Water Pipe Grounding

[bphgravity]

I have a single family home on city water. The pipe from the street to the house is PVC. All interior water piping is copper. This piping is completely underground except for the locations it is stubbed up to feed the sinks, water heater, washer, etc... This piping is underground and in contact with the earth for more than 10'.

Can this metal water piping be used as a grounding electrode? The connection point will be at the water heater no more than 5' from where the stub-up comes from underground.

 

[charlie b]

Re: Water Pipe Grounding

I'd be curious as to how you could know that the pipe was underground (i.e., in physical contact with dirt) and electrically continuous for 10 feet or more, measured to the point at which it stubs up for the water heater. But I suspect you are curious about the same thing, and that is why you are asking the question.

If you can say with confidence that it is, then I think you have to use it as an electrode. If you have to admit that you cannot determine what the condition of the pipe is under the house, if you don't know whether there are any PVC joints for example, then I think you have to not use it as an electrode.

 

[LarryFine]

Re: Water Pipe Grounding

Agreed with Charlie: what will you say if/when the inspector says, "Prove it!"

 

[pierre]

Re: Water Pipe Grounding

In the northeast, with basements (and cold weather), this would probably not be possible. Where Bryan works and plays, they generally do not have basements and this type of installation might be more common than where I play and work.
It never ceases to amaze me that there are so many different situations out there - this is interesting. Who would think that this would occur?
I took another look at 250.52(A)(1) and I would say that this copper water pipe would have to be used as an electrode, as it is present. As far as proving it is in contact with the earth for 10 feet or more... that is what the ever present cameras are good for.

 

[suemarkp]

Re: Water Pipe Grounding

The practical difference is not that much between a ground electrode or just being bonded. In both cases, you use a wire sized by 250.66. If it is a ground electrode, you still have to supplement it with another electrode of some type. All the ground electrode mandates that is different from bonding is that the GEC be clamped within 5' of where the pipe enters the building and be unspliced.

If you can do that, then it doesn't matter whether its metal in the earth or not. I would be one to assume it is a ground electrode and have you prove otherwise. Is there any reason why you can't run an upsliced wire to a segment within 5' of where it enters the slab?

 

[pierre]

Re: Water Pipe Grounding

For bonding the cold water, you would use Table 250.122.
For grounding the cold water you would use Table 250.66

It will generally result in different size conductors in relation to the service.

 

[George Stolz]

Re: Water Pipe Grounding

Originally posted by pierre:
For bonding the cold water, you would use Table 250.122.

No, see 250.104(A)(1). Either way, it's sized to 250.66.

Unless they fixed this in 2005? It seems like I submitted a proposal to change this, or Ryan did, or something?

 

[bphgravity]

Re: Water Pipe Grounding

The discussion originated after I had cited 250.56 on a rough inspection when only one ground rod was present at the service. The contractor called me and said he didn't need the rods because he had water pipe ground. I told him that I am considering the water connection as the required bonding of the water pipe system and not as the grounding electrode, however in either case 250.56 would still come into play.

If the water pipe is an electrode, 250.53(D)(2) references 250.56 when rods are used, and if the ground rods are going to be the only electrodes, 2 are needed as well.

He agreed on the second rod after reviewing the sections I referenced but still felt the water pipe was apart of the grounding system. It doesn't really matter, but I thought it was worth discussing here.

 

[charlie b]

Re: Water Pipe Grounding

Originally posted by bphgravity:. . . and if the ground rods are going to be the only electrodes, 2 are needed as well.

So you are of the school of thought that places the burden of proof on the installer, to show that the resistance of the first rod was below 25 ohms? Just out of curiosity, if you saw only one rod, and the installer said he tested it and found a value of 20 ohms, would you make them repeat the test in your presence, or would you accept the single rod as-is?

I think this has been discussed before, but I don't think it has had, nor can it have, a resolution. I just wanted your opinion.

 

[bphgravity]

Re: Water Pipe Grounding

Unfortunately, noone has ever objected to adding a second rod nor has ever offered to prove resistance testing. 2 rods are basically automatic around here. If the electrician or contractor happened to be on-site with one of those fancy little clamp-on ground resistance testers and showed a value of less than 25-ohms, I wouldn't have a problem approving one rod.

 

[pierre]

Re: Water Pipe Grounding

Thanks George
I learn something new... more than once a day

 

[twistin214]

Re: Water Pipe Grounding

I told him that I am considering the water connection as the required bonding of the water pipe system and not as the grounding electrode

did he attach it with in 1.52m(5') of entrance?

[ December 30, 2005, 01:45 PM: Message edited by: twistin214 ]

 

[augie47]

Re: Water Pipe Grounding

We had a discussion today and it was noted that on jobs in this area the inspector always looks at the GEC to the, what I will call, basic water line providng drinking and sanitary water, however, for some reason, the incoming fire sprinkler water lines seldom have a GEC connection. Is there some reason that these lines should not be treated as grounding electrodes? I understand that the branch piping is often isolated by the type couplings sprinkler systems use, but would the large main line not be a desirable electrode?

 

[George Stolz]

Re: Water Pipe Grounding

I believe (odd as it sounds) the two are connected at some point in the fire room of the buildings I wire. I need to double-check that. It seems like I had that thought before, went to look and was satisfied with whatever it was I saw at the time.

 

[augie47]

Re: Water Pipe Grounding

interesting point, george. here they are not connected in the fire room, but they do normally come off the same water main in the street. I had not thought of it, but, I guess if you bond to one, you have essentially bonded to the "water system" as long as they are innerconnected. Thanks

 

[DaveTap]

Re: Water Pipe Grounding

Better make sure you have a jumper around the water meter if try that argument