Grounding Electrode System NEC 250-50

[bphgravity]

Thanks for the dissertation David. :wink:

I understand that the common method of determining the effectiveness of the grounding electrode system is by determining the resistance of that system, but is there any evidence or data that you are aware of the proves or even indicates a lower ground resistance results in a safer electrical system? I can't find any and I have looked pretty hard.

I agree that steel will corrode with time and under certain conditions however I'm not sure if copper itself does, at least not under typical conditions.

 

[don_resqcapt19]

David,

What are the calculations used to determine the GES will perform its function properly?

What is the function of the GES?
Don

 

[George Stolz]

1. What are the calculations used to determine the GES will perform its function properly?
Answer.
In terms of NEC, the calculation to get a ?Resistance to Ground? with a value less than the ?magical 25ohms? (borrowing Bryan?s term), This condition is the basis if the GES will function properly.

For the peanut gallery: There is no requirement in the NEC mandating that the Grounding Electrode System have less than 25 ohms resistance to the earth.

After that point, my eyes went crossed and I wandered off to pick on easier prey.

I hope my reply is not that long.

It is exactly that long, and no shorter.

Which is long!

 

[peter d]

Here I go with my nitpicking again. :lol: If we are talking about AC systems, we really should be saying "impedance" instead of "resistance."

I know, it's a minor issue to some, and we all know what is being said when we hear "resistance." I also realize that capacitave and inductive effects are usually not an issue at 60 HZ. But impedance is technically correct, and resistance is not.

 

[davidv]

Dear Bryan, Don, George
I just thought that by sharing, some answers will be revealed, or more questions or uncertainties turns out, whichever, we can get something useful or ?something to avoid? with our humble contributions.

1. What is the function of GES?

GES hopes to ?provide a channel? for unwanted electrical energy to be expended at the earth. The ?earth? being a natural energy absorber. These unwanted energies are leakage ( insulation breakdown & faults) or transients (switch surges or lightning). By being effective channel, moving to other energy paths are hopefully avoided although not eliminated such as sideflash or heating or sparking.

Being itself, it cannot do the job of ?Protection of properties?. Quick Energy Source Cut-off and/or ?collection and then divertion to earth? (without being destroyed) is needed or done to do the protection job.

?Protection of Persons(safer electrical systems) by effective GES? will not be a solution, As long as potential differences exists people will still be affected. A GES working properly ( conducting fault currents ), a grounded object can still give a shock when a ?person is in contact? with it. Because electricity will go through all available paths,( its like expecting not to get wet of feel impact when touching a waterfalls, anywhere on its path of travel).

Elevating a location to a level of the energy source is impractical and expensive, (creating bird on a wire condition), Even a substation, with all calculations its goes thru in the possible magnitude of voltages that may exist, the best personal safety solution is still the sign board that reads ? Danger High Voltage, Keep away?

Bonding to keep potentials equal on different magnetic (metal ) surfaces (caused by induction) will work for low energy levels.
If prescence of transient/faulted energy is forseen,at best, keeping away is the most certain solution and Highly insulative PPEs and ?Insurance? for us guys in the field will do.

?Don, if you think otherwise, please let me know?

Low resistance (not impedance coz of the DC tester being used) is a gauge of the performance the GES, how it will not restrict the conduction of unwanted energy. But not of a safer electrical system.

2. In my design, if separate CEEs are not possible as primary GE, Foundation footing CEE can be allowed, provided galvanized steel, or other inert steel must be used as materials, conductor or electrode. Also G.I.Pole line accessories can be used.

Cracks and moisture seepage are typical bad conditions for Reinforced Concrete stuctures, prescence of copper near its rebars, will make it worst and fast !.
If ever I were an inspector, I would push for a local law prohibiting copper or other cathodic materials on foundation footing CEE?s, otherwise use separate CEE?s or other GE types.


3. Again as I said NEC?s 25 ohms or less can be used as basis of comparison, on ground resistance values.
Did I wrote ?NEC mandates that ?? ? Its not important to me anyway but I wonder what would inspectors say if the testing results give say 30 or 50 ohms?

davidv
es

 

[don_resqcapt19]

David,

GES hopes to ?provide a channel? for unwanted electrical energy to be expended at the earth. The ?earth? being a natural energy absorber. These unwanted energies are leakage ( insulation breakdown & faults) or transients (switch surges or lightning). By being effective channel, moving to other energy paths are hopefully avoided although not eliminated such as sideflash or heating or sparking.

For most of those items the grounding electrode system is of little no or very minor importance. The earth is not an energy absorber. It is only a conductor. The unwanted electrical energy cannot be expended in the earth. The only way to get rid of it is to send it back to its source. The only thing that the grounding electrode system is good for is lightning and accidential contact with higher voltage systems.
Don

 

[George Stolz]

3. Again as I said NEC?s 25 ohms or less can be used as basis of comparison, on ground resistance values.
Did I write ?NEC mandates that ?? ?

No, and you didn't imply that very strongly. There is always concern that the casual reader could read something and walk away with a misconception. I chimed in solely for the benefit of that casual reader, nothing more.

Its not important to me anyway but I wonder what would inspectors say if the testing results give say 30 or 50 ohms?

"Wow, neat tester."

Testing is unnecessary. A sole ground rod driven is the only time that testing is called for by the NEC, and if someone were concerned about the resistance of that rod, driving a second rod is the final solution to satisfy the NEC.

If the two ground rods overall resistance to earth were 3000 ohms, then the job will pass under the NEC.

 

[bphgravity]

Hello again David. Thanks again for that explanation, however I was actually looking for data or research that proves what your are stating. I realize this is what all the books and standards tell us grounding does, but I think they may all be wrong or least not accurate.

It appears you have lots of experience with grounding systems and seem to understand what you are hoping the GES will do however do you have any documented experience of all these things you describe actually take place. Meaning, how do you know the GES systems you have installed is working to do all the things you describe other than the fact that you know they have a low resistance?

For example is there an incident or event that you can or have determined would of resulted in property damage or loss of life if the GES was not in place or of high resistance? Is it possible there is no current method or procedure that can absolutely prove when and how the GES functioned?

 

[Cavie]

Trevor. Read the last sentance of 250.50 in blue of the hand book. It states that the rebar IS avalible and WILL be incorporated.

 

[roger]

It appears to me that three code cycles are being discussed in this thread, it may be worth the time to determine which code book everyone is referencing.

Mshield's use of the dash indicates pre 2002 and the correct wording is "available" for that cycle as well as the 2002, in the 05 the word "present" was used.

Cavie, a word of friendly advice, be careful quoting the handbook commentary, although it is informative, it is just opinion and carries no weight as far as being code. :wink:

Roger

 

[iwire]

Cavie I see your an inspector, I hope you are not trying to enforce the NEC handbook.

As Roger points out it is just opinion and has been shown on this forum to have a few mistakes.

This is not meant to slam the handbook, I have one and use it just like I consider the opinions I see posted here.

 

[George Stolz]

I was going to mention that this morning, but I scrolled back to double-check, and...

I have perused through Mike Holts entire Grounding verses Bonding book and the NEC Handbook and can't find a single reference saying that isolated 20' sections of rebar must be bonded together.

In Cavie's defense, Trevor had mentioned that he couldn't locate a printed opinion defending the "multiples of the same type of electrode had to be bonded together" opinion.

I believe Cavie was posting in that vein.

 

[peteo]

I don't mean to barge in here. My limited experience as an ESD program manager with electronics manufacturing has shown me the value of following equipotential plane rules, but I'm not posting to infuriate or tell anyone what to do. Please do not jump on me, I do not have the resources to purchase technical or IEEE publications, etc. I believe that the major issue results from the NEC language, or style. Here's a quote from a HUD publication, 'Residential Strutural Design Guide,'

"Conventional or prescriptive construction practices are based as much on
experience as on technical analysis and theory (HEW, 1931). When incorporated into a building code, prescriptive (sometimes called ?cook book?) construction requirements can be easily followed by a builder and inspected by a code official without the services of a design professional."

Found an IEAI article which addresses the 'multiple foundation' question directly. At least one of my local IAEI members sat on the CMP for the 1999 re-write. It's a very informative article, discussing code cycles, interpretation, and a couple specific situations. I'll quote from that article. Since it's buried in the text, it will look strange.

part of 'Question 1'
"footings at different levels (step footings) may occur. This also may include concrete pads for the support for interior columns, or many concrete piers to support the entire structure. If all of the steel needs to be bonded together this would require a bonding conductor to jump from one footing to the other and possibly the pads, or to each separate pier."

part of 'Answer'
"To answer the second part of this question, if there are multiple concrete-encased electrodes in the same overall concrete footing that are not tied together by the usual tie wire, then by the current minimum requirements in the Code, they should be used and bonded together. This situation can be compared to conditions where multiple water pipe grounding electrodes are in the same structure. They all are required to be used in the grounding electrode system, without exception."

 

[Cavie]

Thanks George. At least some people read the post as they ARE written and not as they THINK the were written. Trevor ASKED for some referance to the bonding requirement and I just provided exactly what HE asked for from one of HIS suggested sources. Nothing more.

 

[George Stolz]

Cavie, no need to get grumpy. You're new here, so I should tell you: whenever someone quotes the handbook, there are six people waiting in line to tell that someone that the opinions expressed in the handbook are not binding. I would have beat Bob and Roger to the punch, but I had a feeling there might have been more to it than first glance.

So when quoting the handbook, or referencing it, it's not a bad idea to express your motive in doing so.

 

[iwire]

Well said George.

Cavie welcome to the forum, as I noted in my post I also use the handbook.

If you stick around here your bound to see me use this graphic to illustrate the differences between GECs and bonding jumpers.

I bet you know where that comes from. :wink:

 

[davidv]

hi. guys, I hope i'm not annoying anybody, but being with all of you here is really wonderfull, no need for tv, just a six pack, few notes & litlle grmbling, wow what a way to end a day.

I'm sorry Bryan, I'd really love to answer your question of how do I know if those GES i placed really works, i just cant, just pray they will.
Its a pain to know after spendin 1 or 2 years of my life on a building or project, taking care of all things electrical, taking all the trouble that plans are followed, nothing in the code is violated. seeing it grow from graveyard to a towering monument it become, that when you went back in to visit, all I'll hear is "your name is not on the list", "do have an appointment, where do you come from, do you work here?", yup compltely forgotten. And the souls I've worked with, I wonder where they
are. Ah life in the field, brings back memories.
see u later guys.

davidv
es

 

[bphgravity]

Thanks for your honesty David. This seems to be the end of the discussion on grounding or at least as far as we can take it right now. Nearly every document I have ever read on electrical system grounding is just a repeat of 250.4 but offer nothing in way of how it accomplishes these functions. In many even this information is contradicting.

 

[roger]

Cavie, I did read Trevor's post as it was written and his question was,

Can anyone provide a written reference that requires this?

The NECH commentary can not require anything, so I simply pointed out that you need to be-careful quoting the commentary.

It was not meant to upset you.

Furthermore, reading the sentence,

this revised text necessitates an awareness and coordinated effort on the part of designers and the construction trades in making sure that the concrete-encased electrode is incorporated into the grounding electrode system.

it seems to be only talking about a singular CEE and wouldn't clear up the question even if it were in the code text.

Roger

 

[Cavie]

I found the IAEI Article posted by peteo to be very interesting. Mr. Michael Johnson seems more than quilified to be able to state what the "intent" of the code is. To me anyway.