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Discussion Starter · #1 ·
I'm replacing some wood paneling with some drywall and want to run some wires while I have access. The area where I want to run a coax cable and speaker wire has power lines running parallel to the floor about 20" off the ground. The outlets seem to be at about 13" (mid-point) off the ground. I've read in this forum that I should stay 18" away from power lines, but I think it was for parallel runs.


Is it ok to cross the power lines and put the new gang boxes at the same height as the others (with 3/4" conduit)?


Another question, should I keep the speaker wire separate from the coax?


Thanks for helping out a wiring newbie.


-- Jeff
 

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Speaker-level signals are relatively immune from induced noise. Conduit is not necessary, and sometimes bad. Crossing power wires is no problem, even for coax. Just avoid parallel runs within a few inches and for several feet.
 

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It is fine to keep speaker wire and RG6 together. Just try to keep the low voltage wire away from the romex (electrical) wire, some say 18" away. Larry said it well about crossing high volt cable and I agree, avoid conduit.
 

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Discussion Starter · #4 ·
Thanks a bunch for the responses. I haven't heard to stay away from conduit before. Any reason why or link to some info on why? I am just curious. I guess I'll go ahead and run what I can without conduit and install the conduit for future runs.


Thanks,

Jeff
 

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Another question: In my neck of the words, I have to use conduit (thin-wall) in my basement for the electrical (i.e. no romex allowed). Does this thin-wall conduit limit the amount of interference that is often caused by running HT cables (e.g. audio, video, etc.) too close to electrical wiring?
 

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Conduit is common in most ares for romex (high-volt cable), but there has been a debate in the low volt world as long as electronics about it's use in prewire. I just saw a discussion on it a month or so back in the forum. I wish I could find some evidence on why, or why not. I believe it was the use of steel conduit that cause impedance issues, but PVC is OK. If you go to www.lsdinc.com and ask for Dan he knows all. I will research this this weekend and try to find if this is a myth, or substantial. Every home I have prewired, whether being trained by bigger companies, or wiring on my own have not use conduit. A couple of times I use conduit under side bores with RG6 when I was with Adelphia. On time the homeowner had about 100' of conduit and some rope in it to pull cable to his home up a mountain below Pikes Peak.


The general rule to avoid EMI/RFI is try to keep low volt 18" away from romex, the thin walls could possibly bring the distance too close. I will check out the use of copper pipe as conduit as well, I have heard good and bad about its use.


Larry, do you having anything on this? Do you remember that thread on conduit?
 

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Discussion Starter · #7 ·
Thanks again for the comments. I just like to learn the "why" part whenever I can :)


FYI - the conduit I was going to use was the 3/4" grey PVC.


-- Jeff
 

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Okay:


PVC conduit will have no electrical effects, either good or bad; it's purely a physical protector (and a provision for pulling wires behind finished walls). It won't reduce interference either from within or without.


Steel conduit (whether EMT or rigid) can protect from interference both from within and without, but can cause inductance issues with low-level signals. I would only use it for power wiring, and if required.


Definitely do not use copper or plastic plumbing pipe as conduit, ever. Besides legal issues, the fittings do not provide for wire-pulling; only sweeping conduit ells do that.


18" clearance is overkill for most wiring methods.
Quote:
Originally posted by nzkiwi71
Another question: In my neck of the words, I have to use conduit (thin-wall) in my basement for the electrical (i.e. no romex allowed). Does this thin-wall conduit limit the amount of interference that is often caused by running HT cables (e.g. audio, video, etc.) too close to electrical wiring?
Yes, it helps, as long as the conduit itself is properly grounded. If it is used as the grounding conductor, as it usually is, then it already is grounded.
 

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Larry, thanks for the clarification on conduit. I was trained at Hi Fi Sales, Az and they taught 12"-18" away from Romex is safe to avoid noise, I have heard this distance is standard from others in the industry. In your opinion, what is a safe distance to segregate low volt from high volt cable? 6"?


TIA
 

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6" is a good distance. The farther the cables (power and LV) must run parallel, the farther they should be. Do not worry about bring them within an inch or two where they emerge at plates and behind equipment.


Theories are fine, but the reality is that there are all kinds of cables in every building, and are often very close. After all, aren't power and signal wires within inches inside and outside most electronic equipment?


Even a power transformer, with it's flux-concentrating core, is tolerated. Shielded cables (such as coax and interconnects) and twisted-pair cables (such as CAT-5) are designed for use in electrically-polluted environments.


The current, not the voltage, traveling in a power cable determines the strength of the electro-magnetic field around the cable. There's probably more electrical noise coming from within your AV system than from without.
 

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Very good point. 6" is fine then. And you are right, there are many times that low voltage wire crosses and sometimes has to touch the romex. I guess the key is to try and prewire LV away from it when you can.
 
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