Grounding Electrode - 4" Water Pipe

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wolfman56

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I,m doing a new service (500 amp.) in an 80 year old retail store. The water service has been upgraded to a PVC main. However there is a 4" steel sprinkler main stubbed into the basement. I assume this becomes the grounding electrode. But I need suggestions on connecting the conductor to it. Any suggestions will be helpful.
Thanks
RAW
 
Re: Grounding Electrode - 4" Water Pipe

From my understanding of the NFPA 72 (which is limitted), you can not use a sprinkler pipe as a grounding electrode. With that said, you still have to bond it with as metal water piping, and it must be sized as a grounding electrode conductor. Perhaps if you did it within 5' of the entrance of the building....?
 
Re: Grounding Electrode - 4" Water Pipe

Ryan I believe you are correct. I would treat it as an electrode, but not count it as one under provisions of 250.104.

In other words I would run a bonding jumper to it from building steel or a driven rod..

What electrodes are availible? Building steel, driven rod, Ufer, etc.?
 
Re: Grounding Electrode - 4" Water Pipe

Doesn't the 4" pipe qualify as a ground electrode, if 10' is in earth contact?
 
Re: Grounding Electrode - 4" Water Pipe

Bennie is correct.

2002 NFPA13 (Sprinkler Systems)
10.6.7* When it is necessary to join metal pipe with pipe of dissimilar metal, the joint shall be insulated against the passage of an electric current using an approved method.
10.6.8 In no case shall pipe specified in 10.6.7 be used for grounding of electrical services.
(Annex-Explainatory material)
A.10.6.7 Gray cast iron is not considered galvanically dissimilar to ductile iron. Rubber gasket joints (unrestrained push-on or mechanical joints) are not considered connected electrically. Metal thickness should not be considered a protection against corrosive environments. In the case of cast-iron or ductile iron pipe for soil evaluation and external protection systems, see Appendix A of AWWA C105, Polyethylene Encasement for Ductile Iron Pipe Systems.
Click to expand...
NFPA 72 has no mention of grounding electrodes.
 
Re: Grounding Electrode - 4" Water Pipe

Good comments!
I was thinking like Bennie. The city has stubbed in for future possible use a 4" main into the building. It only comes in a few feet and ends. There is no sprinkler system installed at this time. This is brand new, and I assume that it's solid all the way into the street. However it's a water main, and it goes at least ten feet out.
This building would has no other grounding means, except for the 2 ground rods, which seems a little lame with such a large service.
Is it possible the NFPA forbids the use of this pipe for a grounding electrode?
RAW
 
Re: Grounding Electrode - 4" Water Pipe

Originally posted by websparky:
NFPA 72 has no mention of grounding electrodes.
Click to expand...
Thanks Dave. I think I started typing too fast...I should have known better (NFPA 72 is the fire alarm code). I was thinking NFPA 13. Thanks again.
 
Re: Grounding Electrode - 4" Water Pipe

If the 4" pipe is ductile iron, they are standard 20 ft length. The joints are normally bell and spigot with rubber gaskets, there is a grounding wedge that is used if the pipe is to be considered electrically conductive (cathodic protection is one example).
If there is a flange on the end of the pipe I will drill and blind tap it, and install a SS bolt with a compression lug. If not then I use a water pipe clamp. Once I had a 8" ductile line to bond, the clamp cost $125.
 
Re: Grounding Electrode - 4" Water Pipe

Thank's for all the info.
Because of you're replys I went to the city engineers and found out:
The pipe is 4" ductile iron, and has a joint that is not conductive at 5' from the building. Therefore it cannot be an electrode!
Thanks
RAW
 
Re: Grounding Electrode - 4" Water Pipe

Would a water pipe, with nine feet, eleven and a half inches, in the dirt, be a grounding electrode? How about if it tested less than 25 Ohms?

This pipe is a ground electrode, no matter how long it is.

Drive supplemental rods and be done.
 
Re: Grounding Electrode - 4" Water Pipe

Bennie
You are correct in saying it is an electrode, but it is not one of the electrodes in the NEC that are spelled out as part of the electrode system.

Pierre
 
Re: Grounding Electrode - 4" Water Pipe

Pierre, Bennie,
Common sense may call the 4" pipe an electrode. However here in the great northwest the inspectors are very critical as to the "letter of the code". Ground rods are always used here, and I could go ahead and bond the 4" pipe, but in this case it would be expensive to take a 1/0 CU wire 110' thru floors and block walls to get there. So I'd rather not.
RAW
 
Re: Grounding Electrode - 4" Water Pipe

Wolfman, you did the right thing going to the AHJ and asking. I agree in concept that the sprinkler pipe can be a very effective ground electrode. However I have ran into a few areas of the country where the fire marshall will not allow the sprinkler pipe to be used. That is why I agreed with Ryan_618, because one of those cities was Salt Lake.

[ April 04, 2004, 10:54 PM: Message edited by: dereckbc ]
 
Re: Grounding Electrode - 4" Water Pipe

How does the Fire Marshall enforce the requirement to not use the pipe for a ground electrode?

Bonding the pipe will make it an electrode unless there is a die-electric fitting to isolate the interior pipe.
 
Re: Grounding Electrode - 4" Water Pipe

Originally posted by bennie:
How does the Fire Marshall enforce the requirement to not use the pipe for a ground electrode?

Bonding the pipe will make it an electrode unless there is a dielectric fitting to isolate the interior pipe.
Click to expand...
The fire marshall enforces it by failing the sprinkler installation and declining or withdrawing his sign off on the U&O. he/she knows that the GC will do the rest of the enforcing for them. I had one do it to a crew I was on in Northern Virginia but when the electrical contractor I was working for filed a notice of appeal with the office of the state fire marshall he backed off. I never did figure out why he didn't like us using the six inch sprinkler supply as a grounding electrode. Can anyone confirm whether this is a problem under NFPA 13.
--
Tom Horne
 
Re: Grounding Electrode - 4" Water Pipe

Bennie-
I think your question ("What about a 9'11" pipe..) is answered in the American Electricians' Handbook.
The 1999 edition has ilustration 8.131, which shows the relationship between ground resistance and depth.
The graph is not linear; rather, you can see where an engineer would be tempted to make a rule based upon the "point of diminishing returns." That is, the missing half inch doesn't mean a lot for an eithg foot rod, but would mean much mor for a two foot rod!
In terms of improvement, the local requirement of a 10-foot rod is a negligible improvement over an eight foot rod.

I believe that a similar sort of logic was used for the "six feet between rods" rule.
 
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