Question by Daniel Rodriguez posted 19 Mar 2005
you once helped me with a conduit grounding issue a while back which was right on. I was wondering if I can pick your brain again. It seems I have an EMI problem. I have cat 6 cables installed in a conference table. Actually the pathway for the cables which originate from below the access floor go thru the legs of the table and then they terminate under the table in small square metal box which house the cat 6 jacks and it also houses the power. Also in the legs of the furniture are the A/V cables and the electrical whips which supply power to the metal boxes which house my jacks and electrical outlets. I cannot reroute my cables because they would be exposed (not to esthetically please in a conference room setting).
1-Can I shield my cables somehow with flexible mc (BX-that what we called it in the old days) and then ground the mc (don't even know if that will work)
2-should we install Sctp.
3-or maybe the whip assembly or the combination jack/power assembly is not properly grounded.
Any suggestions, Thank you sir
Answer by Joseph Golan posted 21 Mar 2005
Great to hear from you again.
You seem convinced that the EMI is taking place within the pathway in the conf room table leg. I find that a little hard to digest since the length of the leg is so short (about 30 inches) but nothing is impossible. Do you know the source of the EMI? It is far easier sometimes to kill EMI at it's source then to try and shield it later. However, assuming this is correct, your idea number 1 may be the best and cheapest way to go if you have the room to install greenfield (empty flexabile metal conduit and bond it with proper connectors and groundable bushings to a good solid ground. I woukld also look into having separate flexabile conduits for the A/V runs and not bundle them with the category 6 cables.
Your thought from number 3 also should not be overlooked and the whip assembly should be tested for proper grounding as well (I am assuming that this is also in a flexabile metal conduit).
Last insure that the boxes that they terminate in have a grounded metal separator partition between the power and any low voltage (cat 5 and AV) compartments.
If you find anything worng with the electrical portion of this installation, make sure that the repairs are made by a qualified, licensed electrican.
Joseph Golan, RCDD
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