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By mowen ·
I have run across a little problem and was wondering if anyone had info for me. I know what the problem and solution are I just need some distancing or shielding info.

I have 2 star LANs and an uplink between them. The problem is the cable for the uplink between the 2 hubs is running parallel to a 220-power line.

What I need to know is how far away from 220 to run the cable or if anyone knows what kind of piping would be good to use for best shielding standards.

Any info would be greatly appreciated.

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Clarification please

by mike.keighley In reply to Cabling

As a general rule, 2 or 3 cable widths separation, without sheilding, should be sufficient to avoid EM interference.

A few questions please, before I can answer intelligently:

What type of data cabling (e.g. Cat5 ?)
What length ?
What type of traffic (e.g. 100Mbps ethernet ?)
Indoors ? Outdoors ? Hazardous environment ? Any building codes to be observed ?

Just for interest's sake, how have you arrived at the conclusion that mains interference is the problem ?

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by mowen In reply to Clarification please

Not sure what you mean buy 2 or 3 cable widths, please clarify. Also, any idea of type of piping, certain type of pcv, lead, straight metal, etc.

Using Cat5 UTP at about 280 feet outdoors through a pcv pipe about 18 inches from 220-line at 100mbps ethernet with a repeater attached somewhere in the middle. It parallels it for about 30 feet. They are running a lot of welding equipment.

About every 50 to 100 feet I have a junction box. I ran the cable to each one and tested until it crashed and it crashed when I ran it parallel to 220s.


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much clearer now !

by mike.keighley In reply to Clarification

by "2 or 3 cable widths" I mean that (in an ordinary domestic, office, or light-industrial environment) it is sufficient to separate the cables by a mere 2 or 3 times the outer diameter of the cable, in order to avoid thermal and EM effects. Your 18 inches is generous spacing.

on the other hand, you are working in a heavy-industrial enviroment, and that welding gear is a prime candidate for EM interference, I agree.

any metal piping will do for screening; lead, copper, steel, alum; square, round; as long as there are no "holes" for EM radiation to leak into.

so not only the piping but the junction boxes, the case enclosing the repeater, etc. must all be metal, and in good electrical contact along the full length.

here in UK, electrical regulations would also dictate that the piping be permanently bonded to an electrical earth (which helps with the screening), and it is advisable to consider lightening-surge protectors at the point(s) where the conduit enters the building. USA regs may differ.

I would recommend that you also consider other possible entry routes for this interference, e.g. :

poor quality twist where cable meets connector, causing near-end-crosstalk (NEXT)

EM interference entering via the electrical supply. Does that repeater draw power from the same distribution as the welders ? an RFI filter on the mains plug, perhaps ?

A hand-held fast-ethernet tester from such as Fluke would help to detect noise, as well as test for NEXT.

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oops, forgot to add ...

by mike.keighley In reply to much clearer now !

poor quality earthing on the cases of, or on the mains supply to, any of the hubs repeaters etc.

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CAT 5 UTP limitations.

by wpteh In reply to Cabling

See if you have exceeded CAT 5 maximum wire length per segment (100+ feet). Normally we only lay 80% of the max allowed length.

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