Single Point Grounding 4 Dummies

Discussion in 'General Technical Questions and Answers' started by AI5DH, May 18, 2020.

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  1. AI5DH

    AI5DH Ham Member

    Correct, a typo.
     
  2. KK5JY

    KK5JY Ham Member QRZ Page

    I got a good chuckle out of (c). :)
     
  3. W6KCS

    W6KCS Ham Member QRZ Page

    Dereck, if you have 12V and/or 48V systems, should they have their common bus bonded to the MGB/PANI bus? Seems like if not there would be no hot to chassis overcurrent protection, but IIRC we haven't been doing that.
     
  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Derek, I have questions about the following.

    I don’t think a ferrite choke on a ground system bonding wire would ever be a good idea since it would raise the impedance during surge current from a nearby lightning event.

    I can’t find anywhere in the NEC where it says that radio equipment inside a building must have a separate grounding conductor from the coax shield and the AC power cord, so I’m not sure why you say it is required.
     
  5. AI5DH

    AI5DH Ham Member

    Absolutely required Steve as you know. Serves the same purpose as bonding the neutral in an AC Service. In the case of a ham radio, the bond is inside the Radio. You radios do not have the battery bonded to the chassis.
     
  6. AI5DH

    AI5DH Ham Member

    OK I can see where you are off track. In a SPG how is the lightning suppose to get in? There is not a path or any place for it to go except straight to dirt outside. What comes in is just open wires. None of the single wire circuits are capable of passing any high frequencies. That can only pass DC and Power Frequencies.

    If you have a compromised antenna to close to the shack, can cause a ground wire to resonate if the length and frequency is right. Example seen a few DC Power Supply AC Equipment Ground sing and cause some TV interference. Real easy to find, Disconnect grounds one at a time until you find the offender. Found many DC supplies to be the cause.

    A Power Quality engineer would use Common Mode Filter on the AC Line that is a basic Low Pass Filter and a nice Common Mode Choke on Line.Neutral and Equipment Ground. A RF weeny uses ugly large Snap-On Cores and wind the AC Power Cord a few times through it. You want to Block any normal operating currents trying to flow in Equipment Grounds Your equipment grounds are for DC and 60 Hz only. They are not capable of doing anything else.
     
  7. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    But there can be magnetically induced lightning surge currents in the loop made up of the house wiring ground and the station ground. A choke on a ground bond wire will present a high impedance leading to a large surge voltage. No?
     
  8. K2WH

    K2WH Premium Subscriber QRZ Page

    While I have a common ground point for everything, 1/4" x 4" x 12" copper plate, when lightning approaches, I just disconnect everything from anything outside the house.

    However, you can't stop lightning and if its going to strike your stuff, it will.

    Don't forget to disconnect your computer also, from the mains and any cables like USB's or wall wart power and land lines.
     
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    I have seen induced voltage from a near by lightning strike smoke every computers network card in the building. :eek:

    Grounding did not help at all.

    Copper phone lines can really be a problem when a utility pole gets hit.
     
    N0TZU likes this.
  10. AI5DH

    AI5DH Ham Member

    What loop Bob? You take a wire, strip the insulation off on one and stick it in the mud. You bring the opposite insulated end inside and it goes no where electrically. It is an Open Circuit and never sees Ground again once it enters.

    That is the point, there is no loop in a Single Point. No way in or out. What you do have is Ground Rise Potential (aka Earth Rise Potential) which is of absolutely of no concern. You are a fishing bobber floating in the ocean. Now if you brought that wire inside , then took it back outside to a different location in the dirt, stripped off insulation and stuck the end in the mud, you got a heck or a problem, You made a complete circuit with a potential of passing 10;s of thousands of amps running through your home and equipment. Now Ground Rise Potential would give you are serious short circuit problem. You have essentially taken a wire and connected it across a battery with a unlimited voltage and current potential.

    Think of it like this. I have an elephant of a battery in a room. This battery is the size of a car or truck, 10,000 volts with enough capacity to deliver 10,000 amps for hours upon hours. Nothing is connected to either battery polarity. Now get up and sit down on or touch one of the polarizes. What happens? Not a dang thing happens. Now make contact with the other polarity and you have a complete circuit. You are vaporized. You gave current a path to flow through and completed a circuit. A point to Enter, and a point to Exit. You made a loop Bob and your equipment is part of the loop. and a Ground Conductor. It is no longer service equipment, its a wire.

    Every Ground Wire is only for safety, and safety only. Single Wires are not capable of being a circuit conductor for anything other than Power Frequencies. Lightning or any electrical charge seeks to return to its source. A radio is not the source of lighting, it is DIRT. Lightning is not going to bypass your antenna , come through your roof, strike your radio, then use a Equipment ground to get to dirt. Only way that can happen is if you provide a path to get inside, then go back outside. Most ham radio operators provide that path and invite lightning and common mode noise inside. Commercial operators do not do that.
     
    WD4ELG likes this.
  11. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yes of course, we’ve all been over that many, many times here.

    To essentially repeat my question from above, it only considers conducted current and ignores magnetic induction of current in the conductors by the intense B field from nearby lightning. (I can use big bold fonts too)

    The flux links through the loop that starts at the service entrance ground rod, along the house wiring, to the radio and computer, USB cable to radio, etc., then through the bonding ground wire (at radio, computer, tuner, etc) and coax back to the service entrance ground rod. If that path is low impedance then voltages are kept lower, no problem, assuming the conductors can handle the surge current.

    But if there is a high impedance point such as a choke on the ground wire as you suggested, then the voltage will be much higher, possibly damaging or lethal. Hence my earlier question about the wisdom of choking such a ground conductor.

    Am I wrong? If so, why?

    Here's a quick little conceptual sketch -

    IMG_3555.jpeg
     
  12. AI5DH

    AI5DH Ham Member



    OK now we are getting somewhere. I have not ignored Magnetic Induction. I already spoke to it and you did not pick up on it. I was speaking to another peer, an Rf Engineer friend of mine, and like myself a ham radio operator. He was with me on everything except one point I brought his attention too with the Transmission Line example. He forgot to apply Ohm's Law, Parallel Circuit Laws, and Mutual Inductance and how they interact. So let's try a different approach, first let's get on the same page to start.

    I agree with you a direct or nearby strike will induce a current in your house and ground wires. No doubt about it. Exactly the same principle I used with Induced RF Current on your equipment ground wires and house wiring having a compromised antenna being within 2 wave lengths of your home. Neither of which have anything to do with Ground. Exact same thing that makes every transformer work. Can we agree on that point? It Happens. Can we put that behind us and move on please?

    Here is where you and I part ways along with many of you. Somehow you have been lead to believe that improving the ground system will solve the problem of both Lightning and RF Currents from flowing on your equipment ground conductors and house wiring. Doing things like using larger wire or braided wire interconnected as many times as possible. This implies you are trying to lower the impedance to earth. Somehow lowering the impedance makes current less in a conductor?

    Certainly not what the Industry does, exact opposite. We impede and limit current to tolerable limits to the extent possible. Industry impedes the unwanted current where it is not wanted, and directs them straight back down to He!! where it came from. We did not forget about Ohm's Law and use it as a tool. Do you know of any tool in our bag with magnetic properties that might hep to that end?

    Statistics tell a good story and speak truth. Agree?

    99% of ham radio operators DO NOT have 200 to 2000 foot towers located in the geographical area highest elevations.
    99% of commercial tower HAVE 200 to 2000 foot towers located in the geographical area highest elevations.
    99% of ham radio operators never suffer a direct lightning strike.
    99% of commercial towers are struck by lightning just about every time a thunderstorm passes over. Many site multiple times every storm
    99% of ham radio operators whose station is struck by lightning suffer significant lightning damage. Does snot even require a direct strike.
    Commercial towers rarely have lightning damage. Takes either a significant strike or a corrupted Single Point Ground System.

    FWIW UL, IEEE, CE, Lightning Protection Institute, and some other alphabet soup orgs have done joint studies concluding 95% of electronic equipment lightning damage is via utility power lines. Something most hams never consider. Commercial Tower operators did not forget.

    To conclude Bob what I am saying to you is if you have an Equipment Ground Conductor like a Station Ground or Power Supply AC EGC singing and causing you problems, choke or reconfigure it properly. I assume you know how to Isolate a Signing Ground right? You temporarily disconnect them one at a time until you find the culprit. Either changes it length, reroute it, or choke the snot out of it.
     
  13. KB0TQ

    KB0TQ XML Subscriber QRZ Page

    Derrick,
    Thanks for this, your other 3-part thread and the time you spent with me on the phone.
    "… a Ground Window, an imaginary window within a 3-feet radius of that spot to effectively be the same spot electrically."
    That is the part I have a hard time wrapping my head around.

    I am doing a compromise single point ground.
    My coax enters on the other side of the house as the power company. There is a ground rod at the coax entrance that has LPS and Coax shield bonded to it.
    This ground rod is bonded to my copper (cold) water pipe with about 10ft of #6 stranded copper.

    The water pipe is bonded to the AC panel via heavy stranded aluminum cable (about 40' of it).

    I'll also have a station ground bar that is about 15 ft from that same water pipe.

    So, at various locations on this cold water pipe, I have
    1) Bond to my "Coax ground rod"
    2) The Power company bond to the water pipe
    3) My station bond to the water pipe.

    Also, (physically) separate from the water pipe, there is the actual power company ground at the building entrance.

    None of these are within a 3-ft radius of each other.

    Does that mean that there is/may be a difference in voltage between the systems? (Which of course is what we are trying to NOT do.).
    Or to put it another way, is the copper water pipe a good enough conductor to make all the points the same electrically?
     
    Last edited: May 24, 2020
  14. AI3V

    AI3V Ham Member QRZ Page

    Back at it again huh?

    The lightning event has a significant radio component due to the dv/dt of the event.

    This is self evident to anybody who has ever lisyened to a radio, and observed the static crashes caused by lightning.

    When ANY ONE of the objects near your station wiring is struck by lightning, there will be a enormous em field set up around that object by the current in the lightning stroke.

    This field is capable of inducing a corresponding voltage/current in any nearby conductor.

    You need to stick to explaining about ground loops vis a vis noise in signal circuits.

    https://archive.org/details/allaboutlightnin0000uman

    https://members.rennlist.com/warren/LightningProtectionAndGrounding.pdf

    Rege
     
  15. AI5DH

    AI5DH Ham Member

    Rege you need to learn Ohms Law and Parallel Circuit Laws. They tell you how to deal with it. Wouldn't hurt if you knew something about Transformers and Single Wire Conductors too.

    Where you and most go wrong is you start with the wrong presumptions and assumptions from the start. Everything else is seriously flawed from the start. Example if you understood Equipment Grounds and Ground Conductors are only for Safety and 0-Volt Touch Reference and not physically capable of doing anything else, you can then begin to understand what does what.

    Example you and most hams completely missed the Transmission Line example. One fine gentleman from Arkansas that calls himself Whiskey Seven stated I was an idiot because I did not realize Equipment Grounds were in parallel with the coax shield, and thus pass RF current. How ignorant can you be? However I remember to apply Ohm's Law, Parallel Circuit Laws and Mutual Conductance. So here is a real easy question Rege you will get this wrong along with a lot hams. Multiple guess choice question a student can answer.

    What is the impedance of your coax shield and center conductor @ 1 Mhz?

    A. 50 Ohms
    b. 75 Ohms
    C 300 Ohms
    D. None of the above.

    Answer = None of the Above. The Impedance should be as low as possible in the milli-ohms. Rege answered either A, B, or C like many of you did. Never occurred to you it would be impossible for your coax to be a Circuit Conductor with a lot of impedance getting in the way. You would have 50 ohms of the shield in series with the antenna 50 Ohms in series with the center conductor of 50 ohms yielding a total circuit impedance of 150 Ohms. You would loose 66% of your transmit power just on the coax being lost as waste heat.

    Next question.

    What is the Impedance @ 1 Mhz of a 10-foot section of 750 MCM copper ground conductor the size of your wrist you used for a Station Ground Wire to ground rod stuck in mud?

    A. 0.1 Ohms
    B. 1 Ohm
    C 10 Ohms
    D 100 Ohms
    E 1000 Ohms

    Answer = E. Really does not matter if it is 12 AWG or 750 MCM, the impedance @ 1 Mhz is roughly 1000 Ohms. If goes up proportionally as frequency does up until you hit resonance at roughly 24 Mhz when the impedance dips to around 30 or 40 ohms which is way to be high to be used as a Circuit Conductor. Perhaps some lights just turned on for some of you?

    So did I consider the fact you will have an Equipment Ground in parallel with coax shields? I dang sure did and knows what will happen if you do and understand impedance ratios and parallel circuits. I know if you put say a 30-Ohm resonant conductor in parallel with a coax shield with an impedance of .033 Ohms is a 1000:1 ratio. Unlikely to create any sort of a problem, and if by odd chance it should, I know how to attenuate the RF Current another 40 dB or an additional 10,000: 1 ratio by CHOKING THE SNOT out of the Equipment Ground Conductor.

    Now the impedance on the 750 MCM cable you used at DC and Power Frequencies is on the order of micro-micro-Ohms. Impress just 1 volt on it and you have all kinds of current inducting a fault, tripping the breaker for your SAFETY. Otherwise all it does is holds your equipment touch potential to 0-Volts under normal operating conditions. Nothing more, nothing less.

    So once you get your noodle wrapped around the fact all Equipment Grounds are for Safety only. They are not capable of passing any frequencies other than power frequencies, you begin to understand what ground does and most importantly what it DOES NOT DO. Then you can understand your Coax Shield is not a Ground, and your Equipment Grounds are not Circuit Conductors. Neither can do what the other does.

    A coax is a Transmission Line exactly like a AC Power Cord or any signal circuit. You have closely and tightly coupled conductors. The current in the two opposing circuit conductors are 180 degrees out of phase cancelling out Mutual Inductance leaving you with just resistance and capacitive coupling between the Circuit Conductors. SINGLE GROUND WIRES are NOT ran with an associated Circuit Conductor. Thus do not get the benefit of Mutual Inductance cancellation.

    I am happy some of you are getting it. Received dozens of of PM's, emails, and many phone calls. I have followed up on all of them and provided additional documentation. Glad to help.
     
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