Can I run antenna coax & ground through metal conduit?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W3IG, Sep 24, 2020.

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  1. W3IG

    W3IG Ham Member QRZ Page

    I'm installing an 8' vertical antenna on a gable mount. I want to keep that wall pretty so I want to run the antenna wires through conduit to keep them bundled and clean looking. Top and bottom (point of entry) of the conduit are service boxes for grounding / bonding, and coax connections. Its a 30' vertical run. I'm using LMR600 and #2thhn for ground wire. (thhn because bare copper would corrode in contact with the galvanized conduit.) At the entry point I've got three 8' ground rods, and those are bonded to the breaker panel with #4 bare solid copper.

    Is it ok to run those exterior wires through metal conduit? (Conduit is bonded top and bottom.) Any other obvious problems with my plans? I'm trying to do things safely and as correctly as I can, within reason.

    Thanks in advance.
     
  2. N1VAU

    N1VAU XML Subscriber QRZ Page

    "Conduit"?
    Thin walled bendable EMT or Ridgid threaded pipe?
     
  3. W3IG

    W3IG Ham Member QRZ Page

    EMT.
     
  4. KB1CKT

    KB1CKT Ham Member QRZ Page

    Coax should not care--should be no signal on the outside of the coax. [If you were using balanced line it'd be a different story.]

    Not sure if I would run GND back inside of the conduit, seems like the conduit itself would be a good conductor, but it won't hurt. Should not have any current on it anyhow, just a safety ground. If the ground system is done right, there should be no current here, and no reason for #2 wire though--that seems overkill.

    What is the vertical antenna, and does it require ground radials?
     
    N5YPJ likes this.
  5. AJ4GQ

    AJ4GQ XML Subscriber QRZ Page

    Your plan is fine.
     
  6. SPEEDSKATER

    SPEEDSKATER QRZ Member

    Note that any 'ground' wires run thru a metal conduit, need to be bonded to the conduit at both ends. Otherwise the conduit will act as a choke.
     
    WA0CBW, W4IOA, W1TRY and 3 others like this.
  7. N1VAU

    N1VAU XML Subscriber QRZ Page

    I don't recommend thin walled EMT outdoors because it rusts and then stains whatever it comes in contact with. It's not designed for outdoor use and in a year or two will probably end up uglier than red lipstick on a pig.

    You really should use the gray UV resistant PVC conduit instead. Use stainless screws everywhere outside.

    When using PVC conduit you must provide for expansion and contraction of the pipe itself. You'll be surprised how much it will move as temperature changes.

    They make expansion tubes to be put in the middle of PVC conduit runs for this purpose. They are ~$12 at Home Depot. When installing the expansion joint keep in mind that day's current temperature as compared to your location yearly minimum/maximum temperature extremes and set the length of the joint accordingly. If you don't understand what I mean PM me for further explanation.

    I would use the flexible gray PVC "liquid-tite" for the bends and install it with expansion and contraction in mind.

    I also recommend using the gray PVC "one hole'r" stand offs to hold your pipe. (Stainless screws won't bleed down your siding!) They handle expansion and contraction better than the clamps that hold the pipe against the mounting surface.

    Use the right gray glue for the pipe too.

    I recommend that you drill a couple 1/16" drain holes in the underside of every PVC box you use and seal the pipe/ liquid-tite with silicone where the wires end up coming out on top.

    73
     
    Last edited: Sep 24, 2020
    W6KCS and KK1N like this.
  8. WR2E

    WR2E Ham Member QRZ Page

    I imagine this could also be painted to match the color of the wall.
     
  9. N1VAU

    N1VAU XML Subscriber QRZ Page

    Probably, but in my profession we don't do that, so I have no first hand experience with painted PVC conduit.

    I speculate that the plastic chair and deck furniture paint would have some strech and shrink accounted for in the chemistry. Again I am speculating!
     
    WR2E likes this.
  10. WN1MB

    WN1MB Ham Member QRZ Page

    If the PVC conduit is that temperature unstable to require expansion tubes, I'm curious how well the paint would adhere to it.
     

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