How many ground rods

[Dennis Alwon]

I'm courious, if the ground rod had less then 25 ohms to ground. Wouldn't the 1 ground rod be ok?

Yes it would.

Roger

I totally agree with Roger but remember it would be very unusual to get 25 ohms with a standard 8' rod, or two or three, etc

 

[George Stolz]

So you count the metal pipe as the main ground even if it changes to pvc before it enters the ground ?

Where did Don say that a plastic pipe is considered a grounding electrode? :roll:

Edit to add: And just what is a metal plastic pipe?

We have to run # 4 to the rods on a 200 amp service here...

Given your proclivity towards embracing phantom codes, have you verified that it is required, or have you taken someone's word for it?

...will you explain what difference it makes who calls what the main when it is done that way .If it makes you happy to say my rods are not the main my water pipes are , then who cares ? :roll:

Do you read what people post? In the OP, the ground rods are clearly supplemental.

 

[roger]

So you count the metal pipe as the main ground even if it changes to pvc before it enters the ground ?

No you don't, if it doesn't meet the NEC requirement of at least 10 feet of metallic pipe in contact with the earth there is no water ground electrode present.

We have to run # 4 to the rods on a 200 amp service here

Jetlag, is that a formal amendment to the NEC requirement or is it another instance of where an inspector has told you something that is not true?

and if metal pipes bond it with #4 ,

Bonding water piping systems are not the same thing as a water pipe grounding electrode as part of the GES.

will you explain what difference it makes who calls what the main when it is done that way .

If a water pipe electrode is availabe it will be the main electrode and would have to have a GEC sized per table 250.66 whereas, the rod(s) or plate electrode would never require a GEC larger than # 6 CU

If it makes you happy to say my rods are not the main my water pipes are , then who cares ? :roll:

The NEC

Roger

 

[jetlag]

Correct-here, the AF boys use what they call a Vibra-Ground or similar meter that runs $2000+ to test and certify grounds at 10 ohms or less on sensitive equip. Has one leg clamped to the rod in question, 2nd to a probe in the ground 20 meters away and 3rd 40 meters away. Thats why no one tests for <25 ohms. In MI, AHJ was a stickler and wanted metal u/g water as primary(if available) and then out to rod as second...or 2 rods.

Darn , no wonder it didnt work, The ahj said I had to apply ohms law to the meg reading , he came up with 14.4 ohms with one rod . I said sounds good to me :grin:

 

[jetlag]

No you don't, if it doesn't meet the NEC requirement of at least 10 feet of metallic pipe in contact with the earth there is no water ground electrode present. Jetlag, is that a formal amendment to the NEC requirement or is it another instance of where an inspector has told you something that is not true?Bonding water piping systems are not the same thing as a water pipe grounding electrode as part of the GES. If a water pipe electrode is availabe it will be the main electrode and would have to have a GEC sized per table 250.66 whereas, the rod(s) or plate electrode would never require a GEC larger than # 6 CU The NEC

Roger

We are still not on the same track , I agree with what you are saying but if you run #4 to the metal pipes and also the rods on a 200 amp service, no one has to worry about if the pipes qualify for the main or not . Are you saying we are not allowed to run over a #6 to the secondary ground ? We run the #4 to both rods and pipe out of our own choice so if the pipes pass for main ground they have the right conductor , if the pipes do not pass for the main they are still bonded and the rods are the main. If you run 6 to the rods and the Ahj wont accept the pipes as a main you get flagged .

 

[George Stolz]

If you run 6 to the rods and the Ahj wont accept the pipes as a main you get flagged .

Why would they not be accepted, if they comply with 250.52(A)?

 

[Dennis Alwon]

Jetlag it seems your AHJ needs some continuing ed classes.

 

[don_resqcapt19]

... If you run 6 to the rods and the Ahj wont accept the pipes as a main you get flagged .

The NEC never requires more than a #6 to a ground rod. Is there a formally adopted amendment to the NEC in your area that requires a GEC larger than #6 to a ground rod?

 

[LEO2854]

We are still not on the same track , I agree with what you are saying but if you run #4 to the metal pipes and also the rods on a 200 amp service, no one has to worry about if the pipes qualify for the main or not . Are you saying we are not allowed to run over a #6 to the secondary ground ? We run the #4 to both rods and pipe out of our own choice so if the pipes pass for main ground they have the right conductor , if the pipes do not pass for the main they are still bonded and the rods are the main. If you run 6 to the rods and the Ahj wont accept the pipes as a main you get flagged .

Look at 250.66(A) 2008 NEC

 

[enteng14]

Nice discussions sirs. Here are my thoughts:

1. Metal water pipes if available and complied with the requirements of NEC as grounding electrode, then it should be used as grounding electrode and should be supplemented with a ground rod (or other made electrodes).

2. If the measured earth resistance is less than 25 ohms (4 point ground tester or other ground tester is used), then additional ground rod should be driven at least 6ft apart and bonded with the existing ground rod (the NEC never said to test the earth resistance if two ground rod are already installed).

3. Grounding electrode conductor are not recommended to be more than #6 copper but you may do so if you want but it's just a waste of money.

 

[jetlag]

I dont know what else to say but this , all the water pipes here on residential for the past 30 years or more are pvc or pex pipe , if you find an old house or new building with metal it connot be used as the grounding electrode because the water lines from the main to the meter are all flex plastic now installed by the water company. We are allowed to use 2 rods as the only means of ground without an ohm test, but we are required to bond metal piping . To the rods we are required to use chart 250.66 for the GEC and for 4/0 alum the size is #4 cu. We are not allowed to reduce the GEC to #6 by 250.66 A. It is that way for every county around here. The only exception is if you do the ground test on metal pipe and it passes for the main ground then #4 is ran to the pipes and #6 to 1 rod is allowed. I am not going to start an argument with 7 counties that I only have to use #6 to the rods on a 200 amp with plastic pipes . These rods are the main electrode ground when there is no metal pipe .

 

[jetlag]

I need to add this . If you can convince the AHJ that the metal pipes qualify as the grounding electrode without the ohm test then the single rod can have a #6 gec , and this is often the case on new buildings but never allowed on old houses.

 

[George Stolz]

if you find an old house or new building with metal it connot be used as the grounding electrode because the water lines from the main to the meter are all flex plastic now installed by the water company.

I seriously doubt the water company has dug up an old existing house's yard for the express purpose of removing the metal and installing copper. However, if you conform to the rules treating it as a GECs, then you'd be compliant whether the AHJ believed the water pipe to be 10' metal underground or not.

To the rods we are required to use chart 250.66 for the GEC and for 4/0 alum the size is #4 cu. We are not allowed to reduce the GEC to #6 by 250.66 A. It is that way for every county around here.

The only exception is if you do the ground test on metal pipe and it passes for the main ground then #4 is ran to the pipes and #6 to 1 rod is allowed.

Well, then the seven counties have either amended the NEC, or are making it up as they go. These two quotes are not congruent with the NEC.

I am not going to start an argument with 7 counties that I only have to use #6 to the rods on a 200 amp with plastic pipes .

We're not asking you to. We are trying to establish that they are wrong.

 

[roger]

I dont know what else to say but this , all the water pipes here on residential for the past 30 years or more are pvc or pex pipe ,

Then there is no water pipe electrode present.

if you find an old house or new building with metal it connot be used as the grounding electrode because the water lines from the main to the meter are all flex plastic now installed by the water company.

And once again if there is not 10 feet of metallic water pipe in contact with the earth there is no water pipe electrode.

We are allowed to use 2 rods as the only means of ground without an ohm test,

As is everywhere under the NEC rules.

but we are required to bond metal piping .

As is everywhere under NEC rules

To the rods we are required to use chart 250.66 for the GEC and for 4/0 alum the size is #4 cu.

Is that in a formal GA code that someone could access online?

We are not allowed to reduce the GEC to #6 by 250.66 A.

It would not be reducing the required GEC size.

It is that way for every county around here.

Can they provide you with a formal set of their codes?

The only exception is if you do the ground test on metal pipe and it passes for the main ground then #4 is ran to the pipes and #6 to 1 rod is allowed.

Once again, can they provide you with a formal set of their codes?

I am not going to start an argument with 7 counties that I only have to use #6 to the rods on a 200 amp with plastic pipes .

That is your perogative but this discussion is in the NEC forum.

These rods are the main electrode ground when there is no metal pipe .

And unless one of the other electrodes listed in 250.50 is present this would be true per the NEC but, there is no reason for these rods to have a larger conductor than a #6. Just for fun, ask your inspector(s) how much current will flow in a 120 volt circuit with 25 ohms?

Roger

 

[jetlag]

Then there is no water pipe electrode present. And once again if there is not 10 feet of metallic water pipe in contact with the earth there is no water pipe electrode. As is everywhere under the NEC rules.
As is everywhere under NEC rules

Is that in a formal GA code that someone could access online? It would not be reducing the required GEC size. Can they provide you with a formal set of their codes?
Once again, can they provide you with a formal set of their codes? That is your perogative but this discussion is in the NEC forum. And unless one of the other electrodes listed in 250.50 is present this would be true per the NEC but, there is no reason for these rods to have a larger conductor than a #6. Just for fun, ask your inspector(s) how much current will flow in a 120 volt circuit with 25 ohms?

Roger

Well to be honest, the code sections on grounding is so confusing , I never questioned the reason for the #4 to the rods . I have read 250.66 A many times and wonder why it conflicts with table 250.66. I still dont see why just listing the rod sizes allowed in 250.52 A 5 is enough reason not to use the full size #4 , if the rods are the only grounding electrode. And yes they have dug up most of the water lines here because they are all galvanized pipes installed in the 60 's and have rusted away because of the soil conditions in Ga. So you maintain that even if a service is 200 amp with plastic pipe and 2 ground rods are used , the EGC only has to be #6 ? Well I will bring it to the AHJ attention and see why they require #4 . It could be a local or state thing , I dont know . But I promise you 7 counties didnt make this up on their own , they are receiving instructions from the state or somewhere, because the big commercial contractors around here know the code very well and would have challenged it long ago.

 

[Dennis Alwon]

From what I am reading jetlag, you are doing what is necessary but your ahj's or you are misunderstanding. What you call the main electrode is not as important, it can be, as the fact that they are used. The water pipe in the ground is the main electrode whether the AHJ thinks so or not. Unless he or you can prove that the integrity of the line is gone then it may not be a good electrode but it still needs bonding. We also have to supplement the water lines with the rods whether the lines are metal or plastic-- rods must be used-- unless a Ufer or other accepted supplemental electrode is used. Personally I prefer the Ufer.

 

[jetlag]

From what I am reading jetlag, you are doing what is necessary but your ahj's or you are misunderstanding. What you call the main electrode is not as important, it can be, as the fact that they are used. The water pipe in the ground is the main electrode whether the AHJ thinks so or not. Unless he or you can prove that the integrity of the line is gone then it may not be a good electrode but it still needs bonding. We also have to supplement the water lines with the rods whether the lines are metal or plastic-- rods must be used-- unless a Ufer or other accepted supplemental electrode is used. Personally I prefer the Ufer.

Thats the thing Dennis , so many of the old metal pipe houses have lost their ground integrity or been tore down or had to be replaced with plastic pipe. I can see where the AHJ doesnt really want to try to prove the integrity of the old pipes as a grounding electrode. We do bond it any way so if the ground is good that is a plus . You have to remember I only remember putting a new service 3 or 4 old houses with metal pipes in the last 20 years at least. By the time the houses need complete new plumbing and wiring , not that many are worth the expense and the house gets condemed by the city . And no one puts metal in a new house any more , its not just the cost , the minerals eat the pipes up . Commercial is a different thing , there still use copper a lot but you still have to use caution because the main to the meter is probably flexible plastic.

 

[don_resqcapt19]

... So you maintain that even if a service is 200 amp with plastic pipe and 2 ground rods are used , the EGC only has to be #6 ? Well I will bring it to the AHJ attention and see why they require #4 . It could be a local or state thing , I dont know . But I promise you 7 counties didnt make this up on their own , they are receiving instructions from the state or somewhere, because the big commercial contractors around here know the code very well and would have challenged it long ago.

It could be a 10,000 amp service and the NEC would only require a #6 to a driven ground rod, even where the rod is the only grounding electrode for the service. This is becuase a #6 can carry more current than a driven ground rod can put into the earth. There is no advantage to running a larger conductor and the rule in the NEC recognizes this fact.
Where ever the information is coming from, it goes beyond what is required by the NEC.

 

[jetlag]

It could be a 10,000 amp service and the NEC would only require a #6 to a driven ground rod, even where the rod is the only grounding electrode for the service. This is becuase a #6 can carry more current than a driven ground rod can put into the earth. There is no advantage to running a larger conductor and the rule in the NEC recognizes this fact.
Where ever the information is coming from, it goes beyond what is required by the NEC.

I have never heard it worded quite that way but everyone posting seems to agree and I cant see where 250.66 A makes any exceptions for the size of the service or the fact that the ground rods are the only grounding electrode . All I can figure is over the years people just got so used to using the # 4 on water pipes that were the grounding electrode that there is a mix up as to what is being called the grounding electrode conductor when only rods are used. The next time I get a new service job I will find out for sure where the communication is wrong. :grin:

 

[jxofaltrds]

I have never heard it worded quite that way but everyone posting seems to agree and I cant see where 250.66 A makes any exceptions for the size of the service or the fact that the ground rods are the only grounding electrode . All I can figure is over the years people just got so used to using the # 4 on water pipes that were the grounding electrode that there is a mix up as to what is being called the grounding electrode conductor when only rods are used. The next time I get a new service job I will find out for sure where the communication is wrong. :grin:

You are correct. No exceptions. I am not trying to be funny but re-read from "shall not be required *******".