How many ground rods

[jetlag]

You are correct. No exceptions. I am not trying to be funny but re-read from "shall not be required *******".

Figure this one out . Most customers at big blue and orange are DIY residential 200 amp are less with pvc water pipes , and yet they sell out of #4 all the time and I get p o and have to go somewhere else. They always have plenty of #6 , Could it be the sales people just repeat what they hear about the #4 ? I hope the ahj doesnt balk when I ask him about the # 6 , I have a lot of it I removed from jobs that I can use . But I have to buy the #4 at approx 1.00 a foot.

 

[don_resqcapt19]

This is one of the cases where the code change to "positive" language in place of the exceptions, in an attempt to make the code easier to understand, has actually made it harder to understand. The "exception" format as found in 1996 and earlier codes was, in my opinion, easier to understand.

 

[don_resqcapt19]

One issue that can drive the use of #4 is the protection rules in 250.64(B).

 

[jxofaltrds]

Figure this one out . Most customers at big blue and orange are DIY residential 200 amp are less with pvc water pipes , and yet they sell out of #4 all the time and I get p o and have to go somewhere else. They always have plenty of #6 , Could it be the sales people just repeat what they hear about the #4 ? I hope the ahj doesnt balk when I ask him about the # 6 , I have a lot of it I removed from jobs that I can use . But I have to buy the #4 at approx 1.00 a foot.

Don't feel bad. I use to not understand this also.

As far as re-using material your AHJ may not allow it. Here you need permission to re-use any material.

Who cares if he 'balks'? Many trades people are afraid to confront an inspector. Why? Is he that revengeful? I challenged inspectors back when I was a helper. You know what? Years I mean years later he remember me. Not in a bad way but respected me even though I lost my first battle with him.

 

[jetlag]

Don't feel bad. I use to not understand this also.

As far as re-using material your AHJ may not allow it. Here you need permission to re-use any material.

Who cares if he 'balks'? Many trades people are afraid to confront an inspector. Why? Is he that revengeful? I challenged inspectors back when I was a helper. You know what? Years I mean years later he remember me. Not in a bad way but respected me even though I lost my first battle with him.

good point about the used material , at 1.00 ft I am tempted to use the vinegar dip , makes it look like a new penny :grin:

 

[Pierre C Belarge]

I am watching the Yankee game tonight, and almost threw up.....

Reading this thread....and I threw up-------------uggggghhh

A megger does not record the resistance of the conductor, it records the resistance if the insulation of the conductor.

 

[leew]

A megger with two auxiliary or referance electrodes can measure the resistance of a grounding electrode or system. This is the system used by utilities to verify grounding system with resistances in the fraction fo an ohm resistance.

 

[lakee911]

Most customers at big blue and orange are DIY residential 200 amp are less with pvc water pipes

I diagree. If one was replacing their panel/service, its most likely on an older house. Those are likely to be copper or galvanized. One can argue that if its old it has been replaced with plastic. Well, most of the time soft copper is pulled through with the old pipe...unless it was completely dug up, which is unlikely.

 

[K8MHZ]

A megger with two auxiliary or referance electrodes can measure the resistance of a grounding electrode or system. This is the system used by utilities to verify grounding system with resistances in the fraction fo an ohm resistance.

You are correct.

The book 'Getting Down to Earth' by AVO explains how to do it. AVO is sort of a publishing company for Megger (formerly Biddle).

The technique is called FOP, or fall of potential.

Here is a link to get a free copy, but for some reason I couldn't see the whole page

http://www.megger.com/us/story/Index.php?ID=146

 

[Electron_Sam78]

If a water pipe electrode is availabe it will be the main electrode and would have to have a GEC sized per table 250.66 whereas, the rod(s) or plate electrode would never require a GEC larger than # 6 CU The NEC

Roger

Roger, you're misquoting the code section 250.66(A) which says rod, PIPE, or plate electrode conductors can be #6 if it is the sole connection to said electrodes.

 

[roger]

Roger, you're misquoting the code section 250.66(A) which says rod, PIPE, or plate electrode conductors can be #6 if it is the sole connection to said electrodes.

Why do you think I was trying to "quote" the article section, if I had intended to I would have done it in it's entirety such as

(A) Connections to Rod, Pipe, or Plate Electrodes Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or (A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

Roger

 

[Electron_Sam78]

ok, my point is that the water pipe is a pipe electrode and it's conductor can be sized at #6 according to 250.66(A)

 

[roger]

ok, my point is that the water pipe is a pipe electrode and it's conductor can be sized at #6 according to 250.66(A)

I knew that was what you were hinting at but, you need to read 250.52(A)(1) and (5) for the difference in "a Metal Underground Water Pipe Grounding Electrode" verses a plane jane "Pipe Grounding Electrode".

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.



(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.
(a) Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

Roger

 

[Electron_Sam78]

The metal underground water pipe is still a pipe electrode. It's even a less resistive electrode than if you were to take an 8 ft section of the same material and use it as a stand alone electrode - as the minimum requirement states in 250.52(A)5. A 10ft minimum length electrode gets the bigger wire but the 8 ft minimum length electrode is allowed an exception for smaller wire? Doesn't add up. That's why I interpret 250.52(A)5 to include 250.52(A)1 as a pipe electrode. In my interpretation of 250.52 a pipe GE must be a minimum 3/4" trade size and at least 8 feet long. If it is part of a water pipe system the length requirement is increased to 10 ft (not sure why). If the pipe that is part of the water pipe system is not entering the builing at a size at least 3/4" then it falls under 250.104 for bonding.

 

[roger]

The metal underground water pipe is still a pipe electrode.

Yes but it is a Water Pipe and is specifically addressed as such.

It's even a less resistive electrode than if you were to take an 8 ft section of the same material and use it as a stand alone electrode - as the minimum requirement states in 250.52(A)5.

I'm not exactly sure of what point you are trying to make here but, I agree with you in that a metallic water pipe would (in most cases) have a lower resistance than a piece of metallic pipe simply driven into the earth.

A 10ft minimum length electrode gets the bigger wire but the 8 ft minimum length electrode is allowed an exception for smaller wire? Doesn't add up.

Yes it does. The rod or pipe would not be able to offer much in the way of the intended purpose of the GES, so why would a GEC or jumper need to be greater?

That's why I interpret 250.52(A)5 to include 250.52(A)1 as a pipe electrode.

Once again a driven pipe would not do much and a # 6 would perform as well as the pipe or rod

In my interpretation of 250.52 a pipe GE must be a minimum 3/4" trade size and at least 8 feet long.

Correct

If it is part of a water pipe system the length requirement is increased to 10 ft (not sure why).

Because it is part of a "water piping system" which makes it a greater overall electrode and somewhere at some time the 10' length length was established.

If the pipe that is part of the water pipe system is not entering the builing at a size at least 3/4" then it falls under 250.104 for bonding.

If the water pipe does not meet the 10' minimum requirement the any indoor metallic water piping must be bonded per 250.104

Roger

 

[Electron_Sam78]

Yes it does. The rod or pipe would not be able to offer much in the way of the intended purpose of the GES, so why would a GEC or jumper need to be greater?
Roger

I'm not saying it would need to be greater on the stand alone pipe electrode. I'm just saying that the water pipe GEC shouldn't need to be greater than the stand alone pipe GEC since the water pipe electrode has less resistivity and would not cause an increase in current as compared to the pipe GE that is not part of the water piping system.

Once again a driven pipe would not do much and a # 6 would perform as well as the pipe or rod
Roger

But a building with a metal water piping system electrode that had a high voltage incident would channel the electrcity into the ground with less resistance and therefore less current than a building without a water pipe electrode that only had a stand alone pipe electrode. The stand alone pipe electrode would need the larger GEC IMO.

If the water pipe does not meet the 10' minimum requirement the any indoor metallic water piping must be bonded per 250.104
Roger

Again the way I'm interpretting 250.52, if you apply 250.52(A)5, talking about all pipe, plate, rod electrodes, to (A)1 then even if it had 10 ft in contact with earth but wasn't entering the building at trade size 3/4" or larger then it would be disqualified as a GE and bonded per 250.104

 

[roger]

since the water pipe electrode has less resistivity and would not cause an increase in current


with less resistance and therefore less current

I think I see where the problem lies, the lesser the resistance, the higher the current would be.

Roger

 

[jxofaltrds]

Again the way I'm interpretting 250.52, if you apply 250.52(A)5, talking about all pipe, plate, rod electrodes, to (A)1 then even if it had 10 ft in contact with earth but wasn't entering the building at trade size 3/4" or larger then it would be disqualified as a GE and bonded per 250.104

What if I used 1/2" ID or 1/4" ID copper? 250.52(A) still calls it an electrode.

So if it is less than 3/4" 'trade size' the NEC does not apply? For grounding or bonding?

 

[Electron_Sam78]

What if I used 1/2" ID or 1/4" ID copper? 250.52(A) still calls it an electrode.

So if it is less than 3/4" 'trade size' the NEC does not apply? For grounding or bonding?

Of course the NEC applies. You misinterpretted my post. If it's smaller than 3/4" then refer to 250.104 for bonding because it's not qualified as an electrode per 250.52(A)5.

 

[Electron_Sam78]

I think I see where the problem lies, the lesser the resistance, the higher the current would be.

Roger

Did I get that backwards!? Shoot there goes my whole argument. :grin: