Concrete encased electrode.

[weressl]

I think I understand the intent of 250.50 Grounding Electrode System to be that all underground metallic objects should be bonded together to minimize and avoid the flow of objectionable current between them by equalizing the potential difference between the different areas and to gain higher grounding resistance.

I personally believe that the Ufer type grounding of utilizing the concrete rebars was what seemed to be a good idea and it gained popularity by avoiding the installation of external additional grounding systems. What I think is lacking is sufficient research and study of the actual installation where it can be proven that the resultant corrosion - due to DC component of any grounding current and the lime content of the concrete as an electrolyte - does not jeopardize the structural integrity that the rebar serves in the first place.

When Epoxy coated rebars are used for additional corrosion resistance then then I presume taht they are not required to be bonded to the grounding system.

The latest addition of the Code seem to ignore or contradict the original purpose. " Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system." This preceeded by the " Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means".

Questions 1: Do they required to be or permitted to be bonded together?
Question 2: Are they permitted to be bonded toegther to form the length of the electrode that is defined under this section?
Question 3: What is the value of effective bonding? How do you measure it?
Question 4: If the original intent is to bond all underground metallic objects - less the exceptions - together why ony one rebar is required to be bonded and not all?

 

[petersonra]

Since the purpose of grounding low voltage circuits seems to be mostly to follow the code, it is doubtful that there really is an effective value for bodning.

 

[weressl]

Since the purpose of grounding low voltage circuits seems to be mostly to follow the code, it is doubtful that there really is an effective value for bodning.

Are you saying that the Code requires something to be done WITHOUT sound technical reasoning? If that is so then we should ceremoniously burn the Book. (No pun is unintended.):roll:

 

[A/A Fuel GTX]

Question 4: If the original intent is to bond all underground metallic objects - less the exceptions - together why ony one rebar is required to be bonded and not all?

On the jobs I do, all of the rebar in the footer is tied together via tie wire. As far as Ufer (CEE) research goes, I know it was proven to be far superior to any other conventional grounding method.

 

[iwire]

I think I understand the intent of 250.50 Grounding Electrode System to be that all underground metallic objects should be bonded together to minimize and avoid the flow of objectionable current between them by equalizing the potential difference between the different areas and to gain higher grounding resistance.

I think you are mistaken from the outset about the intent.

As we do not now, nor have we ever been required bond together all underground metallic objects.

The only objects we have been required to use as electrodes are listed in 250.52(A) and as a result they do end up bonded together but many underground objects on that list are not required to be bonded (Cast iron septic lines) and some that we are prohibited from using such as metal gas lines.

The change in the 2008 is proof of that. The change makes clear that when you have multiple CCEs you are only required to use one. Which was always the intent as I understood it but the original wording could be interpreted either way.

Now that said, the NEC of course is the minimum, many times the job specs do require more then that, sometimes a great deal more.

 

[weressl]

I think you are mistaken from the outset about the intent.

Then please elighten me of it! What is the intent?

As we do not now, nor have we ever been required bond together all underground metallic objects.


The only objects we have been required to use as electrodes are listed in 250.52(A) and as a result they do end up bonded together but many underground objects on that list are not required to be bonded (Cast iron septic lines) and some that we are prohibited from using such as metal gas lines.

(8) Other Local Metal Underground Systems or Structures.​

Other local metal underground systems or structures
such as piping systems, underground tanks, and underground
metal well casings that are not bonded to a metal
water pipe.​

Sounds pretty inclusive to me.........

The change in the 2008 is proof of that. The change makes clear that when you have multiple CCEs you are only required to use one. Which was always the intent as I understood it but the original wording could be interpreted either way.

Now that said, the NEC of course is the minimum, many times the job specs do require more then that, sometimes a great deal more.

You are missing my point. It appears the everything ELSE is required to be bonded together BUT the CCE. So my question is why? Why bond one and not the others. I can ead what is required and I am looking for understanding, logic.

 

[petersonra]

Then please elighten me of it! What is the intent?

(8) Other Local Metal Underground Systems or Structures.​

Other local metal underground systems or structures
such as piping systems, underground tanks, and underground
metal well casings that are not bonded to a metal
water pipe.​

Sounds pretty inclusive to me.........



You are missing my point. It appears the everything ELSE is required to be bonded together BUT the CCE. So my question is why? Why bond one and not the others. I can ead what is required and I am looking for understanding, logic.

250.50 Grounding Electrode System. All grounding electrodes
as described in 250.52(A)(1) through (A)(6)

250.52(A)(7) Other Local Metal Underground Systems or Structures.
Other local metal underground systems or structures
such as piping systems, underground tanks, and underground
metal well casings that are not effectively bonded to
a metal water pipe.

This is the 2005 code. Items listed in 250.52(A)7 can be used as a GE, but are not required to be used as a GE.

 

[iwire]

Then please elighten me of it! What is the intent?

The connection of a grounded system to the earth. See 250.4(A)(1).

Sounds pretty inclusive to me.........

See 250.50, only the items in 250.52(A)(1) through 250.52(A)(7) are normally required.

(A)(8) only comes into play if the others do not exist.

You are missing my point.

No, I understood it, I think you just might have missed the 'optional' part of (8)

 

[weressl]

This is the 2005 code. Items listed in 250.52(A)7 can be used as a GE, but are not required to be used as a GE.

But why is it optional and why others are not?

 

[Rockyd]

Questions 1: Do they required to be or permitted to be bonded together?
Question 2: Are they permitted to be bonded toegther to form the length of the electrode that is defined under this section?
Question 3: What is the value of effective bonding? How do you measure it?
Question 4: If the original intent is to bond all underground metallic objects - less the exceptions - together why ony one rebar is required to be bonded and not all?

Questions 1: Do they required to be or permitted to be bonded together?


250.4(A)(4) Normally non-current carrying electrically conductive materials that are likely to become energized shall be be connected together and to the electrical supply source in a manner that establshes an effective ground fault path.

Question 2: Are they permitted to be bonded toegther to form the length of the electrode that is defined under this section?

250.4(A)(1) Electrical System Grounding - Electrical systems that are grounded shall be connected to the earth in a manner that will limit the voltage imposed by lighting, line surges, or unintentional contact with highter voltage lines and that will stabile the voltage to earth during normal operation. See the FPn that accompany's the text to understand the effort in draining off higher frequency (Lightning strikes), higher voltage imposed on the system.

Question 3: What is the value of effective bonding? How do you measure it? Same answer as #3.

Question 4: If the original intent is to bond all underground metallic objects - less the exceptions - together why ony one rebar is required to be bonded and not all?

Bigger contact area to the actual earth with a hydrous substance (concrete).

See 250.52(3)

I believe in the future that the CEE will become the prevalent, and prefered, grounding method to drain (per250.4(A)(1)) higher voltaage hits to the building system to earth.

Anyone not grasping the conceptuality in total of what I just gave as opinion, supported by code articles, should take the following course -

This is a great course to wrap the head around the direction of grounding. Not Aimed at anyone in particular

 

[iwire]

But why is it optional and why others are not?

If the goal was the bonding of all metal objects then I would be asking the same question. :smile:

But that is not the goal, the goal is a connection of the electrical system to dirt, the items listed in (8) appear IMO to be a last ditch effort to get that connection to dirt accomplished if no better ways are available.

 

[Rockyd]

My "stuff" is coming out of the 08 NEC, and Mike's course.

 

[weressl]

Questions 1: Do they required to be or permitted to be bonded together?


250.4(A)(4) Normally non-current carrying electrically conductive materials that are likely to become energized shall be be connected together and to the electrical supply source in a manner that establshes an effective ground fault path.

The question was refering to the rebars. How will rebars likely to become eenrgized?

Question 2: Are they permitted to be bonded toegther to form the length of the electrode that is defined under this section?

250.4(A)(1) Electrical System Grounding - Electrical systems that are grounded shall be connected to the earth in a manner that will limit the voltage imposed by lighting, line surges, or unintentional contact with highter voltage lines and that will stabile the voltage to earth during normal operation. See the FPn that accompany's the text to understand the effort in draining off higher frequency (Lightning strikes), higher voltage imposed on the system.

Rebars only in question.

Question 3: What is the value of effective bonding? How do you measure it? Same answer as #3.

What is the value. I did not ask for a paragraph from the Code, I asked to define what the value of "effective" is.

Question 4: If the original intent is to bond all underground metallic objects - less the exceptions - together why ony one rebar is required to be bonded and not all?

Bigger contact area to the actual earth with a hydrous substance (concrete).

See 250.52(3)

I believe in the future that the CEE will become the prevalent, and prefered, grounding method to drain (per250.4(A)(1)) higher voltaage hits to the building system to earth.

Anyone not grasping the conceptuality in total of what I just gave as opinion, supported by code articles, should take the following course -

http://www.mikeholt.com/productcategorylist.php?id=31&from=Products&title=Grounding%20versus%20Bonding&year=2008​

Phuleese, spare me. Just because it is packaged, on the Internet, has a "name" on it does not mean is correct.

 

[weressl]

If the goal was the bonding of all metal objects then I would be asking the same question. :smile:

But that is not the goal, the goal is a connection of the electrical system to dirt, the items listed in (8) appear IMO to be a last ditch effort to get that connection to dirt accomplished if no better ways are available.

You still not answered:

I got the "connecting to the dirt" as the primary objective.

If connecting to one item accomplishes the desired Ohmic value then why others need to be bonded to it? What does it accomplishes? Why some items required to be bonded together and others are not?

 

[infinity]

If connecting to one item accomplishes the desired Ohmic value then why others need to be bonded to it? What does it accomplishes? Why some items required to be bonded together and others are not?

Only ground rods, pipes and plate electrodes have an ohm value attached to their usage. A CEE would only require the use of 20' of 1/2" or larger rebar regardless of it's resistance value and regardless of the amount of rebar within the footing.