When you make a code compliant installation of a service in a building that is served by an interconnected metal underground water piping system, some of the current that should be flowing on the grounded conductor will flow on the parallel path provided by the water pipe. Is this a serious hazard? Should the code be changed to prohibit the use of the interconnected metal underground water piping system as a grounding electrode? Why or why not?
By "interconnected" I mean that the water pipe in building one is tied to a metallic main and the water pipes in the surrounding buildings are connected to the same main. This occurs everywhere where both the building water service pipes and the water mains are metallic.
Don(resqcapt19)

That's a good issue. It would be good to get some plumbers' perspective on this..tho sometimes its hard to separate folklore from fact when talking electrolysis.
I wonder if the diciding factor should be whether or not the separate buildings are all fed from the same utility source.
More to the point, two buildings with power coming from the same transformer would effectively be paralleling their grounded conductors when the services are linked through the plumbing. Conceivably, one neutral could open and be fed entirely through the other neutral! This would be a smoker, if not a voltage drop hazard to personnel.

Electrolysis is a DC phenomena and while there may be a small DC component in the AC, I don't think that is a major issue. The American Water Works Association published an article in their magazine in July of 98 that reported at least one water worker gets shocked each day from this neutral current on the water pipes.
Don(resqcapt19)

Don,
I believe if you dig deeper the AWWA has opposed the concept of water mains used as a GE for quite a while.

Quite a while indeed! www.awwa.org/govtaff/groelpol.htm

Yes, I know that the water people have opposed the water pipe as a grounding electrode but they haven't really perused this with the NEC process. There was one proposal for the 2002 cycle but it was rejected.
Don(resqcapt19)

Don, In addition to the things I sent you, I'll pass this along. Article 250 regarding separately derived services says it's ok to connect X0 to the water pipe. I've had a problem with this technique for a good long time. In the mid 80's, my company had a lot of work in one of our large malls in the DC area, and the local AHJ required the use of the water pipe over the use of the bldg steel. The bldg steel had been prepped well in this case, every other one having a ground rod driven and cadwelded to it. (That is the job that actually got me in the middle of the 'discussion' I told you about). I was talking to a plumber one day, and just happened to ask him what the jumper cables were in his tool bucket for. His reply got me drawing a good many little schematics. They were beginning to 'jump' any pipe they took apart for any reason, to make a connection to a new store, maintenance, or whatever, because the pipe was 'energized'. I actually followed him to a joint they were putting in, and witnessed as he jumpered the pipe with the cables, THEN, and only then, cut the pipe. When it got finished draining down, I asked him to move and pulled one end of the cable off the pipe, coming off and going on, there was a sizable arc. I did not have an amprobe nearby and failed to take measurements, something I always regret, but don't forget, I was in business and merely followed (usually) the AHJ's orders.

This is definitely a case that would have been MUCH safer going only to the properly grounded bldg steel. I teach it that way for that reason. I don't know if anyone has been injured (above what we all take as a normal unreported shock), but always worried about the wet (from draining lines), plumbers standing on aluminum ladders.

Yes, before you ask, I did make a quick drawing and 'discussed' it with the AHJ. I was promptly told to mind my own business. I had already taken this group to the State level on several decisions (and won ) and decided to just back off, probably shouldn't have.

I might add, this bunch forced contractors to build an 1 1/2" layer of drywall around the house transformers in the hallways for fire protection. Yes, completely enclosed. I don't know how many transformers had to burn up before they changed that decision, or if they ever did. Put that one on the Fire Marshall.

George,
I think that we always should bond the interior water piping to prevent it from becoming accidentally energized. If we don't bond the metal interior water pipe we could have a problem with an electrical device that is conneted to the water piping failling in a manner that would energize the water pipe creating a different hazard.
It looks that solution will take the cooperation of the plumbing and electrical codes. The electrical code would be changed to prohibit the use of the underground water pipe as an electrode, but still require the interior water piping to be bonded. The plumbing code would be changed to require a non-conductive section of pipe in the water service at some point before it enters the building.

Roger that Don. You realize you're going to get the guys who believe that means the water pipe should not be bonded. We used to have to bond the gas pipe, it still has to be bonded, but some people believe that because you can't use it as an electrode you aren't allowed to bond it. Despite the fact I have a State ruling on it.

George,
Not only does the NEC require that the gas piping be bonded, NFPA 54, The Fuel Gas Code also requires this bonding.
Don(resqcapt19)

George,
U did'nt finish your story, what happened?

back on track,,,
prohibiting a water pipe GEC, and only bonding equates the same conductor. Isolating the metallic system & then bonding makes sense, but would require the plumbing trades interaction.

Would the overall GEC be compromised? Would options be pursued, i.e.-Ufers?

On what grounds was the last proposal shot down?
curious....

I've seen cases where the utility drop tension line/grounded conductor is snapped and there are still 120 volt circuits working properly in residences. I guarantee the neutral current was traveling thru the water pipe to the neighbor's and returning on their neutral.
Yes the plumbing system in each building would have to be isolated from the main system in order for this to work.
I think its a problem and have heard many stories from plumbers about faucets arcing. This also happens when the phone or cable company connects their ground on the load side of a dielectric plumbing fitting.
I am surprised we don't see more accidents. But electrical systems, even the oldest, are not that old, 70 or 80 years tops. The average is probably more around 50. As these systems get older and don't get replaced we may see an increase in injuries from these type of arrangements. If that happens the insurance companies will step in and get things changed.

Welcome to a reactionary society.

I got an addendum question to (DonsResqcapt19). Whenever we do multi-family dwelling we are allowed to daisy-chain all the Service panel together, for example, it there are three panels all the grounding electrode conductors are tied to the neutrals and finally at the end(last panel) goes to the water pipe and ground rods. If you put a clamp-on on those conductors not the last one but the up stream panels you are drawing a significant amount of current almost half of the neutral current. To me this means that the last panels neutral will be carrying a whole lot of extra current than it was designed for.

I can see quite a few problems with this.

I'll add more later this weekend if time allows.

Sound OK??

Scott SET.

Motor,
I don't think so. You have the grounded conductors in parallelwith the grounding electrode conductor. The current will divide in inverse proportion to the impedance of the different conductors. The current will be shared among the grounded conductors in the same manner. There shouldn't be enough difference in the impedances of the grounded conductors to have any of them overloaded.
Have you evr checked the current on all of the different conductors that are in parallel?
Don(resqcapt19)

Don (resqcapt19)
Maybe I missed on the description because I have checked the current on those grounds and the current is divided between the grounding conductor and neutral. From each panel except the one(first one that goes to the water-pipe and ground rod).
For example panel no.3 unbalance load comes back on its neutral to the neutral bar, it will see two pathes back to the transformer via the neutral going to the meter base from that panel and through panel no.2's neutral and through panel no.1's neutral.
Picture this three panels 1, 2, 3; panel no.3 has one copper conductor going to no.2 and then no.2 has a copper conductor going to no.1 then no. 1 goes to water pipe and ground, in all of these panels the neutrals are bonded, therefore the first two have low
Z pathes to the transformer, no.3 will see it through no.3 neutral and no.2 neutral the to no.1 neutral.
when I put a clamp-on on the no4 going to the water pipe it barely bobs the needle but upstream it is almost half of the return current.
I am not trying to be confusing here, but it almost seems like the neutrals on the other two panels should be up-sized.
I hope this explanation helps clear-up what i was saying

-Mark-

Don;
An addendum, to be technically correct these no.4's would be called a bonding jumper.
-Mark-

Mark,
First off, I don't think that the installation complies with 250.64(D), and I don't think it is a bonding jumper, but that doesn't change my answer. All of the neutrals have been connected in parallel by the grounding electrode conductor. The total neutral current will divide among the neutrals based on the impedance of the path from the neutral bus in the panel where the current originates back to the transformer. Why would the impedance of any of the paths be significantly different from the others? When you checked the current on the grounding electrode conductor, did you also check it on the neutral conductors?
Don(resqcapt19)

Don
There are 3 meters in a 3-meter base set-up and 3 separate service conductor cables and 3 service panels,.. for example, think of the panels as (3 2 1) no.3 goes to the ground rods, and as is the case for service panels the neutral is bonded to the grounding conductor, from no.3 to no.2 a jumper is run to its neutral buss, it too is bonded, from no.2 to no. 1 a jumper is run to its neutral buss and it to is bonded.
Yes the current will divide as per the ratio of the resistance of the neutral and the no.4 copper bonding jumper. in this case the no.4 copper copper will have less resistance than the no.4 grounded Neutral conductor of the service.
Now if you put a clamp-on on the jumper from 1 to 2 you will read a good deal of current and from 2 to 3 good current reading. but when you put the clamp on on the no.4 cndtr from no.3 to the ground rods the needle will barely move, why because the current at no. 3 is returning on panel no.3's neutral and the 25 ohms to ground is much larger than the resistance of panel no.3 aluminum neutral.
I hope I writing this clear enough I know what I am seeing but whether I am describing it correctly could well be another.
Yes on panels 1 and 2 its about evenly divided. All I am saying is that those first two panels are dividing their unbalanced current and sharing it with the bonding jumper and does that until it reaches the panel that is tied to the ground rods.

-Mark.

Mark,
All three grounded conductors are connected together. The only difference in the current on any of the conductors will be based on the impedance of the path. There will only be very small differences in the impedances and therefore only a small difference in the current flowing in each grounded conductor. I agree that you will have little current in the grounding electrode conductor between the last panel and water pipe. Take an example of a condition where there is 50 amps of unbalanced current in panels 1 and 3 and 20 amps in panel 2. In this case you would have 10 amps on the grounding electrode conductor from 1 to 2 and from 3 to 2 but each grounded conductor would have 40 amps. If the unbalanced current was 60 on panel 3 and 0 on the other 2 panels, you would have 40 from 3 to 2 and 20 from 2 to 1. Unless there is a problem with one of the grounded conductors between the transformer and the panels, the grounded conductors will never be over loaded.
Don(resqcapt19)

[This message has been edited by resqcapt19 (edited 03-16-2002).]

Don:
I think I have finally described it correctly, as you said whether the two copper are bonding jumpers or not doesnt matter. Now back to my original question. The jumpers between these three panels do carry current, this is the way we are to tie the three of them together, I just dont like the idea of these conductors carrying current. When a Meter/Disconnect is used this is not a problem.
As with wiring to a separate building that has a metal piping system common to both buildings a 4 conductor must be run to prevent Neutral currents from flowing on the grounding conductor thus creating a ground-neutral voltage.
I would like to know too, how you got the proportions of the current distribution in the example you used ?

Thanks again
- Mark