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Grounding Do's Don'ts & Why Part 2

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Feb 28, 2012.

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  1. K9KJM

    K9KJM Ham Member QRZ Page

    Looks like good info to me. My only nit to pick is the diagram, It would be good to show a nice radius on the ground conductors instead of a very sharp 90 degree bend, And/Or explain in the text that gentle bends are needed in all conductors. I try to explain it as pretending you are bending the conductor around a 5 gallon pail. That provides a nice gradual radius bend. NO sharp bends in ground conductors!
     
  2. W8JI

    W8JI Ham Member QRZ Page

    I agree, it is a good diagram. It helps stop the silly practice of throwing a ground rod system in for the shack equipment and /or installing a lightning protector, all without mains ground bonding to a common entrance panel, and thinking it is helping.

    It is frustrating to see so many very poor or non-existent entrance systems, that probably create more problems then they solve.

    73 Tom
     
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Point taken, and I have noticed some other little things I would have liked to done differently in the diagram. Perhaps when I get a little more time I can edit it.

    Well now that I think of it, I cannot edit the OP as the forum has set a time limit on the EDIT function.
     
  4. KD0CAC

    KD0CAC Ham Member QRZ Page

    I noticed an edit for next time , on the paragraph on diagram , were it mentions bonding the coax at top of tower [ then it says { on } antenna jumper ] , I read that it should be " and " .
    Just picken a nit to have a link to future episodes :)
    Thanks John
     
  5. KF7NUA

    KF7NUA Ham Member QRZ Page

    So if I am understanding this drawing correctly, thisoption is for a tower setup, what about just a Vertical antenna as I have, R7in the back yard?
    I do have a 8ft ground rod at the mast site connected to the mast w/#4 solidcopper line. Are you also saying that an additional 8ft ground rod should beutilized at the point where cables enter the home even if you connect the coaxbraid is connected to the power panel ground?

    At this time I have not permanently laid the coax as I am not sure how I amgoing to do this, so in the meantime I install a coax when I want to use theantenna and then remove it when done and bring it inside.

    My pwr panel is nowhere near the shack so this is a dilemma for me, anysuggestions?

     
  6. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yes exactly. If I understand you correctly what would happen is your coax braid would them become the Ground Electrode Bonding Jumper which would be through your radio equipment back through you home AC wiring vie the green ground conductor you use to provide 120 Vac.

    In the event you should take a direct lightning strike your coax, radio equipment, and houes wiring are now taking the brunt of equalizing currents into the thousands of amp which let the magic smoke out of the radio and your house wiring burning it all up. God forbid if you happen to be operating at that time could let the Magic Smoke out of you making your wife and children very rich assuming you have good life insurance. They would also likely have a new house to replace the one you burned down and died in.

    This is why people like myself keep pounding the fact that you cannot have the RF, Lightning, and Electrical grounds electrically isolated from each other. They have to be bonded together and is the exact reason why Electrical Code require it to be done. Anyone who tells you differently does not know what they are talking about, and their advice should be ignored.

    If you will look at the code I cut and pasted NEC 810 will leave no doubt about it, and will give you your options. The diagram I laid out is a good example how to do it with both Safety and optimum operation as it shows how to use OPTIONAL GROUND RADIALS for vertical HF

    In that diagram the RF Radials are doing double duty of providing RF performance for a vertical antenna by making a Ground Plane, and also act as a supplemental Lightning Ground in the event of a lightning strike. The Bonding Jumper between the Tower ground and radials provide the interconnection between your electrical ground and tower ground to equalize potential differences. Without that bonding jumper forces your coax to do something it is not intended to do, nor is it capable of doing. The ADU and ground rod just outside your home before the coax enters is part of the lightning Ground protection to bleed off charges and bypass to ground so it does not come inside. Well at least most of it is bled off so that what is left is minimal and does no damage hopefully..
     
  7. K8MHZ

    K8MHZ Ham Member QRZ Page

    Dereck,

    Bear in mind that some of us (like me) live in areas with sandy soil and a single ground rod is pretty much useless. Don, WB8I, one of our electrical inspectors, saw a test done locally that showed a single 8 foot rod to have a 1300 ohm impedance to ground. That same rod in iron rich wet clay may have a 15-20 ohm impedance to ground.

    I know the vast majority of hams do not have the equipment to test ground impedance, so relying on a single rod without measuring it's impedance may not be appropriate.

    At least two rods should be used, more than the length of the rods apart, if used without measurement and even that may not be sufficient to get the bolt to ground.

    AVI (makers of 'Megger') has a very good book on grounding electrodes called, 'Getting Down to Earth'. I don't know if it's available on line; I have a hard copy from school.

    Not far from me are sand dunes. When lightning hits a sand dune it melts the sand and make little glass formations called 'fulgurites'.

    http://webecoist.momtastic.com/2009/11/03/fulgurites-high-glass-digs-where-lightning-goes-to-die/

    The pics show how the impedance of sand can turn the earth into a raging heating element capable of melting glass in a very small fraction of a second as the bolt going through it on its way to the charge center heats up the sand.

    Ground_conductivity_smallm3.jpg

    Click on the above map to see how much ground conductivity varies from area to area. I am on the west side of Michigan near Lake Michigan. Our rating is 2. The highest I could see was 30. (Sorry about the poor quality).

    I don't know what units the figures are in, but it shows that there are areas of the US that are 15 times more conductive than where I live.
     
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    MHZ:

    The "rule of thumb" for the spacing between ground rods is about twice the length of the rods. Experimentation has shown that about 2.4 times the length of the rods is optimum. The 2.4 times figure is what I recommend especially for those ground rods that are intended for use primarily for r.f. grounding. However, the 2 times figure definitely will not cause any problems at all.

    The "30" rating is the best on the map. Fortunately, I live in a "30" area!

    Glen, K9STH
     
  9. K8MHZ

    K8MHZ Ham Member QRZ Page

    I know the larger the spacing, the better. The figure I used was meant to be a minimum. My bad for not mentioning that.
     
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The 2.4 figure comes from the "hemisphere of grounding" which is basically a half-sphere, in the ground, with a radius of the length of the ground rod. However, the effects of the ground rod are not limited exactly to this hemisphere. Therefore, it has been determined that, to maximize the effective coverage without any real overlapping, the rods have to be placed slightly farther apart.

    Glen, K9STH
     
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