Water line electrically charged

[inspector 102]

Local water department had to repair a water service line and said they received an electrical shock when touching the lead water line. When the line was cut, they received no charge from the house side, but still got shocked from municipal side. I am guessing this is due to some where a back feed through a grounding conductor hooked to the water line, but how would one find such a connection. I suggested the water company place a jumper across the repair in the future so the worker does not serve as the grounding path. How would I be alble to check the voltage being sent from the water line. No current picked up from "Tic Tracer". Thanks for advise.

 

[chris kennedy]

back feed through a grounding conductor

Put a clamp-on amprobe around the water line. My guess is that someone else's grounded conductor feed from the same POCO tranny is compromised.

 

[raider1]

Put a clamp-on amprobe around the water line. My guess is that someone else's grounded conductor feed from the same POCO tranny is compromised.

I agree, that would be my first guess.

Chris

 

[Sierrasparky]

Yea those flexible ground clamps come in quite handy. Wish I had one.

 

[LarryFine]

... how would one find such a connection.

By having each customer turn off their main breaker until the voltage drops.

Of course, this voltage could also be cumulative, from dozens of customers.

 

[hurk27]

By having each customer turn off their main breaker until the voltage drops.

Of course, this voltage could also be cumulative, from dozens of customers.

Or a problem with the MGN feeding all those transformers.

Looks like a good time to call the POCO out and tell them to check the current on the MGN, when they get to the point of the lost connection it will have 0 amps on it.

One of the signs of a bad transformer neutral return (MGN) is water pipes going bad.

 

[Cow]

I can't believe your local water department doesn't require portable jumpers installed when servicing water lines. Seems like a potentially huge safety issue, it can't be the first time they've encountered this problem?:-?

 

[inspector 102]

I suggested that they start placing a jumper any time that they work on broken mains and they said they would make a couple up and start using them. For some reason, they tried to check voltage with digital volt/ohm meter and got 2.8 volts AC byt the worker said he thought is was more than that. Now the meter shows a constant 8.8.8 on the display. Must have shorted something or the meter just decided to die at that moment.

 

[don_resqcapt19]

...
One of the signs of a bad transformer neutral return (MGN) is water pipes going bad.

I have heard that statement many times, but have never found any documentation that says that. In fact the American Water Works Association has a paper that says AC current does not cause damage to water piping systems.

 

[hurk27]

I have heard that statement many times, but have never found any documentation that says that. In fact the American Water Works Association has a paper that says AC current does not cause damage to water piping systems.

If that was true then nicked wires under ground would never dissolve. I have even had post light poles that were partly energized by neutral return current when the neutral broke off in the post, and the load side touched the pole, after a few weeks the pole just fell over, as the aluminum dissolved. I've seen far to many times when a building starts having problems with underground copper water pipes getting holes in them, I usually find current or raised voltage to Earth on them, or at least on the building grounding.

Anytime there is voltage on the grounding that is above the Earth reference point, it will dissolve what ever is in contact with Earth, just some materials take longer to show up.

So in American Water Works statement that says AC current does not cause damage to water piping systems can be said is true as long as the pipe has not been raised above the potential of Earth, other wise it's very misleading.

 

[tom baker]

Corrosion is caused by DC current, not by AC-mostly. I searched and purchased all the AWWA papers on grounding back to 1970. AC current can cause some corrosion but the effect is minor.
Simple solution and that recommeded by AWWA is a non-metallic section of pipe leaving at least ten feet of metal for the NEC required 250.52(A)(1) type.

 

[don_resqcapt19]

If that was true then nicked wires under ground would never dissolve. I have even had post light poles that were partly energized by neutral return current when the neutral broke off in the post, and the load side touched the pole, after a few weeks the pole just fell over, as the aluminum dissolved. I've seen far to many times when a building starts having problems with underground copper water pipes getting holes in them, I usually find current or raised voltage to Earth on them, or at least on the building grounding.

Anytime there is voltage on the grounding that is above the Earth reference point, it will dissolve what ever is in contact with Earth, just some materials take longer to show up.

So in American Water Works statement that says AC current does not cause damage to water piping systems can be said is true as long as the pipe has not been raised above the potential of Earth, other wise it's very misleading.

Please show me some case study or other document that shows damage to copper water pipes as a result of AC current flow.

 

[hurk27]

Please show me some case study or other document that shows damage to copper water pipes as a result of AC current flow.

As I tried to say before, current on a copper water pipe doesn't cause a problem, but when the current such as a lost neutral raises the copper above Earth potential it will. place any conductive metal in Earth and put a voltage on it, that also has a return though earth and see how long it will last, this is the same problem with stray current/voltage in a Marina that can dissolve a metal boat hull, even a copper one.

Here is one statement on this from copper.org:

Other factors that could promote underground corrosion of copper include:

Oxygen differential concentration cells. Preferential corrosion is sometimes found on the underside of copper tubes because they are in contact with undisturbed soil where the oxygen content is reduced, in contrast to the upper portion of the tube which may be exposed to aerated backfill where oxygen content is high.

Variable aeration characteristics. These depend on particle size and distribution, the degree of compaction, and the drainage characteristics of the soil or backfill material.

Deicing practices. If the chloride content of the soil is elevated because of deicing (thawing salts for roadways and side walks) the metal becomes more anodic than the areas where the chloride content of the backfill material is lower.

Stray currents. Direct current (DC) from impressed cathodic current corrosion protections systems or from the grounding of alternating current (AC) systems to the underground copper service can be detrimental.

From this site:
prevent_corrosion_cu_tube_buried.html

I'm still searching for other info, but I have personally seen this happen many times, but every time there was an elevated voltage on the pipe, I have also see where copper ground rods were almost completely gone from the very same thing.

Passing current through the pipe will not cause this, but elevating the voltage on the pipe above Earth potential will.

I can't answer why its more prominent when the elevated voltage is coming from a bad primary neutral connection, but it seems to be, as in 4 cases 3 of them just had the water company replacing the water pipe with plastic then people started getting shocked so we were called, and the reason they had the water pipe replaced was of holes in it.
in one case I looked at the bad pipe they had left behind, and it looked like it was immersed in acid, had green corrosion all over it, and was eaten almost all the way through.

 

[hurk27]

Here is a statement of a research By J.R. Myers and Arthur Cohen
which appeared in American Water Works Association Journal, August 1984

Alternating Current Action
The role of alternating current on the underground corrosion of copper is not well understood.9 Some investigators contend that any metal dissolved during the anodic half-cycle should be redeposited during the cathodic half-cycle. Others believe that the efficiency of the anodic half-cycle is greater than that of the cathodic half-cycle and, therefore, that AC-induced corrosion can occur. The argument persists as to whether cuprous oxide on the outer surface of an underground copper water tube can rectify AC, although some of the recent research suggests that this rectification does not occur.10, 11

Some investigators believe that a critical AC density must be exceeded for AC corrosion to occur.12, 13 It is also possible that AC facilitates depolarization of the local anodes and cathodes on an underground copper surface. 11 This depolarization would be expected to increase the corrosion-current density and the resultant corrosion rate.

Until these differences of opinion are reconciled and recent research results are corroborated, it is reasonable to believe that the commonly used practice of grounding electrical systems to underground copper water systems can lead to corrosion. If the copper plumbing system is connected to a nonconducting main, such as asbestos-cement, some corrosion damage can be anticipated where the current leaves the copper, even if the current is alternating. Further, cuprous oxide could become semiconducting under certain conditions of soil pH and electrical-field intensity. Grounding of the AC system to the underground copper water tubing and unbalance in the AC system could very well be involved in the underground corrosion process.

see the red highlited above, this would cause voltage to be rasied on the piping

While they don't understand what process takes place, they acknowledge that it does take place.

The above quote is found here:
http://www.copper.org/resources/properties/protection/underground.html

 

[don_resqcapt19]

Thanks Wayne.