sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring genius of the day...

Maybe I'm missing something here. The inherent design of twisted pair cable is to vary the lengths of twists as a means to reject (cancel) power induction. It is also designed this way to minimize signal leakage (cross talk).

I can understand the potential for AC induction when cables are placed in close proximity to individual AC power conductors, as with service entrances, being run within the same enclosure/conduit, etc. Rarely are you ever going to see individual AC power conductors run within a building that are not enclosed within a conduit or approved cable jacket.

Granted, I suppose that it is possible that AC induction from non-metallic cable designs can occur, but still, that's a bit of a stretch. It is also not common to encounter AC power wiring enclosed in non-metallic conduit within buildings except under slabs. Commercial construction rarely involves anything but metallic conduit or cable use.

I just don't think that there is really that much of an EMF interference issue out there. You almost have to try to allow this to occur.

Using long runs of quad or cable with imbalanced pairs are a different story.

Ed, in theory you are correct. But residences are wired with Romex® and Sparky tie-wraps his Cat5's tightly to them in huge bundles. The residences here are sometimes in the 8,000 to 20,000 sq. ft size, with 1000 Amp electric service. Lots of wires.

In commercial buildings, metallic is called for by code, but inspectors don't go back a year later. If they did, they'd find non-metallic wiring, pvc conduit, plastic wire-mold and lots of other "expedients" all run right alongside the low-voltage wires.

Like I said, every time I move them away from each other, they play nicely. Maybe I've just been lucky. Your mileage may vary.

There are so many variables that what works in one case may not in the other. A good quality system with the proper installation can deal with a little noise. Where as a cheap switch, poor ground, pinched cable or bad connections will amplify any problems and may even cause them. I have experienced noise from AC line, florescent lights, welders etc. causing problems not only with data but video, audio and control circuits as well.

Hmmm, Ken I'm not sure if you read Arthur's post but it validated that you should NOT place communication wires near high voltage. Ken the NEC cares NOTHING about the telephone or Data world unless it pertains to SAFETY. You cannot read the NEC and figure out how to install telephone cabling any more than you can read a dictionary and learn how to write a book. You obviously have no idea who or what BICSI is. It is comprised mostly of volunteers who WORK in the industry. Its not a bunch of suits sitting around deciding things. These are real people just like everyone here who have worked in the industry and are trying to make sense of the crazy world we work in.

I know of actual testing that has been done using romex and CAT5 in response to these allegations. I wish I could find the link but it was years ago. The results were that no amount of current through a length of romex with the CAT5 ty-rapped directly to it for a long length caused any measureable data loss.

So I submit that, Arthur and Merritt, there are other factors at play. Certainly the fact that there was hum (in what?), disruptions to HVAC and music systems and lost packets or data in the network- all those things going on is very suspicious. Funny thing is that anytime the subject of running low voltage and line voltage together comes up somebody will pipe up with some anecdotal evidence that can't be proven.

Better read it again Tito. You are not correct. While a communications circuit extends to the utilization equipment there is no spacing requirement after the primary protector which needs to be as close as possible to the entrance.

And while you are at it notice that (according to the NEC) data is not a communications circuit. (Which I am in disagreement with.) The only place the NEC even mentions data wiring is under a raised computer room floor.

Mostly of IT types who romanticise IT.

-Hal

Wow, this thread was dead two months ago and now it is the hottest thing going!

Lately I have embraced the advice about "better to keep your mouth shut and be thought a fool than to open it and remove all doubt." But I am going to risk being thought a phool just one more time in order to add this:

60 hertz hum is really not the problem any more. More and more AC powered equipment these days spews great reeking gobs of RF noise back on to the power circuit it is connected to.

Just saying, is all.

Jim
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Speaking from a yadda yadda yadda.

Hal, You might want to give the code another looksee because you are incorrect on all of those points about the NEC code. Ive attached shots of the actual code for you to see that I'm not just pulling this stuff out of thin air.

In Article 800 page 70-669 a communications circuit is defined as

"The circuit that extends voice, audio, video, DATA, interactive services, telegraph (except radio), from the communications utility to the customer's communications equipment up to and including terminal equipment such as telephone, fax machine, or answering machine."



This excerpt is from the 2011 NEC

We then drop down to page 70-675 which covers "Installation methods WITHIN buildings"



We can then go to 800.133 which covers the "Separation from other conductors" Here we are told that communications circuits cannot shared space with Class 1 circuits and that communications circuits must maintain 2" of separation from Class 1 circuits.

Tito, I agree with you 100% about maintaining separation, but unfortunately the NEC does not actually have our back on this.

Re-read all the sections that you highlighted. Now re-read them again, but do it while thinking like a lawyer. It is an adventure in careful wording and loopholes....

Jim
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Speaking from a secure undisclosed location.

Jim I agree but unfortunately for us the NEC is nothing but a guide for the AHJ and ultimately it is their interpretation that wins. Instead of worrying about arguing we will maintain the separation and not have to worry about it at all. Reading this thing gives me a headache for sure!!

Also keep in mind that the 2" separation requirement is from class 1 conductors, not cables. Conductors are the individual wires that comprise a circuit, which are always contained within conduit or a cable jacket inside of buildings.

It's all about the definitions of their wording. It is also a continuous uphill battle to keep up with it.