Cat5 cabling and interference.
 

I spent a day last winter fishing cat5 cable up from the basement to the 2nd floor. It works great. It was a real pain in the ass to do, so I fished a string along side the cat5 cable in case I needed to use the same path again in the future.

Well, it's the future now, and I feel like putting a light in the ceiling above the kitchen sink, because it's really dark there at night when cleaning up after dinner. As you stand at the sink you cast a shadow over the sink.

The location of the light would be right next to where I have this string in place already. Can I pull some romex through the same path as the cat5 cable to power this one light? I know it's not the best practice to put data cable next to power cable, but in the real world, is it ever really a problem? The two would share the same one inch hole going up from the basement into the stud cavity on the first floor, then they would be a few inches from each other in that cavity for maybe 9 feet, and get pulled back into close proximity again as they penetrate the second floor.

Can I get away with this? If it turns out I have to fish the power cable (romex) separately, I probably won't bother. It's a huge pain, and involves asking my wife to empty her closet while I drill around in there.

How susceptible is cat5 (actually I think it might be cat5e) to interference in the real world?

I was curious about this so I did some research.

They say interference will never be a problem if the cables are separated by a foot (30 cm).

Because TCP/IP does error checking and retransmits data, a cable with interference on it may never be noticed. This may be why there is no real world data. Modern switches don't even measure error rates and such!

Current is more of a problem than voltage, and just running a light is almost nothing.

The very worst problem is what happens if an errant nail manages to pierce both cables and send line voltage down the data cable. As long as you are willing to take that risk, I think you get away with this 100%.

I'd also hazard a guess that you'll never notice if it were creating interference: given you'll have local error correction (interference would register as corrupt frames, right, and you'd get retransmission between your computer and your switch/router? it's been a few years), and given that your bandwidth bottleneck is probably whatever your outside internet connection is, which is way way lower than the theoretical max of cat5.

If you test it with a few clamp lights before you go crazy wiring the light, what's the worst that could happen?

<hill>Hold my beer and watch this. </billy>

Thanks guys. That's really helpful. I'm going to do it. You know, eventually. When I get around to it.


I found plenty of stuff on the web about best practices, but the real world is often different, and I knew nothing about the data error checking. That's pretty cool.

I'm not an expert, but I think if you want to be double-sure, you could pull the electric wiring through in some kind of flexible conduit.

Here you go. Better get started. :D

http://1.bp.blogspot.com/_TBA7qgQfRQ.../tuitround.jpg

I got the nickname "Bare Wire" last semester when I borrowed a friend's brand new leatherman to cut a wire. I had chosen it after plugging in a crappy little lamp to check that the wire worked, got distracted by the silly blue bulb that had stringers of silicone hanging off of it, said "this'll do fine" and went snip.

The circuit breaker kicked in just fine, but not before a good chunk of the cutting surface on the pliers part of the tool was removed.

I stand by what I wrote in re: interference, though.

My husband brought down the power on his whole side of the dorm, back in college. Good times, good times. :thumb:

not sharing my stupidity on this subject :headshake

I've got plenty of stupidity to share on the subject. Multimeters smell bad when you fry them, and if you stick the cables in the wrong holes in the voltmeter, you can fry them in a hurry.

Also, it's good that screwdrivers have plastic handles. Very good.

But that's how you learn.

I am utterly terrified of electrocution.


When we were selling our last house, the inspection report showed that there was a missing nut somewhere inside the main box. (The inspector when we bought the house apparently didn't notice the lack.) A bit of calling around determined that to correctly replace this nut, we'd have to shut down power to the whole house from the street, which required a goddamn city permit, not to mention several hundred dollars in electrician's fees.

So instead, we bought a $30 pair of electrician's rubber gloves on the internet, a stupid 10-cent nut from Lowe's, shut down the breakers, and Mr. Clod put it on himself. Everything worked out fine, but I kid you not, I was standing there with a wooden chair ready to beat him back from it if it started electrocuting him.

Then the lady buying the house wanted to see an electrician's receipt. :rolleyes: We told her it had been packed, and sent a digital photo of the new nut in its place instead.

Glatt, I sugest you do a test run outside the wall cavities.

Get some lengths of power cable and Cat5 cable, arrange them along the floor in about the same proximity as they will be when installed, connect them both up, and see what happens.

There comes a point where testing is more time or trouble than it's worth and you have to just give it a shot and see what happens.

Have you already bought the romex, Glatt?

Good workmanship says they should have different holes. Pragmatism says it makes no different electrically. Just do it because I said so.