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data/voice

Posted by jerseybob (My Page) on
Fri, Dec 3, 10 at 15:32

Trying to do a little research for work. What are the spacing requirements for data/voice from house electrical wiring? Concern is from an electrical interference standpoint.
Tried looking online but didn't have any luck.
Thanks.


Follow-Up Postings:

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RE: data/voice

Data isn't usually going to care. Analog voice isn't that succeptable either, but most would try to keep it a foot or so away. If you're using some digital (IP or otherwise) phone system, again it's not usually an issue with separation from power.


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RE: data/voice

But is there some requirement for spacing to meet code?


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RE: data/voice

Don't put them in the same junction box.

Even that is OK if the box is divided so that the low voltage and line voltage circuits are physically separated.

I consider it good wiring practice to maintain several inches of separation between power and control/data lines that run parallel. Others don't seem as concerned, so take your pick.


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RE: data/voice

"But is there some requirement for spacing to meet code?"

None.

The only time spacing comes into play is if the wiring is in the same wiring method (conduit, cable tray, etc.) and even then the rule says insulation must be adequate.

If they are present in the same junction box they must be separated by a suitable barrier.

Any system that cannot cope with all the 60 Hz electric and magnetic fields all over the place is not going to work well.

Twisting and shielding works (even within a cable assembly).


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RE: data/voice

there are code requirements. 18in when run parallel, should only cross perpendicular.


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RE: data/voice

While there are code requirements regarding certain aspects of the interaction of low/high wiring and equipment, distance between cables for the purpose of interference is not one of the. There are "commonly accepted industry practices" but they are not code.

These include such things as: when possible, try to keep cables them at least a foot apart, or in separate stud bays, cross only at right angles, if you have to run close together, no more than 3 feet. Whether building an equipment rack, a studio, or a house, it's just good practice.

While analog audio/video is much more susceptible to interference from AC lines, digital is not totally immune. The difference is that most digital signals have ECC (error correction coding) built-in and do not display an immediate result. However, the cumulative effect, when combined with other sources or error, can push it over the edge.

I think this is an area that can not always be dictated by code as much as by common sense.


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RE: data/voice

jmorrow's statement is one of many general recommendations.

AFAIK, it is not any sort of code.


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RE: data/voice

hmmmmmm.... i must have lost my mind. i could have sworn the minimum separation was 18in but in fact code only requires 2in. sorry about that. check 2008 nec 800.133a(2) as well as 830.133a(2) if necessary. now im driving myself crazy trying to figure out where i got 18in from if it wasn't from the code book haha!


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RE: data/voice

jmorrow, 18" is one of the most common recommendations I've heard, so I'm sure you got it from multiple places. :)

800.133a(2) exception 1 allows us to ignore the 2" rule if the power wiring is in (blah blah), nonmetallic-sheathed, type AC, or type UF cables... so romex (NM-B) is thus excluded, and doesn't have to be 2" from communications.

Exception 2 lets us run them next to knob&tube too.

830.133a(2) has similar exceptions.


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RE: data/voice

"there are code requirements. 18in when run parallel, should only cross perpendicular."

Citation?

Good luck finding one.


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RE: data/voice

He did, it just doesn't apply as long as we're using any real-world wiring method. :)


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RE: data/voice

"He did, it just doesn't apply as long as we're using any real-world wiring method."

In other words, there is NO REQUIREMENT about perpendicular or any other separation applicable in the real world.

This reminds me of how when the coax used for cable TV was really cheap junk so a 'rule' was used to keep the lines away from AC power (and cross at 90 degrees, etc.).

The coax barely had 40% braid coverage.
You couldmake tuned stubs with a piece,then put a wad of aluminum foil on the cable and slide it back and forth for final tuning.


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RE: data/voice

In other words, there is NO REQUIREMENT about perpendicular or any other separation applicable in the real world.

Exactly what I was hinting at :)


You couldmake tuned stubs with a piece,then put a wad of aluminum foil on the cable and slide it back and forth for final tuning.

We used to do that in the correctional system to get HBO. The local cable company's method of "scrambling" the signal was to broadcast a really strong "beeping" signal right next to it so the TV's AFT circuit would lock onto that instead of the actual video signal. Someone figured out how to make a crude notch filter out of a roll of coax and a splitter.


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