Conduit as an EMI Barrier? 1

[marklouie]

Seasons Greetings,

Does anyone here know where I can get information regarding the effeciveness of EMT conduit as a EMI barrier?

I seems that we often have to use pathways that are in close proximity to power. I am wondering how much protection I can get by enclosing Cat 5e cables in EMT.

Thanks,
Mark Louie

 

[Servamatic]

A metallic conduit is the best EMI barrier.
The NEC allows zero separation when the cables are inside a metallic conduit.
The original EIA/TIA 569 standard also addressed this, as does the newer EIA/TIA 569-A standard.


Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[daronwilson]

Grounding and bonding are the key. For the EMT to be effective as a shield, it must be bonded together and grounded.

When using it for an EMI/RFI shield, you should consider compression type fittings since they provide a 360 degree contact around the conduit. Typical set screw couplings often distort the shape of the conduit and leave openings in the shielding.

Also, the conduit must be grounded. Any stray EMI/RFI picked up by the conduit must have a good solid path to ground so it does not stay in the conduit and produce a field around the data cabling.

I don't know where to point you to get measurements of effectiveness, but you should be able to run them right by the power with no problems in a typical installation.

Good Luck

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[marklouie]

Thanks for the help guys, Compression type fittings are a great idea...never would have thought of that.
Mark

 

[buitenhek]

Daron,

“Grounding and bonding are the key. For the EMT to be effective as a shield, it must be bonded together and grounded.”

Do you ground both ends of the conduit? Thanks for the info.


Regards
Peter Buitenhek
Profit Developer.com

 

[daronwilson]

Generally it is grounded at the panel end at not at the distant end where the workstation outlet is, of course it depends on the environment. In radio sites with halo ground rings top and bottom in the building, the conduits get grounded several times inside the building.

I think what you want to avoid is a piece of conduit around your wire that is NOT grounded. Every conduit run (if ungrounded) could be resonant at some frequency. Putting in a nice run of conduit for protection only to calculate that you have a 1/2 wavelength at the local AM broadcast station frequency could induce all sorts of stray currents on the 'shield' thus producing more problem then you had before. Making sure it is continuous and grounded are the important aspects.



It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Servamatic]

To be most efficient you bond both ends. If you run a bonding or grounding wire inside a conduit for telecommunications you must bond both ends. This is to prevent a choke effect.
BTW, just FYI, there is only 1 grounding point in a building, everything else is bonding. Grounding is going to earth, bonding is the joining of metallic parts in a system, to paraphrase the NEC.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[daronwilson]

Not to go too overboard here, but assuming you had a small installation with 15 conduit runs from an equipment room to 15 workstation outlets, the conduits are going to be bonded to ground at the equipment room end. What would you bond them to at the distant/workstation end?

Good point on the terminology indeed, bonding and grounding, depending on your application this is a huge part of the installation.

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Servamatic]

Hopefully construction is metal studs...case solved, if not then you may not be able to bond them at the workstation. I did say for the "most efficient".
In the case of the conduit being used to carry a bonding or grounding conductor, you bond it to the conductor itself on both ends, using a short piece of #6 and a bonding bushing or water pipe clamp.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[PeaveyPhones]

Allright, now I'm getting confused. Am I to understand that it is actually worse to run data cable in an ungrounded piece of conduit?

Richard

 

[daronwilson]

Yes, it certainly can be worse to run wire inside an ungrounded piece of conduit.

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Servamatic]

It can be depending on the environment. It is not automatically a problem; otherwise, most data in commercial buildings would not function properly as we usually place cable in EMT stub ups and stub outs at the workstation, which is not a problem.

Any conduit originating in the TR or going through multiple rooms should be bonded for protection. Typically, in a commercial building this is not difficult to do, since you are usually attaching to building steel and that must be bonded.

Just make sure all conduits in the TR are bonded.



Richard S. Anderson, RCDD

http://www.smartbuilthomes.com