electrical detached garage ?

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Your electrical inspector would know.

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Bill wrote:

option to ask.
s
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I'm not the expert but I'm thinking that because the subpanel is located in a detached building that it also must have a ground rod AND 4 wires back. If anyone is sure about otherwise I'm glad to hear it cause it's save me a couple bucks on the ground rod :-)
*You are correct. The ground rod is for lightning protection. Check with your building inspector to see if he wants two.
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That is correct for your situation. This configuration is always required by the 2008 NEC, and it is required by earlier NECs if there is any other metallic path between the detached building and the building with the service.
Note that you need to have a grounding electrode system at the detached building, and ground rods are just one option. All electrodes present must be attached together, and the possibilities include: ground rods you choose to drive; metallic water service pipe that is buried for at least 10' before entering the building; and the rebar in your foundation, if it is #4 or larger.
The rebar is required to be used if you are pouring a new foundation (not for an existing building), and if you attach to it, there is no need to drive any ground rods. The metallic water pipe is required to be supplemented by at least one other electrode, e.g. a ground rod or the rebar. Lastly, if you are using only ground rods, because no other electrodes are present, you must drive two ground rods.
That's just a quick summary of the rules, see Article 250 of the NEC for the exact text.
Cheers, Wayne
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Water is plastic and it's not worth the hassle to get at the rebar in the footing. Walls are block up to 24" above grade. So I'll be going copper rod at the power entrance.
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OK, so you'll need two ground rods.
Wayne
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Water is plastic and it's not worth the hassle to get at the rebar in the footing. Walls are block up to 24" above grade. So I'll be going copper rod at the power entrance.
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You are correct. Bear in mind, this is electrically speaking regarding a separate grounding conductor. The disconnecting means may be a primary switch box, or the subpanel with breakers and so forth. That is where they (grounding at separate building and introduced power) become all part of the buildings electrical system. I only count one grounding rod in this scenario. I don't know where others are coming up with another as well to be added.
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Dave

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On 2009-02-27, Dioclese <NONE> wrote:

Anytime a grounding rod is your only grounding electrode, unless you can prove that the resistance to ground is less than 25 ohms, you need to install a second ground rod. Since doing a proper ground resistance measurement is alot harder than driving a second ground rod, the only practical solution is to use two ground rods.
In my opinion, this "25 ohms" requirement is a bit of historical fluff without a rational basis, so the requirement should be rewritten to simply require two ground rods.
Cheers, Wayne
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So, let me get this straight. You're driving a solid 8' copper rod into the earth. It may be straight down, it may be at an angle or even approaching sideways. If any part of the earth is greater than 25 ohms, you have to use 2 grounding rods, not one. Y/N?
What about air voids in the driving rods scenario, are they a factor in the scenario of 2 grounding rods? If not, why not?
Are alll the other previous single grounding rod requirements from the former NEC grandfathered, or do I have to go out there and do another grounding rod for each one currently provided? If grandfathered, other than convenience sake, why?
Nevermind, you're just citing code without NEC code designation.
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"Dioclese" <NONE> wrote in message

*Article 250.56 spells it out.
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Saw nothing on "grandfathering" or air voids in the earth.
In one forum, I noticed some inspectors are making the declaration that 2 grounding rods are required, unless the installer can prove the less than 25 ohm requirement on one grounding rod. Not vice versa, that is, the inspector testing one and sole grounding rod and finding greater than 25 ohms megged, and then making the declaration that 2 grounding rods are required.
Since the earth is cumulatively resistant over distance/depth and varies with soil type, various stratas with that soil, and water content, I don't see how megging is of any way of any bearing. This is a farce, just make the 2 rod requirement and be done with it. Stupid code.
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*I'm in NJ and it is currently accepted that there is no place in the state that you will find less than 25 ohms to earth with one ground rod. Consequently the two rods are installed.
Here it is up to the installer to provide the proof that something is acceptable. That's why I always save some labels and packaging until after a job is finalized. If an inspector questions me on something I have the documentation that the item is approved for the use.
You're right that the two rod requirement is a bit of joke. No one seems to know the origins of the 25 ohms. Ask an expert or call up the NFPA and ask them.
I don't recall ever seeing the NEC mentioning grandfathering. If that were so that could mean that every house would need to be upgraded every three years. The NEC is only a guide that can be adopted by states, counties and towns. Some jurisdictions adopt it as is. Others such as NJ adopt most of it, but leave exceptions to certain requirements. During the last code cycle we were not required to install arc fault circuit breakers and as far as I know they still are not required. It would be up to your local jurisdiction to require the upgrading of ground rods.
Regarding air voids in the earth. I have never heard any reference to this and I am not sure how you would determine that your rod passes through one. However an air void would affect the ohms to earth since there would be less earth contact. Another reason to have two rods.
Copper clad ground rods have a rated life of 40 years. Galvanized is much less. If your rod is old I would suggest that you put some new ones in.
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No, the house and detached garage were finished at beginning of 2005. Detached garage, its electrical installation, its entireity, were built by myself. It was within NEC code at the time with one grounding rod. The only enforced building regulations here are for new septic installations. These regulations are county oriented and county enforced.
The air void thing is a question as my area has a lot of fractured limestone. The majority of which begins at the surface, no topsoil to speak of in some cases. In rock barring and digging this up for fence posts, I did find some air voids if I carefully dug without upsetting what's underneath.
Just curious. How does one connect a standard 2 cable megger, with spin handle for current, for testing resistivity for a grounding bar regarding the maximum 25 ohm requirement? How many samples have to be taken to establish the actual maximum resistivity for the NEC regulation?
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On 2009-03-02, Dioclese <NONE> wrote:

That depends on the NEC code in force at the time it was built. The current NEC requires using the foundation rebar as a grounding electrode in new construction. I believe that requirement began with the 2005 NEC. Of course, your garage may have no rebar in its foundation.

You can't. If you use two ground rods far apart, and measure the resistance between them, you are getting the sum of the resistance to earth of the two rods. So for measuring resistance to earth on a single ground rod you typically use a special three point tester, which provides enough information to isolate out the resistance of each of the ground probes. Since the tester is fairly expensive, and the test fairly complicated, it is much simpler just to drive two ground rods and skip any measurements.
Cheers, Wayne
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I had an extra ground rod concern (had one, needed an additional one) a while back. The inspector suggested use of a single ground plate (approx. 15" x 20") instead of the ground rod array. The plate was only 30" deep. This was in northern Ontario. I didn't see plates mentioned up-thread.
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wrote:

I had an extra ground rod concern (had one, needed an additional one) a while back. The inspector suggested use of a single ground plate (approx. 15" x 20") instead of the ground rod array. The plate was only 30" deep. This was in northern Ontario. I didn't see plates mentioned up-thread.
*The plate is certainly a viable and approved option.
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The garage slab and driveway were constructed, poured, and finished by a company that normally does commercial slabs and county road needs. The garage has the standard rebar beam perimeter, remainder has bags with fill overlaid with rebar. I don't know the gauge of the rebar. The rebar was thicker in the beams than the remainder. The rebar in the remainder was thicker than that used in the driveway. They also went out of their way to put a miniature beams (not rebar reinforced vertically) on the driveway perimeter.
I went by the NEC available and approved at the time in the late 2004 era. As did the house builder. Both the house and detached garage have their own single grounding 8' bar (copper), #4 copper bare wire and copper crimp clamp.

Which explains why the inspector don't do such tests... They just enforce code, not establish if something meets code with testing. The 2 grounding bar is his out.
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On 2009-03-03, Dioclese <NONE> wrote:

Since as far as I know #3 bar is the smallest normally used in construction, if the rebar in the beams is thicker than #3, it is thick enough to be as part of a concrete encased electrode.

To answer your other question, here at least the code version in effect at the time of permitting applies to the project; I'm not aware of any jurisdictions that would apply a newly adopted code to ongoing projects, but perhaps there are some.
Under the 2002 NEC, the requirement on which electrodes to use said to use all "available" electrodes. This led to a debate about the concrete encased electrodes. On the one hand, for new construction, they are available in the sense that with proper planning you could use them. On the other hand, common construction practice was for building sites never to see an electrician until well after the foundation was poured, at which point the electrode was not "available". Certainly I expect that under 2002 NEC, there were not many inspectors requiring the use of the concrete encased electrodes.
The 2005 NEC clarified this by changing "available" to "present". Nowadays there are plenty of jurisdictions where the builder will be required to jack out concrete to access the rebar if they fail to connect to it as a conrete-encased electrode.
Hope this helps.
Cheers, Wayne
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That's just stupid. If they are not accessible then they are not present. I'll drive a couple copper clad rods.
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This only applies to new construction. The rebar is certainly accessible before the concrete is poured, and it is the builder's responsibility to see to it that it is use as a grounding electrode.
Cheers, Wayne
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