Grounding Do's Don'ts & Why Part 3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AI5DH, Mar 19, 2012.

ad: L-HROutlet
ad: l-rl
ad: Left-3
ad: L-Geochron
ad: Left-2
ad: MessiPaoloni-1
ad: HRDLLC-2
ad: abrind-2
ad: L-MFJ
  1. W9GB

    W9GB Ham Member QRZ Page

    Another Urban Legend posting ...

    The Sears Tower (now Willis Tower) is hit by lightning hundreds of times each year ... with no damage to hundreds of pieces of communications gear on that roof top. All grounding is per current codes.
    Florida, especially the western Gulf Coast, gets even more lightning strikes to communication towers.

    Damage? A few rare instances when someone does not follow rules and codes. Their career t hat wireless carrier or broadcaster is usually finished -- maybe they relocate in your neighborhood.
     
    Last edited: Jun 3, 2012
  2. K5JY

    K5JY Ham Member QRZ Page

    I'm looking for advice in placing lightning arrestors in coax antenna line. My application is an x-quad Yagi that has two feeds, allowing me to configure the antenna for vertical, horizontal, left circular, and right circular polarization via phasing lines switched by a set of on-mast coax relays.

    As I see it, the options are:
    1. use two arrestors, placed in each feed line within a few feet of the antenna, and before the lines enter the phasing relays.
    2. use one arrestor, placed in the single line coming out of the coax relays, but still on the metal mast within a foot or two of the relay output.
    3. use one arrestor, placed at the base of the tower
    4. use one arrestor, placed on the feedthrough bringing the coax into the shack.

    For option #1, the benefit is that surges are hopefully shunted to ground via the mast, tower, and its grounding rod system before anything other than the antenna itself is damaged. The downside is that it takes twice the number of arrestors.

    For option #2, the benefit is that it only requires one arrestor, and any surge is hopefully sent down what ought to be a low-impedance path of the mast and tower to a ground rod. The downside is that it exposes the coax relays to an un-arrested surge.

    For option #3, the benefit is that it only requires one arrestor, and the path from the arrestor to ground is the shortest, hopefully providing the lowest impedance. The downside is that it exposes the coax relays and the coax coming down the mast and tower to surges.

    For option #4, the benefit is that it only requires one arrestor, it takes care of induced surges in the coax run from the tower to the feedthrough, and I already use arrestors and a grounding bus at my feedthrough. The downside is that a surge is brought very close to my house, and exposes every outside element of the antenna system and its feed to surges.

    A related question would be where to locate surge surpressors for the power lines to the coax relays, and the power/control lines to the rotator. In general, I see the options as:
    1. put the surpressors on the antenna mast or tower, as close to the relays and rotator as possible
    2. put the surpressors at the base of the tower
    3. put the surpressors at or near the shack wall feedthrough.
     
  3. K9KJM

    K9KJM Ham Member QRZ Page

    All of your surge arrestors should be on your "Single Point Ground" panel, Which should be located near where your lines enter the building.

    It is important to understand that "Arrestors" are really one of the LEAST important parts of an effective lightning protection system. MUCH more important is the proper bonding of all grounds/systems.
     
    W1ADE likes this.
  4. K5JY

    K5JY Ham Member QRZ Page

    The best thing going for me in the event of a direct strike is probably insurance <grin>. But in the event of a close strike, inducing surges in my antenna, you're saying that basically the antenna, feedlines, rotator, control lines, phasing relays, and their power lines, are potentially (pun intended) toast, since the surge will travel through them on the way to the "single point ground panel" at my shack wall. I'm looking for a way to protect the equipment outside my shack, as well as inside it.
     
  5. KD0CAC

    KD0CAC Ham Member QRZ Page

    I've wanted to ask this question a few times , but when thinking or talking about it , I haven't been at the keyboard .
    A few have contributed many answers to ground , lightning protection .
    And I have read that they keep operating even in lightning , they get direct hits and no damage , I think I can understand how a well protected shack can survive that , but I do not see how the antenna can survive the hit ?
    Which leads into the question .
    When running feed-line up a tower [ possibly other , but to keep simple ] shouldn't ground straps be attached from the end of the feed-line to tower [ assuming tower is grounded ] .
    I help a few club stations , repeaters and also do net control of a local tech-net , trying to spread good info .
    I am surprised how few of these setups are not using grounded pass-through panels , grounding at both ends of feed-lines , being a relative new guy in many of these groups .
    Thanks
    John
    KD0CAC
     
  6. AI5DH

    AI5DH Ham Member QRZ Page

    I think I can shine some light on that for you. The answer is it depends. First antennas are passive devices so there are no active parts to get damaged. Bu tit really depends on how and what material they are constructed with and whether or not it is DC grounded or not.

    If the active element, directors, and reflectors are made from tubing, then lightning can do quite a bit of damage to them. Lightning can burn holes in a element and then it fills up with water over time. Or lighting can literally shear off an element by burning in into.

    On the flip side a antenna with solid elements has no real problem when struck other than burning a dimple in the element. Know what is likely to happen and I have seen it many times with commercial grade antennas is when lightning strikes one of the elements or ground radial, it strikes it on the tip or end of it. That burns a small bit of the element off shortening its length slightly. A single strike, no noticeable effect. But over time if that one element is constantly struck shortens it enough to effect SWR.

    Will I will answer this from a professional broadcast and cellular operators POV. The hard line is bonded a minimum of two times to the tower. One at the top of the tower where the hardline terminates, and again at the bottom where the hardline leaves the tower. For tall towers they will usually bond at the mid point.

    Oh and there will always be a 3rd and 4th bond. One right at the hatch plate before the hard line enters the building, and again immediately after the hard line enters the shelter with the surge suppressor.
     
  7. KD0CAC

    KD0CAC Ham Member QRZ Page

    I've taken down some antennas for some of the local clubs HF , VHF & UHF and found all kinds of damage .
    A station-master collinear , the tip melted almost completely off , fiberglass blown out , unsoldered joints inside .
    Putting up some replacements this week .
     
  8. MR_HAMWANNAB

    MR_HAMWANNAB QRZ Member

    not sure if this is a correct question for this section, but here it goes

    Can you dump the ground of a Marconi grounded 1/4 th wave to the station's ground, or is that asking for trouble?
     
  9. EA3HOE

    EA3HOE Ham Member QRZ Page

    I LOVE this thread. It makes things clear no matter what discussion follows and we need to appreciate that.
    Now, all this about ground rods and all is nice if you live in a house ground floor. But what about if you live on the 15th floor of a skyscraper where the distance to ground is a bit longer than pictured in these articles? We will assume (ASSUME makes and ASS out of U and ME, i know) that lightning protection is being taken care of. Electrical ground is usually already a problem. Of course you have the ground lead in your power plugs, but is this where you connect the ground connectors of your set, tuner, amplifier, etc? I guess not. According to the sets manual a water or heating pipe is also not the right place. So where to connect those leads if hitting a rod in the ground is not a possibility?
     
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    Tall buildings have a number of grounds built into them , some use cold water pipe supply [ but nowdays not all have metal pipes ] , but they do have AC grounds .
    And depending on when and where it was built there are other options , steel structure / frame under concrete etc.
    Then for lightning / antenna most of what is going to be available is exposed on roof , so it would take someone that has done some of this work to do a site survey , or a lot of questions to give individual help .
    Here's a picture of one of the last roof installs , someone else did the lightning rod & ground install .
    Internet is screwed up at this end so not able to post pic's :(
     

Share This Page