Thread: Grounding question

I bought a multi-family house the upstairs is my house and the finished basement is my in- laws.

We have 2 meters for the seperate units and 2 seperate breaker boxes, I was planning on replacing them with a couple new square D boxes. So I was doing some looking around and realized there was no grounding rod, Both of them are grounded to the water main, and I believe 2 grounding rods 6' apart are required as well as bonding the pipes. My question is, would I need to pound 4 Ground rods in (2 per box)?

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Originally Posted by John Naehring

Both of them are grounded to the water main, and I believe 2 grounding rods 6' apart are required as well as bonding the pipes.

You need to drive in "at least one" ground rod to supplement the water pipe.

It would not hurt to drive in two ground rods, making sure they are at least 6 feet apart from each other - connecting both to the grounding electrode conductor.

Are you sure the water pipe is being used as a grounding electrode, or is the conductor you are looking at simply bonding the interior metal water piping to ground? There is a difference in the too.

Originally Posted by Jerry Peck

You need to drive in "at least one" ground rod to supplement the water pipe.

It would not hurt to drive in two ground rods, making sure they are at least 6 feet apart from each other - connecting both to the grounding electrode conductor.

Are you sure the water pipe is being used as a grounding electrode, or is the conductor you are looking at simply bonding the interior metal water piping to ground? There is a difference in the too.

There was no jumper over the water meter unless thats not a requirement.

The wire that I am assuming is the grounding electrode is a #6 white sheathed wire running from the neutral/ground bus bar through metal conduit to where the water main penetrates the foundation. There were pipes closer to bond to but they weren't within 5' of water main penetration.

Originally Posted by John Naehring

There was no jumper over the water meter unless thats not a requirement.

The wire that I am assuming is the grounding electrode is a #6 white sheathed wire running from the neutral/ground bus bar through metal conduit to where the water main penetrates the foundation. There were pipes closer to bond to but they weren't within 5' of water main penetration.

Did you see the clamp on the pipe? From your description, it sounds like a concrete-encased (Ufer) ground.

Originally Posted by Gunnar Alquist

Did you see the clamp on the pipe? From your description, it sounds like a concrete-encased (Ufer) ground.

Yes there is a clamp there

Originally Posted by John Naehring

The wire that I am assuming is the grounding electrode is a #6 white sheathed wire running from the neutral/ground bus bar through metal conduit to where the water main penetrates the foundation. There were pipes closer to bond to but they weren't within 5' of water main penetration.

John,

From your description, then, this sounds like what is needed, in addition to other things (such as jumping around the water meter with a bond).

Originally Posted by Jerry Peck

You need to drive in "at least one" ground rod to supplement the water pipe.

It would not hurt to drive in two ground rods, making sure they are at least 6 feet apart from each other - connecting both to the grounding electrode conductor.

Last week I had several some what older homes that in this area they used the water lines as a ground in the time period. Almost all had newer service and panel installed. Only one electrician drove a new ground rod in and the rest of them just either used the old panel as a junction box for the old wiring to new and never added a ground or they replaced all the wiring but still did not drive a rod in and continued using the water lines as a ground.

Now I know I am an advocate for most tradesmen in believing that most do a very good job but this past week directed my mind set temporarily that almost all are screw ups. Seriously I do not think that on a general basis but in this case the past week it was seriously evident that most were asleep on the job.

Originally Posted by Jerry Peck

John,

From your description, then, this sounds like what is needed, in addition to other things (such as jumping around the water meter with a bond).

Thanks Jerry, I am going to drive 2 ground rods in so I dont have to worry about rod resistance, and since I am a homeowner doing my own work, I am under the very critical eye of my local electrical inspector.

Originally Posted by John Naehring

Thanks Jerry, I am going to drive 2 ground rods in so I dont have to worry about rod resistance, and since I am a homeowner doing my own work, I am under the very critical eye of my local electrical inspector.

John,

Three things:
- 1) Make sure the rods are *7* feet apart. They are only required to be *6* feet apart, but many people think that says they *are to be* 6 feet apart, when the code really says to be 6 feet apart *minimum*.
- 2) Go down to the tool rental place and they likely have an adapter head for an electric 20 pound or heavier chipping hammer or driver, that will drive those rods in almost like putting a knife into butter - takes "the work" out of driving ground rods. Drive the top of the rods down a couple of inches below grade.
- 3) Get two short piece of 4" to 6" PVC from the hardware store, you only want those pieces about 4" long or so. After you attach the grounding electrode conductor and clamp to the ground rod, place one of the short piece of PVC over each rod and clamp so the top of the PVC is even with grade level. This will protect the end of the rod and clamp from physical damage while allowing for the connection to be inspected - connect the clamp to the ground rod right near the top of the rod as you really want the full length of the rod in contact with earth.

Also, you do not need to worry about resistance if you only use one rod as you are using that to supplement the water pipe, but, what to heck, one extra rod and clamp with a little extra wire does not cost that much, and you have already rented the driver to drive them into the ground ... which is why I suggested to go ahead and install 2 instead of just the 1.

The critical thing with two driven rods, though, is *do not* try to put them '6 feet apart' - if you end up with them at 6' 11-1/2" apart then they are two close ... which is why I said 7 feet. Heck, 20 feet apart is even better, of course, though, that now does take a bit more wire (an extra 13 feet), which costs a little bit more.

Nec only requires 'made electrodes' where the water pipe (in earth) is the only electrode. If there is another electrode used, then no supplement is needed. If there are no electrodes available, then 'made electrodes' must be used ie. rods, plate etc.

Unless u can prove 25 ohms or less, u will have to use 2 rods min 6ft apart, as opposed to just one, 6ft 1in will meet code requirements.

In addition, it was mentioned that the grounding electrode conductor was run in metalic conduit. If this is the case, u will need to bond the 'gec' to both ends of the conduit. This is a code requirement due to the 'choke effect' of running a gec thru metalic conduit.

If u are increasing your service size to 200 amp, u will be installing 4/0 alum or 2/0 copper (residential only). Table 250.66 is then used to determine gec sizing. Therefore, for a 200 amp residential application u would need a #4 copper gec to the water pipe and or foundation concrete encased electrode. Note that a #6 is the max size required for any made electrode as long as it is not subject to physical damage.

Bob Smit, County Electrical Inspector.

Originally Posted by bob smit

Unless u can prove 25 ohms or less, u will have to use 2 rods min 6ft apart, as opposed to just one, 6ft 1in will meet code requirements.

Incorrect as relates to the discussion of using a driven rod (made electrode) as a supplemental electrode.

Making the driven rods 6 feet and 1/1,000 of an inch will also meet code. My point was that there is absolutely NO REASON to try for "6 feet" as it is not a stated given measure to set the driven rods at, it is a MINIMUM distance, so, why not go for more, and unless you go far enough for the cost of the wire to be noticeable (my 20 foot example), why not go further ... to 7 feet.

The resistance of a made electrode only comes into play in the following circumstance (bold is mine): "250.56 Resistance of Rod, Pipe, and Plate Electrodes. A single electrode consisting of ", being as that is a supplemental electrode, it is not a "single" electrode, thus the resistance of it does not matter - just like the resistance of two made electrodes does not matter.

In addition, it was mentioned that the grounding electrode conductor was run in metalic conduit. If this is the case, u will need to bond the 'gec' to both ends of the conduit. This is a code requirement due to the 'choke effect' of running a gec thru metalic conduit.

Quite correct, and something I presumed was existing and done by the electrician, although I know I should never presume that as I have found so many where that was not done.

Originally Posted by Jerry Peck

Quite correct, and something I presumed was existing and done by the electrician, although I know I should never presume that as I have found so many where that was not done.

I just went and looked, the conduit is not bonded, the sheath wire runs out of it and to the ground bus bar.

Jerry;
250.53(a)(2) reads, "A metal under-ground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(a)(2) through (a)(7). Where the supplemental electrode is a rod, pipe, or plate type, it shall comply with 250.56".
and then, 250.56 states "A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(a)(2) through (a)(7).

In summary: If all one has available for a grounding electrode is a water pipe at least 10ft in earth, then it must be supplemented by one of the made electrodes listed. ANY of these made electrodes must have 25 ohms or less to ground. If they do not, an additional rod, plate, or pipe type electrode must be added.

In regards to your comment about spacing more than 6ft and using 7ft as an example, I would agree, however, an Inspector of any perswation (sp) only has the right to inspect and inforce what is actually written in the code adapted by that juristiction.

When I write a violation for a missing g-rod I write "augment ground rod with an additional g-rod at least 6ft apart unless 25 ohms to ground can be proven". I Have not found anyone who could get even close to 25 ohms in Michigan as of yet.

I wish you were correct in the single rod idea for supplemental Jerry.
All my inspectors have reviewed this issue before in order to save us and our contractors/homeowners from having to install the additional rod for supplemental purposes, but the State requires us to 'enforce the code'.
Bob Smit, County Electrical Inspector

Originally Posted by bob smit

Jerry;
250.53(a)(2) reads, "A metal under-ground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(a)(2) through (a)(7). Where the supplemental electrode is a rod, pipe, or plate type, it shall comply with 250.56".
and then, 250.56 states "A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(a)(2) through (a)(7).

In summary: If all one has available for a grounding electrode is a water pipe at least 10ft in earth, then it must be supplemented by one of the made electrodes listed.

Bob,

That part is correct.

ANY of these made electrodes must have 25 ohms or less to ground. If they do not, an additional rod, plate, or pipe type electrode must be added.

That part is incorrect as the made electrode (yes, of any type, but what was being discussed was a driven rod) is not "a single electrode", it is a "supplemental" or (if you will) "a secondary" electrode, meaning there are now more than one, i.e., more than "a single" electrode.

Thus, as with made electrodes and when a second made electrode is required due to too much resistance, and if there is still too much resistance, then no additional electrodes are required.

The resistance only comes into play when there is ONLY "a single" made electrode.

Not where there is more than one electrode.

And when a made electrode serves as a supplemental electrode, that made electrode is, by definition, no "a single" electrode.

That is the way I've had all other electrical inspectors and electrical instructors say it and teach it.

In regards to your comment about spacing more than 6ft and using 7ft as an example, I would agree, however, an Inspector of any perswation (sp) only has the right to inspect and inforce what is actually written in the code adapted by that juristiction.

Agreed, which is why I said "I would recommend" ...

I wish you were correct in the single rod idea for supplemental Jerry.
All my inspectors have reviewed this issue before in order to save us and our contractors/homeowners from having to install the additional rod for supplemental purposes, but the State requires us to 'enforce the code'.

And "enforce the code" says "a single" electrode.

As I said, every other electrical code professional I have talked with says and teaches the same thing - if the made electrode is a supplemental electrode, then it is not "a single" electrode and therefore the resistance does not matter, because there are two electrodes and just like if there are two made electrodes it does not matter what the resistance is.

Jerry, I can see your point regarding how 'single electrode' could be interpt to include any other electrode ie. water pipe making it more than one electrode.
I will visit this issue yet again with my associates.

It is always prudent to find out exactly why the code req was written.
As Electrical Inspectors, we are given the auth to interpret the code.
WE are given access to info that others do not, which allows us decide the 'intent' of the requirement. The vast majority of us are interested in the intent....as we also are given the auth to allow different installations than that of the code if the intent is meant.

Before i go.....i will leave u with the original intent for requiring 'an additional electrode' when the only electrode is a water pipe.

Please note, if the only electrode is a properly grounded building steel frame, a concrete encased electrode in earth, a ufer type....the code does not req an additional electrode.....U have to ask yourself why????
What makes the water pipe any less effective???
The answer to this question is in the intent.
Fact is, the water pipe is an excellent electrode, but case history has proven that it is not always maintained and/or remains for the life of the structure.
Thus an 'additional electrode' is required. Now, if the additional electrode is of the made type, and code views as inferior, and the code wants this made electrode to be able to replace the water pipe if necessary....
then why would only one rod be sufficient in that case?

Because your aurgument has merit (at least as it could be interpreted),
I will again visit this idea w/the 75+ inspectors of my local circle and of course visit the idea with the IAEI & the code making panel.
I doubt I will find any change of mind amongst them, again, as they are also aware of the intent that the 'additional electrode' is there to possibly take the place of the water pipe some time in the future.
Thanks to u Jerry, now i have even more to add on my plate.
Will get back to u on this.....
Bob Smit, County Electrical Inspector

Originally Posted by bob smit

Jerry, I can see your point regarding how 'single electrode' could be interpt to include any other electrode ie. water pipe making it more than one electrode.
I will visit this issue yet again with my associates.

Bob,

I just found something when re-reading that section which supports your reading of it and does not support what all the others have said. Them, and myself, have missed this since it was added into that section in 2002.

- 250.53
- - (D) Metal Underground Water Pipe. Where used as a grounding electrode, metal underground water pipe shall meet the requirements of 250.53(D)(1) and (D)(2).
- - - (1) Continuity. Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters or filtering devices and similar equipment.
- - - (2) Supplemental Electrode Required. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). Where the supplemental electrode is a rod, pipe, or plate type, it shall comply with 250.56. The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the nonflexible grounded service raceway, or any grounded service enclosure.
- - - - - Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping at any convenient point as covered in 250.52(A)(1), Exception.

- 250.56 Resistance of Rod, Pipe, and Plate Electrodes.
- - A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.
- - - FPN: The paralleling efficiency of rods longer than 2.5 m (8 ft) is improved by spacing greater than 1.8 m (6 ft).

That was either a change I missed or forgot about, however, you are correct in that the made electrode used for supplementing the water pipe much NOW (since 2002) meet the resistance requirements.

The NEC really isn't clear on this common situation.

Commercial artwork will often show both panels with a wire to the fround rod, and one of these is often simply shown spliced to the other (continuous) wire. Yet, the NEC does not explicitly require this.

Running separate wires to separate ground rods is contrary to code, unless both rods are also bonded to each other.

Let's look at a very simple model: you bond the ground wires to the PoCo beutral, so that faults will clear (blow fuses, trip breakers, etc.). The ground rod, however, is there for lightning.

Why does a detached building require it's own ground rood? Because it's a separate lightning target. Why do alarms, phone systems, cable systems, satellite dishes, and antennas (ultimately) tie to the ground rod? Because they're all lightning targets.

So ... how many lightning targets is a duplex? O, even, an apartment building with 25 apartments? Just one ... so you only need one ground rod.

Originally Posted by John Steinke

The NEC really isn't clear on this common situation.

Commercial artwork will often show both panels with a wire to the fround rod, and one of these is often simply shown spliced to the other (continuous) wire. Yet, the NEC does not explicitly require this.

Running separate wires to separate ground rods is contrary to code, unless both rods are also bonded to each other.

Let's look at a very simple model: you bond the ground wires to the PoCo beutral, so that faults will clear (blow fuses, trip breakers, etc.). The ground rod, however, is there for lightning.

Why does a detached building require it's own ground rood? Because it's a separate lightning target. Why do alarms, phone systems, cable systems, satellite dishes, and antennas (ultimately) tie to the ground rod? Because they're all lightning targets.

So ... how many lightning targets is a duplex? O, even, an apartment building with 25 apartments? Just one ... so you only need one ground rod.

But two couldn't hurt right?

John, Grounding rods which are made electrodes are not lightning rods!
They may assist to a small degree in dissipating the enormous energy provided from a lightning strike.

Purpose of grounding the service regardless of method used:
To stabilize the voltage.
To establish a reference of voltage to ground.
To establish a 'zero reference' for ground.

Purpose of grounding the neutral thus making it the grounded conductor in a three (3) wire feeder to an accessory structure is to establish a 'zero reference' to ground in that surrounding area. Note that a main bonding jumper would be installed in this scenario. Note also that there cannot be any parallel metallic paths back to the structure where the feeders receive their power, such as but not limited to; a water pipe, gas line, shield on a phone cable.... Doing so may allow objectionable neutral current to follow them back.
Remember, electricity does not take the path of least resistance, it takes all paths provided and divides according to their impedance.

Purpose of grounding the 'grounding bar ONLY' when running a four (4) wire system to an accessory structure is to establish a zero reference ground between any grounded surface and/or tool etc. and the surrounding earth in that area. Note that the grounding electrode conductor would be run to the grounding buss/enclosure ONLY and a main bonding jumper would NOT be installed in this scenario. If the structure was a metal sided 'pole barn', the siding would have to be bonded.

In short, which I'm not very good at doing obviously, is that installing an grounding electrode in the area of an accessory structure is to create an equipotential plane and eliminate any voltage gradients that may present themselves. This is of a major concern regarding outdoor pools and spas.
When I inspect a natural gas production field it usually takes me a half day due to all the work required to establish an equipotential plane in those areas. Sorry guys, got carried away.
Bob Smit, County Electrical Inspector

Originally Posted by bob smit

John, Grounding rods which are made electrodes are not lightning rods!
They may assist to a small degree in dissipating the enormous energy provided from a lightning strike.

Purpose of grounding the service regardless of method used:
To stabilize the voltage.
To establish a reference of voltage to ground.
To establish a 'zero reference' for ground.

Purpose of grounding the neutral thus making it the grounded conductor in a three (3) wire feeder to an accessory structure is to establish a 'zero reference' to ground in that surrounding area. Note that a main bonding jumper would be installed in this scenario. Note also that there cannot be any parallel metallic paths back to the structure where the feeders receive their power, such as but not limited to; a water pipe, gas line, shield on a phone cable.... Doing so may allow objectionable neutral current to follow them back.
Remember, electricity does not take the path of least resistance, it takes all paths provided and divides according to their impedance.

Purpose of grounding the 'grounding bar ONLY' when running a four (4) wire system to an accessory structure is to establish a zero reference ground between any grounded surface and/or tool etc. and the surrounding earth in that area. Note that the grounding electrode conductor would be run to the grounding buss/enclosure ONLY and a main bonding jumper would NOT be installed in this scenario. If the structure was a metal sided 'pole barn', the siding would have to be bonded.

In short, which I'm not very good at doing obviously, is that installing an grounding electrode in the area of an accessory structure is to create an equipotential plane and eliminate any voltage gradients that may present themselves. This is of a major concern regarding outdoor pools and spas.
When I inspect a natural gas production field it usually takes me a half day due to all the work required to establish an equipotential plane in those areas. Sorry guys, got carried away.
Bob Smit, County Electrical Inspector

Bob, this is copied from an earlier thread.

Quote:

Originally Posted by Vern Heiler
Wasn't the neutral and ground still isolated on the old 3-wire feeds to remote structure? Just a driven ground at the remote for the ECG?


Vern,

From the 2008 NEC, which allows the old practice to remain on existing buildings and existing installations.
- 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
- - (B) Grounded Systems. For a grounded system at the separate building or structure, an equipment grounding conductor as described in 250.118 shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
- - - Exception: For existing premises wiring systems only, the grounded conductor run with the supply to the building or structure shall be permitted to be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded where all the requirements of (1), (2), and (3) are met:
- - - - (1) An equipment grounding conductor is not run with the supply to the building or structure.
- - - - (2) There are no continuous metallic paths bonded to the grounding system in each building or structure involved.
- - - - (3) Ground-fault protection of equipment has not been installed on the supply side of the feeder(s).
- - - - Where the grounded conductor is used for grounding in accordance with the provision of this exception, the size of the grounded conductor shall not be smaller than the larger of either of the following:
- - - - - (1) That required by 220.61
- - - - - (2) That required by 250.122

I always remembered it as you said, then I was corrected and found out that either I had remembered it incorrectly or it changed and I did not catch the change - not sure which it was, but, nonetheless, it is now allowed to be connected to ground at the separate building IF IT IS EXISTING as such.
__________________
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( Construction and Litigation Consultants )
AskCodeMan.com - Ask Codeman Building Code Q & A

Help me understand. Is the neutral tied to the ground at the remote building or not?

John, there is nothing in the code to discourage you from placing as many rods as you like - just make sure they're properly bonded together.

Bob, I'm well aware of all that 'ground reference' theory, etc., but it is my position that discussing such theories here will only confuse matters. Suffice it to say that several modern countries -Norway is ine- do not use any form of grounding electrode.

I did not say that a ground rod was a lightning rod. I said that their purpose was for lightning .... and, if you choose to install a system of lightning rods, guess where they tie in? At the ground rod.

The ground rod does absolutely nothing to help electricity to 'get back home' to the transformer that made it. The only electricity that considers Planet Earth 'home' comes from the sky- not the power company.

By stressing the 'lightning issue,' the code requirement for detached buildings to have a ground rod is self-evident.

I'll leave it for the enginnering wonks to discuss the finer points of electrical theory .... but I have yet to find a code scenario where the 'lightning vs. fault clearing' model steers you wrong. IMO, as Article 250 continues to be severley edited, this relationship between the two types of 'grounding' will become more evident.

Not that I've checked, or been to Norway, but if I recall correctly isn't most of Western Europe and Scandinavia 50 Hz true single phase 240v not 60 Hz split (single) phase 120/240v (or 120/208v) like we do for residential for most of the US?

Single Wire, Earth Return, (i.e. no neutral to or from the SP 7.5 kva or 14.4 kva or 19 kv transformer...isn't that a method of residential power distribution still being used in some parts of this country and Canada (especially smaller residential rural/semi-rural areas separated by distance from more concentrated urban areas and Alaska)?

Anyway, us old timers always referred to the grounding system and the back-up rod/rods (always push two more than six feet apart unless you want to leave a megger and personel to baby-sit for every code inspection, wherever the code inspector shows up - that's a mighty expensive piece of equipment and a journeyman to sit around doing nothing else, i.e. cheaper to push two for the materials cost) as the "safety ground". It is there to protect in the event the grounding at the utility pole fails or is damaged. Mighty important if the pot on the pole gets zapped by lightening, pole blows down, is pulled over by weight of ice, some car/lawntractor/snow plow snags the ground, etc. Keeps the grounded conductor (for the 120/240 VAC Service) from the PoCo grounded. We used to think this was mighty important as we swapped out the original fused (both hots & neutral) services & knife switches and upgraded them with "modern" equipment feeding loads of MWBCs (before the days of three-prong receptacles ).

For those who wish to understand some of the code requirements regarding the size and placement of ground rofs, I direct you to the data presented in the "American Electricians' Handbook." There you will see the reality explained - realities that are completely unchanged whether you have an electrician there with a megger, or a gypsy with a crystal ball.

The ground rod does absolutely nothing to cleat faults. About the only time a 'grounding electrode' provides any assistance for the PoCo transformer is when a) one hous has lost it's PoCo neutral, b) that house is in turn bonded to a metal pipe that runs uninterrupted to another house, c) that other house is also bonded to that pipe, and d) both houses get their power from the same transformer. Only whan ALL four conditions are met does the grounding electrode provide any route to the PoCo equipment.

As for 'safety,' though, the ground rod is useless. The math tells the tale: let's assume a ground rod with a very low impedance of 10 ohms. Ohms' law tells us that only 12 amps of 120 will flow - nowhere near enough to trip even the smallest breaker.

Please re-read my post above. Also, did anyone even suggest the grounding electrode sys was required in order to clear a fault...as if it could even in the greatest of conducting soil conditions?.

Stabilize the voltage by having a zero to ground reference.
Establishing an equipotential field relative to the surrounding earth and any metallic/conducting material in the area of the structure.
Establishing a point where all items to be grounded can terminate.
Not to be relied upon to dissipate the joules of power provided by a lightning strike but may inadvertently handle a small fraction of such.

Remember, where no difference of potential exists no current can flow.
Bob Smit, County Electrical Inspector