Hurk27,
With all this noted, do you have an opinion on remote services say past 200' from the structure in which an EGC is run as part of the feeder. Generally, the service equipment (OCD) is close to a grounded transformer -- the structure is being fed will have its own electrode system. We now have a path for the excess voltage to both locations. Years past the grounded conductor was the path as the EGC was not mandated. The EGC is usually smaller than the grounded conductor which seems to offer more resistance. Seems like the energy induced is now forced upon the wiring system due to the resistance. I know general terms do not fit in all occasions. I Appreciate comments to increased my knowledge.
Not sure if you are meaning induced current from a near field point of attachment or using this as just an expression of a direct voltage path that includes your conductors in the path of the current flow of a lightning strike?
Lightning strikes do not have to make contact with a buildings electrical system to cause damage, and even if it does some of the damage can be caused by the lightning electro magnetic pulse (LEPM) that can induce circulatory currents into circuits that may exhibit a loop to the magnetic field, many times when we run our conductors in a building we don't think about the other conductors that may be connected to the same equipment that can form a loop, phone, cable TV, networks, and even the low level audio cables that run from a home surround system to a self powered subwooffer that is on the other side of the room and plugged into a receptacle that may be on another circuit, these smaller cables can cause a loop that can act as a secondary of a high frequency transformer with the near field lightning strike that maybe hit a tree a couple hundred feet from the house being the primary, and here is a twist just like an isolation transformer these induced currents are isolated from the primary that was referenced to earth and no longer are seeking a path to earth, they are just seeking the return path created within the loop created by the power cables and the network cables that run to computers that may be on different circuits, draw a line prom the panel from circuit A to computer A, then draw a line from circuit B to computer B, then draw a line from computer A to computer B with a router in between to represent the network and we can see the circle, now heres the kicker that many don't think about, since all three conductors of lets say a 14/2NM cable are run withing the same cable, they will be all referenced as one conductor, the same goes for the cat5 path between the computers, this renders plug in surge protectors useless as they are only looking at the voltages between the hot,neutral, and EGC, but if all three have the same potential they can do nothing to protect the computer.
Common damage from near field (induced) lightning strikes is they very rarely cause damage to the electrical system of the building including the NM cable, but the damage one might see is in the case of a network is failed routers, network cards, and even over heated cat 5 cable in some rare cases, in the case of cable TV will be the loss of the TV tuners and some IF sections of the TV, or damaged cable box's, or analog to digital over the air converter box's, with the surround sound system with a remotely self powered sub woofer I have seen the small audio cable melt, along with damaging the input pre amp to the woofer and the sub woofer and audio output electronics in the surround receiver up to and including several stages into the receiver, one common thing I find is many times the computer, TV's and surround receiver still power up and may function just fine except the affected sections that were damaged like a computer will still boot up just fine but you find you can no longer access your network, or the TV will come on but you can't tune in anything, which means the power supplies in them was not subject to any damaging voltage and was isolated to just the affected areas that had the loop cables connected to, even a garage door opener that has the safety eyes mounted on the common metal door frame can take these eyes out and the electronic circuits on the control board in it.
Again no amount of bonding to earth much less surge suppressors can protect against this kind of a strike, running cables including network, cable TV, and NM cable in a spider where they originate from one point and all run in the same paths only to branch out to each circuits loads kind of like spidering without any inter connecting between the loads in any other paths can lower the amount of induced current, but would be very hard and expensive way to wire, conduit will help but only if you also use it for the cable TV and networks and phones, by shielding the cables from the induced currents, but there is always a chance of other metallic pathways that can cause a loop.
A lightning electro magnetic pulse (LEMP) is just like the electro magnetic pulse caused by a nuclear explosion (NEMP) just no where near the same level of strength, that our government spends millions of dollars to protect against by EMP hardening electronics from, but many of the same procedures used to protect from NEMP will also protect from LEMP's the airline manufactures also use these methods to protect against both, as they can be struck while in flight, or if a country is testing a H-bomb above ground.
As to your question of conductors in ground under at least 18" of soil, I wouldn't think they could receive much induced current from a near field lightning event, at least enough that could be damaging and never seen a case where this was determined as to what had happened, most under ground cables would be more subject to direct lightning current that can travel through earth from some distance giving the high voltage nature of the strike, unlike lower voltages discussed above that do not travel very far from a voltage source in earth.
I have hopefully learned not to make statements as I did at the onset "how do I stop them from mandating two ground rods"? I see where that may still be a valid question, relative to your stating they do next to nothing with lightning and may not do a lot with high voltage lines falling on the lower voltage lines.
I guess I should have simply asked why two, are they necessary? Resonance and high frequency paths of resistance, well, this is over my head, but I understand the application. How great you were able to study the phenomenon with expert and that you are an expert at it as well, AND....you have shared all of this with us.. Nice job.
To answer your original question which I thought was already posted, because the requirement of proving that you have 25 ohms or less or just installing two rods and going home is still in the code then you have no way to get around it, if your state requires concrete encased electrodes then the supplemental electrode for the water line has been met and you don't even need one rod, but other then that all I can say is install two rods as it is cheaper then getting the test done, and it is required by code, so even here in Indiana with state wide codes, I still install two rods and include it in my price of the job.
