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Separation of Data Lines from Electric Lines

Posted by spafrica2003 (My Page) on
Mon, Jan 24, 11 at 10:31

I know I'm supposed to keep data lines (cable, Cat 6, etc) away from electric lines, but I don't know the details.
1) How far is a minimum distance to keep between electric and data lines?
2) Does this apply only to parallel lines or lines crossing at right angles as well?
3) Does conduit provide adequate insulation of the data wires?
4) Can I run cable and Cat 6 together or do they need to be separated too?


Follow-Up Postings:

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RE: Separation of Data Lines from Electric Lines

There is NO SUCH requirement either mandated by the electrical code, nor recommended by the standards bodies that set the rules for the cabling or the current popular networking protocols that run over it.

The whole point of using TP wiring is to design circuits that are resistant to such forms of interference. In practice, no matter how far away you are from the power wiring, absent conduit, you're going to get coupling to the power lines.

The only issues are when you run the low voltage wiring into boxes or other places where power wiring terminations are made. The low voltage wiring may not have insulation rated for that use (600V) and further you don't want to subject LV terminations to possibly coming in contact with higher voltages. While they make dividers, etc..., it's just better practice to use separate boxes for power versus phone and data.


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RE: Separation of Data Lines from Electric Lines

Perhaps I should clarify:
I'm talking about just running the wires through the walls of my home. I need to know what recommended (not code required) distance to keep my Cat6 and cable lines from my standard 110v 12-2 power lines running through those same walls. Also, does running cable and Cat6 side-by-side create interference with each other, or is it just power that causes interference?


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RE: Separation of Data Lines from Electric Lines

I don't know how to make it any clearer. There's no requirement nor recommendation (from any authoritative body) that 12-2 power wire and your cat6 data wiring need to be separated.


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RE: Separation of Data Lines from Electric Lines

I'm not a pro, but rather a long-time audio guy and electronics hobbyist. So some of the pros may disagree, but I base this recommendation on my own practical experience.

While code doesn't mandate any separation, IMO good practice calls for keeping electrical wiring and signal or data wiring at least several inches apart where they run parallel.

The problem is the possibility of induced noise in the signal or data cable. The electrical wiring will not be affected in any way.

There is little concern if the wiring is in a grounded metallic raceway, or if the data/signal cable is well shielded. Using thinwall conduit or AC cable instead of NM would take care of the problem easily.

I still wouldn't zip tie an unshielded data or signal cable to conduit, but otherwise you should be fine.

If you're using NM cable, in addition to the separation, I recommend a twist or two per foot in the electrical wires, to help cancel out EM radiation from them.


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RE: Separation of Data Lines from Electric Lines

Davidr, thank you. That is very helpful.


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RE: Separation of Data Lines from Electric Lines

And if low-voltage and electric cables need to cross, doing it at right angles minimizes the interference.


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RE: Separation of Data Lines from Electric Lines

Believe the golden ear nonsense if you like, but the fact is as I stated, nobody who has a clue recommends what David and Steve suggest. There is so much induced EMF in your house that all this voodoo they are suggesting (twisting the power lines, crikes) is going to do squat. The TP networking stuff is all already well equiped to deal with such.


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RE: Separation of Data Lines from Electric Lines

"If you're using NM cable, in addition to the separation, I recommend a twist or two per foot in the electrical wires, to help cancel out EM radiation from them. "

Twisted pairs are already that, twisted.

At about one turn per inch.

Twisting the power lines is not going to make any real difference.

Perpendicular crossing is only effective against magnetic field coupling.

Any communications system that is going to have problems with 60 Hz power electric and magnetic fields is not going to work well no matter what.
The fields are endemic in buildings from the wiring (though magnetic fields from power conductors actually cancel nicely at any reasonable distance).

Ballasts and larger electric motors are not nearly as nice, especially when they are turned off.
The collapsing field in the motor tends to put a lot of noise onto the power lines, with a frequency that decreases as the motor slows to a halt.

Low frequency noise is much harder to filter, requiring larger values of capacitors and inductors.

Coax with both braid and foil coverage is very effective at isolating noise.

High power magnetic fields are the hardest to shield.
If they are a low frequency it can take a very thick shield to have any effect (and better conductors like copper are more effective on time varying magnetic fields than poorer conductors).

A magnetic field can couple in to ground loops, but multiple grounds are required for effective electric field shielding at high frequencies.

In many cases what works for one type of coupling can make the other worse.


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