# How many ground rods needed?



## HackWork (Oct 2, 2009)

Nope, it doesn’t matter what else you bond to.

Code requires one ground rod and you prove 25 ohms, or two ground rods and you don’t have to prove it.


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## macmikeman (Jan 23, 2007)

John M. said:


> i couldn't find it in the NEC...I am upgrading a service to 200 amp. I will be bonding to the public water main. Am i correct that only one rod is needed since I am bonding to the water main?


2 rods, minimum 6 foot apart. Unless you can show less than .25 ohms resistance. It's easier to just bang in #2 and forget trying to prove the lower resistance of the rod connections. They supplement the water pipe electrode


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## Dennis Alwon (May 9, 2009)

Here is the section

2


> 50.53 Grounding Electrode System Installation.
> (A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate
> electrodes shall meet the requirements of 250.53(A)(1)
> through (A)(3).
> ...


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## flyboy (Jun 13, 2011)

As an aside. Be sure to check the utilities specifications on this. Many require 2 grounds regardless of the Exception. NYSE&G is an example.


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## CoolWill (Jan 5, 2019)

flyboy said:


> As an aside. Be sure to check the utilities specifications on this. Many require 2 grounds regardless of the Exception. NYSE&G is an example.


As an aside to this aside, some local inspection departments defer to the utility spec, which is often just one rod. I was putting two rods in by default when an inspector asked why I did it. After I told him, he pointed out the POCO cut sheet just required one and thats all he was worried about. Okie dokie.


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## JoeSparky (Mar 25, 2010)

Some unnamed members here that do hackwork :wink: only drive one. Half of a rod 6+ feet apart :hammer: They are useless anyways unless you drive a ton of 10+ footers in a ring and connect them all with bare wire. Even then, they are still probably a waste of time


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## macmikeman (Jan 23, 2007)

JoeSparky said:


> Some unnamed members here that do hackwork :wink: only drive one. Half of a rod 6+ feet apart :hammer: They are useless anyways unless you drive a ton of 10+ footers in a ring and connect them all with bare wire. Even then, they are still probably a waste of time


I used to think that myself, till one time when some guy from the utility co shows up here and teaches me about the zig zag system and how when their transformers break down you can get 15k volts into your house if you don't have a good ground. So I have stopped ranting about having to pound in useless rods since that time...............


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



HackWork said:


> Nope, it doesn’t matter what else you bond to.
> 
> Code requires one ground rod and you prove 25 ohms, or two ground rods and you don’t have to prove it.


The code shows more that two rods installed and how to check for resistance. If multiple rod,pipe or plate electrodes as installed to meet the requirements I would think that the requirements is 25 ohms. not how many rods


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## macmikeman (Jan 23, 2007)

John R said:


> The code shows more that two rods installed and how to check for resistance. If multiple rod,pipe or plate electrodes as installed to meet the requirements I would think that the requirements is 25 ohms. not how many rods


No. The requirement is 2 rods spaced at least six feet apart unless you can prove one rod will turn less than 25 ohms resistance. That is all the requirement is. Run all the extras you want, the requirement for rods is two unless there is less than 25 ohms on one rod. If you get in a uffer bond to the footing rebar you can dispense with rods altogether, unless you happen to have one there already , in which case all electrodes must be used so you still have to bond to that one rod in addition to the uffer and the water connections if you have them. 

When I am upgrading a service from 100 to 200 and a remodel is going on such that I can bond the rebar in the footer, any existing ground rod disappears magically when I pull out my mallet hammer from my van and suddenly there is none present as far as ground rods go...........


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



macmikeman said:


> No. The requirement is 2 rods spaced at least six feet apart unless you can prove one rod will turn less than 25 ohms resistance. That is all the requirement is. Run all the extras you want, the requirement for rods is two unless there is less than 25 ohms on one rod. If you get in a uffer bond to the footing rebar you can dispense with rods altogether, unless you happen to have one there already , in which case all electrodes must be used so you still have to bond to that one rod in addition to the uffer and the water connections if you have them.
> 
> When I am upgrading a service from 100 to 200 and a remodel is going on such that I can bond the rebar in the footer, any existing ground rod disappears magically when I pull out my mallet hammer from my van and suddenly there is none present as far as ground rods go...........


uffer we call footings, have done 4 in the last year for a co that makes underground equipment. If the code has not changed you are required to install footing grd on new construction. (around here you have to prove 25 ohms)


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## Southeast Power (Jan 18, 2009)

John M. said:


> i couldn't find it in the NEC...I am upgrading a service to 200 amp. I will be bonding to the public water main. Am i correct that only one rod is needed since I am bonding to the water main?


Bend 12" 90 on each end of an 8' ground rod. One and done!:biggrin:


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## HackWork (Oct 2, 2009)

John R said:


> The code shows more that two rods installed and how to check for resistance. If multiple rod,pipe or plate electrodes as installed to meet the requirements I would think that the requirements is 25 ohms. not how many rods


 I have no idea what you just said. But since it seems to go against what I said, you are wrong.


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## HackWork (Oct 2, 2009)

Southeast Power said:


> Bend 12" 90 on each end of an 8' ground rod. One and done!:biggrin:


 That requires a 6 foot trench 1 foot deep. Way too much work. Just cut the ground rod in half. 

https://www.electriciantalk.com/f2/whats-better-than-one-8-foot-ground-rod-204474/


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## joebanana (Dec 21, 2010)

John R said:


> uffer we call footings, have done 4 in the last year for a co that makes underground equipment. If the code has not changed you are required to install footing grd on new construction. (*around here* you have to prove 25 ohms)


Where's here? Please take a minute and fill out your profile so we know what page you're on. Because around here we call footings, footings, and ufers, ufers. And, the slab guys install the rebar in the footings, which we use for the ufer.


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## CoolWill (Jan 5, 2019)

HackWork said:


> That requires a 6 foot trench 1 foot deep. Way too much work. Just cut the ground rod in half.
> 
> https://www.electriciantalk.com/f2/whats-better-than-one-8-foot-ground-rod-204474/


Ahckshully, the code requires the trench to be 30" deep... Jus' sayin'...


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## HackWork (Oct 2, 2009)

CoolWill said:


> Ahckshully, the code requires the trench to be 30" deep... Jus' sayin'...


The code would require 2 ground rods in the first place. We are ignoring code :biggrin:


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## Dennis Alwon (May 9, 2009)

John R said:


> uffer we call footings, have done 4 in the last year for a co that makes underground equipment. If the code has not changed you are required to install footing grd on new construction. (around here you have to prove 25 ohms)


John I don't know where around is but the NEC does not require you to get 25 ohms. You may have a local amendment or some government rules but that is not what is written in the code book.

Some times people think you need 25 ohms and then it becomes law in the area without justification.


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## brian john (Mar 11, 2007)

John R said:


> The code shows more that two rods installed and how to check for resistance. If multiple rod,pipe or plate electrodes as installed to meet the requirements I would think that the requirements is 25 ohms. not how many rods


Show me where the code tells you how to check ground resistance


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



brian john said:


> Show me where the code tells you how to check ground resistance


Exhibit 250-24 of the 2017 Handbook page 192
Also you could use ohms law.


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## HackWork (Oct 2, 2009)

John R said:


> Exhibit 250-24 of the 2017 Handbook page 192
> Also you could use ohms law.


The handbook is not the codebook. It is absolutely meaningless. It is not adopted into law and not enforceable. 

The code does not require you to prove 25ohms if you install a second ground rod. That is the reason why we install a second rod, to avoid having to deal with the 25ohm BS.

If you install a CEE/UFER, then you don't need to rod/s at all.


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## paulengr (Oct 8, 2017)

Agreed that the clear intent is to get under 25 ohms but whoever wrote the two rod rule knows nothing about grounding. Try getting under 25 ohms in a desert. You could drive a hundred rods. Ufer grounds there work but not rod grids. In other areas one rod can be 1-2 ohms.

It’s an area where Code is a joke. Setting up and running a 3 point ground test (clamp ons don’t work on just one rod) takes a lot more time than driving a second rod on a new install. Even if you measure it you’d need to be there with the paperwork for the inspector. Most of them wouldn’t even understand the 3 point grounding test. More time wasted. And nothing stopping you from watering in the rod so it easily “passes”.

I do grounding inspections (NFPA 780) and testing for mines which have to test every ground annually. Lightning systems automatically require two grounds. It is faster to test with a clamp on to verify two points are in use and picks up on stuff I can’t see underground. What I actually see in practice is that most grounds are easily under 5 ohms on one rod. Once in a while, usually sandy dry soil, they go up to 50-500 ohms. Usually it’s just that something is broken. Adding a second rod (at least one rod length apart) almost cuts the resistance in half which is what we expect. However a third rod drops it maybe 10% more. After that it barely moves the needle. All those massive civil engineer designed building grids with loops of cable or a bunch of rods linked together hardly does anything at all. Electrically it’s just one big fat ground rod. More isn’t better. Utility substations use a lot but they are trying to keep ground potential rise down somewhat.

BUT if you use threaded rods so 3 rods is just one long rod it goes down to a third of the resistance and keeps improving with each rod.



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## brian john (Mar 11, 2007)

John R said:


> Exhibit 250-24 of the 2017 Handbook page 192
> Also you could use ohms law.


The handbook is NOT the codebook.

And explain how you are using ohms law to MEASURE ground resistance.

Since it is required in your area how do you measure the ground resistance?


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## paulengr (Oct 8, 2017)

John R said:


> Exhibit 250-24 of the 2017 Handbook page 192
> 
> Also you could use ohms law.



Handbook has a lot of things in it explaining Code and includes the Code but the stuff that is not Code isn’t Code. The annexes in the Code are not Code either. I thought the Code and the Handbook are very clear on that.

Explain how you can use Ohms Law to measure resistance of a ground rod. How do you measure resistance to remote Earth? If I have a 240/120 system with a grounded neutral on a 200 A service and for the sake of argument say I’m pulling 100 A balanced (50 A on each hot), what is my ground rod resistance to remote Earth (the utility sub)? Does it change if it’s 100 A, 100% unbalanced (all on one hot leg)? And before you go there, are you using a multimeter with say a 1 ohm minimum and 0.1 ohm resolution to do it or something else?



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## manchestersparky (Mar 25, 2007)

John M. said:


> i couldn't find it in the NEC...I am upgrading a service to 200 amp. I will be bonding to the public water main. Am i correct that only one rod is needed since I am bonding to the water main?


YES you are correct 
Hit the incoming metallic water pipe within 5' of where it enters the structure , then drive 1 ground rod.


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## HackWork (Oct 2, 2009)

manchestersparky said:


> YES you are correct
> Hit the incoming metallic water pipe within 5' of where it enters the structure , then drive 1 ground rod.


Ummmm, no.


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## Dennis Alwon (May 9, 2009)

manchestersparky said:


> YES you are correct
> Hit the incoming metallic water pipe within 5' of where it enters the structure , then drive 1 ground rod.


I agree with Hax-- 2 rods are needed not one. Read the section I posted early on


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## joe-nwt (Mar 28, 2019)

macmikeman said:


> I used to think that myself, till one time when some guy from the utility co shows up here and teaches me about the zig zag system and how when their transformers break down you can get 15k volts into your house if you don't have a good ground. So I have stopped ranting about having to pound in useless rods since that time...............


I would like to see an explanation of that. I call BS.


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## HackWork (Oct 2, 2009)

joe-nwt said:


> I would like to see an explanation of that. I call BS.


I don’t doubt it happened or could happen. What I doubt is that a second ground rod will make any difference. I also doubt that using a ground rod in the first place would make any difference if already using the metallic water pipe, which is a much better electrode.


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## Fist of lightning (Aug 15, 2019)

Isn’t the nuetral coming in to the house bonded up on the poles to ground from the utility company and then you bond your nuetral and gecs to your mdp I would think thats the strongest path to ground in the system even tho I guess it’s not considered a gec .


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## JoeSparky (Mar 25, 2010)

HackWork said:


> That requires a 6 foot trench 1 foot deep. Way too much work. Just cut the ground rod in half.
> 
> https://www.electriciantalk.com/f2/whats-better-than-one-8-foot-ground-rod-204474/


Hopefully none of your NJ inspectors read this forum. The inspectors around here are already checking the ground rods of every handsome electrician that resembles an alligator :wink::biggrin:


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



paulengr said:


> Agreed that the clear intent is to get under 25 ohms but whoever wrote the two rod rule knows nothing about grounding. Try getting under 25 ohms in a desert. You could drive a hundred rods. Ufer grounds there work but not rod grids. In other areas one rod can be 1-2 ohms.
> 
> It’s an area where Code is a joke. Setting up and running a 3 point ground test (clamp ons don’t work on just one rod) takes a lot more time than driving a second rod on a new install. Even if you measure it you’d need to be there with the paperwork for the inspector. Most of them wouldn’t even understand the 3 point grounding test. More time wasted. And nothing stopping you from watering in the rod so it easily “passes”.
> 
> ...


 I agree with what you say.While working for the FEDS, all the electrical contracts stated that they had to prove 25 ohms, also no ground clamps, only cadweld Also worked in the caribbean, a lot of sand and rock, they were trying ever thing, pouring sale in bottom before setting pole..


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## HackWork (Oct 2, 2009)

John R said:


> I agree with what you say.While working for the FEDS, all the electrical contracts stated that they had to prove 25 ohms, also no ground clamps, only cadweld Also worked in the caribbean, a lot of sand and rock, they were trying ever thing, pouring sale in bottom before setting pole..


A very tiny percentage of the people here work for the FEDS. When we speak about code and requirements, we generally speak about NEC or CEC requirements. When we speak of local amendments or specialty requirements like government work, we mention that fact so others don't get confused.


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



paulengr said:


> Handbook has a lot of things in it explaining Code and includes the Code but the stuff that is not Code isn’t Code. The annexes in the Code are not Code either. I thought the Code and the Handbook are very clear on that.
> 
> Explain how you can use Ohms Law to measure resistance of a ground rod. How do you measure resistance to remote Earth? If I have a 240/120 system with a grounded neutral on a 200 A service and for the sake of argument say I’m pulling 100 A balanced (50 A on each hot), what is my ground rod resistance to remote Earth (the utility sub)? Does it change if it’s 100 A, 100% unbalanced (all on one hot leg)? And before you go there, are you using a multimeter with say a 1 ohm minimum and 0.1 ohm resolution to do it or something else?
> 
> ...


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## HackWork (Oct 2, 2009)

John R said:


> paulengr said:
> 
> 
> > Handbook has a lot of things in it explaining Code and includes the Code but the stuff that is not Code isn’t Code. The annexes in the Code are not Code either. I thought the Code and the Handbook are very clear on that.
> ...


You did not answer his questions. Please read what he asked and answer his questions. Thank you.


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## splatz (May 23, 2015)

Mike Holt has a video where they simply energized a ground rod and measured current flow with a clamp meter. They also measured ground resistance with a clamp on ground resistance tester. I think it was an AEG. The ground resistance calculated by V/I was pretty close to the measurement from the ground resistance tester. 

That would, if I am not mistaken, be a one point ground resistance test; the one point being the utility ground at the pole. But arguably it is a one point test to the one point that really matters. 

I have no idea how a clamp on ground resistance tester works. 

The Mike Holt video also showed a point of diminishing returns as they continued to couple on ground rods and keep driving, which made sense to me when I try to visualize the gradient.


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## CoolWill (Jan 5, 2019)

paulengr said:


> Handbook has a lot of things in it explaining Code and includes the Code but the stuff that is not Code isn’t Code. The annexes in the Code are not Code either. I thought the Code and the Handbook are very clear on that.
> 
> Explain how you can use Ohms Law to measure resistance of a ground rod. How do you measure resistance to remote Earth? If I have a 240/120 system with a grounded neutral on a 200 A service and for the sake of argument say I’m pulling 100 A balanced (50 A on each hot), what is my ground rod resistance to remote Earth (the utility sub)? Does it change if it’s 100 A, 100% unbalanced (all on one hot leg)? And before you go there, are you using a multimeter with say a 1 ohm minimum and 0.1 ohm resolution to do it or something else?
> 
> ...


You connect an energized conductor to the ground rod and measure the current. Since you know the applied voltage, you then use Ohm's Law to find the resistance.


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## HackWork (Oct 2, 2009)

CoolWill said:


> You connect an energized conductor to the ground rod and measure the current. Since you know the applied voltage, you then use Ohm's Law to find the resistance.


What else is your power connected to? Another rod? Or back to the tranny via one of the other electrodes?


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## splatz (May 23, 2015)

HackWork said:


> What else is your power connected to? Another rod? Or back to the tranny via one of the other electrodes?


Nothing, just the rod. If you use a 15A breaker it won't trip unless the ground resistance is less than 8 ohms. The current you measure can be used to calculate the ground resistance.


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## Incognito (Apr 14, 2019)

So those who say your required to prove 25 ohms, does energizing the rod and taking a reading count as proof? Does the inspector need to witness it or does he take your word for it?

Seems odd and possibly a safety issue to energize a ground rod for a test, I’d be surprised to hear an inspector would want you to do it.


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## HackWork (Oct 2, 2009)

Incognito said:


> So those who say your required to prove 25 ohms, does energizing the rod and taking a reading count as proof? Does the inspector need to witness it or does he take your word for it?
> 
> Seems odd and possibly a safety issue to energize a ground rod for a test, I’d be surprised to hear an inspector would want you to do it.


There is no answer. The NEC doesn't specify it, so ultimately this would be up to the AHJ. That is why we drive a second ground rod, it is easier than worrying about testing it.


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## Incognito (Apr 14, 2019)

HackWork said:


> There is no answer. The NEC doesn't specify it, so ultimately this would be up to the AHJ. That is why we drive a second ground rod, it is easier than worrying about testing it.


Our code says 2 rods. 

10-102 Grounding electrodes (see Appendix B)
1) Grounding electrodes shall consist of
a) manufactured grounding electrodes;
b) field-assembled grounding electrodes; or
c) in-situ grounding electrodes forming part of existing infrastructure.
2) Manufactured grounding electrodes shall
a) in the case of a rod grounding electrode, *consist of two rod electrodes*
i) spaced not less than 3 m apart;
ii) interconnected with a grounding conductor sized as prescribed for grounding conductors;
and
iii) driven to the full length of the rod;


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## splatz (May 23, 2015)

Incognito said:


> So those who say your required to prove 25 ohms, does energizing the rod and taking a reading count as proof? Does the inspector need to witness it or does he take your word for it?
> 
> Seems odd and possibly a safety issue to energize a ground rod for a test, I’d be surprised to hear an inspector would want you to do it.


There is a safety issue; you have a voltage gradient in the ground and therefore a step voltage present when you energize a ground rod.


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## macmikeman (Jan 23, 2007)

joe-nwt said:


> I would like to see an explanation of that. I call BS.


It was here. 4-5 years ago maybe? Big John maybe? Try searching old ground rod threads . Cause I used to rant like hell about ground rods being ineffective at low voltage and just a freebie to the utility companies to save them from having to provide an extra "safety ground" wire to structures they supplied. I might have even saved it once, but I been thru three at least coffee hurl /spit up incidents in the same amount of time, and this is the fourth Apple laptop now thanks to liquid ruining the other ones.


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## Bird dog (Oct 27, 2015)

macmikeman said:


> It was here. 4-5 years ago maybe? Big John maybe? Try searching old ground rod threads . Cause I used to rant like hell about ground rods being ineffective at low voltage and just a freebie to the utility companies to save them from having to provide an extra "safety ground" wire to structures they supplied. I might have even saved it once, but I been thru three at least coffee hurl /spit up incidents in the same amount of time, and this is the fourth Apple laptop now thanks to liquid ruining the other ones.


Put your coffee down before reading...

https://www.electriciantalk.com/f2/purpose-ground-rod-57953/


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## HackWork (Oct 2, 2009)

macmikeman said:


> It was here. 4-5 years ago maybe? Big John maybe? Try searching old ground rod threads . Cause I used to rant like hell about ground rods being ineffective at low voltage and just a freebie to the utility companies to save them from having to provide an extra "safety ground" wire to structures they supplied. I might have even saved it once, but I been thru three at least coffee hurl /spit up incidents in the same amount of time, and this is the fourth Apple laptop now thanks to liquid ruining the other ones.


If I remember correctly, Big John (who is a smart feller) was one who said the 25ohm and second ground rod thing was arbitrary and stupid.

ETA: Birddog found it! Jeeze, beaten by a nose lol


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## Bird dog (Oct 27, 2015)

From EC&M

If that's the case, what's the function of the grounding electrode? Believe it or not, it has several, including the following:


 Limiting voltages imposed by lightning, surges, or accidental contact with higher voltage lines.
 Stabilizing the voltage to earth during normal operation, helping to maintain the voltage within predictable limits.
 Assisting the utility in clearing its own faults by basically becoming part of the utility's multi-point grounding system.
 Providing a path to earth for static dissipation.
https://www.ecmweb.com/content/bringing-grounding-down-earth


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## macmikeman (Jan 23, 2007)

Bird dog said:


> Put your coffee down before reading...
> 
> https://www.electriciantalk.com/f2/purpose-ground-rod-57953/


That wasn't it, but thanks for making me read all that all the way thru. 2013 sounds about right though......


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## Bird dog (Oct 27, 2015)

One additional note if someone lives near or at the end of a POCO distribution line they may have more lightning related problems.


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## macmikeman (Jan 23, 2007)

This much I do remember. Ground rods first got started by telegraph companies. The 25 ohms number is the number they picked . Old habits die hard.


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## joe-nwt (Mar 28, 2019)

A ground rod is a reference point for your system neutral. Fault currents are trying to get back to the source and usually take the path of least resistance; the neutral conductor. This is evidenced by the new code rules for grounding and bonding. A #6 is all that's required to the grounding electrode because it's primary function is as a reference. Meanwhile, there is a whole table dedicated to system and equipment bonds. Because those bonds carry whatever fault current the system can generate before the protection for the ungrounded conductors operates.

So what is it referencing? The neutral at the utility transformer, which should also have a reference to ground. This ensures that the whole system shares the same neutral reference. The problem I have with the 25ohm requirement is why the customer has to adhere to this but the utility companies do not?


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## Bird dog (Oct 27, 2015)

joe-nwt said:


> why the customer has to adhere to this but the utility companies do not?


Because the POCO doesn't follow the NEC. They have their own rules (NESC?).


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## macmikeman (Jan 23, 2007)

joe-nwt said:


> A ground rod is a reference point for your system neutral. *Fault currents are trying to get back to the source and usually take the path of least resistance; the neutral conductor. *This is evidenced by the new code rules for grounding and bonding. A #6 is all that's required to the grounding electrode because it's primary function is as a reference. Meanwhile, there is a whole table dedicated to system and equipment bonds. Because those bonds carry whatever fault current the system can generate before the protection for the ungrounded conductors operates.
> 
> So what is it referencing? The neutral at the utility transformer, which should also have a reference to ground. This ensures that the whole system shares the same neutral reference. The problem I have with the 25ohm requirement is why the customer has to adhere to this but the utility companies do not?


This is not exactly true as stated. Fault currents ,and all currents, take *all* paths back to the source of generation, but are split due to the impedance presented by each source- so some you have 99% going back on one conductive path and the other is 1% due to higher impedance of the second path. The numbers I picked are insignificant- the impedance of each path will determine the percentage of current of the circuit it gets. Neutrals tend to have the bulk of current on them, but almost never carry all the current in the circuit, simply due to other available paths. Impedance in each path determines things. And sometimes impedance on one of the paths is so high it won't allow current to flow, and as such that path to the source is not a path at all, at least at that voltage. It might become one at a higher voltage though.


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## joe-nwt (Mar 28, 2019)

macmikeman said:


> This is not exactly true as stated. Fault currents ,and all currents, take *all* paths back to the source of generation, but are split due to the impedance presented by each source- so some you have 99% going back on one conductive path and the other is 1% due to higher impedance of the second path. The numbers I picked are insignificant- the impedance of each path will determine the percentage of current of the circuit it gets. Neutrals tend to have the bulk of current on them, but almost never carry all the current in the circuit, simply due to other available paths. Impedance in each path determines things. And sometimes impedance on one of the paths is so high it won't allow current to flow, and as such that path to the source is not a path at all, at least at that voltage. It might become one at a higher voltage though.


All true, and in the case of a neutral conductor vs. ground rods and x feet of variable resistance earth, it's not hard to fathom that the bulk of the current would go to the source via the neutral. Otherwise, there would always be some of the load neutral current on the ground, no?

I wonder if that has anything to do with the 25ohm requirement?:wink:


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## brian john (Mar 11, 2007)

John R said:


> I agree with what you say.While working for the FEDS, all the electrical contracts stated that they had to prove 25 ohms, also no ground clamps, only cadweld Also worked in the caribbean, a lot of sand and rock, they were trying ever thing, pouring sale in bottom before setting pole..


I read specifications for testing all aspects of of electrical installations weekly and typically on government projects I see anywhere from 1 ohm to the 25 ohms but if you ask the engineers why they will most likely tell you that is how we have always done it. 

Typical commercial office buildings specifications state 25 ohms
Telco sites specifications state 5 ohms 
Data Centers 1-5 ohms


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## brian john (Mar 11, 2007)

joe-nwt said:


> A ground rod is a reference point for your system neutral. Fault currents are trying to get back to the source and usually take the path of least resistance; the neutral conductor. This is evidenced by the new code rules for grounding and bonding. *A #6 is all that's required to the grounding electrode because it's primary function is as a reference*. Meanwhile, there is a whole table dedicated to system and equipment bonds. Because those bonds carry whatever fault current the system can generate before the protection for the ungrounded conductors operates.
> 
> So what is it referencing? The neutral at the utility transformer, which should also have a reference to ground. This ensures that the whole system shares the same neutral reference. The problem I have with the 25ohm requirement is why the customer has to adhere to this but the utility companies do not?


That is not why we are required to ground electrical systems to mother earth we ground for lightning strikes and accidental utility faults in the transformer placing MV voltage on low volta=ge distribution. 

Earth could care less if you drive a rod or not unless one of the two I mentioned happen. 

As you noted bonding/grounding in a facility of residential is whats 
important.



1.


> Limiting voltages imposed by lightning, surges, or accidental contact with higher voltage lines


.

2.


> Stabilizing the voltage to earth during normal operation, helping to maintain the voltage within predictable limits.


Measure the voltage to Earth and see how stabilized it is depending on the Earths resistance you could get 5 different readings in a 5' x5' area.

3.


> Assisting the utility in clearing its own faults by basically becoming part of the utility's multi-point grounding system.


This is basically what number one says.


> Providing a path to earth for static dissipation.


See number 1 again.


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## brian john (Mar 11, 2007)

Incognito said:


> So those who say your required to prove 25 ohms, does energizing the rod and taking a reading count as proof? Does the inspector need to witness it or does he take your word for it?
> 
> Seems odd and possibly a safety issue to energize a ground rod for a test, I’d be surprised to hear an inspector would want you to do it.


You can measure Earth Ground Resistance in one of two methods, 3-point test or use a Ground Clamp. Both tests require you to understand the proper use of the test instrument, I have seen too many reports and test that were performed improperly


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



CoolWill said:


> You connect an energized conductor to the ground rod and measure the current. Since you know the applied voltage, you then use Ohm's Law to find the resistance.[ How about a 5 amp fuse, are a 100 watt bulb, not led


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## joe-nwt (Mar 28, 2019)

brian john said:


> That is not why we are required to ground electrical systems to mother earth we ground for lightning strikes and accidental utility faults in the transformer placing MV voltage on low volta=ge distribution.


If you believe a #6 will mitigate a lightning strike, well there's not much I can say to that.

Also, if you believe the utility is depending on the consumer's ground connection instead of their own, well, I don't think there is much I can say about that either. :icon_confused:


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## Bird dog (Oct 27, 2015)

joe-nwt said:


> If you believe a #6 will mitigate a lightning strike, well there's not much I can say to that.
> 
> Also, if you believe the utility is depending on the consumer's ground connection instead of their own, well, I don't think there is much I can say about that either. :icon_confused:


A substation ckt supplies how many consumer line xfmrs & homes? That's how many ground points you have. One substation ckt doesn't feed one house.


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## HackWork (Oct 2, 2009)

joe-nwt said:


> If you believe a #6 will mitigate a lightning strike, well there's not much I can say to that.


I'm not really smart enough to enter this discussion, but I will say that all of the lightning protection I have seen on various buildings has been around #6. It was that breaded conductor which I know helps, but still a relatively small gauge.


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## brian john (Mar 11, 2007)

joe-nwt said:


> If you believe a #6 will mitigate a lightning strike, well there's not much I can say to that.
> 
> Also, if you believe the utility is depending on the consumer's ground connection instead of their own, well, I don't think there is much I can say about that either. :icon_confused:


I was stating why the NEC Requires it.

I have done many lightning investigations and have seen #6 blacked, burnt in two and not touched.

How well an electrode conductor will work depends on the length of the conductor, minimizing bends and keeping any bends large radius with solid connections*1. Whether a grounding electrode conductor will depend on where the stroke occurs in a facility or external to the facility, the duration, and magnitude of the strike. 

*1- If you have ever seen a large instantaneous current around 20,000 amps+ or - a few thousand amps pulsed you will see how poorly a screw connection such as is used on a ground rod clamp will hold a conductor.

Additionally, after the first use, the dirt (depending on the type of dirt) 
surrounding the ground rod may be turned into glass. https://www.thoughtco.com/fulgurite-overview-and-instructions-603676


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## Zog (Apr 15, 2009)

I have some fulgurites in a storage box around here somewhere.


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## Zog (Apr 15, 2009)

If anyone here cares about how to properly measure ground resistance I suggest reading this 


https://assets.tequipment.net/assets/3/7/GettingDownToEarth.pdf


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## brian john (Mar 11, 2007)

John R said:


> CoolWill said:
> 
> 
> > You connect an energized conductor to the ground rod and measure the current. Since you know the applied voltage, you then use Ohm's Law to find the resistance.[ How about a 5 amp fuse, are a 100 watt bulb, not led
> ...


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## CoolWill (Jan 5, 2019)

brian john said:


> While connecting 120 VAC to a rod might be fun, I would not make a practice of this as a method of testing.



I don't test them at all. I just drive two and I'm done.


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## Incognito (Apr 14, 2019)

Does the NEC allow ground plates? That’s pretty much all we use. So much easier to install and you only need one. Our code is two rods or one plate


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## CoolWill (Jan 5, 2019)

Incognito said:


> Does the NEC allow ground plates? That’s pretty much all we use. So much easier to install and you only need one. Our code is two rods or one plate



Yes, but I have never seen one.


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## MTW (Aug 28, 2013)

Zero. That's how many ground rods you need for a safe installation.


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## CoolWill (Jan 5, 2019)

HackWork said:


> I'm not really smart enough to enter this discussion, but I will say that all of the lightning protection I have seen on various buildings has been around #6. It was that breaded conductor which I know helps, but still a relatively small gauge.



The theory of lightning protection isn't usually about taking a direct hit. It is about draining the charge from the atmosphere before it reaches the potential for a strike. Whether or not that actually works is still a discussion among physicists. I have seen plenty of air terminals melted sideways but still have their conductors intact, so I dunno.


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## HackWork (Oct 2, 2009)

Incognito said:


> Does the NEC allow ground plates? That’s pretty much all we use. So much easier to install and you only need one. Our code is two rods or one plate


They need to be installed in a 3' hole, right? That's a lot of work and disruption to the landscaping.

I can generally drive 2 ground rods with the rotary hammer in a couple of minutes. Then use a hammer to dig a little trench up against the foundation to run the GEC from one to the other. Or strap the GEC to the foundation.


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## joe-nwt (Mar 28, 2019)

HackWork said:


> I'm not really smart enough to enter this discussion, but I will say that all of the lightning protection I have seen on various buildings has been around #6. It was that breaded conductor which I know helps, but still a relatively small gauge.


Lightning protection is a different animal. How often do you see lightning protection cabling starting outside a building, go inside the building, through several connection points and then back outside the building to the electrode?

I'll address other comments later, have to run.


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## Incognito (Apr 14, 2019)

HackWork said:


> Incognito said:
> 
> 
> > Does the NEC allow ground plates? Thatâ€™️s pretty much all we use. So much easier to install and you only need one. Our code is two rods or one plate
> ...


Actually only 600mm deep so just under 2 feet. 

They work well when doing an underground service because there is already a trench dug for the wires and a pit under the meter for the utility guys to get their wires in.


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## HackWork (Oct 2, 2009)

joe-nwt said:


> Lightning protection is a different animal. How often do you see lightning protection cabling starting outside a building, go inside the building, through several connection points and then back outside the building to the electrode?
> 
> I'll address other comments later, have to run.


But if #6 is used for that and handle the lightning, why can't it be used for the ground rod and handle the lightning?

My post was in reply to you saying this earlier:



joe-nwt said:


> If you believe a #6 will mitigate a lightning strike, well there's not much I can say to that.


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## CoolWill (Jan 5, 2019)

Incognito said:


> Actually only 600mm deep so just under 2 feet.
> 
> They work well when doing an underground service because there is already a trench dug for the wires and a pit under the meter for the utility guys to get their wires in.



That's too deep for me. I'd only be willing to go 60 cm.


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## HackWork (Oct 2, 2009)

Incognito said:


> Actually only 600mm deep so just under 2 feet.
> 
> They work well when doing an underground service because there is already a trench dug for the wires and a pit under the meter for the utility guys to get their wires in.


That sounds like a good method for a new service.

Most of my service work is upgrading them on existing houses, so even a 2' hole by the size of the plate is way more work than driving 2 rods.


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## Kawicrash (Aug 21, 2018)

Incognito said:


> HackWork said:
> 
> 
> > There is no answer. The NEC doesn't specify it, so ultimately this would be up to the AHJ. That is why we drive a second ground rod, it is easier than worrying about testing it.
> ...


Don't need the rods if there is a metallic water system though.


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## CoolWill (Jan 5, 2019)

Kawicrash said:


> Don't need the rods if there is a metallic water system though.



By the NEC we do. Unless there is a ufer.


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## HackWork (Oct 2, 2009)

Kawicrash said:


> Don't need the rods if there is a metallic water system though.


Our code requires us to supplement the metallic water pipe, so we also use the UFER in the foundation or if that is not available we use rods.


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## MTW (Aug 28, 2013)

HackWork said:


> I'm not really smart enough


We know.


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## HackWork (Oct 2, 2009)

MTW said:


> We know.


I found out today that I am a Mensa player. Beat that, bucko.


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## MTW (Aug 28, 2013)

HackWork said:


> I found out today that I am a Mensa player. Beat that, bucko.



Easily. I'm 10 standard deviations above average IQ.


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## Incognito (Apr 14, 2019)

Most of our services are underground and when upgrading the ground is already there. We only need one so if you have a water pipe your good. 

We rarely drive rods. 

Last time I drove a ground rod was for a phone booth so that kinda tells you how long ago that was! Lol


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## HackWork (Oct 2, 2009)

MTW said:


> Easily. I'm 10 standard deviations above average IQ.


Well, at my high school graduation my guidance counselor said I was really smart and I had 20 pages of cum, or something like that.


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## CoolWill (Jan 5, 2019)

Incognito said:


> Most of our services are underground and when upgrading the ground is already there. We only need one so if you have a water pipe your good.
> 
> We rarely drive rods.
> 
> Last time I drove a ground rod was for a phone booth so that kinda tells you how long ago that was! Lol



The thing is, old services that need upgrading usually only have one rod because no one was enforcing the 25 ohm code 70 years ago. But when we upgrade, the inspector will expect to see the two rods, so driving at least one rod is standard for every service upgrade.


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## HackWork (Oct 2, 2009)

CoolWill said:


> The thing is, old services that need upgrading usually only have one rod because no one was enforcing the 25 ohm code 70 years ago. But when we upgrade, the inspector will expect to see the two rods, so driving at least one rod is standard for every service upgrade.


Maybe it's a local thing, but I can count on 1 hand how many services I upgraded that has any rod at all. Always just the water. 

The few that had a rod had only 1 like you mentioned.


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## MTW (Aug 28, 2013)

HackWork said:


> Well, at my high school graduation my guidance counselor said I was really smart and I had 20 pages of cum, or something like that.


:vs_laugh::vs_laugh:

I still don't know what he meant by that.


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## brian john (Mar 11, 2007)

joe-nwt said:


> Lightning protection is a different animal. *How often do you see lightning protection cabling starting outside a building, go inside the building, through several connection points and then back outside the building to the electrode?
> *
> I'll address other comments later, have to run.


Many times, why do you ask?


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## joe-nwt (Mar 28, 2019)

brian john said:


> I was stating why the NEC Requires it.
> 
> I have done many lightning investigations and have seen #6 blacked, burnt in two and not touched.
> 
> ...


Then why doesn't the code mandate large radii bends and cadweld for the ground conductor if that's what it's there for?

https://en.wikipedia.org/wiki/Ground_(electricity)

In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.

Electrical circuits may be connected to ground (earth) for several reasons. Exposed metal parts of electrical equipment are connected to ground, so that failures of internal insulation will trigger protective mechanisms such as fuses or circuit breakers in the circuit to remove power from the device. This ensures that exposed parts can never have a dangerous voltage with respect to ground, which could cause an electric shock if a grounded person touched them. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system.

Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor (see single-wire earth return).

For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard.

https://iaeimagazine.org/magazine/2000/05/16/grounding-electrodes/

General

For many applications, grounding electrodes provide the essential function of connecting the electrical system to the earth. The earth is considered to be at zero potential. In some cases, the grounding electrode serves to ground the electrical system. In other instances, the electrode is used to connect noncurrent carrying metallic portions of electrical equipment to the earth. In both situations, the primary purpose of the grounding electrode is to maintain the electrical equipment at the earth potential present at the grounding electrode.

Another essential function of the grounding electrode is to dissipate over-voltages into the earth. These over-voltages can be caused by high-voltage conductors being accidentally connected to the lower-voltage system such as by a failure in a transformer or by an overhead conductor dropping on the lower-voltage conductor. Over-voltages can also be caused from lightning.

This one indicates we are both right. But my claim was verified first.....:devil3:

Anyone here ever intentionally ungrounded the neutral on a generator? What potential exists between the "hot" lines and ground in this case? Zero. Because the generator has no reference to ground. You could touch any one lead from that generator with your bare hands standing in water up to your knees and nothing would happen. ( I used a 1A fuse and a known ground):wink::biggrin: 

Question for the apprentii that might be reading this: What does the voltage do in a generator feeding only unbalanced line to line loads when the ground reference is removed from the star point? Think it over before you reply.


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## brian john (Mar 11, 2007)

I have worked on many ungrounded systems and impedance grounded systems and I have seen systems installed by others with a large portable generator that were grounded to Earth with a driven electrode but no ground the building (they lifted the Neutral ground bond for safety:vs_OMG::surprise and the system was floating when phase and neutral were measured to any metallic component of the facility because Earth is meaningless in grounding for a facility.


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## brian john (Mar 11, 2007)

joe-nwt said:


> Then why doesn't the code mandate large radii bends and cadweld for the ground conductor if that's what it's there for?


Ask them not me I can only tell you what studies have shown. If you are questioning my knowledge of the subk=ject please take the time to google the subject.

https://en.wikipedia.org/wiki/Ground_(electricity)



> In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.
> 
> E*lectrical circuits may be connected to ground (earth) for several reasons. Exposed metal parts of electrical equipment are connected to ground, so that failures of internal insulation will trigger protective mechanisms such as fuses or circuit breakers in the circuit to remove power from the device. This ensures that exposed parts can never have a dangerous voltage with respect to ground, which could cause an electric shock if a grounded person touched them. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system[*/QUOTE].
> 
> ...


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## joe-nwt (Mar 28, 2019)

brian john said:


> Many times, why do you ask?


Well our code prohibits using the lightning protection conductors for anything else so I'm not sure why you would. Further, the only place a LP system can tie into and electrical system electrode is at or below ground level. I'll admit I'm NOT any kind of lightning protection specialist. The LP systems I've seen have all been exterior. 

They channel lightning into buildings where you're from?:wink:


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## joe-nwt (Mar 28, 2019)

You type way too fast for me to keep up! 

One last thing before you go on believing what you do and I go my way is your comment on measuring to earth. How do you get a good enough connection to earth to obtain an accurate voltage reading? Ground rods? Do you get a better reading with 2 rods?


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## macmikeman (Jan 23, 2007)

This thread is exactly why I hate grounding and grounding electrode threads. Invariably they soon enough turn into the lightning discussion, and somebody resents the lightning on the grounding system, and somebody else decides to inform us that electricity follows the path of least resistance, and then somebody else informs us that grounding stabilizes the voltages to ground when they haven't a slightest clue as to what that possibly actually means. And some other jackass will show up and declare that pounding a ground rod in to the ground will limit the voltage any metal surface with wiring involved within it can offer to a simple minded fool walking around the area barefoot. 

And last- we have MTW who has decided that any grounding is bad. He is stuck on the 120 volts test to a ground rod Mike Holt performed ten years ago. Mike Holt should have put 1.5 million volts down that rod and then seen how well it would trip the circuit breaker. I know a couple of housing developments where clapboard townhouses are built right next to those 150 foot high towers running that 1.5 million volts up to and over the mountains. One of those wires comes loose and contacts some metal connected to your ground rod, and your ground rod might save your life cause 1.5 million volts will travel a hell of a lot further thru dirt and might be able to trip a utility breaker or shunt someplace up the line. So yeah, we don't wanna bang em in, but the code guru's at the NEC want us to. Maybe they get to read the results and we don't.


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## macmikeman (Jan 23, 2007)

joe-nwt said:


> You type way too fast for me to keep up!
> 
> One last thing before you go on believing what you do and I go my way is your comment on measuring to earth. How do you get a good enough connection to earth to obtain an accurate voltage reading? Ground rods? Do you get a better reading with 2 rods?


I'm gonna guess a three point fall of potential tester.


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## joe-nwt (Mar 28, 2019)

macmikeman said:


> I'm gonna guess a three point fall of potential tester.


You are probably right. Almost seems like a waste of time making sure you have a good earth connection for lightning which has travelled a mile or two to get there instead of the puny voltages us mere mortals get to play with....

If the utility is using the ground rods as a reference, why is it unfathomable that the consumer's service is doing the same?

I like these discussions. You're never too old to perhaps learn something.


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## brian john (Mar 11, 2007)

joe-nwt said:


> Well our code prohibits using the lightning protection conductors for anything else so I'm not sure why you would. Further, the only place a LP system can tie into and electrical system electrode is at or below ground level. I'll admit I'm NOT any kind of lightning protection specialist. The LP systems I've seen have all been exterior.
> 
> They channel lightning into buildings where you're from?:wink:


Done all the time, your embassy does it in DC.


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## brian john (Mar 11, 2007)

joe-nwt said:


> You type way too fast for me to keep up!
> 
> One last thing before you go on believing what you do and I go my way is your comment on measuring to earth. How do you get a good enough connection to earth to obtain an accurate voltage reading? Ground rods? Do you get a better reading with 2 rods?


You would do better with 3, 4, 5 ,6........


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## brian john (Mar 11, 2007)

joe-nwt said:


> You are probably right. Almost seems like a waste of time making sure you have a good earth connection for lightning which has travelled a mile or two to get there instead of the puny voltages us mere mortals get to play with....
> 
> If the utility is using the ground rods as a reference, why is it unfathomable that the consumer's service is doing the same?
> 
> I like these discussions. You're never too old to perhaps learn something.


For lighting Utilities and Telco
They are trying to do as buildings that have LPS do minimize their exposure based on past experience.

As for why they ground to earth it goes way beyond using 240/120 VAC in a residence. In substations, they are concerned about lighting and step potential and operating OCP devices, while the earth may not pass 120 VAC all that well drop a 13.2kv and higher line and things change.


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## brian john (Mar 11, 2007)

joe-nwt said:


> You are probably right. Almost seems like a waste of time making sure you have a good earth connection for lightning which has travelled a mile or two to get there instead of the puny voltages us mere mortals get to play with....
> 
> If the utility is using the ground rods as a reference, why is it unfathomable that the consumer's service is doing the same?
> 
> I like these discussions. You're never too old to perhaps learn something.


There are three separate tests performed, 2-point basically a continuity test measuring resistance between two points, 3-point measuring the resistance of an electrode, 4-point measuring the resistance of a plot of land to determine the design for a low resistance electrode system. There is also a Ground Clamp-on and an ART 3-point test.


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## joe-nwt (Mar 28, 2019)

brian john said:


> For lighting Utilities and Telco
> They are trying to do as buildings that have LPS do minimize their exposure based on past experience.
> 
> As for why they ground to earth it goes way beyond using 240/120 VAC in a residence. In substations, they are concerned about lighting and step potential and operating OCP devices, while the earth may not pass 120 VAC all that well drop a 13.2kv and higher line and things change.


I'm well aware of what goes on in substations. I've spent most of my career in the generation/utility field. We use 2/0 for grounding/lightning protection, not #6. And we do get some lightning up here (NWT) not nearly as much as you probably get where you are from.

Also, for the most part, we have very poor ground connections here, mostly bedrock. The buried ground grid itself becomes the electrode, rods are not always possible. Sometimes we supplement with a lake ground.


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## brian john (Mar 11, 2007)

joe-nwt said:


> I'm well aware of what goes on in substations. I've spent most of my career in the generation/utility field. We use 2/0 for grounding/lightning protection, not #6. And we do get some lightning up here (NWT) not nearly as much as you probably get where you are from.
> 
> Also, for the most part, we have very poor ground connections here, mostly bedrock. The buried ground grid itself becomes the electrode, rods are not always possible. Sometimes we supplement with a lake ground.


In regards to residential and small commercial buildings to think a number 6 to two 8' driven electrodes is going to make a significant difference is sort of foolish. THOUGH they may help in same cases if the Code was generally concerned studies would be completed and a standard would be set be it 1, 5, 25 or 100 ohms.


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## joe-nwt (Mar 28, 2019)

brian john said:


> *In regards to residential and small commercial buildings to think a number 6 to two 8' driven electrodes is going to make a significant difference is sort of foolish.* THOUGH they may help in same cases if the Code was generally concerned studies would be completed and a standard would be set be it 1, 5, 25 or 100 ohms.


I agree 100% and said so several posts back. 

So is lightning protection your specialty, or just part of your normal routine? You mentioned being involved in investigations.


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## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



brian john said:


> In regards to residential and small commercial buildings to think a number 6 to two 8' driven electrodes is going to make a significant difference is sort of foolish. THOUGH they may help in same cases if the Code was generally concerned studies would be completed and a standard would be set be it 1, 5, 25 or 100 ohms.


I ran a 300 A circuit to a plaz cutter, 240 three phase. Eng and tech came to start it and we had to install 14 ground rods threw 8 inch concrete around the table to obtain the resistance they required before they would start the cutter


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## Signal1 (Feb 10, 2016)

Two.


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## brian john (Mar 11, 2007)

Signal1 said:


> Two.


To you also.

Better yet an old toast

Heres *to* you, here's *to* me, may we never disagree and if we do F you, here's *to* me.


----------

