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?

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.

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

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.

Hal, the way our luck is here lately it might just be lightning!!

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.

#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.

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

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.

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

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

Part of it is that most of the guys on the forum cut to the chase. They don't believe in dazzling you with brilliance, OR baffling you with BS. They have work to do, jobs to bid/finish and a life with no room for minutia! ME, however, I've got the time. But I don't talk about stuff that other folks have more knowledge about. I sit back and learn! (That's an 'attaboy' for all the contributors on this site!!!!!!!) John C.

I second the attaboy!

Should I scrape away the paint for the grounding position (given the rack doesn't have one already)?

After all this new-found knowledge, I decided to project around at work today and properly ground a repeater that has an antenna 50' in the air

Definitely scrape away the paint. Or, if you explore the grounding products from Panduit you will find paint piercing washers. They have kits that come with the washers, and tubes of grease that inhibit oxidization. It's pricey, and maybe overkill, but it's handy to have an off the shelf solution. You wouldn't want to cut yourself while scraping paint off your racks.

Should I scrape away the paint for the grounding position...

:bang: :bang: :bang:

-Hal

I think what Hal is trying to say, is that if you bang your head against the rack enough you will eventually chip away the paint to expose the metal underneath.

Aww come'on Hal...did you forget, I'm an IT Guy!

Hal, do you carve your turkey that way too?

I use one of those USB powered chainsaws to keep you guys happy.

-Hal

The lockwashers are "Internally-Toothed Lockwashers". Probably get them at Home Depot, Lowes, etc. And by all means,scrape away the paint. The 'teeth' on the lockwashers are meant to 'bite' into the metal, not try to pierce the paint and THEN bite into the metal.
The stack of washers on the bolt would be, starting at the bolt head, standard split lockwasher, flat washer, internally-toothed lockwasher, wire, with jacket stripped off, wrapped around the shank so that looking at the bolt from the head the wire wraps clockwise, OR BETTER, a Spade Lug, crimped correctly on the end of the wire, then in either case, 1 more internally-toothed lockwasher, then chassis you are grounding. By the way, I prefer #6 GREEN THHN STRANDED wire. It's easier to handle and place, and technically, it will carry more current.

#6 GREEN THHN STRANDED wire. It's easier to handle and place, and technically, it will carry more current.

Tell me you aren't saying that stranded will handle more current than sold for a given size.

Besides that, other than our Bell spec #6 ground wire, you won't find anything larger than #8 in solid per the NEC.

-Hal

Hal, where do I find one of those USB chainsaws? Could come in handy when I get really frustrated fixing a computer :p

I kinda think it will stop working when you start cutting up the computer.

I think this is a joint effort by the IT "professionals" and that Chernoble Dr. guy over on Sandman.

-Hal

Don't you know that a $200 "2 meter" power cord is at least 20 times better than a $10 6-foot one? And it's quoted in metric, which as everybody knows, signifies high quality.
Seriously, I know people whose "home theatre" system is probably worth more than their homes, what with the housing crisis. And I have seen situations where the grounding of a system cost more than what the install of a small KSU system would cost. As far as I could see, the installer just run some jumper cables from the components to a perfectly ordinary rackmount busbar and then some green wire to a rod in the basement. The sales literature was full of terms like "custom isolated ground", "enhanced operation", blah blah blah.

Hal, "Skin Effect". The power in a wire actually flows on the outside surface and power density gets lower the closer to the center you get. Compare the circumference of 10?-18ga? wires to 1-6ga wire. (The 10-18ga wires is a guess, I never really thought about the number of strands in a 6 ga wire, or any other stranded wire, for that matter.) And the higher the frequency, the more important "skin effect" gets. Consider the microwave 'wave guide'. It's nothing more than a wire that has been cored out, in effect. Because microwaves truly run only on the outer 10% or less of a wire.

Skin effect? At 60 Hz? There's a nice comfy room waiting for you over at the asylum...

-Hal

I believe we have just entered....

I am no electrician wait let me repeat I am no electrician.

But I can place a pretty good bet that skinning will be very small if at all. Especially with the ground being larger than a 3/0. But I have to tell you this has now peaked my interest. I really didn't think this conversation would make it this far.



I really have to applaud the brain power here. It impresses me every time I think it could not get any better.

We have a very large customer that is a financial institution. They have set standards for the data racks at their bank branchs. Their standards on grounding/bonding is extensive. They have us bond a TMGB to the main distribution panel. Depending how far away the MDP is away determines the wire size. In some banks this has been 2/0 wire. Then we also have to run a wire from the TMGB to building steel. Also length determining the wire size. It's a least a #6. Then we bond from the TMGB on the backboard (thats usually mounted behind the rack) to the TGB on the data rack. Also the ladder tray is bonded to the TMGB. Then we provide a ground wire from the TGB to their Cisco router in the rack. We have to use 2 hole compression lugs for every termination. We have probably done this at maybe 1000 banks. Seems overkill, but its their standards and they are paying.

the fun thing is building steel may not be a clean ground depending on how the place was built. so now you are attaching the bonded electrical ground to the floating structure.

The reason I learned for bonding the rack separate from the device was more for static dissipation. True the self tapping rack screws should take enough off with the scraping washers to make a solid connection and a clean path. I have also seen computer power supplies fail to the case instead of failing to the ground on the cord. so additionally bonding the rack will safely shunt that current to a real ground 'IF' the bonding was done correctly.

Bonding gone wrong...
I saw one idiot bond to what they thought was a cold water pipe and instead turned out to be a gas line. I've also seen cold water pipes that have new plastic fittings in places where cheap work was done making the pipe an isolated hunk of metal. A high quality mega-ohm meter should let you check continuity of ground.

" A high quality mega-ohm meter should let you check continuity of ground."
-------------------------------------------------
But, make D--- Sure it's NOT a gas pipe before you use that MEGGER!

Actually it is not their standard. As it follows TIA 607-B (grounding and bonding data and telecom equipment) to the letter. And that's a good thing, IMO, as both customer & installer have an objective frame of reference. But the OP mentioned only a single rack. Not the complicated infrastructure (component->rack->telecom closet->equipment room) that would necessitate structured/hierarchical bonding/grounding as described in the standard. Within a single rack, a #6 copper (or maybe #4 aluminum-as per your code) would be more than enough, as it would handle close to 200A (I don't remember the exact figure offhand).
Don't forget this is a performance or to use the proper term technical ground. Its main function is to protect equipment against electrical noise. There has been loads of research on this, as these problems are the hardest to pin down. And yes, paint can act as an insulator. All bonding surfaces should be bare. Another reason is that bonding/grounding effectivesness is related to the geometry of apparatus such as the TelecomMainGroundBar. IE thickness, dimensions, number & size of terminals, material of construction, AND contact-surface area. If you use a certain size ground lug/screw it is understood that its bonding surface (however many square millimeters it is) should be the one expected as per the standard. I agree that maybe this is all too much. On the other hand, if the budget is there, they're pretty easy to implement, and as I've said above the standard does provide with an objective reference.

Yes I'm sure your right. I wouldn't think the bank would come up with their standards without following EIA/TIA or NEC standards.