Panel Grounding vs. Lightning Rod Grounding

Best is to route the earthing wire directly as short as practicable with minimal bends and separated from anything else that might be an alternate (even though less conductive) path to earth.

Any bonding of a lightning ground earthing electrode to Ufer ground means the lightning electrode is an expansion of the building's single point earth ground.

For example, this application note shows how single point grounds for separate structures are also interconnected via a buried wire:

Is that too much complexity for the actual risk? That decision is the art - how much risk is a building at? How much protection is really required? Telcos do this layering of earth ground; each protection layer is defined each earth ground. But then 99.5% protection is insufficient for telcos. So they spend more on earthing.

Another and maybe simpler solution is to connect each air terminal earthing electrode (also by buried bare copper wire) to a nearest point on the Ufer ground loop. This still creates equipotential. Not as good as in the previous paragraph. But typically would be more than sufficient.

However most do not even do that much. Most only install air terminals to an earthing electrode (outside of the Ufer ground loop) and let earth conductivity be sufficient to make a conductive connection between the two earthing systems.

Ufer ground creates a loop so that anything inside the loop is at equipotential. As long as the air terminals are earthed outside that loop, then building equipotential is not violated. Each above suggestion is how to make that internal equipotential better; more robust. How much need you do? That judgment call is best determined by conductivity of geology (also taking into account any variations in soil on different sides of the building created by soil of conductive pipes/wires in that soil), history of surges over the past decade, and how necessary that protection is. Remember numbers from the IEEE citation. We are discussing protection where all solutions well exceed 95% effective. So it is really more about what is practicable verses how much protection is really required.

Now, let's say the air terminal is grounded by a separate earthing electrode. So, where are earthborne charges that a cloud is connecting to? If an earth conductive path goes away from the building, then a connection to Ufer ground increases conductivity and does little for increasing or decreasing equipotential. However if those earthborne charges are beyond the building, then the Ufer ground must conduct earthborne lightning currents around the building. Any weakness in that conductive loop (and no loop is perfect) means less equipotential inside the Ufer ground. Installing an air terminal ground loop outside the Ufer ground means less current flows through the Ufer ground; means the building inside that Ufer ground has even better equipotential. This paragraph to better explain how the direction of earthborne currents is relevant to why the same earthing system can be better or worse. This paragraph also explains why other geological features (ie nearby buried transcontinental pipeline) can change the behavior of an earthing system by changing the direction of earthborne surge currents.

BTW, research also says blunt air terminals are more effective than pointy ones. Research that contradicts popular beliefs.

BTW, some put a wire net to eliminate cracks in a poured concrete basement floor. Integrating a concrete floor into the Ufer ground is another trick to create both better conductivity and equipotential beneath the entire building.

BTW, better bonding of Ufer ground rebar involves cadwelding so that bonding is not degraded by large currents. If using some cadwelding, cadweld rebar closest to the single point ground connection - where most surge currents may be conducted.

Again, the art is to decide how much protection is required. Earthing mostly defines protection. To better appreciate this art (if possible), learn more from what telcos or other nearby high reliability facilities have done.

Interesting the construction is that solid. .

If you have a lightning strike with ten thousand amps to earth I wouldn=92t bet on keeping equipotenital. Few houses in the US would give you equipotential for a strong surge.

I have not worked on lightning rod systems and they are a specialty. You probably would have a conductor between the lightning rods on the roof with a down conductor from one or both lightning rods and a short route to earth. In the US, the NEC requires the lightning earthing system to be bonded to the building earthing system. I would use a buried wire outside the foundation. A =93ground ring=94 (buried wire) is better than just ground rods for earthing the lightning rods as some of the sources below say. (This is not a =93halo=94 ground, which is a wire just below the ceiling which may be used in transmitter rooms.) You could bond to the =93ground ring=94 where it goes past the power system earthing electrode.

Some sources I have looked at in the past:

The National Lightning Safety Institute has information on protecting buildings with an index at

. It is always fun when the sources disagree. You could ask if they follow any installation standard. There are many standards from different countries. (But installers may not like having their judgement questioned.)

-- bud--

Guys, thank you for the great responses! I have read both several times, (as I have everything else that has been posted). I am actually beginning to feel that I can put a handle on this thing now. But not until I finish studying all of the references that you have provided. That will take me weeks or months, but I will!

The buried ground loop idea, as a layered defense, is really starting to talk to me.

Probably to the relief of the rest of the group, I am going to let this topic rest now. My apologies if I have dragged it too far off-topic for ASA. I had no idea where it was going to lead when I first posted. If anyone has a suggestion as to where "Lightning Rod Grounding", by itself, should better be discussed, I will take it there next time.

Again, thank you so much, Bud and Tom, (in alphabetical order ), and everyone else that has contributed to this long discussion!

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. It was your thread. Most of the thread strayed off of your topic.

Other possible newsgroups: alt.home.repair - includes power wiring in the US and Canada uk.d-i-y - includes power wiring in England alt.engineering.electrical - international but primarily US, Canada, England I don=92t remember discussion of lightning rods at the 1st and 3rd groups but the engineering group might have some knowledgeable people.

Some of the comments in this thread are specific to the US, like the tangent what to use for a grounding electrode.

The 2 guides are specific to the US, but the principles are general.

And there are several ways power systems are earthed. In the US the neutral and ground are bonded at the service with that point connected to earth electrodes (also at the transformer). Thailand may do it differently. I would hope your system ground is connected to an earthing electrode. If the neutral is not bonded to ground at the service a service panel suppressor would have a MOV from neutral to ground which is not useful in the US. The location of the service panel suppressor is then where signal entry protector grounds should be connected.

It is long established (and required) practice to have phone wires enter the building through a protector in the US. If that is not the practice in Thailand you should add a protector similar to what w_ posted. Similarly cable entry.

-- bud--

Thanks again for your reply, Bud.

Not to worry. Everything that I have learned in this thread is useful to me. As in DIY, I may not end up doing it myself; but I may well end up directing it myself.

I am embarrassed to say it, but in this rural part of the country, "code" appears to have little or no meaning, (at least as far as I have as far been able to discern.) For example, out in the sticks, and even in renovations of older structures here in town, the convention is still ungrounded two-wire! To be fair though, the modern new constructions do install grounded three-wire. And it is my understanding that the standards for the whole country are modernizing, but I am not knowledgeable enough to say much more than that. The bottom line is that the local electricians here will pretty much do what you tell them to do. And if you don't tell them, they will do what they are used to doing... So, I am very grateful for what I have learned in this thread.

Please be assured that I will insist upon single-point grounding, including neutral, at the main panel, for power and all comm services. And the earthing electrode, at least in part, will be concrete-encased, as part of the foundation.

BTW, I am now reading your NLSI report on Structural Lightning Safety, which, if anyone else is interested, I am finding to be very educational. But still, many more links I have yet to follow...

. Geez - someone who is interested in sources--

As I wrote before, Francois Martzloff was the NIST guru on surges and wrote the NIST guide.

Another of his guides is:

A couple of Martzloff technical papers are summarized in a newsgroup post at:

Martzloff has an internet archive with many of his papers which is available at :

-- bud--

Thanks again, Bud. These will be next on my list!

Since we're still talking, I might say that your Internet Archive sounds intriguing; but I wasn't able to get either of your two references that follow to work. Might you try them again?:

And also, since we're still talking, I have another question:

Suppose I use, for example, a #2AWG CU conductor from the air terminals down to the ground ring. What kind of stand-off distance would be required, for an average amp. strike, to preclude flashover to the metal struts and rebars in the structure?

. I thought the link went directly to a download. One copy is at:

This downloaded OK for me - length 759kB .

. Still doesn=92t download successfully for me. .

. Don=92t know. An installer should.

As a basic principle nearby metal should be bonded to the lightning rod system including down conductors. From what I have read 6 feet may be =91near=92.

Surges resulting from lightning are a very short event, well under a millisecond. That makes them a high frequency event. That means the inductance of the wire is significant and may be more important than resistance. Combined with high currents the potential at the lightning rods may be far above the potential at the earthing electrode. You probably don=92t want to look at an =93average=94 strike.

-- bud--