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Recent installation, grounding looks shaky

Discussion in 'DIRECTV Installation/MDU Discussion' started by aabrea2, Aug 4, 2009.

  1. Aug 4, 2009 #1 of 16
    aabrea2

    aabrea2 Cool Member

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    Jul 20, 2009
    First post - hello all.

    I know grounding of sat systems is an often debated topic, but I just wanted to hear others take on my recent installation. My dish (SWM 5 LNB) is mounted on an out building about 120 feet away from my house. The coax from the dish routes through the out building and into a conduit back to the house. At the house, the coax connects to a ground block which is then connected to the house ground. However, the installer did not run and separate ground wire from the dish assembly back to the house ground. I questioned him on this during the installation and he informed me that the shield on the coax (RG-11) was sufficient to ground the dish assembly. I am beginning to doubt this after looking at the manual at:

    (Being a newbie I can't post the DirecTV URL)

    and other posts on DBSTalk.com that reference similar diagrams.

    At this point, if the grounding is incorrect, I'm not sure what to do. I suppose I could try to fish a ground wire through the conduit since there was no messenger wire on the RG-11 coax or possibly drive a new ground near the out building and attach to that. The only problem with the latter is that I thought this could set up a potential between the house ground and the new out building ground which could be another problem. I also suppose if this grounding is incorrect, the easiest thing to do is to get the DirecTV installer back to my house and tell him to correct the issue.

    Thanks in advance for your help.
     
  2. Aug 4, 2009 #2 of 16
    Mertzen

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    I've had conflicting 'teachings' on this.
    At D* they want a #17 messenger from ODU to ground location
    At W* they state that the 60%shield in a double coax serves as ground

    I personally prefer to see the #17.
     
  3. Aug 4, 2009 #3 of 16
    aabrea2

    aabrea2 Cool Member

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    Mertzen, thank you for your response. At this point, would you recommend doing anything or leaving things as is? I guess my biggest concern is lightning and doing everything I can to avoid damage caused by it.
     
  4. Aug 4, 2009 #4 of 16
    Mertzen

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    No matter what you do no grounding will save a dish from lightning.
     
  5. Aug 4, 2009 #5 of 16
    taz291819

    taz291819 Godfather

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    As mentioned, grounding won't save anything from lightning. Also, in the cable world, the shield is what's used for grounding.
     
  6. Aug 4, 2009 #6 of 16
    armophob

    armophob Difficulty Concen........

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    Sometimes it is best to do it yourself. I would pull back the cable with a string attached. Then re-pull the cable with a small ground wire with it. Then drive a ground rod or use the out buildings ground source at the dish.
    That is what "I" would do. But I am OCD. You should be fine with the shielding for potential differences. But I would make sure the dish itself is attached to the closest ground source. Although in a direct strike it won't save you, an indirect one might be averted.
     
  7. Aug 4, 2009 #7 of 16
    joe diamond

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    Every lightning hit (both of them) I have seen the cable and ground had "burned open" and there was no damage to the cable or ground or anything else after the first twenty feet. However, it was the phone connections that blew stuff. Phones were damaged and the one receiver that was connected was burned at the phone port.

    Ask the Florida folks about lightning.

    Messenger is for hanging CATV lines. Attached ground is for grounding components. Little green screws are also required.
    Somewhere in the code I recall that a different size ground wire is required IF the ground is not attached to the coax along its' length.

    I would just ground the rig at the ground block and kill a chicken at the alter of Thor. (or Zeus).

    Joe
     
  8. Aug 4, 2009 #8 of 16
    armophob

    armophob Difficulty Concen........

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    One thing about Florida, nothing but sand. The only ground lightning finds is things buried in it and the water below.
     
  9. Aug 5, 2009 #9 of 16
    aabrea2

    aabrea2 Cool Member

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    Jul 20, 2009
    Again, thanks to all for your insight. I may have been unclear in my one post about lightning. I know a direct hit or one close to my dish would pretty much put end to my TV viewing enjoyment no matter how the dish was grounded. I was more concerned that the current grounding configuration might be making the dish a more attractive target for lightning. When the coax was run from the house to the out building, I put a pull string in the conduit just in case. Maybe I'll use it to pull a new ground wire for peace of mind.
     
  10. wildbill129

    wildbill129 Godfather

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    Me personally, I wouldn't sweat it. (Mines grounded with the shield only) But if you want to follow the NEC, or it will help you sleep at night, pull a ground through the conduit.
     
  11. westom

    westom Mentor

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    Aug 8, 2009
    Earth so that direct lightning strikes cause no damage. Routine. Well proven for over 100 years. If earthing is done improperly, then damage can result anyway.

    First, you discuss running a ground wire inside the conduit. Wrong. Metallic conduit means the ground wire carries (earths) no surge.

    Some principles. Every wire that enters the building must connect short (ie 'less than 10 feet') to earth ground. All incoming utilities must make the short connection to the same earth ground. Also no sharp wire bends, no splices, separated from other non-grounding wires, (not inside conduit), etc. All these are necessary so that earthing is effective. Then a surge approaching a building need not enter it. How effective? How good is the earthing? Protection is only as good as that earth ground.

    What happens if lightning strikes the dish? Better is to have that dish connect as short as possible to earth. Same conditions (ie no sharp wire bends) apply. Lightning that may otherwise find earth destructively via household appliances will, instead, take the lower impedance (shorter, no splices, etc) connection to earth.

    To make that earthing even better, the household 'single point earth ground' could be connected to the dish earth ground via a buried bare copper wire. (To be strictly technical while having better protection, that buried wire is required by code.)

    Earthing means a low impedance connection. Increased wire diameter does little to reduce impedance. Shorter wire length (no sharp bends, not inside conduit, etc) means lower impedance.

    What happens if a direct lightning strike causes damage? Then a human mistake must be located and corrected. That starts with an analysis of the earthing system. Routine is to have direct lightning strikes and no damage. But that protection is only as good as the earth ground - and connections to that earthing.

    Ground wire in a metallic conduit obviously is bad practice.
     
  12. aabrea2

    aabrea2 Cool Member

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    Jul 20, 2009
    The conduit is plastic.
     
  13. joe diamond

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    Good point,

    And I just know I have seen various specifications that no not specify metallic conduit as an acceptable bonding point.

    I think the result would be the same.......in plastic the ground would burn open real close to the point of contact.........in steel conduit it would jump to ground after following for some distance.

    Smoking rig would result in either case.

    Joe
     
  14. SledDog

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    Wow.. I guess you have never seen a direct lightning strike. Usual nothing survives a direct hit. Welcome to Florida. The lighting capital of the USA! It starts house fires, kills people standing in their garage and fries electronic equipment faster than a deep fryer fries a turkey.

    For those of you that live in Florida or visit our great state, the next time you pass by a newer truck weigh station, take a good look at it. You will see some strange looking towers with metal umbrellas on them around the station. That's the grounding system used to protect the station's equipment from being fried by lightning.

    Take a good look at the Space Shuttle launch platforms, next time you see them on your TV (please don't some down here to see a launch. We have enough tourists). You'll see a large mast on the top of the shuttle support structure. Yep, it's a lightning rod. They are the same ones that were on the top of the Apollo launch towers.

    I've been in ATC control towers that have taken a direct strike. The only reason we did not loose our equipment is because of the design of the grounding system. Same for the motor control center buildings I work in now. Purpose designed grounding system to protect, PLCs, motors, VFDs, and controls systems.

    I have also seen what happen to SCADA equipment (radios, control card and PLCs) when a 25' tall radio tower takes a direct strike. And it ends up looking and smelling very bad. And that's with NEC approved bonding, polyphasers, and additional ground rods.

    So in most cases, it's toast, unless you have spent the dollars, in design and equipment, to protect against a direct strike. Otherwise, don't plan on looking for "human error".
     
  15. joe diamond

    joe diamond Hall Of Fame

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    You are getting into what I have seen referred to as a "cone of safety" that extends out at 45 degrees from the tip of a lightning arrestment system. As in the top of a sail boat mast or the ridge of a building, a series of points connected to a ground cable that guides lightning.

    I saw a story about a lightning strike & damage where the property owner tried to sue a satellite installer for lightning damage because the dish was not grounded. I think the defense was a lack of proper lightning rods to protect the building.

    Thor knows this stuff. So does Zeus.

    Joe
     
  16. westom

    westom Mentor

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    Aug 8, 2009
    Routine is for well over 98% of all trees struck by lightning to have no apparent damage. But many only see the rare exception - then assume nothing can survive a direct lighting strike. A conclusion based in classic junk science reasoning.

    When a telco switching station is damaged (phone service lost all over town for four day), that is normal? Of course not, when damage happens, the ground mistakes are discovered and corrected. A switching station may suffer 100 surges with each thunderstorm - and must never have damage.

    A protector simply gives lightning more paths to find earth ground. An effective protector makes one of those paths the preferred path for lightning. Lightning that has a low impedance (not resistance) connection to earth need not go inside and damage electronics. Routinely done in FL.

    BTW, those umbrella things in truck weigh stations sound like ESE devices. Best called scams. They claim to stop lightning. They were even used in Cape Canaveral. Some were even removed by the lightning they did not stop. The myth promoted by ESE retailers is well documents. And still many know otherwise for the same reason that many know direct lighting strikes always cause damage.

    Nothing stops the surge. No protector stops or absorbs the surge. Either surge energy dissipates harmlessly in earth. Or it finds destructive paths to earth via electronics. The latter is classic human created failure.

    An effective solution is to provide a short (low impedance, no sharp wire bends, etc) connection to earth. The antenna is best earthed directly. And then its lead wire is also earthed where is enters the building. Routing a ground wire alongside the lead wire accomplishes little. Better is to get that lightning into earth by a shortest (and therefore low impedance) path.
     

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