atcomsystems.ca/forum Forums VOIP Phones & IP PBX Networking Cabling myths

I recently attended a refresher class on Cat5e/6 cabling. It was put on by Hitachi Cabling. The instructor was a member of the TIA & IEEE standards boards, so basically one of the people responsible for implementing cable standards. One thing that she(yes she, very sharp by the way) mentioned as a big myth was how power affects data transmissions. We were informed that power has no affect on data. It runs at a much lower hertz, and affects the positive and negative voltage equally, thus canceling it out. I specifically asked her if she was telling use that having cat5 cable in proximaty to power does not affect it and the answers was no. Kind of goes against what they have been telling us for the last 10 years, but this was from the source, so I gotta beleive her. She did say locating equipment such as switches and servers close to transformers and such could cause some noise, and also the main reason to aviod Cat5 and power contact was for safety. She told me would send me a white sheet that address the subject. When I get it, I will post a link.

That's interesting.

I'm definetely not an expert but...

Power runs in the 50/60 hertz range, whereas data transmission over twisted pair cabling is in the megahertz range.

And as far as the negative positive thing, I think that's in reference to phase cancellation.

I think the magnetic field does indeed have an effect, but moreso on terminations than runs. The twisted nature is important to keep up to the termination point.

Hmmm,

Ever try using a cable that runs directly over the top of a light ballast? How about one that is near a welder? I've even seen excessive noise on cables that paralelled power lines going to 2 hp motors that had brushes going bad.

IMHO I just don't believe it based on field experience. Relocating the CAT5 in the above situations has worked for me many times.

I don't think the problem in the above cases were actually caused by the power itself, just that the strong magnetic fields involved DO have an effect.

Had a floor fan in our office that caused all kinds of bad spiles on the AC wiring. had to throw it out. Also if you have a dimmer switch the SCR's cut the AC sine wave off at mid setting causing all kinds of hi frequence side band on the AC. The AC power is not the problem, its what you connect to it.

Hey Z-man did you ever get that white sheet??

Main problem when voice or data cables are run too close to 240v A.C (In Oz) or above(415v) is EMI -Electromagnetic Interference -If separation issues are ignored ,equipment may work quite well and even test OK while there is no load on the power cable.But turn on a welder,Bench saw etc and watch as the PC's attached to the outlets at end of these cables start to crash,digital system xtn phones start having heart attacks and watch the tech who ran the cables without separation, start headbutting the concrete floor.He has just cost himself heaps of time and more importantly, dollars ,having to re-run all the cables,which of course are now too short and will all have to be totally replaced.

MAINTAIN YOUR SEPARATION AND MAINTAIN YOUR SANITY!!

I can't see how inductance can be disgarded. We had an issue in a hospital years ago that was intermittent. Sometimes it worked fine, others every connection would time-out. We followed the line through the ceiling of two different buildings and then found where it was draped over an electric motor that didn't run all the time. Once we moved the line, the problem went away.

A little different situation but any of your Inter-Tel guys remember having trunk lines too close to station lines on the Premier. Every time the phone would ring you'd lose the station connection.

Similar to MacGyver's issue, I had one PC in a hospital that would drop from the network intermittently. Took a while, but we found that the cable had been run directly on top of a fluorescent light ballast in the maintenance storage room below. When the guys went in and turned the light on, the PC would drop.

In another instance, a local optometrist built a new office with open floor plan, where he let the electrican pull the data and phone lines. You guessed it: "Sparky" pulled phone and data through the same conduit as the electric under the concrete slab. We can run the network dependably at only 10mb/half duplex.

On the other hand, we do some large-scale data centers where we have the patch panels on the same racks as the servers. I have data lines (5e) running in the same management and across the same ladders with both 110 v and 230 v power for the servers with absolutely no problems.

We are meticulous about maintaining twist to point of termination and, where possible, do maintain a seperation between power and data lines.

Wonder how Sparky got the inspector to pass ac running in the same conduit as voice and data? Dangerous!!

We could start a whole new thread on inspectors!