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- Licensed Electrician
He answered your question.You didn't answer his. Do you agree with the statement in bold or not.
HOW FREQUENTLY GROUNDING RESISTANCE NEEDS TO BE INSPECTED ??
- Thread starter Anwar Pasha
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He answered your question.You didn't answer his. Do you agree with the statement in bold or not.
You didn't answer my question. (Sorry Dave, I didn't see your reply)
And here's another one.
Do you believe driving a rod solved all the faclities problems as stated?
I know you are pretty new to the site but learners have been coming here for a long time, and finding out about myths is one part of what they learn here.
The paper in the link is titled "DEEP EARTH GROUNDING" and at 600 V and below deep earth grounding is not providing personnel shock prevention, opening OCPD's in a fault, protecting insulation, etc.....
The paper also mentions the NEC in a effort to give it some legitimacy yet the NEC makes it clear that the earth is not an effective ground fault current path in what seems to be contradictory to their claims.
Before you get to upset about something think about what the others might be pointing out.
Yes, earthing does serve a purpose and at our voltages it's purpose is explained in 250.4(A)(1)&(2), bonding all conductive parts together to create a low impedance path back to source is what provides personnel protection and even that is limited, see 250.4(A)(5)
Roger
- Location
- Wisconsin
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- PE (Retired) - Power Systems
That white paper is 25 years old. It does not address current NEC requirements nor new generation 'electronic equipment' recommendations.
In +40 years of experience, this paper is the only place I have heard of 'deep driven' grounds rods being promoted as a solution to poor equipment bonding.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
Again, have you read that page?
RumRunner
Senior Member
- Location
- SCV Ca, USA
- Occupation
- Retired EE
I've read most of the links that I consider worthy of spending my time on. I attended a lot of seminars and workshops probably more than you have spent being an electrician, and you don't have to bully me if I read that link or not.
I don't know you and you don't know what I'm capable of.
I usually ignore posters that I include in my "Ignore List" (and you are one of them) if I find them having a pattern of useless information.
I don't know you and you don't know what I'm capable of.
I usually ignore posters that I include in my "Ignore List" (and you are one of them) if I find them having a pattern of useless information.
K8MHZ
Senior Member
- Occupation
- Electrician
I just did.
I just dug out my 1990 code book. There is no 1991. The phrase ""intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current carrying capacity to prevent the build up of voltages that may result in undue hazard to connected equipment or to persons." is an FPN in 800-30 concerning the grounding of communication shields.
I don't see anything like the above in 2011. That tells me the information on the page is extremely outdated. Especially if they are trying to use the NEC as a basis of their conclusions.
Although the paper has some likely valid data on grounding resistance based on size and type of electrodes, but obviously there is some lack of understanding on what a low impedance grounding system will provide.
You are just wasting your time....
- Occupation
- Licensed Electrician
You still haven't answered the question whether or not you consider this true or not,
"In order to understand earth grounding and test procedures, it is necessary to review why grounding is important. The list below gives some of the basic requirements of an effective ground system. .....
provides grounding of all conductive enclosures that may be touched by personnel, thereby eliminating shock hazard"
I find it incredible how two simple sentences can mean different things to different people. I think it may have something to do with if a person approaches something with a bias they interpret what they read differently than someone else.
Quote from white paper:
"In order to understand earth grounding and test procedures, it is necessary to review why grounding is important. The list below gives some of the basic requirements of an effective ground system.
| limits voltage in a electrical distribution system to definite fixed values |
|
| limits voltage to within insulation ratings |
|
| provides a more stable system with a minimum of transient over voltage and electrical noise |
|
| provides a path to ground in fault conditions for quick isolation of equipment with operation of ground fault protection |
|
| provides grounding of all conductive enclosures that may be touched by personnel, thereby eliminating shock hazards |
|
| reduces static electricity that may be generated within facilities |
|
| provides protection from large electrical disturbances (such as lightning) by creating a low resistive path to earth |
I find it incredible how you can read two sentences and come away with an entirely different meaning than when I read the same two sentences.
Lets break the two sentences down.
In order to understand earth grounding and test procedures, it is necessary to review why grounding is important.
See the comma?
Lets try it again.
"In order to understand earth grounding and test procedures,
it is necessary to review why grounding is important."
Did he say, it is necessary to review why EARTH grounding is important?
It seems you read it that way. I didn't. And I would be willing to bet myspark didn't read it the way you did either.
The second sentence.
"The list below gives some of the basic requirements of an effective ground system."
effective ground system.....
To me that does not refer strictly to earth grounding. It refers to the basic requirements of an effective ground system.
Now lets look at the list again:
And I find it incredible that after that lengthy post it is apparent you did not read the title of the paper.I find it incredible how two simple sentences can mean different things to different people. I think it may have something to do with if a person approaches something with a bias they interpret what they read differently than someone else.
Quote from white paper:
"In order to understand earth grounding and test procedures, it is necessary to review why grounding is important. The list below gives some of the basic requirements of an effective ground system.
A ground system must meet NEC (National Electrical Code) Article 250 requirements."
limits voltage in a electrical distribution system to definite fixed values limits voltage to within insulation ratings provides a more stable system with a minimum of transient over voltage and electrical noise provides a path to ground in fault conditions for quick isolation of equipment with operation of ground fault protection provides grounding of all conductive enclosures that may be touched by personnel, thereby eliminating shock hazards reduces static electricity that may be generated within facilities provides protection from large electrical disturbances (such as lightning) by creating a low resistive path to earth
I find it incredible how you can read two sentences and come away with an entirely different meaning than when I read the same two sentences.
Lets break the two sentences down.
In order to understand earth grounding and test procedures, it is necessary to review why grounding is important.
See the comma?
Lets try it again.
"In order to understand earth grounding and test procedures,
it is necessary to review why grounding is important."
Did he say, it is necessary to review why EARTH grounding is important?
It seems you read it that way. I didn't. And I would be willing to bet myspark didn't read it the way you did either.
The second sentence.
"The list below gives some of the basic requirements of an effective ground system."
effective ground system.....
To me that does not refer strictly to earth grounding. It refers to the basic requirements of an effective ground system.
The whole premise of the document is "Earthing" which by the way would eliminate some confusion if the term was used.
Roger
Your bias is still showing.
You can't address the two sentences and admit you read them wrong, can you? So you change the subject. Jmho, I don't think you understand the intent of the White Paper either.
I am not going to get into a pissing contest with you. I just don't feel you should trash the names of the authors who wrote the White Paper just because you didn't understand the true meaning of the two sentences.
Well until you take the time to read the document you will not see what they are talking about so you are correct, discussing it won't go anywhere.
As far as the difference in the NEC Grounding verses Bonding rules, I pointed them out in the last sentence of post #22.
Roger
Roger you are stuck in NEC, I understand that. That is why in my first post I told the OP he posted his question in the wrong type of forum.
Mike Holt's Forum is NEC.
NEC does not address Power Quality. You have to go elsewhere.
What does NEC 90.1(A)&(B) Tell us? You don't use NEC for Power Quality. For Power Quality most EEs use IEEE the Green Book. Real studies, tests, to back up what IEEE recommends for best practices for Power Quality.
As for reading the White Paper I understand it quite well. The authors don't say you have to drive a ground rod to the center of the earth. What they do say is the rod needs to be driven to a depth to were the ground resistance is 5 ohms or less. The lower the resistance the better.
Where you live and the type of soil you have can make a difference. The 4 seasons of the year can make a difference. Droughts can make a difference.
Soil moisture.
https://www.drought.gov/drought/data-maps-tools/soil-moisture
http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtml
NEC 250.53(A)(1) Below Permanent Moisture Level.
Can you guarantee no mater where you go in the US you can meet that with an 8ft ground rod? Think you could average less than 5 ohms ground resistance? Yes I know Nec just references 25 ohms. And that's only a goal. It could be 200 ohms and NEC only says the ground rod shall be supplemented by one additional ground rod. No testing required after the the second rod is driven.Though it may only bring the 200 ohms down to 100 ohms. Not your problem..... Yo have met NEC requirements.
IEEE 142 Importance of grounding for Power Quality.
142-5.1
The grounding of sensitive electronic equipment, such as computers, programmable logic controllers, process plants, distributed control systems, and similar electronic equipment, has been found to be one of the important items in achieving useful operation from these systems.
The low operating voltage of computers and other sensitive electronic equipment makes then susceptible to random voltages far below levels that are perceptible to humans and that have no effect on electrical power equipment.
Certainly the voltages injected into the earth by lightning strokes even within several thousand feet, unless suitable neutralization is accomplished, can cause malfunction and possibly damage the equipment.
IEEE 142 4.1.2 states the ground resistance should be 1 ohm for substations and 1-5 ohms for commercial and industrial services. 3 ohms or less is preferred.
Fluke. More snake oil?
https://support.fluke.com/find-sales/Download/Asset/2633834_6115_ENG_A_W.PDF
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- Licensed Electrician
Why? I know there is great value in equal potential bonding for electronic equipment, but I think forty foot ground rods are snake oil.
Somewhere there is a scientist working at the South Pole with some sensitive electronic equipment. How deep is his ground rod?
What about the Navy submarines? How do they manage?
The document in question brought the NEC to the table, I pointed out the NEC sections that would have been relevant
You need to do a forum search and see how many times we have discussed performance grounding, (which is not exactly the same thing as Power Quality) it is not a new subject here.
Has no relevance in this conversation except the authors of the document wanted to use the NEC for credibility I guess.
Uh uh, go to this thread and pay close attention to what Dereckbc has to say.
Low resistance is a good thing but it is better to be low impedance through equipment bonding for personnel safety.
It can change by the minute, that's not in question.
Except for temporary Poles I never used 8' rods in my line of work.
Well I hate to do this and I have thousands of dollars invested in Fluke tools but, see this thread, so don't be putting a whole lot of confidence in their advertising brochures.
Roger
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Jamesco, A few points:
1. The importance of the GES earth resistance is widely overstated. It is the second most prevalent grounding myth. Many are aware that at LV the GES isnt for and cant clear faults, but they often still hang into this idea that the resistance value is very important. Please give me a "side by side comparison" of two systems with high and low ground resistance , and describe a specific event that results in something bad or worse happening to the system with higher ground resistance.
2. Engineers and manufacturers are not immune to grounding myths. Manufacturers are notoriously bad (at least what is said in manuals and instructions). I dont think engineers are any less prone than electricians.
3. I am not familiar with that IEEE document and dont know the context of it, such as what voltage it is discussing. Considering #2 above, I would not at all be surprised if there was incorrect information there.
4. The CPC article was interesting from an academic standpoint on the resistance values of various lengths of rods. I am not saying that was made up or inaccurate. What is inaccurate is the claims about the importance of that value.
5. I see a potential value for these "grounding" companies where you need help achieving a low ground resistance value because its a job spec and that is just what you have to do. I did several cell towers once and they spec'ed 4 ohms. It was on a mountain with about a foot of soil, but we were able to get it without much trouble. Testing on a rainy day might have helped.
6. I am not sure what all this "sensitive electronic equipment" is. Modern electronics are designed to withstand a certain level of transients and most SWPS's can accept a wide range of voltage and frequency.
7. Interesting to consider, is that the vast majority of utility distribution systems are MGN's, thus you have a very very low ground resistance thru the utility neutral, even without a local GES.
8. Keep in mind lightning doesnt really care about DC resistance.
Finally, There are no doubt some specialized applications where an elaborate GES is helpful. The problem is the rampant overemphasis on the grounding electrode system for the vast majority of general applications.
1. The importance of the GES earth resistance is widely overstated. It is the second most prevalent grounding myth. Many are aware that at LV the GES isnt for and cant clear faults, but they often still hang into this idea that the resistance value is very important. Please give me a "side by side comparison" of two systems with high and low ground resistance , and describe a specific event that results in something bad or worse happening to the system with higher ground resistance.
2. Engineers and manufacturers are not immune to grounding myths. Manufacturers are notoriously bad (at least what is said in manuals and instructions). I dont think engineers are any less prone than electricians.
3. I am not familiar with that IEEE document and dont know the context of it, such as what voltage it is discussing. Considering #2 above, I would not at all be surprised if there was incorrect information there.
4. The CPC article was interesting from an academic standpoint on the resistance values of various lengths of rods. I am not saying that was made up or inaccurate. What is inaccurate is the claims about the importance of that value.
5. I see a potential value for these "grounding" companies where you need help achieving a low ground resistance value because its a job spec and that is just what you have to do. I did several cell towers once and they spec'ed 4 ohms. It was on a mountain with about a foot of soil, but we were able to get it without much trouble. Testing on a rainy day might have helped.
6. I am not sure what all this "sensitive electronic equipment" is. Modern electronics are designed to withstand a certain level of transients and most SWPS's can accept a wide range of voltage and frequency.
7. Interesting to consider, is that the vast majority of utility distribution systems are MGN's, thus you have a very very low ground resistance thru the utility neutral, even without a local GES.
8. Keep in mind lightning doesnt really care about DC resistance.
Finally, There are no doubt some specialized applications where an elaborate GES is helpful. The problem is the rampant overemphasis on the grounding electrode system for the vast majority of general applications.
a good primer
https://assets.tequipment.net/assets/3/7/GettingDownToEarth.pdf
as was mentioned in mining we require testing
we require 2 beds, one for the substation, the other isolated with NGR for the mine
the beds must be <4 Ohm, most measure ~2 some as low as 1
they are tested at installation and every 6 months after that
no salt, bentonite, etc, just Cu, sometimes perforated bored steel casings
all conductors are bare 4/0 Cu
exothermic welds or hydraulic comp fittings, no mech connections UG
We use the 3 point method with the far probe set out 5-7 times the beds largest dimension
https://assets.tequipment.net/assets/3/7/GettingDownToEarth.pdf
as was mentioned in mining we require testing
we require 2 beds, one for the substation, the other isolated with NGR for the mine
the beds must be <4 Ohm, most measure ~2 some as low as 1
they are tested at installation and every 6 months after that
no salt, bentonite, etc, just Cu, sometimes perforated bored steel casings
all conductors are bare 4/0 Cu
exothermic welds or hydraulic comp fittings, no mech connections UG
We use the 3 point method with the far probe set out 5-7 times the beds largest dimension
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
As an illustration of how ground electrode impedance can vary with rod length, Mike H. worked his way up one 10' segment at a time to 50' ground rods in his Florida soil in a nice video on measuring ground electrode impedance.
Here's a good white paper on substations. Note the touch and step potentials.
https://ccaps.umn.edu/documents/CPE...ts/2017/TutIIISubstationGroundingTutorial.pdf
Here is an IEEE white paper.
http://www.dee.ufrj.br/~acsl/grad/equipamentos/IEEE-std80.pdf
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What does that have to do with low voltage systems?
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