Does a raised floor need to be grounded?

[kwpatriot]

Hello there, I have a question about a raised floor and it needing to be grounded or not. (I posted this question on a different forum but didn't receive an answer )

My only past experience with grounding a floor has been in data centers, where there is 120/208/480v above and below a raised floor that is 3-4 feet tall. In one case, the engineer designed a cross-over grid system where every other raised floor pedestal was grounded, and each grounding clamp was quite expensive. So that is sort of one extreme.

Anyways, now we are faced with a 'low profile' raised floor that is only approximately 2 inches tall. The raised floor panels are made out of plastic and the floor has metal trench covers. The basic layout is there is a 2 foot x 2 foot grid of cable/wire trenches, and the electrical and data cabling is placed into the trench, the metal trench covers are put on top, then you put the floor carpet or tile on top of that.

This particular installation is a standard office building, so each user will have a 1-2 computers, a phone, personal power strip, etc. No medium voltage equipment, but likely some small desktop UPS systems.

There have been some recent discussions (for this project) that code might require the raised floor and/or the metal cable trench covers to be grounded. The problem we are having is the inspector does not have experience with this type of raised floor (honestly do not know if he has any experience with any type of raised floor) and is taking a very conservative interpretation of the code.

Can anyone recommend what to do? The floor manufacturer tells us that 99.9% of their customers do not require grounding but did say it is ultimately up to the local code and inspector. The project engineer apparently did not consider there to need to be grounding because it wasn't shown on any drawings and is deferring to the inspector.

Thank you very much for your help!

PS- This is for a project located in the U.S.

 

[CalcNerd]

You need to review the specifications of your client or check if they are requiring you to meet standards. It is a good idea to ground the floor. Grounding a bonded floor is easy. Any advice that I provide after this is pure speculation. You should consult an EE with plans or what the purpose of the room is.

 

[jim hardy]

Look through this article
http://ecmweb.com/code-basics/grounding-and-bonding-part-1-3

IMHO - if your raceways are metal they should be "bonded" to a service ground.

 

[rbelli1]

Electricity+un-grounded metal=accident waiting to happen.

BoB

 

[berkeman]

Hello there, I have a question about a raised floor and it needing to be grounded or not. (I posted this question on a different forum but didn't receive an answer )

My only past experience with grounding a floor has been in data centers, where there is 120/208/480v above and below a raised floor that is 3-4 feet tall. In one case, the engineer designed a cross-over grid system where every other raised floor pedestal was grounded, and each grounding clamp was quite expensive. So that is sort of one extreme.

Anyways, now we are faced with a 'low profile' raised floor that is only approximately 2 inches tall. The raised floor panels are made out of plastic and the floor has metal trench covers. The basic layout is there is a 2 foot x 2 foot grid of cable/wire trenches, and the electrical and data cabling is placed into the trench, the metal trench covers are put on top, then you put the floor carpet or tile on top of that.

This particular installation is a standard office building, so each user will have a 1-2 computers, a phone, personal power strip, etc. No medium voltage equipment, but likely some small desktop UPS systems.

There have been some recent discussions (for this project) that code might require the raised floor and/or the metal cable trench covers to be grounded. The problem we are having is the inspector does not have experience with this type of raised floor (honestly do not know if he has any experience with any type of raised floor) and is taking a very conservative interpretation of the code.

Can anyone recommend what to do? The floor manufacturer tells us that 99.9% of their customers do not require grounding but did say it is ultimately up to the local code and inspector. The project engineer apparently did not consider there to need to be grounding because it wasn't shown on any drawings and is deferring to the inspector.

Thank you very much for your help!

PS- This is for a project located in the U.S.

It's not clear whether you are talking about grounding the electrical distribution raceways (which is definitely required by code), or installing an anti-static floor. Anti-static flooring is generally only required in electronics production areas, where open powered-up electronics devices are worked on. In those areas, managing ESD is a big issue with respect to product quality control (EOS = electrical overstress can cause serious product quality issues in the field).

Can you say more about the installation and maybe post some pictures of plans, etc.? There is a big difference between AC Mains safety grounding and ESD management.

 

[kwpatriot]

Hi there and thank you everyone for the replies. I'm sorry it has taken a while for me to reply.

So I can provide a photo of the product here, this is from the manufacturer. The actual installation has not happened yet.

And just to provide some background, I work for an IT company. We are installing the data cabling for this project, as well as setting up their LAN and some A/V equipment. So, during a project construction meeting, this question about grounding came up, and no one there at the meeting had an answer (the electrical contractor, myself or the customer). But the inspector pushed back and wants more information on grounding.

Just to clarify what I mean by 'cable trench', I think the picture would show that the best. Again, this is from the manufacturer. I can't take a photo on the jobsite because the access floor isn't scheduled to be installed for 2 more weeks.

So the above photo shows plastic floor panels, and the black part are the metal covers for the "trench". The customer on our project is wanting to lay in the power wires (in flex conduit), and lay in the Cat5e cables in the same trench. Then there are electrical floor boxes with power and data connections. The floor boxes have grounding lugs or tabs where the electrician will connect the ground wire as he runs the power cables throughout the access floor. (just like an electrician would if they were wiring in a switch, an outlet, etc.)

Any ides or suggestions? I am not sure what the inspector's concern is exactly, but it affects us if we are to lay the data cables in the trenches. In my past experience in data centers, the ground wire was always landed on the metal case of any sort of electrical device or an electrical outlet. I believe that is what the electrician was planning to do here. Thank you very much!

 

[berkeman]

And just to provide some background, I work for an IT company. We are installing the data cabling for this project, as well as setting up their LAN and some A/V equipment.

For most IT rooms that I'm familiar with, they do use anti-static floor materials. Electrical power distribution raceways will be grounded per NEC code, and the anti-static flooring will have connections to ground per the company that makes the flooring.