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Ground Rod or Water Pipe Ground? #61044
01/16/06 10:54 AM
01/16/06 10:54 AM
W
wendel  Offline OP
Member
Joined: Aug 2004
Posts: 55
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.

Work Gear for Electricians and the Trades
Re: Ground Rod or Water Pipe Ground? #61045
01/16/06 11:22 AM
01/16/06 11:22 AM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Ground Rod or Water Pipe Ground? #61046
01/16/06 01:45 PM
01/16/06 01:45 PM
W
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
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

Re: Ground Rod or Water Pipe Ground? #61047
01/16/06 04:38 PM
01/16/06 04:38 PM
M
mshaw  Offline
Member
Joined: Jan 2006
Posts: 44
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.

Re: Ground Rod or Water Pipe Ground? #61048
01/16/06 04:43 PM
01/16/06 04:43 PM
E
Electricmanscott  Offline
Member
Joined: Jan 2002
Posts: 1,457
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.

Re: Ground Rod or Water Pipe Ground? #61049
01/16/06 08:38 PM
01/16/06 08:38 PM
D
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
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).]

Re: Ground Rod or Water Pipe Ground? #61050
01/16/06 08:45 PM
01/16/06 08:45 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Ground Rod or Water Pipe Ground? #61051
01/16/06 09:04 PM
01/16/06 09:04 PM
D
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
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).]

Re: Ground Rod or Water Pipe Ground? #61052
01/16/06 09:11 PM
01/16/06 09:11 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
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
Re: Ground Rod or Water Pipe Ground? #61053
01/16/06 09:19 PM
01/16/06 09:19 PM
V
vlad_tepish  Offline
Member
Joined: Oct 2005
Posts: 39
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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