Grounding Do's Don'ts & Why Part 3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Mar 19, 2012.

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  1. W6KCS

    W6KCS Ham Member QRZ Page

    Dereck, does the ground rod's resistance to earth (measured with a tester at power line frequencies) have anything at all to do with the impedance the rod presents to a lightning strike? In other words if the ground rod is 5 ohms, 25 ohms or 300 ohms as measured on a tester, does that matter as far as being able to dissipate a strike? Since we drive multiple rods at our sites, there is no requirement for any particular resistance to ground, and I've never cared what it was anyway, but wondered if it mattered during a lightning "event."
     
  2. KF5LJW

    KF5LJW Ham Member QRZ Page

    No Steve makes no difference and you hit the nail on the head in your assessment. That is the short answer I know you are looking for. Read on if you or others want to know why. But it is Stupid Simple electrical fundamentals.

    As you noted you are talking POWER FREQUENCIES which has absolutely nothing to do with frequencies above 180 Hz is where we start. To start make sure the GEC and Bonding Conductors are adequately sized to safely handle imposed currents. Minimum size for Lightning Protection is Solid Bare Tinned Copper is 4 AWG up to a 200-Amp service. NEC will require larger if the service conductors are larger than those in Table 250.66. Bu t4 AWG will handle most any Lightning imposed currents due to th ever fast rise time and extremely short duration to handle the heat.

    You are also aware of Motorola, Military, Telecom 5-Ohm requirement which is long ago antiquated. Ask any of them why; and they cannot answer or make it up. You are also aware of the NEC statement, not requirement of 25 Ohms which is also ancient history. Both originate come from the Civil War error, and early beginnings of telephone service. Remember the TELEGRAPH? The Union's secret weapon of the Civil War. Telegraph used a single wire ran above ground on poles, and a battery. Dirt was used as the second conductor, or battery return circuit. 5-Ohm dirt was a lot lower resistance than say even 1 of steel wire and way lower than 1o or 20 miles. Dirt is cheap and could not be cut down by Confederate, and required no repairs.

    That same 5-Ohm requirement bled over into the early days of Telephone for the Ringer Bell on your telephone. Telcos used dirt as part of the Ring Circuit for th esame reasons, it is cheap and a lot lower resistance than 10000 feet of 22 AWG copper. Ring Voltage was applied to Tip-to-Ground, Ring-to-Ground, and Tip-to-Ring. Combine that with Frequency Selective ringers of 20, 30, 40, and 50 Hz, and you could carry 16 parties on a single line. Which now leads us to the antiquated 25-Ohm statement long ago removed as a requirment to make your phone ringer work on a party line from Ma-Bell. None of that is done today, but yet remains imbedded in antiquated standards which are useless today. Yet they still exist ironically.

    Next any Bonding Jumper of GEC is a Single Conductor not ran or magnetically coupled to any associated phase conductor which means will have very high impedance to even 60Hz power frequencies. Example look in IEEE and LPI standards and you will note once you get up to 10 Khz and you are exceeding over 100 Ohms impedance for a 10-foot section of 4 AWG. Going from 4 AWG to 750 MCM does not change things. Get up to 1 Mhz and now you are up to 1000 Ohms and higher. So tell me what the Impedance is of a 5-Ohm Power Frequency ground in series with that 10-Foot 750 MCM cable you over paid for? Who cares right, you pissed away a lot of money that bought you nothing. Only one happy about it is the contractor and supply houses you emptied your wallet into.

    This is not to say the GES is not important because it is. Just not the impedance. Rods do very little for lightning because lightning runs along the surface away from entry point. Rods are good for DC and power frequencies and this point is also lost on most engineers and way above the pay grade of amateur radio operators who heads have been filled with BS for generations. They have been told BS so much for so long they believe it and never question it. So tell me what happens if you paid up $10,000 sinking rods, and if you are lucky achieved 10-Ohms impedance at 60 Hz. What happens if say your 20-amp distribution circuit goes to ground through your body? Nothing, 120 volts / 10 -Ohms = 12 amps on a 20 amp circuit. Fuse is happy, but you could be killed. Silly fools.

    Again Steve you know what professionals use at cell towers, commercial broadcast, data centers, and the list goes on right? They use forms of laterals like Ground Rings or Radials (NOT RF RADIALS on a tower). Ground Rings shunt Lightning currents around the protected area and Radials carry lightning away from the protected area. Again lightning faults travel along the surface. Rods are there Spaced out 2 x the depth of rods to short out the Capacitance of the radials, and the impedance is irrelevant. Take away here is the topology and technique used. Basic idea is bond everything below grade together, bond everything above grade together, then bond the two together at one point (SINGLE POINT GROUND), and it makes no fricking difference what the Impedance is. Lightning only has one point to get to dirt and will not flow inside the protected area. It stays outside where it belongs. That poin tis lost on a lo tof engineers, and just about all ham radio operators because they have been lied to their whole lives and believe it.

    Last point is a pet peeve I have is RF GROUNDS aka Tower RF Ground and silly dang hams who throw money away with their silly dang ideas. They end up making the system extremely dangerous and NOISY with their misplaced ideas because they have been taught JUNK SCIENCE and promoted by money hungry Ham Radio Industry playing ham radio operators for fools. Chaps my butt. Is this you? Not you Steve, you know better. You buy a Ring Plate for the Tower Base and it comes with upteen gillion feet of insulated 12 or 14 you are instructed to lay on top of the ground or just get below the surface. You silly dang fool. Not your fault, you have been given really bad half baked advice all your life. Sure it works great, at HF (similar to lightning frequencies you get a nice low impedance with all those radials with respect to DIRT. You get nice low take-off angles and great signal reports. How could it possible be the wrong thing to do? Because it is a half baked idea, and misses the point lacking fundamentals. Then you compound the error because you have been told not to BOND the RF Radio Ground to Station Ground or your homes Power Ground. You silly dang fools. All you have done is eliminated a great lightning sink by using insulated wires, added a lot of RX noise, and have INVITED LIGHTNING inside your home to have a look around you shack and home wiring system you silly fools. All that could be minimized if you had done one simple thing, and eliminated doing 2 simple things.

    1. Follow simple basic electrical code and RF practice. Run a Bonding Conductor from your Station GES to the Tower Base. But no you have been lied too and told not to do that. So now what you have done is used the shield of your coax to connect the Tower Base ground to your radio. So when lightning strikes it comes right on inside to you radio equipment and finds DIRT through your house wiring you fool. That is exactly what you asked for, and you got it.

    2. Use bare solid wire, not insulated pinned to the ground. It cost less, and adds a good deal of lightning protection you silly ole fool.

    Steve here is the funny part and the inside joke between you and I because we are pros, plus a few knowledgeable hams. We already know this. :p
     
  3. W6KCS

    W6KCS Ham Member QRZ Page

    I had forgotten about the lightning currents being mainly at the surface. It sounds like they might be dissipated more by the radials and the ring bonding conductors than the rods themselves. We use radials and ground rings too, in fact we follow R56 pretty much except we bolt the racks directly to the concrete, so unfortunately we don't have a single point ground at the feedthrough plate, and we don't use halos. Could you explain the part about the rods shunting the capacitance of the radials? Does this make the radials "look" like a lower impedance at the tower bond?
     
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Halos are not that big of a deal IMO. Not that they do no toffer anything, Just never seen a failure from EMP without them. Have way to many sites in Florida through Texas without Halos and never had an issue with EMP. It Will be an issue IMO when Chi-Coms and Ruskies detonate EMP device over the USA and knock out all communications, power, electronic devices, and vehicles. But who cares right as that will be the least of problems. But a Halo would not likely help in that event because non of the Arestors are EMP rated. DOD is the only entity that can afford them and most of DOD is underground and shielded.

    The racks being bolted to the floor can cause you a problem with a direct strike. Most problems I have encountered is from lazy clueless Installers. Either they forget a bushing, over torque a bushing cracking it, or forget the phenolic isolation pad under the racks, etc. When that happen you get a path inside coming in on the hardlines > radio chassis > rack corruption > concrete floor. Easy to find, just look for the burnt spots around the floor anchors or corners of the rack. I can easily catch them if I get to inspect when installation is complete. A Meggar will find and violation anywhere inside the shelter.



    Sure, no problem. Even though you use bare conductors, dirt is a poor conductor, so you get capacitive coupling. If you stop and think about, remember Sphere of Influence with ground rods? Lightning mostly flows along the surface and will go down to some degree. Bottom line is Rods shout out the capacitance somewhat to the dirt, just like it shorts out cable capacitance in a Grounded System vs Delta. Takes the stress of the GES.

    Still have your Polyphaser book? It covers it pretty good, or IEEE Green Book.

    Hope that helps
     
  5. W6KCS

    W6KCS Ham Member QRZ Page

    Thanks! I have both books, I never get enough time to read them. I think I'll put them in the bathroom.
     
    N4FFL likes this.
  6. N4FFL

    N4FFL Ham Member QRZ Page

    LOL!!!! :D
     
    W6KCS likes this.
  7. W6KCS

    W6KCS Ham Member QRZ Page

    Well, the night before last we tried a new Mexican place that opened up recently, yadda yadda yadda, and now I'm finished with both books.
     
    KX4O and KA2CZU like this.
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    Peace and Taco Grease.
     
  9. MIKESM

    MIKESM QRZ Member

    Ok, we found a way to route the wire around the house and take it to the ISBT bounding point where the isolation transformer and station ground go.

    However, the city won't let us do this! In fact, they refuse to allow us to connect the Ufer to the ground point that will feed the station either. They are OK with the rooftop antenna ground going to a separate ground rod (as if that makes much difference), but they don't want anything that could carry lightning and such touching the Ufer or the station ground!

    Now, this is what the GC told me after discussing it with the city. And they didn't quote any NEC requirement etc... I am going to have to talk to them myself.

    I should point out that the service utilities (power, cable, telco) connect to ground at a detached garage, and are grounded there, and to a Ufer to the rebar in the garage slab. THe main power feeds to the house all come from that panel. However, the Ufer in the house is not connected to the Ufer in the garage, which is why I thought I could bond it to the station ground on the other side of the isolation transformer. Otherwise it's not bonded to anything.

    Am I doing something wrong?



    Thx
    Mike
     
  10. OG6Z

    OG6Z Ham Member QRZ Page

    Well i have only a simple grounding a copper pipe which goes 10 ft down under ground. Welded with 20 gauge copper wire from tuner. And even though i use loop antennas and yes i know that loop does not need grounding. But somehow i have a quieter remote whit this system.
     

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