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Posted by John Grabowski on March 2, 2009, 3:44 pm
>>>>>>> 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.
>>>>>> 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
>>>>> 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.
>>>> *Article 250.56 spells it out.
>>> 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.
>> *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.
> 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?
*My you have a lot of questions. Quite frankly I don't know. The ground
testers that I have used were of the three point type and the clamp on type
and were battery operated.
Many years ago I was a foreman on a shopping center being built in Burbank,
Ca. The power company had very strict requirements for their transformer
pad. They wanted less than 25 ohms and the soil was sandy. We had already
installed two ground rods prior to the arrival of the tester from the power
company, but I had a few more handy with clamps. When the guy did his first
measurement he said it was no good. We drove a third rod and it was still
no good. After the fourth rod he said it was close enough.
Try doing a search on the internet for instructions on using the meggar.
Maybe try the manufacturer directly.
Incidentally the two rod requirement was in the 2005 code.
|
|
Posted by Dioclese on March 3, 2009, 10:05 am
>>>>>>>> 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.
>>>>>>> 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
>>>>>> 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.
>>>>> *Article 250.56 spells it out.
>>>> 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.
>>> *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.
>> 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?
> *My you have a lot of questions. Quite frankly I don't know. The ground
> testers that I have used were of the three point type and the clamp on
> type and were battery operated.
> Many years ago I was a foreman on a shopping center being built in
> Burbank, Ca. The power company had very strict requirements for their
> transformer pad. They wanted less than 25 ohms and the soil was sandy.
> We had already installed two ground rods prior to the arrival of the
> tester from the power company, but I had a few more handy with clamps.
> When the guy did his first measurement he said it was no good. We drove a
> third rod and it was still no good. After the fourth rod he said it was
> close enough.
> Try doing a search on the internet for instructions on using the meggar.
> Maybe try the manufacturer directly.
> Incidentally the two rod requirement was in the 2005 code.
The two point, hand-cranked megger that I'm used to (ex-Navy) were used to
determine high resistivity, not low resistivity. That's why the question.
House was turned over to me by the builder on Feb 28th, 2005. Builder
started house in November, 2004.
I started the detached garage in late November, 2004. Finished in early
January, 2005.
Which brings the question, if the most current NEC code is enforced by the
local municipality, is the start date or the finish date of the structure
that bears importance to meet local code? I know its unlikely in my case as
the municipality has to pass that most current NEC code into their current
code before the municipality's inspector can enforce it.
--
Dave
CDOs are how we got here.
A modified version, new taxes in the future, is how Congress will get us
out?
|
|
Posted by John Grabowski on March 3, 2009, 8:48 pm
"Dioclese" <NONE> wrote in message
>>>>>>>>> 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.
>>>>>>>> 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
>>>>>>> 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.
>>>>>> *Article 250.56 spells it out.
>>>>> 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.
>>>> *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.
>>> 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?
>> *My you have a lot of questions. Quite frankly I don't know. The ground
>> testers that I have used were of the three point type and the clamp on
>> type and were battery operated.
>> Many years ago I was a foreman on a shopping center being built in
>> Burbank, Ca. The power company had very strict requirements for their
>> transformer pad. They wanted less than 25 ohms and the soil was sandy.
>> We had already installed two ground rods prior to the arrival of the
>> tester from the power company, but I had a few more handy with clamps.
>> When the guy did his first measurement he said it was no good. We drove
>> a third rod and it was still no good. After the fourth rod he said it
>> was close enough.
>> Try doing a search on the internet for instructions on using the meggar.
>> Maybe try the manufacturer directly.
>> Incidentally the two rod requirement was in the 2005 code.
> The two point, hand-cranked megger that I'm used to (ex-Navy) were used to
> determine high resistivity, not low resistivity. That's why the question.
> House was turned over to me by the builder on Feb 28th, 2005. Builder
> started house in November, 2004.
> I started the detached garage in late November, 2004. Finished in early
> January, 2005.
> Which brings the question, if the most current NEC code is enforced by the
> local municipality, is the start date or the finish date of the structure
> that bears importance to meet local code? I know its unlikely in my case
> as the municipality has to pass that most current NEC code into their
> current code before the municipality's inspector can enforce it.
*In NJ we go by the code that was in effect at the time the permit was
issued. It would be too confusing and a big hassle to change codes during
the middle of a project. It could also affect the construction cost.
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|
Posted by Bill on March 1, 2009, 11:51 am
I would bet the only time you will need to add the second ground rod, is if
you pull another permit. You would then be required to be up to the current
code.
> 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?
> A modified version, new taxes in the future, is how Congress will get us
> out?
WhoKnew?????
>
|
|
Posted by Steve Barker on February 25, 2009, 4:01 pm
Dioclese wrote:
> NEC article 250-32(b)(1)
>
> Its called a "grounding rod". He will also need the appropriate gauge bare
> copper wire and copper clamp for the grounding rod.
>
> The ground from the main panel is not connected at the secondary location's
> subpanel.
>
Better study it again.
|
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>>>>>>> others are coming up with another as well to be added.
>>>>>> 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
>>>>> 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.
>>>> *Article 250.56 spells it out.
>>> 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.