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#61044 - 01/16/06 06:54 AM Ground Rod or Water Pipe Ground?
wendel Offline
Member

Registered: 08/07/04
Posts: 57
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.

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#61045 - 01/16/06 07:22 AM Re: Ground Rod or Water Pipe Ground?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#61046 - 01/16/06 09:45 AM Re: Ground Rod or Water Pipe Ground?
winnie Offline
Member

Registered: 09/15/03
Posts: 652
Loc: boston, ma
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

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#61047 - 01/16/06 12:38 PM Re: Ground Rod or Water Pipe Ground?
mshaw Offline
Member

Registered: 01/11/06
Posts: 45
Loc: Fairborn, Oh, USA
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.

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#61048 - 01/16/06 12:43 PM Re: Ground Rod or Water Pipe Ground?
Electricmanscott Offline
Member

Registered: 01/12/02
Posts: 1478
Loc: Holden, MA USA
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.

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#61049 - 01/16/06 04:38 PM Re: Ground Rod or Water Pipe Ground?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
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).]

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#61050 - 01/16/06 04:45 PM Re: Ground Rod or Water Pipe Ground?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Dnk I am not interested in Hammering you but I am confused why you think the water line is optional.

 Quote:
250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system.


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 Badger
Construction & Maintenance Electrician
Massachusetts

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#61051 - 01/16/06 05:04 PM Re: Ground Rod or Water Pipe Ground?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
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).]

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#61052 - 01/16/06 05:11 PM Re: Ground Rod or Water Pipe Ground?
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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?
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#61053 - 01/16/06 05:19 PM Re: Ground Rod or Water Pipe Ground?
vlad_tepish Offline
Member

Registered: 10/30/05
Posts: 39
Loc: Delavan,Wis,USA
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.
_________________________
Patrick

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