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. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK in the first part I covered the importance of the Ground Electrode System. Now it is time to put it in details and I can think of no better way than a drawing. Also included are the NEC Article 810 applicable requirements.

    So first the supporting NEC 810 requirements:

    810.20 Antenna Discharge Units (ADU)

    (A) Where Required. Each conductor of a lead-in from an outdoor antenna shall be provided with a listed antenna discharge unit.

    Exception: Where the lead-in conductors are enclosed in a continuous metallic shield that either is grounded with a conductor in accordance with 810.21 or is protected by an antenna discharge unit.

    (B) Location. Antenna discharge units shall be located outside the building or inside the building between the point of entrance of the lead-in and the radio set or transformers and as near as practicable to the entrance of the conductors to the building. The antenna discharge unit shall not be located near combustible material or in a hazardous (classified) location as defined in Article 500.

    (C) Grounding. The antenna discharge unit shall be grounded in accordance with 810.21.

    810.21 Grounding Conductors.

    Grounding conductors shall comply with 810.21(A) through (K).

    (A) Material. The grounding conductor shall be of copper, aluminum, copper-clad steel, bronze, or similar corrosionresistant material. Aluminum or copper-clad aluminum grounding conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum shall not be installed within 450 mm (18 in.) of the earth.

    (B) Insulation. Insulation on grounding conductors shall not be required.

    (C) Supports. The grounding conductors shall be securely fastened in place and shall be permitted to be directly attached
    to the surface wired over without the use of insulating supports.

    Exception: Where proper support cannot be provided, the size of the grounding conductors shall be increased proportionately.

    (D) Mechanical Protection. The grounding conductor shall be protected where exposed to physical damage. Where the grounding conductor is run in a metal raceway, both ends of the raceway shall be bonded to the grounding conductor or to the same terminal or electrode to which the grounding conductor is connected.

    (E) Run in Straight Line. The grounding conductor for an antenna mast or antenna discharge unit shall be run in as straight a line as practicable from the mast or discharge unit to the grounding electrode.

    (F) Electrode. The grounding conductor shall be connected as required in (F)(1) through (F)(3).

    (1) In Buildings or Structures with an Intersystem Bonding Termination. If the building or structure served has an intersystem bonding termination, the grounding conductor shall be connected to the intersystem bonding termination.

    (2) In Buildings or Structures with Grounding Means. If the building or structure served has no intersystem bonding termination, the grounding conductor shall be connected to the nearest accessible location on the following:

    (1) The building or structure grounding electrode system as covered in 250.50

    (2) The grounded interior metal water piping systems, within 1.52 m (5 ft) from its point of entrance to the building, as covered in 250.52

    (3) The power service accessible means external to the building, as covered in 250.94

    (4) The metallic power service raceway

    (5) The service equipment enclosure, or

    (6) The grounding electrode conductor or the grounding electrode conductor metal enclosures A bonding device intended to provide a termination point for the grounding conductor (intersystem bonding) shall not interfere with the opening of an equipment enclosure. A bonding device shall be mounted on non-removable parts. A bonding device shall not be mounted on a door or cover even if the door or cover is non-removable.

    (3) In Buildings or Structures Without Intersystem Bonding Termination or Grounding Means. If the building or structure served has no intersystem bonding termination or grounding means, as described in 810.21(F)(1).

    (1) To any one of the individual electrodes described in 250.52; or

    (2) If the building or structure served has no grounding means, as described in 810.21(F)(1) or (F)(2), to an effectively grounded metal structure.

    (G) Inside or Outside Building. The grounding conductor shall be permitted to be run either inside or outside the building.

    (H) Size. The grounding conductor shall not be smaller than 10 AWG copper, 8 AWG aluminum, or 17 AWG copper-clad steel or bronze.

    (I) Common Ground. A single grounding conductor shall be permitted for both protective and operating purposes.

    (J) Bonding of Electrodes. A bonding jumper not smaller than 6 AWG copper or equivalent shall be connected between the radio and television equipment grounding electrode and the power grounding electrode system at the building or structure served where separate electrodes are used.

    (K) Electrode Connection. Connections to grounding electrodes shall comply with 250.70.

    Lastly here is NEC 810 shown in a drawing.

    [​IMG]
     
    Last edited: Feb 28, 2012
  2. K8MHZ

    K8MHZ Ham Member QRZ Page

    Great threads!!!

    I really like how you are attempting to cut the subject into bite sized chunks.

    Extra credit for the drawings, BTW.
     
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Thanks Mark, it has to be divided up in steps as it is too comprehensive of a subject to lay out all at once. The most important part is the Ground Electrode System aka GES. It is the foundation in which the rest is built from. and in most cases is all that is needed. Later I will address what goes on inside the Shack.
     
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    This is good information.
    Good reading on a cool cloudy morning. :)
     
  5. K8MHZ

    K8MHZ Ham Member QRZ Page

    Too comprehensive is an understatement. It's so bad that engineers and electricians nearly come to blows during discussions over the subject. Hard to believe, isn't it?:p For the unwashed masses, grounding is covered in Article 250 (referred to in 810) and consists of 28 telephone book sized pages with #10 text worded pretty much like the excerpt from Article 810, above.

    I do have a question for you, Dereck. On a receptacle, is it supposed to be 'ground up' or 'ground down' ?

    (Mark runs and hides) :cool:
     
    Last edited: Feb 28, 2012
  6. KF5LJW

    KF5LJW Ham Member QRZ Page

    Oh I believe it for sure. I came close to blows as Co-Author of Chapter 9, IEEE STD 1100, aka EMERALD Power and Grounding Sensitive Electronic Equipment. :eek:
     
    Last edited: Feb 28, 2012
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK I know where this came from Mike Holt, err I mean Mark. That will cost you either a right hook on your left jaw, or a beer. Your choice. :cool:
     
  8. K8MHZ

    K8MHZ Ham Member QRZ Page

    I'm glad it's multiple choice. I'll take beer.
     
  9. K8MHZ

    K8MHZ Ham Member QRZ Page

    I don't think the Zedizens know how lucky they are to have you here Elmering us on the subject. Although I know a bit about you, the rest may just see you as a newbie with less than 500 posts.

    Zedizens, hear this:

    Dereck knows his stuff. I know him from another forum (Mike Holt's NEC code forum for professionals, not amateurs :D) Hopefully he will stick around here to become a regular. The other forum is the very best forum on the planet for the electrical profession and the owner of the site is the author of perhaps the most popular NEC code update classes in existence. Dereck is one of the moderators there. I didn't know he was a ham until today.

    Again, thanks to Dereck for sharing his knowledge with us and hopefully destroying some myths in the process.
     
  10. WA9SVD

    WA9SVD Ham Member QRZ Page

    I truly appreciate the explanations given here. And how they can (or should be) implemented.

    So, in all honor and explanations, HOW do I explain "Coffee grounds" to our recent licensees?

    I just explain they are a product of the boat anchors from tune bygone daze.

    With all facetiousness aside, we (Associated Radio Amateurs of Long Bach CA, INC,) just finished another Tech Class training session, and have an overall "pass" rate over 90% for all of our (Tech AND General Class) students, through the greater Los ANgeles CA. area. We are (apparently) the ONLY ARRL affiliated club that will be providing Amateur Extra class preparation training sessions this side of the Mississippi River at this time in 2012.
    It is a service and commitment we want and need to provide as an ARRL Special Service Club.

    Look up : ARALB.org, and our club station: W6RO on QRZ for details.
     
    Last edited: Feb 28, 2012
  11. 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!
     
  12. 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
     
  13. 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.
     
  14. 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
     
  15. 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?

     
  16. 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..
     
  17. 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.
     
  18. K9STH

    K9STH Ham Member 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
     
  19. 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.
     
  20. K9STH

    K9STH Ham Member 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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