Electric Utility to Blame???

[tmet]

An underground distribution department of an electrical utility is blamed for causing 'pin holes' in copper water lines. A housing district has had 7 complaints from plumbers that the electric utility's bonding to the water line has caused these pin holes. Has anyone had an experience like this before and is this really even possible? Is electrolysis possible in this situation? Being the occurrences are in a similar area, is it safe to assume they all received a "bad" batch of pipe??

Thanks,

tmet

 

[Laplacian]

http://www.corrosion-doctors.org/SoilCorrosion/Frames.htm

That website has a lot of useful information.

 

[kyruby]

tmet, I would doubt if the electric utility is at fault. Utilities do not bond to water lines. Their grounding system originates at the substation for a 4-wire wye system and is carried on the overhead by pole grounds bonded to the neutral. At a riser pole (transistion from overhead to underground) a copper (5/8" x 8') ground rod is installed in addition to the pole butt plate.

The underground cable has a copper concentric neutral over the insulation which is bonded at the riser pole to the pole ground and to a driven ground rod at each junction and pad mounted transformer along the primary route.

At the meter base, code requires a driven ground rod, which is bonded to the ground connector on the meter base. The neutral wire of the underground service, from the transformer to the meter base is also bonded to this terminal.

If the customer installed an additional ground to his copper water pipes and for some reason lost his ground at the meter base, and the utility ground was lost (possibily due to neutral corrosion for direct buried conductors not using a protective jacket), then I could see the possibility of pin holes in the water pipe. This would normally be limited to the customer's service line, as most water mains are installed using ductile iron or PVC pipe.

I hope this helps.

 

[dpc]

kyruby,

I'm not sure where you are located, but in the US, grounding electrodes at service entrances are generally bonded to the cold water pipe. In fact, this is required by the National Electrical Code. This is not done by the utility, but the net effect is that the utility system ground, established at their transformer, is bonded to the water line.

However, this should not create any significant corrosion, especially for a copper water line. As noted above, this is done in millions of houses and other building in the US.

There has been some concern about corrosion of reinforcing steel when bonded to copper ground wires, however, the corrosion engineers that I have worked with on this have told me that rebar embedded in concrete should have any signficant galvanic reaction when bonded to copper.

AC currents are not nearly so much as cause for concerns as dc currents.

It's possible that, due to highly unusual soil conditions, there is some issue here, but it seems unlikely to me.

 

[jghrist]

Bonding to the copper water pipe could possibly cause corrosion of the utility's grounded galvanized anchor rods (not likely, however), but not the other way around.

 

[kyruby]

dcp,

Thanks for the clarification. I am located in the US and I agree the NEC does require bonding to the metal water pipe. The point I was trying to make,and apparently failed at, utilities do not actually make the physical connection to the water pipe. As you pointed out, this is done by others, normally the electrician, and does provide a path to the grounding lug at the utility transformer.

A problem we have experienced is the loss of the utility neutral due to corrosion of the copper concentric on a direct buried cable. During the late 60's and 70's utilities did not use jacketed cable and/or conduit. During this same time, in some areas, the NEC was not properly enforced and coupling that with the lack of proper grounding at the meter base and the transformer the potential for problems develops. Would this cause pin holes in the copper water pipe, I don't know, but if the copper water pipe became the current carrying return, maybe.

Again thanks for your clarification, and I also agree, this scenario is unlikely.

 

[jbartos]

Suggestion: Visit

http://cru.cahe.wsu.edu/CEPublications/eb1837e/eb1837e.html

for:
How Long Can You Expect the System to Last?
The plumbing components of your solar hot water system will last as long as a regular system might. This can vary depending on water characteristics, such as hardness, or acidity. The tank is prone to the same problems of corrosion as conventional hot water tanks - - they develop pin hole leaks. You can expect 10 to 12 years from a hot water tank, although stone-lined tanks (more expensive) generally outlast glass-lined tanks. This assumes regular maintenance of your system.

The mechanical and electrical components of the system will need replacement at varying rates. Most systems need a pump replacement or some mechanical/electrical repair by the time the system is 10 years old.