Connecting low-voltage conduit to electrical boxes

Discussion in 'Electrical Forum discussion & Blog' started by Taylor, Jun 21, 2008.

  1. Taylor

    Taylor New Member

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    143
    Location:
    Northern Joisey
    I'm rewiring old BX to MC, and adding cat5e in the walls. For aesthetic reasons I'd like to combine high and low voltage in receptacle boxes. I'd like to use conduit and enclosed boxes on outside (to be insulated) walls so I can rewire the cat5e some day if necessary. Carlon makes a box divider for their Super Blue boxes that meets NEC requirements for separating high and low in a box.

    My issue is that I'm not sure of the ramifications of bringing MC into a plastic box. I'm using MC because I plan to insulate with foam and we sometimes have mouse issues. I imagine the issue with MC is grounding the sheathing (even if it isn't a ground path), is there a bushing I can use to bond the aluminum armor to the grounding cable?

    Does anyone know of a box divider for metal boxes? I am getting the impression that nothing innovative has happened with metal boxes in about 80 years, all the innovative products are in plastic. Even so, it looks like I would need to drill a hole in a Super Blue box to bring in the conduit.
  2. Bill Arden

    Bill Arden Computer Programmer

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    1. Regular Cat5 wire can NOT be ran threw metal conduit due to capacitance to the wires. They do make plenum rated Cat5, but you would be better off running plastic conduit.

    2. UL states you can NOT run low voltage wires with high voltage wires without classifying all the wires as high voltage. This would prevent you from using standard cat-5 connectors.

    So you are better off running separate plastic conduit and combining Phone, CatV and the cat-5 and then use either plastic boxes or "wrap" plates.

    note: I am not shure what to call that metal plate that wraps around the Sheetrock so you can add a cover.

    Edit: #2 above also means that you have to run two conduits even if you use a divider in the box.
  3. Bob NH

    Bob NH In the Trades

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    You can run 1/2" and 3/4" PVC conduit through stud walls if you are reasonably careful in locating the holes. I have even run 1" through joists about 3.5" from the lower edge but it was quite a chore.

    You can also run ENT (The blue corrugated plastic, also known as "Smurf tube") in the walls, although I don't like the stuff and it is more expensive than PVC conduit.
  4. Chris75

    Chris75 Electrician

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    Location:
    Litchfield, CT
    Any info? Never heard of this before.
  5. Taylor

    Taylor New Member

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    143
    Location:
    Northern Joisey
    Conduit

    I'm running Resi-gard (orange-colored) corrugated PVC conduit, designed specifically for low-voltage wiring (is this "orange smurf"?). I'm running 3/4" Resi-gard to each box, and MC wire in a parallel stud bay. I'd like to bring them together in a single box, to avoid proliferation of plates on the walls. I'm starting to think my options are use NM instead of MC (unless I can safely bring MC into a plastic box), or keep the high and low voltage boxes separate.

    Thanks for your comments.
  6. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    You could always just use a bonding bushing on the mc connector if you really wanted to use the MC with a plastic box
  7. alternety

    alternety Like an engineer

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    Location:
    Washington
    Plenum rated cables are an issue of fire/smoke characteristics of the outer insulation; not an electrical issue.
  8. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    I'm still waiting for proof you cannot run cat 5 in a metel conduit, wonder what they do in metal buildings... :rolleyes:
  9. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    Seems like I have seen a lot of Cat. 5 run along the metal studs in the interior walls of commercial buildings???
  10. alternety

    alternety Like an engineer

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    Location:
    Washington
    I do not believe there is a problem with metal conduit; but I have no proof handy. The primary characteristics of the cable are the result of the tightly twisted pairs and their relationship to each other. If you have ground currents flowing through the the conduit from multiple grounding points, any coupled signal should be eliminated because of the balanced circuits. Even running next to power lines will tend to be canceled, but if the imposed signal gets large enough it can exceed the operable range of common mode rejection. It also transfers noise spikes. That is why you should stay away from adjacent power circuits. Steel conduit may make it OK to be near power. Aluminum and plastic will not. It is magnetic coupling that causes the transfer.

    In addition to the code issues, I would never put power and CAT 5 in the same conduit because of noise transfer.

    A maybe proof - you can get shielded CAT 5. Sort of like a tiny conduit around the active wires. That analogy is wrong on rigorous examination, but maybe a useful analogy.
  11. Billy_Bob

    Billy_Bob In the Trades

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    422
    I too have seen plenty of commercial buildings where *everything* electrical is run in metal conduit.

    Then there is the fire and "plenum" thing where burning wires can put off toxic fumes unless they are manufactured to not do so. The solution to this is to run the wire in conduit or use plenum rated wire.

    Then there is the government "Tempest" security specification which does not allow any electronic signals to be emitted from any electronic wiring or devices. (So no one can listen in.) They use metal conduit big time for this.

    Then government "hardened" wiring which protects all electrical/electronics from "EMP" which is a pulse of electricity designed to disrupt these things in a war. Again they use tons of metal conduit and big time grounding of everything.

    So I thought I could do a simple search and find a specification for running cat 5 in metal conduit... But couldn't find much of anything except the following...

    Here they are recommending that Cat 5 be run in metal conduit...

    Quote from: http://www.wi-fiplanet.com/tutorials/article.php/3300311
    ["With most office buildings, each new tenant installs their own communication cabling and leaves the old cabling in place. This creates what the NFPA calls a 'high fuel load' because of the excess cable capacity and increased fire and smoke hazard. In 2002 the NEC created new rules that require the latest installer to remove all abandoned cables from a building upon performing a new installation. For communications cabling the removal applies only to cable not enclosed in a metal raceway. This means that if there is unused Cat 5 in the plenum on a cable hanger it must be removed. To avoid this problem in the future, it may be a good idea to use metal conduit."]
  12. Bill Arden

    Bill Arden Computer Programmer

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    584
    Location:
    MN, USA
    I might be wrong about the Cat 5 in metal conduit issue, but I do know that UL won't allow both Cat 5 and power wires in the same conduit.

    Maybe it was an issue with coax Ethernet or POE(Power over Ethernet)?

    Back to the question in hand.

    Chris75 suggested a bonding bushing.
  13. kornbln

    kornbln New Member

    Messages:
    6
    Taylor,

    I did something similar recently involving mixed voltages in a metal box. I brought 3/4" ENT into a 3/4" knockout in the box and attached it using a Carlon threaded adapter (A243E) with a rigid locknut. You could also just use the snap-in type (A253E).

    They do make a divider plate for 4" square metal boxes. RACO 707RAC for 2-1/8" boxes, 706RAC for 1-1/2" boxes, or Steel City 52PD1, etc.

    If you want to use plastic, take a look at Carlon's ENT catalog. They make plastic boxes with knockouts for ENT. They even have one for dual-voltage applications (A238).
    Last edited: Jun 23, 2008
  14. kd

    kd New Member

    Messages:
    207
    It is OK to run cat5 or phone wires in metal conduit as long as you ground all the conduit. If you run any shielded (foil wrapped) communication wire, you must ground the shield or it will create its own interference.
    Do not try to have high and low voltage in a "separated" plastic box--I think you will get noise on the electronics. There are (expensive) metal plug mold baseboard systems that mix high and low voltage, but it is engineered to solve the noise problems.
    Do not worry about a proliferation of boxes, it just looks that way in the rough. When the finish is done you will wish you had more outlet boxes.
    NEC prohibits installing any below 50 v. wiring in conduit with 120 v. or higher wiring, but you did not want to do that anyway.
  15. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    Location:
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    FWIW, in my last job, in new construction we ran all Cat5 cable in EMC, often violated the length restrictions, and in some cases ran 1Gb traffic through them. No known problems.
  16. Furd

    Furd Engineer

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    446
    Location:
    Wet side of Washington State
    Please cite the Article where this prohibition exists.
  17. Taylor

    Taylor New Member

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    143
    Location:
    Northern Joisey
    Thanks for the replies

    I did not realize that RACO made dividing plates for metal boxes, now I just have to find someone that sells them. Someone advises against having both HV and LV in the same box, but clearly manufacturers are providing products for this purpose. Is there any evidence that this would cause problems? I can try to bring the wires in in different stud bays, except for old work where both HV and LV lines will have to be fished. I am worried about the look of separate HV and LV wallplates side by side but enough out of alignment to be an eyesore to the installer whenever he looks at them.

    I had hoped to run LV through conduit, but now I realize that Carlon old work boxes do not provide support for conduit. For external walls where I am doing complete demo, insulate (with foam) and re-rock, it seems like I have no alternative but to run closed (HV) electrical boxes with conduit going into them. I won't be able to finish connections until after rocking, which must follow insulation, so wiring must be protected from insulation. I guess I have to be careful on pulling the wire back at the other end when pushing it back into the box, so I achieve the right turn radius.

    Kornbln, the A253X adapters look similar to adapters for Resi-gard, just different color. Did you bring your conduit into plastic or metal boxes?

    A couple of people have mentioned a bonding bushing for MC in plastic. Here's where I demonstrate my ignorance: what's a bonding bushing? Didn't see anything like that at the big box.

    Thanks again for your help.
  18. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    Location:
    Central Florida
    I'm sure this isn't legal, but a hole saw makes a dandy conduit hole in a plastic box. I've also used hole punches to allow use of conduit in steel boxes manufactured for Romex.

    I'd really like to see a system for ganging different kinds of boxes, partitions, etc., to accomodate all this stuff in one product family.
  19. Billy_Bob

    Billy_Bob In the Trades

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  20. Taylor

    Taylor New Member

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    143
    Location:
    Northern Joisey
    Thanks again for all the help!
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