water pipe grounding electrode

[resqcapt19]

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)

 

[lyledunn]

Yes this could be a serious hazard, consider diverted neutral current in a metallic fuel line in a hazardous area where perhaps a joint is of high resistance.

 

[dpc]

As I understand your situation, this is a concern only if there are multiple services from the same utility transformer secondary. In this situation, it would seem that it is possible for some current to flow along the water pipe, rather than in the grounded circuit conductor. But this should be a rather small amount provided the neutral and grounding conductors are installed properly and intact.

The issue of grounding water pipes is more complicated than this, I think. The NEC requires metallic water pipes be grounded even if they are physically isolated from the earth and cannot be used for a grounding electrode. To NOT ground the metal water pipe can present a hazard to someone if the water pipe should become energized for some reason.

The NEC does not allow ONLY a water pipe as a grounding electrode conductor - it must be supplemented by a made electrode of some kind. But this was not always a requirement.

I have seen situations where only the cold water pipe was used for a ground and hazardous voltages developed when the pipe was separated at a joint (because the neutral conductor was broken and the water pipe was the ONLY return path). That is a definite hazard.

Hope this helps.

 

[resqcapt19]

While I fully agree that the interior metal water piping system must be bonded to the electrical grounding system, it appears that our use of the underground water piping system presents a serious hazard to those who must work on the water pipes. Breaking apart the water pipe to make changes or repairs would put that worker in series with the grounded conductor current that is flowing in the water pipe. I think that the only solution would be for changes in both the NEC and the plumbing codes. The NEC would be changed to prohibit the use of the metal underground water piping as a grounding electrode while still requiring the metal interior piping to be bonded. The plumbing code would be changed to require a seciton of non-conducting water pipe between the building and the water main.
The American Water Works Association reported in a July '98 article that on average one water worker per day receives an electrical shock beacuse of the grounded conductor current that is flowing in their water pipes.
Don(resqcapt19)

 

[dpc]

Don,

There has been a lot of discussion regarding grounding of water pipes of the years in the NEC panels (this is Code-Making Panel #5, I believe).

The requirement for grounding of water pipes is quite old, pre-dating nearly every other grounding requirement. If the electrical system is properly installed, there should be little or no current flowing in the water pipe. The main concern of the NEC recently has been the increasing use of non-metallic piping and the reduced effectiveness of the water pipe as a grounding electrode.

I suspect getting this requirement out of the NEC would be an uphill battle.

Your concern could be addressed by installation of insulating sections of plastic pipe to break up the continuity of the metal water pipe. This would not violate any codes that I am aware of.

dpc

 

[resqcapt19]

There will always be grounded conductor current on the water pipe if it is used as a grounding electrode. It is in parallel with the grounded conductor and in areas where copper water services are used the water pipe many vey well have less resistance than the actual grounded conductor. Put an amp clamp on your water pipe and check. Mine has 2 amps flowing on it. I have no idea if this is comming into my house and out on my grounded conductor, or if it is my unballanced current going to some other house. I didn't check the current on the two hots in my panel so I'm not sure what my total grounded conductor current is. I also have 0.15 amps on the TV cable coax and 0.02 amps on my driven ground rod. The current on the coax is also because of the parallel path that is created when the TV cable company grounds the coax shield to the electrical grounding system at every building as required by 820-33.

The only way not to have current on the water pipe under the NEC would be to have the plumber install an insulating section in the water pipe outside of the building. If the metal underground water pipe enters the building, the NEC requires that it be used as a grounding electrode. As soon as you make this connection, some of the grounded conductor current will flow in the water pipe.
Don(resqcapt19)

 

[dpc]

Don,

There may be stray currents in the ground conductors, but unless the water pipe becomes the **only** low resistance path for neutral current, this does not create a safety hazard. If the water pipe becomes disconnected, even with current flowing in it, the current will just find another low impedance path.

I agree that there can be problems if the neutral conductor is broken for some reason. It takes a combination of more than one Code violation for this to become a major safety issue, at least for new installations. In most cases, the solution is to improve the overall grounding of the system.

 

[resqcapt19]

So if I take apart my water pipe while standing in the water in the ditch and soaking wet I can't can't get hurt by touching the two parts of the pipe??? I have 2 amps flowing in my water pipe and it only takes 5ma to trip a GFCI. I have talked with plumbers who won't break a water service unless they first jumper it out with a car battery jumper cable.
Don(resqcapt19)