Grounding question -- ping gfretwell

[Doug Miller]

My house, built in 1962, has one grounding electrode: the metal plumbing system. Doesn't meet Code now, but I'm pretty sure it did in 1962. The grounding electrode conductor is attached to the plumbing directly inside the point at which it enters from the outside -- pretty much completely on the opposite side of the house from the electrical service entrance.

In conjunction with a renovation project completely unrelated to the electrical system, I'm going to have to temporarily disconnect and possibly relocate the grounding electrode conductor.

I know that current Code: (a) does not permit the metal water plumbing system to be the *only* grounding electrode; (b) does not require the metal water plumbing to be a grounding electrode *at all*; (c) requires that *if* it is used as a grounding electrode, the conductor must be attached within 5 feet of the point of entrance to the building; and (d) does require it to be bonded to *other* grounding electrode(s).

Here's what I propose to do:

(1) Sink a 10-foot grounding rod directly outside the service entrance, and connect an appropriately-sized grounding conductor (AWG 4 for 200A service?) to it and the service entrance panel. That will give me a grounding electrode other than the water pipes. (2) Cut the existing grounding electrode conductor short, and bond it to the water pipes at the most convenient location, about ten feet from the service entrance -- which is some forty feet from the point at which the water pipe enters the building.

Am I correct in believing that this meets current Code?

Here's my reasoning: The connection to the water pipe is much more than the five-foot minimum required if the water pipe is used as a grounding electrode -- but because the system will be grounded to a grounding rod, *that* is the grounding electrode, *not* the water pipes, which are merely *bonded* to the grounding electrode.

[bob haller]

you will need multiple ground rods. there a hammer tool that fits on a drill bit to put the rod in, leave the ground wire to the water line where it is, and install a jumper across the meter....

[gfretwell]

True

Not true, water pipe shall be bonded

Entrance of the water pipe

All available electrodes shall be used

OK

Just leave it the way it is

The 5' refers to the water pipe, not the distance from the electrical service entrance. They are just minimizing the chance that a piece of plastic will end up in that metal pipe. If this is still the good old copper pipe all the way to the street, it will still be your best electrode. The GEC to a rod only has to be 6 gauge, no matter how big the service is, just because that is about all it will end up grounding anyway. The water pipe, being the better electrode still needs a full sized 250.66 conductor (#4 for typical 200a)

[Doug Miller]

[e-mail] wrote in news: [e-mail]:

Bonded to the grounding electrode, right, I know that. Maybe I'm not using the correct terminology here.

Right, that's what I meant, sorry for not being specific.

Yep.

I *can't*. I have to disconnect and move it, at least temporarily, for the other project -- it's in the way. And that's going to be a pain in the neck: it's inside EMT. I was hoping to be able to avoid reinstalling it in the same manner.

Understood.

And that *must* be connected within 5' of where the water pipe enters the building, regardless of the presence of any other grounding electrodes in the system?

[Ralph Mowery]

Check with the local codes. Sometimes you may need 2 or more ground rods spaced a certain distance apart due to poor soil conduction.

[trader_4]

From my reading of the code your problem comes down to this:

250.50 says that all grounding electrodes that *are present* must be bonded together to form the grounding system. Since you have an incoming metal water pipe, it's present and hence must be used as part of the electrode system. That means that you have to bond to it within 5 ft of where it enters.

If it were not for 250.50, you could use your ground rod, plus another grounding electrode, eg another ground rod to form the grounding electrode system and then bond the metal water pipe system to electrode system at a convenient point near the panel. Sounds like that is what you want to do, but 250.50 appears to say that you can't. 250.50 is a bit weird. Suppose for example you had an old ground rod on the other side of the house. That is also present, so strictly following the code, you'd have to either pull that out of the ground or use it too?

That's my two cents.

[DerbyDad03]

...snip...

Your description of "old ground rod" is not clear to me. Are you talking about an abandoned ground rod with no conductor attached to it? If so, IMO that would not have to be used. If it did, then all those spare grounds rods stashed in the shed would also have to be used. Aren't they "present" also?

I take 250.50 to mean that if an object is *used* as a grounding electrode then it must be *bonded to all other grounding electrodes*. Just having a piece of metal - even if the receipt says "ground rod" - pounded into the ground doesn't make it a grounding electrode.

...and that's mine.

...and I could be wrong. ;-)

[gfretwell]

You "ground" to electrodes and you "bond" everything else, at least that is the current terminology but they do get used interchangeably.

This is a unique thing about GECs and conduit, If you use metal, the conduit has to be bonded at both ends and it becomes part of the grounding electrode conductor. If it is plastic, obviously you don't have anything but the wire. The problem is, if you use any metal at all, it has to be all metal, bonded at both ends. This has to do with the "choke" effect of metal pipe around a conductor.

Yes.

[gfretwell]

That is the NEC. It says if you can not verify that one rod brings you in under 25 ohms, you drive another one 6' or more away. After that, it is probably not going to get much better with more rods so you are done. A ground rod is the least capable electrode that is allowed.

[trader_4]

The ones stored in the shed aren't permitted grounding electrodes because they aren't in the ground. But one that meets code, at the house, in the ground would be. Another example would be a Ufer. Suppose it's present, can I choose not to use it and just use two ground rods instead? 250.50 would seem to say that I have to use it, because it's present.

Then that's what they should have said, but they didn't. I agree that what you suggest would seem to be more reasonable. And if you interpret it that way, then it would seem that Doug could do what he wants to do, ie ignore that the metal water pipe is a grounding electrode that is present and follow the more lenient bonding of the house metal water piping where that piping is not part of the grounding electrode system, only bonded to it.

250.50 is the only thing I see that prevents him from doing what he wants to do. But I also see Bud saying that the metal water piping must be used, maybe he has a section other than 250.50 that says so?

[gfretwell]

I have never heard of inspectors going looking for unused "made electrodes" but the ones that are inherent in the building shall be used. I have heard of it going so far that people have had to chip into foundations to get to the rebar for a Ufer on new construction. The reality is that the ufer connection is part of the foundation inspection so it should be available after the concrete is placed. In our area they allow connection to turned up rebar so it is not likely to be broken off or stolen like you get with a copper wire. The issue would be that the core gets poured solid along with the other doweled cells. They paint that block green.

OTOH if the inspector actually insists that the Ufer is totally encased in concrete, the fix is to pour that cell full after the panel is set and the GEC is run, near the end of construction when the thieves are less likely to steal it and it is less likely to be broken off.

[bud--]

The NEC is a code for new work. What you have was compliant when installed and thus has no problem with the current NEC.

Totally false.

Not true. Water pipe (10 or more feet metal in contact with the earth) shall be used as an earthing electrode.

If the water pipe is not "10 or more feet" the interior water pipe shall be "bonded" with slightly different rules.

This must have just been a misstatement. The rest of your answer indicates the water pipe is an electrode. I agree with everything else you wrote, including that ground rods suck.

The NEC requires the resistance to earth for a ground rod to be 25 ohms or less. [What happens if you connect a hot wire to a rod that is 25 ohms to earth? Ground rods suck.]

Virtually no one will measure the resistance. A second rod is installed and the resistance can be anything.

Rods are minimum 8 ft length.

>

[bud--]

If the conductor is #4 it "shall be protected if exposed to physical damage". Usually additional protection is not required.

If run in a ferrous metal raceway, each end of the raceway shall be bonded to the conductor (so the raceway is a parallel conductor). The raceway and conductor form an electrical "choke" which raises the impedance of the conductor. On a heavy fault a significant percentage of the current will flow through the bonded raceway.

[trader_4]

Sounds reasonable to me. So the underground water pipe and Ufer, if present have to be used. How about:

A ground rod that happens to exist on the other side of the building?

A ground rod that's close to the panel?

Assuming neither of those is required to meet the min ground system reqt, would either have to be used? Sounds to me like you're saying the answer is no, or probably no, depending on the inspector?

[Doug Miller]

[e-mail] wrote in news: [e-mail]:

Got it. I understand now. Thank you for your patient explanations.

For the other project, I *must* disconnect and relocate that conductor. It sounds like I'm going to have to re-route it where it won't be in the way, and reconnect it to the same point where it's connected now.

I think I probably should open the main breakers while I'm handling that: if the system is live, and I'm holding a disconnected ground, a fault anywhere could kill me.

[Scott Lurndal]

Can't you disconnect the ground at the panel first, then disconnect the other end from the pipe?

[Doug Miller]

[e-mail] (Scott Lurndal) wrote in news:srslz.13240$ [e-mail]:

Of course I could, but then the entire system isn't grounded... and I'm not sure that's much of an improvement.

[gfretwell]

I am not quite sure why anyone would know a rod was there. We don't carry metal detectors ;-) They are supposed to be driven flush or below grade. There would also be the question of how long it is. The Telcos and Satellite companies have less than legal rods.

[gfretwell]

That is true and you should still be careful. I have a few amps on my GEC with the main breaker open. In a place where the water pipe is the primary electrode, that may not be as likely. We are electrodes in sand here and there are significant amounts of objectionable current floating around.

[gfretwell]

It might be a good idea to run a jumper wire from the ground bus to the GEC while you are working, in case something happens beyond your control.