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Does conduit eliminate the effects of flourescent lights and or electrical interference on CAT5E cabling?

Posted on 2007-03-19
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Last Modified: 2013-11-09
I need to run CAT5E ethernet cabling (CAT5E was purchased for this project already, thus CAT6 is not a great option at this point) across a ceiling (yes a ceiling in a 'maintenance' area) and of course there are flourescent lights everywhere.  I'm running the cables inside conduit (underground rated) so they are nicely organized and meet (to my knowledge) code requirements.  The path goes directly over one of the flourescent lights (there happened to be a 2inch clearance space between the light and the ceiling).  Of course, I want to run a straight line to allow me to 'fish' the cables through the conduit.

Has anyone installed such as this before and if so, is the network performance as you would expect?  Of course, the two most important connections in the work area need to run through this path, so I don't want to run the cable only to find that their connections are going to have constant issues.

Thanks much to anyone who can offer insight!
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Question by:atroutcatcher
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by:Rob Williams
ID: 18749896
CAT6 wouldn't help with the fluorescents anyway. Conduit, assuming metal and grounded is supposed to dissipate the interference/noise "completely".
Without the conduit you are supposed to maintain a minimum of 18" clearance from the bulbs and ballast. If wiring is 570 (often is in offices) that distance may be greater. Go with the conduit and make sure it is properly grounded/bonded by the electrician.
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by:Alan Huseyin Kayahan
ID: 18775360
     I disagree with RobWill. I have faced this issue many times in my corporate network. Conduits can not be assumed metal and grounded. Solution is simple.
     CAT5, CAT5E and CAT6 network cables are widely used, but there is a simple word on the cable. It is "UTP".  UTP means "Unfoiled Twisted Pair". And you need "FTP" which means "Foiled Twisted Pair" CAT cable (5,5E or 6 how you like). These cables are designed for this kind of conditions. A thin foil surrounds 4 twisted pair of wires in cable and protects the data flow.
    And also you need shielded (SRS) RJ-45 connectors, which are surrounded by a thin metal and contacts computer case and the foil in FTP cable. This makes the grounding.
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by:Rob Williams
ID: 18775413
I too will disagree :-)
a) >>"Conduits can not be assumed metal and grounded. "
Agree 100% therefore my comment; "make sure it is properly grounded/bonded by the electrician"
b) Shielded cable is a wonderful concept, only getting it properly grounded is near impossible. If you ground at both ends you will likely find there is a potential (voltage) difference between it and ground ,that differs at both ends. This occurs because the 2 pieces of equipment are using different grounds. As a result "noise" is actually induced into the cable making matter worse.
If you can properly "bond" your shielded cable to the same building ground, with no interruptions fine. But it will not wok any better than your conduit, assuming as MrHusy stated, the conduit is properly grounded/bonded.
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Alan Huseyin Kayahan earned 200 total points
ID: 18781087
   Hi Robwill
      As you know, the shielded rj45 connector contacs the metal surface of Network interface card, and this metal surface is screwed to the computer case. And the computer case is grounded by the Power cord's third female pin (which is in the middle) because it directly contacts the power supply (if you open your power supply, you will see that there is a secondary link to the case from ground). And this is same for the other end of course. Since your computer's electric plug is grounded by your electrician and you use a grounded power cord for your PC, there is no matter. Even one end is enough too. And wont be any potential difference.
     If you want to make sure, buy an AVOmeter, set it to the buzzer mode (when two probes touch eachother, it will beep). Unplug power cord from the electric plug. Contact one probe to the hole in the plug (grounding) and contact other ent to computer case. You will hear it beep. Now contact this probe to the shielded surface of rj45. It will beep again. Now contact this probe to the sheild of rj45 connector of the other end of this cable. It will beep again if you firmly/correctly connected the shielded rj45 connector to ftp cable.
      FTP cable is produced for this purpose, and if technician can not ground it "near impossible"  as you said, this is not the fault of FTP concept, this is the fault of this technician. And %90 percent reasons of this fault is using normal rj45 connectors instead shielded SRS RJ45 connectors.
     First rule of electricty= "Electric flows through the shortest path". So it doesnt matter if both ends use different groundings or not.  And also it doesnt matter if you have more than 2 ends. 3,4 or five or only 1. Potentieal difference is not valid for this case.
     I dont claim that bonding/grounding a conduit (which are plastic and the inside surface has to be covered with an aluminum folio for grounding/bonding which is impossible if the conduit is long or has curves through building and an unusual act for an electrician where as he is able to use FTP cable) is not a solution. But not a logic one in my opinion, with my all respect to my m8 Robwill.
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by:Rob Williams
ID: 18781210
I have to agree in principal  MrHusy. Not trying to be difficult, but for discussion purposes, having dealt with this and a military installer, RJ-45 shielded cable has been known to cause more problems than it solves. Again it is due to the fact that the devices at either end of the cable are ultimately connected to different physical grounds. I think you will find there is a very slight potential difference between chassis ground and a true ground in any two locations. The military like to use shielded cable to prevent any one "listening in" on transmissions from within the cable, but it has been a very delicate problem for them. Though my personal knowledge of the solution is limited, I believe their solution is to ground one end of the cable only.

Regardless, I believe the original discussion came about as atroutcatcher already has conduit in place, and purchased CAT5E cable . Not a decision between shielded cable and conduit. Assuming metal conduit and verified grounding and bonding, it should eliminate the noise.
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by:atroutcatcher
ID: 18820202
Status update:

The client decided to go with normal 'gray' conduit as he felt there was not a need to worry about the light.

We are going online with the project next week and I will let you know how it goes.

I really appreciate the fast turnaround on your comments.  They have been interested and, most of all, helped to ease my mind during the process.
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by:Rob Williams
ID: 18820295
By "normal 'gray' conduit " do you mean metal, or plastic? I assume metal as plastic doesn't meet firecode. The metal will definitely help, but only if properly grounded. By code it must be, but stress that with the electrician.
Good luck with it.
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by:Alan Huseyin Kayahan
ID: 18823713
              Gray one is the plastic one as i know.
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by:atroutcatcher
ID: 18824030
Yes, it's the rigid, gray conduit (I see it all the time in buildings in the area).  And most conduit in commercial facilities here is the same type (but of varying sizes -- as you would expect).

I placed a call to the local 'electrical inspector' and never heard anything back.  Will give them another call and see what I need to do (from a code perspective).

If acceptable to you guys, I want to leave this conversation open until next week so I can let you know the outcome of the testing (irregardless of the code issue for the moment).

Thanks again.  I gotta say, this service is great!
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by:Rob Williams
ID: 18824246
I only mentioned the "Gray Conduit" as PVC is Gray as well, but cannot be used in most exposed commercial applications, and it doesn't give you any shielding.

Electrical inspector will probably give you a hard time when you tell him it has to be properly grounded. Kind of like telling an IT guy to use passwords for security <G>. However, you can stress why you are concerned.

No problem to leave open. Let us know how it goes.
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by:Alan Huseyin Kayahan
ID: 18824899
       So the current status is, you have got a plastic conduit and UTP cable. You have to choose either shielding/grounding the plastic conduit which is not a common process, or change the conduit, or buy FTP cable and keep the UTP cable for further use.

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by:Rob Williams
ID: 18825203
I assumed that meant it was gray/silver metal conduit. You will have problems if it's plastic. However, I am doubtful it is plastic unless your fire codes are different than most.
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by:pseudocyber
pseudocyber earned 100 total points
ID: 19033516
Hi all,

I've been reading this topic with interest.  I've been through BiCSI's RCDD class and have just received my NC Electrical Contractor's License - Low Voltage.

So, basically, I'm not an electrical expert, but I did stay at a Holiday Inn last night ...

I believe the gray PVC conduit is referred to as RNC - Rigid Non-Metalic Conduit.  The silverish metal conduit is referred to as RMC.  From what I've read and heard, most electrical inspectors don't give a flip (to be polite) about low voltage cabling as far as inspections go.  

RMC trumps RNC - and since data cabling doesn't need to be installed in either one as far as the National Electrical Code goes, the inspectors don't really give a ... flip.  However, if RMC is used, it is supposed to be bonded to ground (which is different than grounded but meaning essentially the same thing).

I haven't heard of FTP.  I have heard of STP which is Shielded Twisted Pair, which can have a metalic type braid with foil inside.  I think it just really depends on the cabling.  And the shield should be bonded as well - but I think it depends on the installation procedures called for by the manufacturer.

Regarding grounding - since I studied LOW VOLTAGE I'm not an expert on grounding, but basically, all the metal infrastructure of the building (steel beams, metal pipes, ceiling grid, wiring, cabling, etc.) is supposed to be bonded to each other forming a path to the common building ground.  If seperate grouding rods are used, they in turn are also supposed to be bonded to each other, so that in effect, there is ONE building ground without potential differences.

I don't believe RNC does anything for RFI coming from the lights.  The advantage of using it, where called for by code, is cheaper, lighter, easier to work with, and you don't have to worry about grounding.

Hope this helps
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by:Rob Williams
Rob Williams earned 200 total points
ID: 19034499
Nice summary pseudocyber.
I think a lot of the confusion above is what is gray. If gray = metal,, and properly grounded/bonded it should eliminate most EMI. If gray = plastic, it my keep the wires from getting damaged by other contractors <G>. Around here we are pretty limited as to where we can use plastic conduit due to fire code regulations.

Here, NS Canada, we actually have a provincial code that covers communications cabling, that is quite particular. You have to be a certified cable installer to be able to run cable. You do not have to be an electrician, however as you say still quite a few electricians "don't give a flip" as they were grandfathered into the program.
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by:atroutcatcher
ID: 19120941
Ok.  The client has been running for two weeks now with the RNC and has experienced NO PROBLEMS related to the flourescent light.  Great news!

As for the code issues, possibly each case has to be handled separately?

Anyway, thanks to everyone on this.  Great input and discussion.
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by:Rob Williams
ID: 19120950
How do you know they have had no problems <G>
Noise from a fluorescent light causes packets to be lost. This typically slows network traffic. It can be minor, it can be major. Only using network certification equipment set to measure noise can you verify there is no risk.
However, glad to hear it is working well.
As for the codes; fire and electrical codes vary from city to city, country to country and so on. However, they should not vary case to case. In any code though, if using metal conduit, it must be properly grounded/bonded.
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by:Rob Williams
ID: 19120998
Thanks atroutcatcher.
Cheers !
--Rob
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