RF Ground Rod vs Concrete Patio (

Dave, KO4DLQ, lives in Florida and has to deal with mass amounts of lightning. Dave can relate having served there for several years when he was younger. His main problem is that his shack is on the other side of the house as his utility ground, and he needs to know how to set up his grounding system to be most safe and efficient. Dave has an Idea that involves the concrete patio in front of Dave's house.
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[@bcaflyboy]

Oh wow !!! I was in radio repair (mos 30454) in the 1926th EIG and went to MacDill every summer from 1978 until 1981 during the storm season to repair or rebuild lightning damaged radios at the Airways Transmitter and Receiver sites. Enjoy your training videos Dave. 73s, Sam N5BBU

[@thecarys563]

DANGER - my home is on a prestressed concrete slab. Coring on one of those could get someone killed if you nick the steel cable in a prestressed concrete slab. I would recommend you add "have a professional check the coring and electrical plan of action before you start" as safety advice.

[@davecasler]

I've never heard of a prestressed concrete slab. All the ones I've seen are poured in place with rebar here and there. Why is your slab prestressed with cables? Is there space underneath it?

[@thecarys563]

@@davecasler CA earthquake country perhaps? All 56 units here use them. Perhaps not widely used in FL.

[@donaldsmith3048]

I have worked for years with lighting troubles in Florida! Just to give an idea what is in the lighting. I have seen the sandy soil in Florida turned to Glass from a hit. Blow the connector off of coax where it connected to the radio, the antenna fanned out where it was hit and exploded. You Do Not Want That In Your House, Or Under Your House! If you get a direct hit, all bets are off! You just want to keep the damage down! The one with your name on it is going give you troubles that you did think could happen! But you need to be able to deal with the one that hit in the next block, or a half mile away, that will put some very high voltage in your antenna system! You studied about the magnetic field around a connector. And when you put an antenna near that connector there is a very strong voltage put into the antenna! Most don't think of it as a transformer, but but it is! I will tell something most don't understand. Lighting doesn't like to make turns! The books all say not to make sharp bends in the ground wires! I saw where lighting hit and came down a 200 foot hardline until the hardline made sharp turn and the light didn't turn, there was a hole in the hardline where the lightning keep going when the hardline turned! Yes it saw the ground rod 2 or 3 feet below it. But it came down 200 feet straped to the grounded tower every 5 feet so. It jumped the outside plastic jacket at the turn! Lightning kind of makes its own rules! If we don't like it that is our problem! But lighting follows the same rules as everything but we don't understand that the very high voltage that is there! And it is fast! Think of it as a Trillion volts in the Gigahertz range! It does jump from around 30,000 feet to the ground! I don't know how many volts it takes to do that! I have seen what it does! Just think about how much power it takes to turn sand into Glass! It does that! And you don't need to take my word for! It is well documented!

[@davecasler]

My station once took a direct strike when I lived on the Colorado Front Range. Nasty!

[@timmack2415]

I would just like to add that the ground rods MUST be more than 6 feet apart, NEC code). I use the 150% rule as a minimum, meaning that 8 foot ground rods be at least 12' apart. (Motorola recommends 200% spacing, meaning 8' ground rods can be 16' apart). So, depending on how large your house is, you may need another ground rod or two to accomplish this. Mike Holt has about the best info on grounding on his site. Good luck and 73!

[@nathancross405]

ideally twice the length of the rod. Good book on grounding from ARRL that Dave references multiple times in other videos.

[@timmack2415]

@@nathancross405 We could likely write many posts about "optimal" spacing as both the Motorola and Poly-Phaser manuals (who are arguably the best in the business) are hundreds of pages, but the real answer is "it depends". While 200% spacing (in average soil) is a good "rule of thumb" it's not optimal. Two ground rods spaced very close together will be less effective than two rods with sufficient spacing, but still more effective than just one. So it's not like adding the additional rod will make things worse, but it won't add as much as it 'may' have. The reason for this: real earth isn't a perfect conductor (in fact, pretty far from it). You can think of it as something like an infinite grid of resistors, with "true ground" out at infinity, literally. If you raise the voltage at one point (by feeding power into your ground rod), each resistor will drop a little bit of voltage, and the potential at any node in the grid will be a decreasing function of the distance between that point and the source. Now consider adding a second ground rod - the further it is from the first one, the lower the potential at the point where it ties in, and the more current it will be able to accept, and vice-versa. Caveats of this simple explanation: of course, it should be a 3D mesh, and not a 2D grid - this affects how quickly the potential drops off, and also explains why the length of the ground rod matters. And this explanation is done at DC. But for RF (or lightning, which has a very fast rise time), you would need to consider capacitive and inductive contributions as well. But hopefully it gives us a rough intuition of why we need to space ground rods apart to get more benefit from having more than one. If one ground rod is placed very near another, the current from one ground rod will increase the electric potential of the other, thus making it a less effective sink for current. Two ground rods near each other is never worse than just one ground rod, but increasing the spacing of the ground rods reduces their interaction and makes an overall lower impedance path to ground. Putting ground rods too far apart is also not ideal, because at some length the inductance of the conductor between them becomes quite detrimental. The optimal spacing depends on soil conductivity and what's connecting them, but a simple rule of thumb is the distance between ground rods should be about 2X equal to the length of the rods, but is it? Research for the National Academy of Science found that the optimal spacing of 8' ground rods to be

[@nathancross405]

@@timmack2415 I think you got cut off mid sentence…

[@timmack2415]

@@nathancross405 LoL. I think KZbin doesn't like my lengthy reply (just imagine how my wife feels) 😁 Finding from the NAS: "Measurement of grounding resistances at various distances from grounding electrode spacing (in typical soil) have shown that the following percentages of the total grounding resistance will occur at the following distances from the rod: 25% of total at .03 m (.1 foot) 52% of total at .15 m (.5 foot) 94% of total at 3.0 m 9.8 feet) 98.% at 4.0m (13 feet) Nearly 100% of total at 7.6 m (25 feet) This tells us that 8 foot ground rods would need to be spaced 7.6 m (or 25 feet apart to achieve the best grounding effect.) Obviously, the guidelines provided by The National Electrical Code is a compromise, at best, but not perfect. Likewise, the spacing between 13 to 16 feet is effectively negligible. 2 times spacing vs 1.5 times may be slightly better (in some conditions), but for practical purposes, and space requirements, saving 1/10 of 1%, at best, isn't always practical. Also, Just to complicate things, lightning is transient impulse. Its neither AC nor DC but a composition of AC and DC. ( both) meaning that both inductance and capacitance can play a significant roll on spacing Solid wire, stranded wire, copper strap, connectors, cad-welding, soil and other factors come into play with spacing. I've been an electrician for 32 years and although I typically do commercial electrical work (very little residential work) I have done work for towers and shelters a few times. But being one of the Indians, not a Chief, I work with and follow the engineered specs. When I put the tower at my house, I had an engineering analysis done (required by my homeowners insurance) they came up with 8' ground rods, 3" copper strap and 13' ground rod spacing and a large Delta shape around the tower. It was 12 years ago, but I recall things like "distributed symmetry" and a few other factors were used to arrive at that conclusion. I'm no expert in lightning protection and it can be rather unpredictable. I guess this is a long way to agree with you that 2X ground rod spacing is a good rule of thumb among the many variables, but not always the best. Hey, as we both know, the majority of hams put up an antenna, hammer a ground rod (not even connected to the utility ground) don't use lightning arrestors and call it a day. I think we're both ahead of the curve on many. 73, AA2HA

[@rangersmith4652]

My shack window faces east, but my house ground is on the south side of the house. There is a concrete patio between. I have an 8-ft station ground rod outside the shack window. All my gear is grounded to a single copper element on the shack wall, and that element is grounded by 5/8" copper braid to the station grounding rod. I use 6-ga solid copper wire (that's what the electrician used for the house ground) to bond this rod to the house ground. It runs briefly underground then emerges to run across the patio inside a 1/2" PVC pipe nestled up to the wall of the house. It then goes back underground and emerges again under the house ground bus, where it's tied in. It's totally out of the way on the patio, and it's protected from damage by that pipe.

[@paulplack490]

In Florida, a "utility" is "a company which connects your home appliances to lightning rods for miles in every direction." When I lived there, a contractor I knew had a blueprint for an airport building which required a "1 ohm ground" in a hangar. They had to core down 180 feet to find any conductivity. A ham friend had a neighbor's house get struck, and lost every appliance and even the outlets in his home two doors away. Lightning in Florida!

[@davecasler]

Indeed! I lived in Tampa for 3 years while I was in the Air Force.

[@n8sot]

Excellent Dave!!!!!

[@earlfossler3577]

W4MPH - I live in Tampa and worked at TRAK for 21 years as an Engineer from 1976 to1997.

[@davecasler]

Cool! Are they still around?

[@earlfossler3577]

@@davecasler TRAK has been sold to an English company and the name was changed. There are many less cars now parked the parking lot! I am retired..

[@billryland6199]

You need an 8' ground rod as close to the shack as possible. Drill a hole through the concrete if you have to.

[@kenrnet6706]

Hi Dave - Question regarding bonding with utility ground, what do you recommend when the utility power is underground and there is no visible or accessible utility ground? Our meter has a ~3.5" conduit leaving the meter box that extends under ground. The only visible ground is a wire from the cable box drops to below ground, but that is a bare wire perhaps 3/16" -- not a rod. Thoughts?

[@gonebamboo4116]

How long until those copper clad steel rods are corroded to nothing. There was an outfit that made them from bronze, can't remember the name.

[@MrTpanozzo]

I always see it talked about that we need 6 gauge copper "uninsulated" wire for bonding things together ... Why is "uninsulated" always referred to ? I have a spool of insulated 6 gauge id like to use ... Is uninsulated a requirement and why ? Can anyone educate me ?

[@davecasler]

Uninsulated is often recommended because when buried it acts a bit like a ground rod itself.

[@nathancross405]

If you have a bond going through the house in the setup above, why would lightning go down the antenna and then into the house when it has a low resistance path through the ground rod? Talked to our local building inspector office and they said bonding through a crawlspace is acceptable given the above scenario...

[@davecasler]

If that’s what your inspector says, then by all means. However if I were to do that, I would not be able to sleep at night. I think grounds should be kept out of the house.

[@Trinitystillmyname]

I have much respect for keoog. But you speak of Nec code minimum ( wire size used) for grounding. And then turn around and go way over the top with multiple ground rods for this particular installation. The point of grounding/bonding is to get everything on the same ground plane. Do you know your water line and gas lines are bonded to your main grounding rods too? Inside your house. You are not wrong in your answer, but your uneasiness with bonding is strange. The only way to truly save your electronic equipment is to totally detach it from all grounds, antennas, and power sources. That way no path will be available for lightning to access and ham equipment.

[@BryanTorok]

What most people don't get is the vast voltage and current discharged in milliseconds. That amount of current can develop 10s of thousands of volts across what would normally be an insignificant resistance. Thus, a person standing on ground with lightning flowing through it and with their feet apart can receive a lethal shock up one leg and down the other. And, even if one has multiple bonded grounds, there can be thousands of volts at each ground rod and differences of thousands of volts between ground rods.