I was wondering about the most effective residential service grounding method. Many use the domestic water piping (assume no plastic pipe/fittings in the lines). My concern with a copper piping system used as a ground involves possible electrolysis and slow damage to the pipe itself and the sweat joints. I have measured a small potential difference between the power company neutral and the piping ground. Could this small potential be a cause of electrolysis?

It seems the safest way to a ground residential system would be using a ground rod. Is there an effectiveness difference between the two methods? Any thoughts welcomed.

Welcome Wendel.

I would like to first point out that we do not get a choice of which to use.

If there is a metal underground water pipe available we must use it to comply with the NEC.

Once we use it it is highly likely to be carrying a few amps of current.

It is very likely that the metal water pipe in one house is electrically continuous with many other houses each with their services bonded to the water pipe.

The entire areas metal water system becomes a conductor for unbalanced neutral current.

Considering the high number of services done this way and the relatively few plumbing problems I do not believe that this current flow is a problem as far as electrolysis.

I think for electrolysis to be a problem you would need a difference of potential. The entire pipe and water would be very close to, if not the same potential.

I have also heard stories, but have no reviewed references nor personal experience, that _AC_ current on the metal water pipes is much less of an issue than very small _DC_ currents on the pipes. This makes some sense, since AC would tend to redeposit any materials removed.

-Jon

I use both a ground rod and the domestic water line. I also bond the hot and cold at the water heater to asssure complete bonding of the water system. This pratice gives all the residential water supply systems the same potential within the structure.

When you use the underground water pipe as required you must supplement it with at least one ground rod and if that rod does not meet the 25 ohms or less requirement you must add a second.

Quote
"If there is a metal underground water pipe available we must use it to comply with the NEC."

I still haven't seen the MUST in the code book yet, it gives you several options. Unless you can prove it is in the ground 10'. Even then, the book says it MUST be supplemented.

Some homes have no metal water pipes, they are all plastic..

My view is your better with 2 ground rods, and/or the other electrodes allowed, and then bond the water pipe or water system to this ground electrode system that you created.

But I'm sure I'll get hammered for this one....


Dnk....

[This message has been edited by Dnkldorf (edited 01-16-2006).]

Dnk I am not interested in Hammering you but I am confused why you think the water line is optional.


A metal water line is on the list, if it is there it must be used.

Bob

[This message has been edited by iwire (edited 01-16-2006).]

BOB, the only thing that quote you posted states, is, if available, they shall be bonded together.

It does not state you MUST use a water pipe as a GE.

Dnk...

[This message has been edited by Dnkldorf (edited 01-16-2006).]

Dnk I am trying to understand your view but it is going by me.

250.50 requires all the items in the list if available to be as you said bonded together... into a bonding electrode system

By your view there are no required grounding electrodes?

here we use two ground rods 6 feet apart outside,inside we run a ground wire to the water pipe ,also bond the water and gas.

You can use any and all on the list if you want.

My point is the use of the word MUST.

Unless you are there while the foundation is dug, or while the water pipe is being installed, or if you decide to dig down 3' and at least 10' long to prove the water pipe actually meets the critia, you can't use it...

So why use it, unless you can prove it.

Also, the water pipe is the only electrode that MUST be supplemented by at least one of the others on the list. The only one that the code calls out to be supplemented.

I went to Mike's bonding/grounding course a while back and asked the same question to him, after a decussion we had on the same topic a while back, and I got hammered by some of you guys about this.

After searching and thinking about this, he concluded the same thing I am stating here.

It is a technical thing with regards to using the word MUST.
It doesn't really say that you MUST use it as a GE. It only states it MUST be supplemented, and it shall be bonded to the GES.

2 ground rods constitute a GES, then bond the water pipe to it, that way you don't have to prove or dig.


Dnk....




[This message has been edited by Dnkldorf (edited 01-16-2006).]

OK if you feel better not calling it a grounding electrode so be it.

Has this change of name changed anything at all?

It's either a GE and connected with a conductor per 250.66 or it metal stuff that has to be bonded with a conductor sized per 250.66.

Again going with your view none of the items on the list have to be used as GEs only bonded to the GES.

I can see why you feel so strongly about this.

Bob

This is why I often refer to water as a bond/electrode, once you bond it, it is by proxy an electrode in the grand sceme of things. (In the world of copper piping at least) Part of the system.

And "shall" does in effect mean "must'...


"Shall: indicating that something must happen or somebody is obliged to do something because of a rule or law."

Or: "Mandatory"

If a metal water pipe is there, it has to become part of the system. Many places considered it as the primary electrode... I think just because it was on top of the list...

Now if it were a metal pipe inside, and a PVC underground outside, that would be different. At which point it is no longer an electrode. But it still would have to be bonded due to 250.104.

BTW Bob.... What is it about grounding these days that has you in such a tizzy? Is there a problem with the grounding system at home? Feel free to lay back on the couch and relax... It's better if you talk about it...

I will make a deal, you explain to me what a 'primary electrode' is


and I will tell you what is getting me in a 'tizzy'.


Bob

Did we forget equalizing the potential in the building systems? Why do we bond water lines and structural steel in commercial settings, place bare copper in concrete and yet we still use multipal grounding rods as well. Even if multipal ground rods get the job done should we not bond the water line (if it is not plastic) to insure equalizing the potential? I think I would leave the gas line alone,yeikes.

Is this an accurate statement relative to primary and secondary grounding electrodes?

A grounding electrode system usually consists of a primary
grounding electrode, plus possibly a secondary electrode. A
primary electrode can be (if in direct contact with the earth):
10' of ground rod. 10' of well casing or metallic water pipe
(must be connected within 5' of pipe entrance to house). 20'
of copper wire buried in the bottom of the footings. A
secondary electrode will be required if the primary is a water
pipe or (NEC) if the primary electrode is >25 ohms to the
dirt.
It seems a secondary electrode is needed where a water pipe is used due to the fact water pipes deterioriate and can therefore be replaces with a nonconducting material like plastic at some time in the future.

[This message has been edited by wendel (edited 01-17-2006).]

'Primary' versus 'secondary' grounding electrodes is a meaningless distinction _electrically_. There may be a legal/code/historical ramification, but in the present code there is no electrical distinction.

You can have effective versus ineffective grounding electrodes, and you can have bonded metal piping that is not a grounding electrode.

If it looks, smells, tastes, or conducts like a grounding electrode, the it must be tied to the grounding electrode system. All grounding electrodes tied to the grounding electrode system will function to a greater or lessor extent as part of the grounding electrode system.

250.50 tells you that _if available_, you must use all of the items listed in 250.52(A)(1) to (A)(6) as the grounding electrode system. If the electrodes are _not avaialble_, then you _must_ install one of items (A)(5) - (A)(7). So you _must_ have a grounding electrode that meets certain minimum requirements (size, material, depth, etc)

250.53(D)(2) tells us that item 250.52(A)(1) is not in and of itself sufficient, and that you must have additional grounding electrodes.

250.56 tells us that items 250.52(A)(5) and (A)(6) must meet certain performance criteria, _or_ that you must have yet another grounding electrode.

-Jon

Once again, a great explanation from Jon..


Dnk..

Grounds rods are cheap.

Unless you live in an area where the ground is so hard you can't drive one, I don't know why you wouldn't just drive a ground rod or two to make sure you have a good ground.

The Code is the bare minimum.

[This message has been edited by Amazingmg (edited 01-17-2006).]

Jon, the 2005 has changed the wording from if available to All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used.

This new wording does not give any exception to say a concrete encased electrode that was poured and buried before it could be bonded, it is in fact present and shall (or must to those who prefer must ) be bonded to the others that are present even if it means dragging out the dreaded chipping hammer.

Amazingmg, you do realize that rods are pretty much a waste of time don't you? Even if you drive 10 rods that might combine to get to 25 ohms they will only assist in dispersing lightning or a HV surge but really do nothing as far as people safety at our low voltages.

Roger

Didn't we already have like an 80 page thread about this?

Deal made Bob... (Everybody)It is not my opinion! But for a while I got hit on inspections for taking the full sized GEC to the rods instead of water. (With the guise that the rods were suplimenting the water.) Take a look at 250.66(A) through (C), notice that water, and stuctural steel do not have a minimum size exception... They are always full sized. I learned the hard corrective way about this. Rods on the other hand, need only be in #6....

So back in the day, learning the hard way to break the thinking that I could go full sized to any one of the electrodes, and only #6 to whatever the other was, several Inspectors reffered to it as the "Primary". (Not that I am of that opinion....)

So as mentioned before both electrodes are part of the "system'! (As a whole, the way I see it, there is no primary, or seconary.) So now, why is the water always full sized? Why are the rods allowed to be only #6?

(You might mention that water is in a "Pipe" as listed in 250.66A, then why is an "Metal Underground Water Pipe" listed seperately in 250.52A, and 250.53?)

Although some of the wording has changed a little over the years, and 250.66 used to be 250.94 back in '93, it hasn't changed much...

Roger, I know a few GC's at this point who are well aquainted with chipping hammers to find that Ufer they forgot....

Oh, I forgot to put in bold... "It is not my opinion!"