Fluke "noise detected"

[lopes1211]

I have a bunch of cat-5 runs which are passing yet yeilding "noise detected" during NEXT via a Fluke DSP4000. All of the documentation states this is voltage spikes on the line caused by alien crosstalk and/or EMF/RF interference. Many cat-5E replacements were pulled to the problem areas and fixed some of the runs (all runs are about 100' BTW). All cables also seemed to work fine for the last 3 years and now suddenly are have all sorts of network issues. Short of rerunning everything with sheilded cat-5, does anyone know of anything to rectify my situation?

-CL

 

[AvayaNovice]

What are these runs next to? How are they supported? Are they in conduit? Give us full details on the path they take. You may just need to move them away from devices that can cause such interference, or you may need to place them in some type of raceway that would provide more protection. Shielded cat5 may fix the problem, but may also be an improper solution.

 

[Servamatic]

Since you mentioned Alien Crosstalk, are the cables nice and neatly bundled and zip-tied?
AXT is from adjoining cables or cables that run parallel to cables for more than a few feet bundled together.
Fluke DSP 4000 tends to be rather sensitive to noise issues.

BTW, they don't make a shielded Cat5, it is a screened Cat5 known as ScTP instead of UTP. True STP or Shielded Twisted Pair is Token Ring or IBM Type cables which have the pairs individually shielded and an overall shield. Screened is just an overall foil and drain wire which is referred to as FTP in Europe where it is very common.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[AvayaNovice]

Doesn't the screen act as a shield from outside interference?

 

[lopes1211]

The runs were installed on j-hooks a good 4' above the ceiling, ballasts, etc.. There are about 150 cables in the bundle leading 65' down a straight hallway where they then split off to feed banks of 8 cubes each. I don't see any "tight" cable ties but I did see 1 point rounding a corner where the entire bundle appeared to be twisted about a 1/4 turn. I had 12 new runs pulled to the worst area and about 9 of the 12 new ones do not have "noise detected". The other 3 do and continue to have network issues. These were run along the same route as the original cables but I don't believe they are cable tied to the main bundle or zig-zag in and out in any way. Any advise would be appreciated.

-CL

 

[Servamatic]

So when you said "where the entire bundle appeared to be twisted about a 1/4 turn" does that mean the cables are all neatly bundled together? So neatly that a little twist looks out of place? How often are they zip-tied? Whether they are tight or not...
It sounds to me like you are creating your own AXT problem.

Cables should NOT be bundled so that the cables run parallel for any length greater than about 5 feet. Over than distance and they can begin to talk to each other..."Alien Crosstalk" which is what your documentation was telling you.

I know installers want "pretty" bundles, but it can hinder performance.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[Servamatic]

Much of this was discussed and there are some links in this thread...

thread575-683788

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[Bobg1]

Lopes, since you say this is over 3 years old, most likely you should be able to rule out the install itself.
Looking away from that, Has anyone else been doing any type work in the area recently that might relate to when it started? This could be as small as replacing a light, flourescents can be very noisy, especially with the newer solid state ballasts. A dimmer switch can also generate a lot of noise. Did the problem happen to coincide with the start of the heating (or cooling) season? You might look toward any reheat coils and/or boost pumps that could be in the area.
You might try walking through the area with something as simple as a portable radio to see what noise you can detect.

 

[lopes1211]

I'm going to have my vendor retest on Saturday when all of the PC's are shut down. Hopefully this will help isolate if the issue is AXT or some other interference. All of the mechanical systems should still be 100% operational so if the trouble goes away on Saturday (PC's off) and reappears Monday (PC's on), it may point to AXT.

-CL

 

[Servamatic]

Why would you think you could rule out the installation?
I certainly wouldn't given the changing nature of networks.
If the client is adding traffic, or has replaced 10BaseT NICs it could most certainly be the install. Especially since it sounds like they are elevated above the grid quite a bit.
While you make some valid points, never rule anything out till you have verified it. Automatically ruling things out can lead to lots of tail-chasing.

Richard S. Anderson, RCDD

http://www.smartbuilthomes.com

 

[technome]

Please read the definition of NEXT before you talk about wires near ballasts, dimmers etc causing noise in cat5.

http://www.cabletesting.com/CableTesting/Testing/Definitions/Definitions_NEXT.htm

At the termination ends are your wire twists maintained very closely?. The noise cancellation ability of quality cat5 is very good as long as the twist is maintained. Twisted wire cancels extraneous signals, but small lengths of untwisted wire picks up noise readily.

Personally with the tester you have, I would worry only if your tests pass intermittently on the same wire. I had situations where the Next was just barely passing, on a redo of the test the test would fail. I would re-terminate the wire.

Rarely have I seen this over multiple wires in an installation, the worst I have come across was an installation which was wired with PVC cat5 from HomeDepot, probably just a batch of crap wire. By redoing the terminations I was able too get the wires passing, on multiple tests per wire

From a previous post I made at another forum.....

Worried about emf pulses from nearby lightning strikes, power lines, lighting fixtures affecting cat5 wire...

I have a client where very high current welding proceeded for 1 week, no more than 6 feet from a bundle of 28 cat 5 cables( in an unshielded wood raceway), much of the welding occurred within 12 inches. The server was also within 6 feet. End result, not one computer in the system had any machine or program lockups, no data errors.

This situation occurred in an office structure built on a large steel barge, located in the New York harbor. The wire were running parallel, for the full length of the structure, to the welding. Every monitor in the building was suffering from the constant emf pulses from the welding arcs, the screens would actually become unreadable. The owner became worried about the monitors fading in and out. After 4 days of welding, he called me to the site.
If I was asked about the situation before the welding started, I would have advised him to close shop for the week. But after 4 days, I actually had full faith in the wire twist cancellation; I was more concerned with the monitors surviving the week.