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Satellite antenna grounding

Discussion in 'Electronic Repair' started by Leonard Caillouet, Oct 21, 2004.

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  1. I continue to see satellite receiver installations that are not grounded to
    the electrical service ground or any other ground at all. I thought the NEC
    was pretty clear that they must be grounded. Is there something that I
    don't know? I service TVs all the time and encourage people to check the
    grounding on the electrical service regularly. I often check them for
    clients and notice that antenna and sat, sometimes cable are not grounded at
    all. Antenna installers seem to be better about it, and cable installations
    are better than they once were on this matter, but very few of the sat
    antennas are grounded. What am I missing?

    I just serviced a commercial installation in a medical facility and found
    the same thing on the Direct TV installation. Checking the continuity b/w
    the coax shield and the ac ground found an open ( in the Mohm range) with
    about 8 volts induced ac. The leakage current was under the limit of 500
    microamps, but shouldn't the damned system be grounded?

    What has me wondering is that I see it so often.

    Leonard
     
  2. Jeff Wiseman

    Jeff Wiseman Guest


    I'm not super familiar with dish grounding requirements but I'm
    pretty sure that minimally, the shield of the coax needs to be
    grounded at its service entrance and that needs to be the same
    place as your power's service entrance ground. There are some
    issues about grounding the shields at the dish and the dish's
    metal mount, etc., but I can't remember those (e.g., it may be
    required that the mast of the dish is NOT grounded, etc.)


    What you are seeing might be a Red Herring for you. In order to
    avoid ground loops in the system, there may be coaxial isolation
    transformers on the coax feeds within the facility. Distribution
    amps may also provide DC and power line frequency isolation on
    the shield to reduce ground loops. These would break the DC
    connectivity along the shield within the facility which is a
    desireable thing. It is not a requirement that the shield on coax
    provide an AC power protection ground--the ground wire for the
    power wiring is for this.

    As far as I know there is no requirement (or need) for DC
    connectivity along a coax shield WITHIN a facility to that
    facility's service entrance ground. The shield on the cable only
    needs to be an RF ground. Making it a DC ground can be
    counter-productive in MANY applications.

    A proper test would be a conductivity test from the cable shield
    at the Dish itself to the serivce entrance ground post. This
    assumes that there is no arrestor equipment providing that
    connectivity which could make it appear as though that link was
    open too (e.g., like on your telephone line entrance where a low
    voltage DC connection to ground isn't provided).

    If I've misstated something here I welcome any corrections.

    - Jeff
     
  3. I think you are right on, Jeff, not misstating anything. There was no
    ground from the dish or the coax coming into the building nor anywhere that
    I could find inside. There were no isolation transformers that I could see,
    just a switch and splitters.

    I don't see the isolation of the shield at the receiver as necessarily being
    a problem, and since the leakage both ways was acceptable, that is not an
    issue, but the lack of grounding at the entrance is what puzzles me. The
    reason that I wonder if there is something that I don't know is that most of
    the sat installs that I see are not grounded. In practice it might not be a
    big issue, since the geometry of the dish will not make it an effective
    lightning rod, but it seems that leaving it ungrounded is just asking for
    trouble. Also, it appears to be a code violation to me, if the coax
    entering the building is not grounded to the electrical service ground rod.

    Any satellite installers out there?

    Leonard
     
  4. electrictym

    electrictym Guest

    snipped:
    + + + + + + + + + + +


    YES ..... according to just about any code.... it must be grounded.
    A quick glance at the Dish Network or Direct TV user installation
    guides will indicate safety grounding procedures.
     
  5. TOM

    TOM Guest

    Here's the kind of grounding block you want:

    http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=090-338

    Specially designed for type-f connectors, provides a code compliant
    compression
    ground connection.

    By the way - putting a grounding connection right at the TV receiver and
    bonding to the
    AC power ground right at the receiver also significantly reduces
    interference problems because it
    drastically reduces the common-mode cable impedance at the TV set.

    -- Tom
     
  6. Robotron Tom

    Robotron Tom Guest

    Leonard Caillouet started a controversy when he said... :
    I'm not an istaller, but I did install my own satellite system. In the
    instructions, there was a connection to earth ground at the junction
    block, which looks like a splitter but isn't. That would make it shield
    to ground.

    Perhaps you miss this ground block, which would be somewhere inline.

    Did you trace it from dish to receiver?

    --
    Robotron Tom *remove nospam to email*
    See the Flashback Arcade at: http:// www.arcadeguy.net

    Standing for right when it is unpopular is a true test of moral
    character.
    -M. Smith
     
  7. Jeff Wiseman

    Jeff Wiseman Guest


    I think that that is only partially true. Having a second ground
    at the set that is not DIRECTLY connected to the power ground at
    the sme set is guaranteed to create a ground loop. Some sets by
    themselves can ignore this but other equipment such as home
    theater stuff very frequently ends up being sensitive to it
    resulting in humming througout the audio system.

    - Jeff
     
  8. ron

    ron Guest

    to expect all dish installs to be grounded to the utility ground is
    wishful thinking..it would eliminate a large percentage of installs
    due to the inability to install the dish near enough to that ground...
    most installers will at least install a ground rod of their own, so
    that there is some grounding, albeit that isn't to "code" though..
    alot of newer homes, you will never find that ground rod as the
    service is all underground and nothing is visible..unless the code is
    strictly enforced, installers will cut corners to keep their jobs...
     
  9. That is what I assume is going on. The curious thing is that not only are a
    few not grounded, but virtually none that I check are grounded at all.

    Leonard
     
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