have lower impedance to ground than a 20' ground rod, because the capacitance between the false floor and ground is essentially a short at higher frequencies, wheras the ground wire and rod function as a 0-loop inductor and have a high impedance.

Google MIL-HDBK-1012/1, it's a miliary handbook dealing with datacenters. It's free, and a good design reference smile MIL-HDBK-419 also deals with grounding. You can ignore TEMPEST (security) and HEMP (nuclear) requirements.

Joined: Aug 2007
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Originally Posted by gfretwell
The ground bus plates an my radio equipment shelters were more like 4" x 16" and had a bunch of 1/4-20 tapped holes with brass screws in them already. They usually used a #4 cu solid to the ground electrode system, landing in the service disconnect can.


This is usually what I saw when I worked on the big nortel meridian phone systems as well.

~Matt


I would rather beg for forgiveness then beg for permission.
Joined: Aug 2001
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All of our new schools have exactly what gfretwell describes (in the server room). 4x16 by 1/4" thick with a lot of threaded holes. A #4 to the main electrical room via a pipe below the slab. Every piece of eqpt has an 8 or 6 to this plate. Seems to work well. We've been using this system for about 6 or 8 years now and have very few probs.

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Thats the same I see all the time,additionaly they are all on raised Isolators.

Joined: Mar 2007
Posts: 404
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Here's the ground bar in one of our switch closets, for reference:

[Linked Image from hsiprodsvcs.com]

Joined: May 2007
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In our area you can get a 1/4" X 12" (or 24") X4" from the local sheet metal fabricator. These ground bars in the typical server room do little the expend natural resources and make the end user feel good (oh and it adds profits to the installing electrical contractors pockets always a bonus)


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