Grounding Do's Don'ts & Why Part 1

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Feb 27, 2012.

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  1. W8JI

    W8JI Ham Member QRZ Page

    Anyone who thinks for a second an RF ground is always the same as a lightning and safety ground, and that they all need bonded to be common, really needs to rethink his position or study antennas and RF systems.

    They certainly *can* be the same, in many cases it is required or best that they are bonded, but in many cases not isolating the RF ground or counterpoise will harm a system's performance, and at the same time not improve safety one bit.

    If the world treated all lightning, safety, and RF grounds the same, we would be in big trouble with some systems.

    73 Tom
     
    KR3DX likes this.
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    JI:

    You need to take your case to the National Fire Protection Association which produces the National Electrical Code. To meet the NEC, which virtually every city, town, and even most counties, requires adherence, requires that all grounds be connected together. Doing otherwise, may definitely result in the denial of claims by your insurance company if you sustain any damage as well as possible fines, etc., from your municipality or other governmental agency.

    If your area does not require adherence to the NEC, and if you are not worried about insurance claims, then, of course, you can do whatever you please. If you are required to adhere to the NEC, then you have no real choice. The National Electrical Code is something that most of us have to "live with".

    Glen, K9STH
     
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  3. J85K

    J85K Ham Member QRZ Page

    'Ground' loop isolation........


    Ground loop isolation problems are commonly overlooked, and they can cause RFI :mad: to get into your transmissions, via the microphone. This is especially pronounced when using outboard audio assets like mixers, equalisers, noise gates etc. When it is really awful, you sound like a blow torch on frequency. Any 'potential' difference between two or more points in your Earth/Ground system will introduce noise and other audio interference. There is a 'slight' shock or tickle as the chassis discharges through you. Always ensure that ALL of the Earth's / Ground's are bonded together.
    On a secondary note, use shielded cables to connect outboard audio assets to reduce or eliminate electromagnetic coupling.
     
    Last edited: Feb 28, 2012
  4. W8JI

    W8JI Ham Member QRZ Page

    The NEC, and the NFPA, have nothing to do with, and no influence on, antenna or RF system internal design.

    You are confusing an isolated RF ground on antennas or equipment with an entrance ground.

    Let me give an example, a groundplane with 4 radials. If we directly ground the radials to the mast, and the coax shield to the radials with direct connections, the antenna SWR and antenna pattern with vary significantly with mast and feedline length. While the radials can and should have either a gap to the mast and a decoupling system for RF to the coax, the antenna will have pattern issues and SWR issues if we pretend the common point can be directly grounded.

    This case generally extends to all end-fed antennas with small counterpoise systems, even elevated radials on the ground or sparse radial systems. It also includes dipole elements, in which the "shield" element side cannot be bonded directly to a boom or support mast, or a ground conductor, without RF isolation.

    At the entrance, all grounds must be bonded. But anyone who, in blanket terms, gets into the antenna system and proclaims all RF grounds are the same as lightning and safety grounds, or who thinks all grounds function the same, or thinks all grounds and counterpoises must be directly bonded at other non-regulated areas, really just shows a distinct lack of understanding of how RF systems work.

    RF grounds are NOT the same as safety and lighting grounds. They are not always interchangeable, and cannot always be bonded any place we have a whim to bond them.

    73 Tom
     
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  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    No problem but I am not referring to the premises wiring of a residence or biz (outside plant), they could care less about that as it is not their responsibility to make sure the residence or business is wired properly or not. All they are responsible for is the demarc and making sure they are bonded to the service ground meeting local and NEC electrical codes. What happens after that is the customers problem. The poin tI am trying to make is they know what the code requires, and that is all ground electrodes are to be bonded. Otherwise houses can burn down. They have had to pay for a few of them.

    I am very familiar with BICSI TR-EOP-000295 standard as i have worked with it for 30 years, but that specification is becoming antiquated as grounding topologies are moving away from Isolated Ground Planes to Mesh Grounding and Integrated Ground Planes.
     
  6. KF5LJW

    KF5LJW Ham Member QRZ Page

    Sorry Tom but you do not understand the principles of proper grounding like you think you do. You are talking about 3 separate systems, and each have their own job to do. But there is no electrical standard, code, or practice that will tell you they have to be isolated from each other. Quite the opposite they all have to be bonded together. If not; not only do you have a huge safety and life issue, you got one heck of an operating problem full of noise and intermodulation.
     
    Last edited: Feb 28, 2012
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are taking me out of context. I am not referring to signal grounds at this point in the discussion. I am strictly speaking ground electrode systems which encompass RF, Lightning, and Electrical. In those case ground loops are desired with Lightning and Electrical. RF in the HF spectrum is about radials and their impedance to earth is not important.

    In every electric sub station, generation plants, cellular tower, and commercial broadcast stations the whole compound has what is called by various names, are ground mats constructed of copper wire ranging in size from 6 AWG to 750 MCM arranged in a grid like pattern. The grid centers can be anywhere from 40 feet on center to a foot or two based on application and frequency of interest. They have much lower impedance than any or single wire can come close too between any two points.
     
  8. W8JI

    W8JI Ham Member QRZ Page

    Maybe you are the one who doesn't understand like you think you do? :)

    I explained my position accurately.

    If we directly bond the radials in a 1/4 wave groundplane antenna to the mast or to the coax shield, without isolation, the system will have SWR and pattern problems with common mode impedance variations in the mast or coax. The same is true in many antennas and many RF systems.

    It is also true, in audio systems, that grounds very often cannot be common-connected at some points. So signal grounds, chassis grounds, and safety grounds are not always the same or able to be treated as the same.

    RF grounds and counterpoises are NOT always the same as lightning grounds and safety ground, and cannot always be bonded. All grounds should be bonded at the building entrance, but we have to be very careful to not get inside that point or outside that point and apply the same logic without understanding the system.
     
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  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    You just agreed with me. Thank you for the acknowledgement.
     
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    LJW:

    I was referring to the grounding at the demarc! Although not true in the "goode olde dayes", telephone wiring on the user side of the demarc is now the responsibility of the user. Cable television is tending to this as well. However, there are still a number of those companies that still maintain the premises wiring.

    Since telephone service installation is usually made after the final inspection on most structures, there are very few, if any, inspections made of the telephone installations. The same is true for cable television and Internet service installations. The result is a general carelessness, if not actual disregard, for proper grounding techniques especially where residential and small business customers are concerned. Even when the business customer is large, there are individual telephone installers who pay little attention to proper grounding. The fact that there is usually no inspection, and that there are few customers who actually are familiar with proper techniques, is another reason that the installers do not pay that much attention to doing a proper job of grounding.

    Then, there are omissions, clerical errors, etc., in the building codes of various municipalities which can result in unsatisfactory, sometimes dangerous, situations. For example, sometime during the 1960s the need for a ground at the entrance to the building for the AC mains was eliminated here in the City of Richardson. This probably happened when some clerk-typist was copying text from the NEC. The result was, to comply with the building code, that home builders did NOT provide a ground connection! It took several years before that mistake was corrected.

    My house was built in early 1969 and did not have a ground on the AC entrance. Neither did any of the houses around mine. After taking possession of the house on 1 April 1972, one of the first things that I did was to install a ground rod and connect it to the meter base. This is in the Canyon Creek area of Richardson which is entirely "custom built" homes (not tract homes). As the houses have "turned over", proper grounding has been done at the other houses in the neighborhood. Unfortunately, the subcontractor that Oncor used when replacing the old type meters with the new "smart meters", cut loose the ground from the meter base when the meter was replaced and did NOT reconnect the ground! This was a violation of "code". When I contacted Oncor, they referred me to the subcontractor saying that it was their responsibility to replace the ground. The subcontractor said no, it was Oncor's responsibility. After going round and round, and getting nowhere, I just went out and redid the ground myself. Had I still been working for TXU, I would have known the specific individual to call and the situation would have been resolved in a matter of hours! But, since I had not been employed for well over a decade, I did not know exactly the person to call. It was just easier to make the repair myself.

    Glen, K9STH
     
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