Conflicting info, RG 6 & ROMEX®

Discussion in 'Electrical Forum discussion & Blog' started by kalanikaau, Apr 24, 2008.

  1. kalanikaau

    kalanikaau New Member

    Messages:
    12
    New construction, is it OK to run RG 6 cable adjacent to Romex cable?
    That is, in the same hole in the studs?
    Cable people (Time Warner) telling me it's OK, electrician tells me it's not.
    While I am not a IT geek, due to interference (stray signals and such) between each other cable, I would think that these would need to be distanced from each other..........
    Insight most welcome, Thanks in advance !
    :eek:
  2. Cookie

    Cookie .

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    5,660
    Location:
    .
    Hmmm, cable people or electrician. My vote would be the electrician. I always consider the source.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Good question, and we have some professional electricians who I am sure will help us out with current trade standards and codes.

    Many moons ago, ('60s and ''70s) I was involved in electronics in the Navy. Our guidline was that you avoided running signal cable parallel to electric wires within so many inches ( who knows now HOW many!). It was considered ok for a signal cable to cross an electric wire at a 90 degree angle.
  4. PEW

    PEW DIY Senior Member

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    487
    Normally 12 inches when running parallel.
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

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    2,531
    Location:
    North Carolina
    If we were talking about conductors then there would be a 4 inch requirement as outlined in 810.70 but we are talking about cables here and no separation is required.

    In spec houses I pull the cable, phone and line cables all in the same hole to save on labor and materials.
  6. alternety

    alternety Like an engineer

    Messages:
    650
    Location:
    Washington
    I would not (and do not) run signal level cables close to power lines. When you run wires close together (particularly parallel for some distance) there is coupling just like what a transformer does. The intensity of the field is a function of current in the conductor and distance. A little bit does not generally cause a lot of problems. A lot can. Twisted pair (e.g., Ethernet and modern phone) are designed to minimize pickup. RG-6, if used for RF signals, is not so critical. The things it carries are not really impacted by 60Hz. But the shield layers are grounded to the chassis of connected equipment. Any 60Hz signals induced into the shields will then generate "ground currents" between things like you cable box and the TV or receiver. If the signal levels are low, and interfering fields are high, there can be problems. Audible hum or bad packets of data.

    Now you have a choice- run them close together and if there is a problem tear open the walls and move them, or don't put them close together. In a large number, if not most, cases either approach will work. Good industry practice (not the electrical guys, but the electronics guys) is keep them apart.

    Pick one.
    Last edited: Apr 25, 2008
  7. BigLou

    BigLou New Member

    Messages:
    138
    i agree with all you said except this sorry to nit pick. The current will be induced on these wires just as easily as on any other wire if not a little more so. The key is that the many many twists per inch allow for equal induction on both conducts. Twisted pair equipment works by polling the difference between the two lines so as long as the current is induced equally its a not really a big issue.

    Lou
  8. alternety

    alternety Like an engineer

    Messages:
    650
    Location:
    Washington
    Yes, the inherent balancing helps reject power line (and other) uniform induced current. The twisted pair must end in a transformer or a circuit that can reject the induced current. Transformers are also an easy way to isolate the cable wires from external voltage sources (e.g., a short from the power line running across it) or common ground loops between equipment.

    Once upon a time I was asked to evaluate a twisted pair networking system (before Ethernet was real widespread) before it was adopted as a company product. It did not work very well and I warned them that the cable conductors were not isolated from equipment ground. They ignored everything I said, and started buying them. They took my test system over to manufacturing and they set it up in their lab. Worked as well (badly) as it had for me) and then they added one new station. They blew/burned holes through every network card in the system and trashed many of the PC mother boards. The last PC was plugged into an outlet that was connected to a different distribution power transformer. Ground voltage difference caused hundred of amps to flow. This is why you have to be real careful about knowing how grounds really behave. You usually don't run into this in residential because code specifies only one earth ground and everything is usually coming from a single transformer. But in commercial and industrial settings this can happen if they are not careful.

    The twist helps to cancel the induced current between adjacent twisted pairs. This characteristic is why the twisted pair works so well at high frequencies with multiple signals in the same cable. Twists are a function of the wavelength of the signals for which the cable is designed. If you look closley at cat 5 you will see that each pair is a different rate of twist. This is to enhance the cancellation between pairs.

    The regularity and tightness of the twist and the orientation of the pairs is extremely important to high frequency performance. That is why you should never stretch (hey Bob, its stuck, pull harder), pinch (e.g., staple improperly), or bend below a prescribed radius for twisted pair or coax. Much of the signal deterioration in things like cat 5 occurs where the pairs are untwisted to install connectors. You have to untwist the absolute minimum amount of wire and use the shortest possible lengths to get to the connector. It really matters. These points may not be well recognized by everyone string the "low voltage stuff".

    If you abuse the cat 5, it may work at 100 Mbps, but not well at 1000 Mbps. Ideally you should test all cables before you close everything up for frequency response and continuity.
    Last edited: May 6, 2008
  9. kalanikaau

    kalanikaau New Member

    Messages:
    12
    They will be run seperately
  10. Marv

    Marv New Member

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    24
    Location:
    Northern Illinois
    I'm not an electrician, but I believe it is against the electrical code to run them thru the same hole.
  11. alternety

    alternety Like an engineer

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    650
    Location:
    Washington
    That is also what I understood. I do believe that when I looked for that in code it seemed to be OK if the low voltage wire had at least the voltage rating of the high voltage wires. I am not sure either way. I always keep them apart.
  12. jparrie

    jparrie Automotive Locksmith

    Messages:
    17
    Location:
    California
    Imagine a nail being driven thru both cables. Don't think you want 120vac running thru your RG6. Seperate them.
  13. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    It's not, its quite legal.
  14. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    I dont do what if's... we'd be here all day. ;)
  15. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    Do you guys separate your low voltage and high voltage after your wires leave the wall? Its pretty hard once all the wires connect to the back of the equipment. :rolleyes:
  16. alternety

    alternety Like an engineer

    Messages:
    650
    Location:
    Washington
    I certainly don't bundle them together when they are out of the wall. The key to picking up junk has several parameters. Distance between conductors, current level and patterns of the power wires, length of close parallel proximity. And as I recollect it drops off as the square of distance. If you have to cross a power wire in the wall, make them perpendicular.

    Once you get out of the wall it is fairly simple to keep them a bit apart. The thing that helps is that the amount of length where they run close and parallel to each other is short. If I was wiring a rack I would route them as far apart as feasible. The currents in those wires going to equipment tend to be lower than the aggregate from a bundle of power wire in the wall and will pretty much be limited to under 20 amps.

    If anyone insists on using the same hole for HV and LV you could get them away from each other after the hole. But that would mostly just use more copper than doing it right in the first place.

    I would suggest talking to any electrical contractor who is being hired to include LV wiring in a power installation. If a complete understanding is not reached about how to route and handle the LV wire; hire someone who specializes in LV. Let the HV guy go first. And the plumber.

    In the same vein; beware the drywaller. Make sure they understand about the LV wiring. If you have your wire rolled up in the electrical box, there is a real good chance they will cut it off when cutting out the box opening. They put up the wall and then roto-zip the hole. Mark the wires and then put a protective layer over the markings that can be removed after painting. A little baggie on the wires will keep the spray paint off. If no protection is provided or just in case use the little marker tape that you can buy for this purpose and wrap it a couple of times. Later just unwrap some and it will uncover clean numbers. Keep as much wire as you can outside the box (in the wall) but be sure to anchor it to the box so that you can find it and pull it into the box when you need it. Use the open backed boxes as much as you can. Much easier. I like to put two labels on the end. One near the end (far enough back to strip without destroying) and another back further just in case the end gets damaged. If there are few and easily identifiable wires in the box, you don't need two labels.

    Obviously you need to thoroughly label and document what wires went where as you install them. Do not use any fasteners that pinch (e.g., staples not made for this purpose) or put tension on any of the cat 5 or coax. Don't make sharp 90 degree turns. Don't apply more than the manufacturers specified tension when pulling any of the wires (yes, there is a spec). Do support the wires. Pinching the cables can cause ghosting on video and errors on Ethernet. If you need to bring LV and HV into the same box you need to use a separator made for such installations to keep them apart. The LV signal wires can be bundled.
  17. edlentz

    edlentz New Member

    Messages:
    70
    Location:
    Michigan
    In Michigan low voltage and 120 volt or more cannot occupy the same raceway without a separator. I have run low voltage for over 25 years. I have never heard of an electrician or inspector who would allow the two to be run together like that. Just my 2 cents.
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