Astron PS and Your Ground

Discussion in 'General Technical Questions and Answers' started by KF5LJW, Oct 29, 2019.

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  1. K0OKS

    K0OKS Premium Subscriber QRZ Page



    Is that not the purpose of the #8 or better buried bonding wire outside that connects the two ground rods together as required by code?

    This is insufficient?

    My Astron was grounded on the negative, but I removed that years ago when I first got it (used) and rebuilt it. As mentioned earlier here, and on RepeaterBuilder (a great site with tons of info on Astrons and other stuff), it is almost random which Astrons are negative grounded and which are not where the same model may be either way depending on when it was made, etc.
     
    WA7ARK likes this.
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Adding a jumper or ground buss isn't going to eliminate a typical incidental path through the radios and associated equipment and isolate them on their own "star" path. The best either can do is add a shorter lower impedance path in parallel.

    My shack is an example. There are two star ground systems, one for the AC power centered at the service entrance rod and one for the station centered at the antenna cable entrance rod. They are, of course, bonded together per code with about 25 feet of #6 wire. The radio DC power supply negative is isolated from green wire ground. I experience no hum, RF in the shack, GFCI tripping, little shocks, or other anomalies.

    However, there is still an inadvertent loop connection between the AC branch circuit ground and the RF ground. It originates at the computer display green wire ground, goes through the HDMI cable, through the Mac Mini, through the USB/serial port converter, and ends at the radio serial port, which is chassis grounded and thence to the antenna shields and RF ground. (the Mac Mini has a two wire AC supply, so it only contributes continuity here).

    I can easily detect a very small AC current flowing on the coax shield using a highly amplified pickup coil. If any of the path described above is broken, the current stops. If I add a jumper between the RF cable entrance ground and its closest AC receptacle on the same branch circuit (about 6 feet) the current is reduced but not eliminated. This is expected, since the jumper path is in parallel with the inadvertent path which still exists. At higher frequencies, there are other paths that also come into play, such as AC bypass capacitors (as has been mentioned).

    It would have been nice to have built a custom house for radio, with co-located AC and RF entrances, one shared ground rod, and with the shack on the other side of the wall, but very, very few of us have that option. Maybe in the next life!
     
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  3. K6CLS

    K6CLS Ham Member QRZ Page

    good detective work to isolate that...

    would an optoisolator interfac helpe, perhaps on the USB or RS232?
     
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  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, a USB isolator could be used, but I have no operational problems as a result of the inadvertent connection so I see no reason to complicate things solely on that account.

    However lightning transient protection is another matter, so I’m planning to install the parallel ground jumper. It will certainly have a lower impedance than the inadvertent path. Again, it’s not going to eliminate or somehow isolate the inadvertent path, just reduce the transient current on it, but that will still be helpful.

    With computer interfaces to ham radios common these days, I suspect most ham shacks have similar inadvertent paths through them.
     
    Last edited: Nov 3, 2019
    WA7ARK likes this.
  5. K8AI

    K8AI Ham Member QRZ Page

    Is it #8 or #6 that's required? I thought it was #6.
     
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  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    It’s usually #6 or better for typical house service. If more than 200A service maybe it gets larger. Some jurisdictions might differ.
     
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  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Yes it is required by code, but that does not prevent current from running inside. The NEC assumes you have been educated and already know to make only one connection to the ground system. If you were to make two connections you would not pass inspection and would not be allowed to connect to a utility.

    So here is the problem most of you are not understanding. There is a gradient voltage along the surface of the dirt and it is cause by utilities. Take a rod, stick it in the ground. place another rod some distance and stick it in the ground. Then take a volt meter and you will read AC voltage @ 60 Hz. Now when you bond the two rods together you will have current flowing because there is a voltage present that is pushing the current. So now say that is the 6 AWG used to bond rods together. We now bond the AC service Neutral to the Ground Electrode System. No we have a nice single point ground as intended. Now you come along and want to being in your coax on the other side of the house. That second rod was placed so it is right outside the shack. We have a 120 Volt AC circuit with AC Ground, that connects to say you linear amp which requires a the AC Ground bonded to the chassis of the amp. From there out the coax shield to the ground rod and now we make the second and complete the circuit loop.

    So now the 12 AWG AC ground wire is in series with your radio and bonded to ground through your coax shield. Please do not think the 6 AWG outside stops that current because that is impossible. If you look at the circuit, if it were a snake would bite you. What you have is two rods bonded together. On the outside you have the 6 AWG required by code. Then inside you have a 12 AWG AC Ground Wire in parallel with the 6 AWG wire going to the amp chassis and through the coax. All adding the 12 AWG did was increase the amount of current flowing because you have two conductors in parallel. What happens when you put two resistors in parallel? Resistance goes down. 2 x 1-ohm resistors in parallel = 0.5 Ohms. So now you have current flowing in both ground Conductors, something you never want to happen. But that is what you get when you bring you coax in from a different location than the AC.

    You cannot prevent the loop because you made a bad decision to bring in the coax on a different side of the house. No one ever told you all the bad things that can happen when you do that. What you can do is take your radio out of the Loop and solve most of the problems, except for one. If lightning strikes the tower or nearby, you are going to have lightning entering your home. You set out the Welcome Mat out that says Lightning Enter Here and take a trip through my homes electrical wiring. You provided the path when brought in the second earth ground. Best you can do is prevent it from flowing through your radio. It is real easy and I have drawn the circuit several times so you can see it.

    Complete the loop with a shunt as described , then configure your ground so AC Ground and RF Ground are the same point. Think about that for a minute. With a single point, it is impossible for any current to flow. Once you wrap your noodle around that fact, then you will understand what I am telling you. This is very basic fundementals taught th efirst week of school.
     
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    OK time for the correct answer. In NEC code there are two wires used for ground. One is very specific and is called the Ground Electrode Conductor (GEC) and there can only be one Ground Electrode Conductor in any given AC System. The Ground Electrode Conductor is the conductor that runs from your meter can or Disconnect Device to the Ground Electrode System. The size of the GEC is determined by Table 250.66 and is based on the size of the Service Conductors from the utility. Example say the utility runs a 2/0 AWG service conductor which is what they would likely use on a 200-amp service. That being said the GEC ios required to be a minimum #4 AWG copper or #2 AWG alu. A 1/0 AWG service would be #6 AWG copper.

    Everything else used in the ground electrode system is a BONDING JUMPER as is every other ground in an AC system. The green wire ran with your 120 volt circuits is called a Equipment Bonding Jumper, no longer called a Equipment Ground Conductor. OK back to Electrode Bonding Jumper shall be #6 AWG or larger.

    For antenna Mast, coax, or anything radio outside only requires minimum #14 AWG copper.

    So the correct answer is what wire are you referring too? It depends on where and how it is used.
     
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Sorry that is not correct. You can short the loop and create a Single Point Ground.
     
  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    That is why I started this thread to remind hams and alert new hams if you have an Astron check for the defect as it is well known and documented. Only bad things happen with the jumper in place. One of the bad things is it completes the AC and DC Loop. It connects AC and RF Ground together which is 100% factual. Then someone went off on a tangent that it does not matter and impossible to isolate them. Well in fact there is a better way to arrange the grounds. Not to Isolate them, Relocate the AC Ground at the same point where the coax shield is bonded to the rod outside vs opposite side of house. So when you plug in an AC powered equipment the ground wire in the power cord goes straight the same point you bonded the coax. Real simple to do. All you are doing is taking the 12 AWG ground wire from your main panel and extending it to the ground rod you bond the coax too. That shorts the Loop out, removes the radio equipment from the Loop with a Single Point Ground. All it requires you to do is use a Power Strip with 6 receptacles and most come with surge protection devices for Ethernet RJ45. That allows you to plug in a lot of AC equipment and not cause any breaches in a single point ground plane.

    Perhaps this will help. In practice there are two steps:

    1 Complete the Ground Loop by shorting it out. To do this we extend the 12 or 14 AWG AC Ground wire from AC Breaker Panel to the Rod outside shack used as RF Ground where we bond the coax.

    2. Move AC Ground from the other side of the house, to the same place the Coax is bonded too outside the shack on the ground rod. Easy Peasy. We Shunt the Coax and bond it twice. We already have it bonded once outside on the ground rod right. So we are going to bond the shield again inside the shack with our Power Strip. Use a Coax Surge Protector or a Ground Block made to be mounted to a metal surface. You need a Ground Plane like a small buss bar or even sheet metal glued to a plywood board. Install both Surge Protector and Power Strip to Ground Plane. Most likely will require you to drill a hole in Power Strip and bond the Ground Plane to the AC Ground Buss inside Power Strip. Terminate coax to Surge Protector and use a coax jumper to Radio.

    Now when you plug any AC powered equipment into the Power Strip, is the exact same ground point the RF Ground, and with a dedicated conductor in the power cord.
     
    Last edited: Nov 3, 2019

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