Using 2 ground rods as a substitute for a H2O ground

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reynoldsk

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Amongst other electrical work, I have been replacing/upgrading residential services for about five years. There have been situations when it is very difficult and would cause significant damage to the customers house if I were to upgrade the water pipe bonding conductor from a #6 to a #4, these sizes were picked for simplicity. My boss has told me that it is okay to substitute upgrading the water pipe bond with a second ground rod. In other words a 200 Amp service will have two 1/C #6 bare copper connected to two separate ground rods and a #4 aluminum bonding the water service; all of them being terminated at the main panel's neutral/grounding bar.

Is this acceptable as per the NEC and are there ever local/utility regulations regarding this? If there are local/utility regulations which takes precedence the NEC or the local?

Thank you in advance.
 
Re: Using 2 ground rods as a substitute for a H2O ground

I believe the NEC says to use the water pipe first as the electrode

I am trying to figure out the damage part????
 
Re: Using 2 ground rods as a substitute for a H2O ground

The second ground rod rule doesnt apply to this one as far as I can see.

A supplementary ground rod may be used by connecting it to the water pipe.

Thus still using the pipe.
 
Re: Using 2 ground rods as a substitute for a H2O ground

reynoldsk
NEC 250.50 says to connect to a list of electrodes if available. In an existing dwelling, most of those electrodes aren't available. Then 250.50 says to go to one or more made electrodes, ground rods being one.
250.56 says if you have one electrode, a driven ground rod, you must test the resistance to ground. If more than 25 ohms you should drive one more at least 6' away, and then leave. That's probably where the two ground rod idea comes from.

That is not a substitute for bonding hot and cold water together and bonding to the electrode system per 250.104. Water must be bonded if you drive 10 ground rods.
 
Re: Using 2 ground rods as a substitute for a H2O ground

Thanks guys.....I didnt think it was acceptable according to the NEC either. As far as the "damage" goes. In a finished garage or basement when the water service is on the other side of the house, the customer usually gets frustrated if you break sheetrock or run conduit. ; )
 
Re: Using 2 ground rods as a substitute for a H2O ground

Check out this section.

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. Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used.
Click to expand...
You must connect to every available electrode, you do not get to substitute one electrode for the other.

IMO just because it is hard to access does not make it unavailable. :D
 
Re: Using 2 ground rods as a substitute for a H2O ground

We are connecting to every electrode. However, we are not upgrading the conductor the water pipe. For a 100 Amp service being upgraded to a 200 Amp service we are not upgrading the water pipe conductor to a #4 Cu we are keeping it as a #6 Al and adding another ground rod.


In this situation is it OK?
 
Re: Using 2 ground rods as a substitute for a H2O ground

Originally posted by reynoldsk:
We are connecting to every electrode. However, we are not upgrading the conductor the water pipe. For a 100 Amp service being upgraded to a 200 Amp service we are not upgrading the water pipe conductor to a #4 Cu we are keeping it as a #6 Al and adding another ground rod.


In this situation is it OK?
Click to expand...
No, it is not OK.

You are not connecting to the water pipe.

The conductor is to small and does not 'count' as a connection, it must be sized per 250.66.
 
Re: Using 2 ground rods as a substitute for a H2O ground

If you are upgrading the service, then you must bring it up to current code requirements. To do otherwise would be to endanger the client?s life.

When you talk about this causing damage to the house, do you mean that you would have to tear up walls and floors? If so, then so be it. That is part of the cost of the project. You can tell in a quick initial inspection, before you bid the job, that a particular house is going to have this problem. Tell the customer about it, and let them decide if the upgrade is worth the price.
 
Re: Using 2 ground rods as a substitute for a H2O ground

A remedy that the customer may find more palatable is to un the grounding electrode conductor outside the house. It can be buried, run under the lower edge of the siding, or run under the eaves. Just find a route and run the number four copper.
--
Tom Horne
 
Re: Using 2 ground rods as a substitute for a H2O ground

Don't lose sight of the reason for the GEC going to the grounding electrode. If a lightning strike were to happen, all those twists and turns may torch the house. :(
 
Re: Using 2 ground rods as a substitute for a H2O ground

This question is kind of scary. (So are some of the answers) Not only do you have to properly size and install the gec to the water pipe, you must install the two gound rods as well.One will not give you less than 25 ohms. Not to flame but sheesh, I see this on service upgrades and I can't beleive it passes inspection.
 
Re: Using 2 ground rods as a substitute for a H2O ground

Running outside seems like a good idea. After I started trying to find information on this I noticed that the NEC specifically says it can be run outside.

hornet Why would one ground rod not be less than 25 ohms?
 
Re: Using 2 ground rods as a substitute for a H2O ground

quote from reynoldsk
Why would one ground rod not be less than 25 ohms?
I work in southern NM, and one ground rod would give you 100 ohms or more in most locations. We have silica sand and no moisture.

Jim T
 
Re: Using 2 ground rods as a substitute for a H2O ground

The resistance at the groundrod varies with the geography.

Up here in MN no one, in my experience, has ever requested a resistance check of a single groundrod. . .and this is my 25th year. Whether the rod is driven right next to the basement wall, out in the back yard, in the basement in the watermeter pit or through the parking lot asphalt. Put in a single ground rod and the AHJ, here, approves it.
 
Re: Using 2 ground rods as a substitute for a H2O ground

Same here AL. Seems many folks are under the impression we have to prove the 25 ohm rule. In over 15 years not only have I never been asked about a ground rod's resistance but I have never even heard of anyone being checked.
We have mostly rocky but moist soil conditions around here. It's funny when someone says; "You can never get 25 ohms, you have to install two rods". Then you come to find out they live in the desert. Personally I like a little moisture.
 
Re: Using 2 ground rods as a substitute for a H2O ground

Pete
I am from lower NY and we ask for 25 ohms to ground or you drive a second ground rod. It is customary here to see two ground rods at all new installations, unless they use a different electrode (effectively grounded steel, footing, etc).

I am a firm believer that a second ground rod is a total waste of money and time, but code is code. If we start allowing contractor 'A' exemption from one code rule, and contractor 'B' exemption for another code rule, etc... then there would be no need for a codes at all, hence all code rules are enforced as necessary.

Pierre
 
Re: Using 2 ground rods as a substitute for a H2O ground

From everything I have read one ground rod does not even come close to 25 ohms in my area. Two doesn't do it either but the NEC stops there. Speedypetey, acording the NEC 250.56 you do have to prove that the rod is 25 ohms or less. If it is not you "shall" install an addtional rod. Al, is MN on using the NEC. If so do they generally pick and choose what rules to enforce?
 
Re: Using 2 ground rods as a substitute for a H2O ground

Scott, all it says is "A single electrode that does not havea resistance to ground of 25 ohms or less shall be augmented by one additional electrode...".

I see no burden of proof. Who carries this burden and where is it written?

Pierre, you say 'We ask for 25 ohms". Who does the testing at who's cost?
I am not asking for an exemption but no way in hell I am going to invest in a several hundred dollar tester to do someone else's test. If it is written that it is my burden to make this test, so be it.
If an inspector want to test the electrode and prove another electrode is required, so be that as well.

[ December 11, 2004, 08:24 AM: Message edited by: speedypetey ]
 
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