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Old 09-17-2003, 07:47 AM   #1
Gilion
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Electro Magnetic Interference in UTP


Hi,

During my network setup I came accross a problem, probably related to electro-magnetic interference (EMI) in my UTP ethernet wiring. (UTP cables function at my desk, but not below my desk). I haven't been able to find sources about this topic, and still need some answers.

Is it correct that UTP wires are extra sensitive to EMI when placed in loops/coils?

Is the fact that no network traffic is possible, the only way EMI will be recognized?

What happened to STP (shielded twisted pair) wires? Somehow, none of the shops around selss STP. Is EMI that erelevant?

I read somewhere that cat5 UTP wires should be at 12'' (=30,5 cm) from electrical power lines. My box doesn't enable me to put my ethernet interfaces at that distance of the power unit in the computer. What are my options?

Are there guidelines for placing UTP wires reducing the possibility of EMI?

Any tips are welcome.

Gilion
 
Old 09-17-2003, 08:37 AM   #2
Paul_assheton
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Looks like you have a real problem there somewhere. I cannot tell you answers to all you questions but I can tell you something about my own experience. I networked the office up with Cat5. Not quite knowing what I was doing at the time I just draped the cables through the false ceiling (allowable in this country). Not having thought about EMI I ran the cables right over the fluorescent light fittings. I had no problems. The cables quite happily ran at 100mb. The cables also criss crossed mains cables and here they are 230v also with no problems. Our new office has a network wired by professionals and that has CAT5e running in the same conduit as mains cables. This carries gigabit without any problems. We also have a mobile phone mast on the roof. Even this causes no network dropout. My whole point is that under your desk you must have one hell of a EM source. I would think about moving your desk before you legs cook.

Paul
 
Old 09-17-2003, 09:19 AM   #3
Gilion
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Well, I've placed the server which I am setting up in a cupboard, inwhich there is also stereo incl. a audio cd burner. On top of the cupboard I run my laptop, tv, video and the monitor linked to the server. So there's lots of wiring.

Whenever I place the utp cable of my laptop allong the outside of the server, the laptops network hangs. Simply relocating the utp cable starts the network again. Both, the newer and older wires invoke this 'phenomenon'.

Simply relocating the server is not option in my rather small, student accomodation.

Gilion
 
Old 09-17-2003, 09:34 AM   #4
Paul_assheton
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Do you run the server with the case off? With the case on the server should be encased in a Faraday cage and very little EM should get out. This is why plastic computers like Dells (spit) still have metal sheets on the inside of the plastic. If the lid is on then check that the power supply is properly earthed to the case. If there is still the level of EM leakage that you are seeing then the earth point on the wall socket may be bad. You should get the landlord to look at it. They will probably do this no problem as frying students is bad for business plus leaves a nasty smell that takes ages to go. In the old office I had about 8 computer stacked in a heap (quite literally they where on top of each other) because we did not have room for a server room. They all functioned fine.

Paul
 
Old 09-17-2003, 09:47 AM   #5
Gilion
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I think this is getting somewhere. The computer isn't connected to a socket with an earth point.

A quick look around in the building brings up the fact that only the sockets in the kitchen have earth points. Oi, oi.

The fact that the computer is about 10 years old makes this EMI assumption even more likely I guess.

Now what?

Getting earth points will probably take a couple of years, given bureaucracy.

This seems to be an ending path. Any other suggestions?
 
Old 09-17-2003, 10:02 AM   #6
Paul_assheton
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You are in America?

If so suggest that you have been getting electric shocks of appliances lately. Suggest that the electrics are not safe and 110V is a lethal voltage. Have you got any friends on campus who are doing civil engineering or something similar who you can get safety advice from. Suggest that if some one is hurt or killed by an unearthed appliance that the housing agency or whoever runs the accommodation my get sued. If you have any friends doing legal studies the so much the better!

On a more realistic note if you have an earthed extension lead try plugging your server into one of the outlets in the kitchen. See if this cures the problem. If is does then you have your problem if not the you have to look else ware. Note: plug all the appliances that are near to the server as well to the earthed lead.

If it is lack of earthing that is causing you your problems and you are not likely to get earthed outlets then you will have to earth you computer some other way. If you intend to do this I recommend that you find a friendly electronics student to advice you as there can be some safety issues with this.

Paul
 
  


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