http://www.artikel-software.com/file/Bonding_and_grounding.pdf
Compliments of the Pentagon...via Delhi, India...

You could look forever for data.
But just think about the surface area difference in contact with the earth.
But anyway.
Here is a article by the iaei:
http://www.iaei.org/magazine/?p=3626

Thanks you guys.
I think I'll start with the IAEI article.

Another dumb question.
If there is plastic barrier (visqueen) between the earth and the concrete encase electrode can it still be used as an electrode?



Neal

The "performance" of the grounding electrode system is all in the bonding aspects of the system. The actual grounding component does not have all that much signifigance. In order for a hazard to be present during a 250.4(A)(1) event, there must be an imposed voltage. If all the non-current carrying metal parts of the system(s), the grounded service conductor, the system EGC's, the service equipment enclousres, and the earth are all bonded together per code, there will be no voltage potential between those parts thus no current will flow for the duration of the event.

So why it is important that the earth be a component of this protection system, it is not the essential or critical aspect. The overall circuit impedance of the earthing connection are really not all that important. Clearly, a single #6 AWG conductor terminating at a single 8' ground rod is all that is really needed to perform effective grounding of the system. However, it is essential that you BOND any other electrode that is present to ensure no potential is created between the different grounded elements.

So in essence, the pupose of 250.50 is NOT an attempt to create as many grounding connections as possible, but rather to ensure that all present grounding connections are bonded together.

GET IT?

Neal, the visqueen should not be extended under the footer, only to the edge of the floor.

Bryan, I will throw more gas on the fire.
How much neutral current do you figure the earth is carrying?
I know on my street where we have wye distribution there is current on all of the transformer grounding electrode conductors going down the pole and I have a couple of amps on the drop neutral coming into the house with the main breaker off.
I talked to my FPL lineman neighbor about it and he didn't even grasp the concept that all of the current was not going to go down that aluminum/steel 2 gauge strand they bond to and he assumed that ground wire would assure zero volts because a foot or so of the #6 was coiled and stapled to the bottom of a pole 6-8 feet in the ground. When I started talking about voltage drop his eyes glazed over.
This particular string of 20 transformers is about a 3/4 mile long. How many volts do you figure they drop along that strand? How much do you figure the earth tries to make that up?
This does take some of the mystery out of where "stray voltage" can come from. The street behind my house is fed from another phase on the distribution and I have always wondered what the voltage difference would be between his ground electrode and mine. I certainly would not want to string a LAN cable between our houses.

I really need to be studying for my P1 exam rather then discussing something that has been some of the most unclear and poorly written code sections for over 75 years, but here I go again.

And by the way I do “Get It” as I have designed and installed many approved grounding electrode systems that are still performing as required by the NEC for over 25 years,as well as having inspected a 1,000 or so GES in the last five years.

Part of the problem here is not understanding what word “system” means. “System (noun) a group or combination of interrelated, interdependent, or interacting elements forming a collective entity; a methodical or coordinated assemblage of parts, facts, concepts.”


“250.50 Grounding Electrode System (there is that word).
All (not just one electrode but all) grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present (only (A)(1), (2), (3), or (8) would be present during normal construction all other electrodes are only present if you bring them, why do they include (A)(4) – (A)(7)????) at each building or structure served shall be bonded together to form the grounding electrode system (there is that word again). Where none of these grounding electrodes exist, one or more (I choose more) of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.


Even the NEC handbook encourages the formation of a system of electrodes, which adds reliability and ensures performance.


“Section 250.50 introduces the important concept of a “grounding electrode system,” in which all electrodes are bonded together. Rather than total reliance on a single grounding electrode to perform its function over the life of the electrical installation, the NEC encourages the formation of a system of electrodes “that are present at each building or structure served.” No doubt, building a system of electrodes adds a level of reliability and helps ensure system performance over a long period of time.”


In the City of Tampa on a non-reviewed new construction services we encourage and get a concrete encased electrode, and two ground rods. The electrode to the CCE is sized to table 250.66 based on the service entrance conductors. For a service upgrade on an existing structure we require two ground rods, and a water connection if still metallic pipe, once again sized according to 250.66. This has been the practice in Tampa longer than the 5 years I have been there, and I believe the systems installed are meeting the “intent” of the code for the GES.


In my opinion if an electrical contractor, electrical engineer, plans examiner, electrical inspector, installed, designed, approved the plans, approved an inspection on a grounding electrode system that only had a #4 copper wire connected to a concrete encased electrode on a service with larger than 3/0 copper service conductors, rhey should look for a new career.


Well I need to go study plumbing, I’m done with this one thanks for reading.

Neal Burdick

My Opinions and Mine alone

I don't think anyone here is questioning what you know Neal, certainly not me.  I've seen the CMP-5 members themselves argue over the meaning of a section.  If they can't figure it out, no wonder we have these discussions out in the real world.The grounding electrode system is more than just the electrodes.  The system is the electrodes, the GEC, the fittings and connectors, etc.  The reason 250.50 requires ALL the electrodes that are present to be bonded is to prevent an electrode that is present from not be bonded.  So, if someone were to drive a ground rod, required or not, it is now present and must be bonded to the grounding electrode system.  Again, a designer can include as many electrodes as they wish, however the code stipulates they must all be bonded.That's great, but not enforceable.  The code is a minimum and the minimum is all that is required.Why not require two or more of everything required by the code?  That would certainly be better.  Instead of just one required lighting outlet per room, lets make it two just in case one doesn't work.  Instead of just one receptacle within 3' of a bathroom sink, let's make it two just because redundancy is better.  You can quickly see how this can get out-of-hand.I think this is an incorrect interpretation of the code.  If the city of Tampa believes this is the appropriate method of grounding for their jurisidiction, they should submit a proposal to the NFPA or the Florida Building Commission to have the rule changed.  Until then, the city really has no legal basis for requiring anything more than the code.

I agree with Neal as to what the customer should demand and what the EC should install but Bryan is right about what the AHJ can require. Perhaps it is time to get CMP-5 to look at this again. I do believe it is a waste of copper to put in a GEC that carries more current than the electrode can sink but that just means we need better electrodes. One rod driven in dry sand is not much of an electrode and another one right next to it does not improve that much. Dr Ufer's CEE is probably sufficient for most single family (typically 200a) but that gets troubling when you get into large commercial buildings with 1600a services if you believe 250.66.

Maybe we need to review what the GES does for us. We know it does not clear faults. Why is the service size important?
Are going to admit the earth really does carry circuit current?

It does clear faults. It may not be designed for that purpose, but in real life it can perform that function. Better that current return through it......than through me.

I know that up North, at least two methods of grounding were REQUIRED. Down here, no, just NEC. OK, I'm going to shut up now, I promised myself I would not even post on this subject.

You just can't resist can you?