Server rack grounding

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
Here is my situation In more detail so you guys can advise me with the better method to go

I have couple of server racks and customer wants me to bring a ground conductor to the room. At first, I assumed the server racks should be already grounded with the branch circuit but customer admits the server racks are not grounded.

However, my first thought is to Install telecom ground busbar next to the server rack. Then, Pull a ground conductor from the nearest panel and connect it to the ground busbar. Now, that Tom explains about the high impedance it causes when ground wire is separately installed I’m worried.

The second thought is if the branch circuit is in EMT, instead of pulling ground conductor from the panel that is further away, I can tap from the EMT and use #6 AWG to ground bus bar

Now, let’s say if the nearest panel is 40 ft away from the server rack, what size of ground conductor would you guys use? Per Ron slide 23, 2kcmil per ft, that makes it 1AWG ground conductor
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Here is my situation In more detail so you guys can advise me with the better method to go

I have couple of server racks and customer wants me to bring a ground conductor to the room. At first, I assumed the server racks should be already grounded with the branch circuit but customer admits the server racks are not grounded.

However, my first thought is to Install telecom ground busbar next to the server rack. Then, Pull a ground conductor from the nearest panel and connect it to the ground busbar. Now, that Tom explains about the high impedance it causes when ground wire is separately installed I’m worried.

The second thought is if the branch circuit is in EMT, instead of pulling ground conductor from the panel that is further away, I can tap from the EMT and use #6 AWG to ground bus bar

Now, let’s say if the nearest panel is 40 ft away from the server rack, what size of ground conductor would you guys use? Per Ron slide 23, 2kcmil per ft, that makes it 1AWG ground conductor
We install a ground bar on the wall of the IT room or IDF closest and run a bonding jumper to the nearest structural steel. From there we bond the racks, floor, etc.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
I see. What wire size do you use ? And do you use EMT or PVC?
You don't need to use anything. There is a difference between an Equipment Grounding Conductor which would be run in the conduit with the conductors bringing power to the server rack, or if the conduit is EMT can serve just as well as a wire EGC, and Auxiliary Grounding which is found all over IT equipment.
Here is a picture. It's the inside of a cell tower shelter, not a server room but the idea is the same. The wire can be any size you want it to be.

grounding.jpg
 
One of the problems here is that just because it's green doesn't make it an official (equipment) grounding (electrode) conductor.


Virtually all equipment in a NEC compliant installation is connected with an Equipment Grounding Conductor. Make sure the power feed has one and IMHO, you can stop there. Note that this is for protection and nothing else, as long as the impedance is low enough to trip the breaker, it's low enough.

Some people want additional grounding conductors for their own reasons (RF suppression? Static or magic discharge?). That's engineering design, not code compliance.
IMHO, most of those conductors do nothing except static discharge; a noble function but hardly one that needs 1/0 of a field of driven rods.

Years ago, before fiber and twisted-pair Ethernet connections, having a low impedance ground mesh made sense because there were a lot of single-ended/unbalanced connections between equipment (RS-232 and coax being common). This is no longer the case, even telecom is almost always isolated somehow- metallic T3 or T1 lines from the TelCo are pretty much all gone.

Customer wants a green wire from the panel? Run some #6, jump between lugs on each rack, go home.
 

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
You don't need to use anything. There is a difference between an Equipment Grounding Conductor which would be run in the conduit with the conductors bringing power to the server rack, or if the conduit is EMT can serve just as well as a wire EGC, and Auxiliary Grounding which is found all over IT equipment.
Here is a picture. It's the inside of a cell tower shelter, not a server room but the idea is the same. The wire can be any size you want it to be.

View attachment 2555634
Thank you very much very helpful
 

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
One of the problems here is that just because it's green doesn't make it an official (equipment) grounding (electrode) conductor.


Virtually all equipment in a NEC compliant installation is connected with an Equipment Grounding Conductor. Make sure the power feed has one and IMHO, you can stop there. Note that this is for protection and nothing else, as long as the impedance is low enough to trip the breaker, it's low enough.

Some people want additional grounding conductors for their own reasons (RF suppression? Static or magic discharge?). That's engineering design, not code compliance.
IMHO, most of those conductors do nothing except static discharge; a noble function but hardly one that needs 1/0 of a field of driven rods.

Years ago, before fiber and twisted-pair Ethernet connections, having a low impedance ground mesh made sense because there were a lot of single-ended/unbalanced connections between equipment (RS-232 and coax being common). This is no longer the case, even telecom is almost always isolated somehow- metallic T3 or T1 lines from the TelCo are pretty much all gone.

Customer wants a green wire from the panel? Run some #6, jump between lugs on each rack, go home.
According to customer, the power feed does not have EGC but now that I think customer probably didn’t know that EMT can be used as EGC.

and customer only wants for protection and nothing else
 

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
One thing you'll find from reading MH is that until there is an earned trust, pretty much everything a customer says about local conditions is probably wrong.
That is true. so I found out that there must be misunderstanding with the customer, I was able to find drawing and the server rack is grounded with the branch circuit. Customer requirements is to ground small electronic devices
 

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
You don't need to use anything. There is a difference between an Equipment Grounding Conductor which would be run in the conduit with the conductors bringing power to the server rack, or if the conduit is EMT can serve just as well as a wire EGC, and Auxiliary Grounding which is found all over IT equipment.
Here is a picture. It's the inside of a cell tower shelter, not a server room but the idea is the same. The wire can be any size you want it to be.

View attachment 2555634
To protect from physical protection, can I put this #6 AWG in EMT?
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Usually, a 6 awg or larger EGC doesnt need protection from damage. If you want to protect it, a ferrous raceway should be your last choice because of inductive effects if it is not run with the ungrounded conductor.
 

Etanuye

Member
Location
Los Angeles
Occupation
Junior Engineer
Usually, a 6 awg or larger EGC doesnt need protection from damage. If you want to protect it, a ferrous raceway should be your last choice because of inductive effects if it is not run with the ungrounded conductor.
The reason I want to protect is because this Ground conductor is passing through the wall so I was thinking I should use EMT or PVC
 
Last edited by a moderator:

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
You could treat it like a GEC where you also ground the sleeve to the wire passing through it. As long as the feeder has an EGC, this is a supplemental ground for some purpose - noise, static drain, good feelings.... So the NEC may not care much about this wire as it is not required to be there.
 

paulengr

Senior Member
One thing missing in all of this is that grounding is necessary for grounded metal raceways and enclosures. If it is simply structural support for the equipment, which is what most racks in rack mounted equipment is, no grounding is required: The metal enclosures of the servers (if any) are bonded to a 3 prong IEC style connector then bonded to the electrical system which is bonded either via an actual physical green or bare wire or via metal raceways. You often see metal building structural columns grounded but this is a lightning issue more than anything and has little to do with the electrical system directly. Lightning Codes require 2 paths to ground and have a minimum size but this doesn’t apply.

In certain processing equipment where static charges are a concern (grain, gasoline storage, powder coatings) they bond the equipment and building structure. There is no current to speak of so no size requirement.

In telecom equipment (TIA) where noise and ground loops are a big issue they have extensive grounding to make everything a Faraday cage. In analog POTS and broadcasting this stuff is an issue. But copper Ethernet by design filters everything under about 100 Hz (30+ dB down) and fiber is immune. So old TIA standards aren’t used when there is no POTS or very limited.

If someone wires it all with 2 wire ungrounded equipment, chances are nothing else was done to Code either. I’d be reluctant to do less than starting over. I’ll bet none of the wireways are mechanically sound either. Did they just run open THHN or put it in LFNC with zip ties dangling it loose?
 
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