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.
Re: water pipe grounding electrode#127821 01/13/0205:18 PM01/13/0205:18 PM
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)
Re: water pipe grounding electrode#127822 01/13/0208:09 PM01/13/0208:09 PM
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)
Re: water pipe grounding electrode#127825 01/14/0208:14 AM01/14/0208:14 AM
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.
Re: water pipe grounding electrode#127826 01/14/0211:43 AM01/14/0211:43 AM
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.
Re: water pipe grounding electrode#127827 01/14/0212:19 PM01/14/0212:19 PM
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.
Re: water pipe grounding electrode#127828 01/14/0202:36 PM01/14/0202:36 PM