grounding whats wrong with this situation

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cschmid

cschmid

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I do have an interesting situation to share, at one of the buildings I maintain there is a supplemental connection to the water main (bonding of water line). This line is connected to another building and when you disconnect the ground wire from it you can maintain a spark between the wire and the pipe. I have pics of it. It is a galvanized water line and many years old. It is also bonded in both buildings. Why the spark?
 
cschmid said:
Why the spark?
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The most likely answer is that everything is done to NEC requirements and what you have is the water pipe system carrying part of the unbalanced current from the neutral conductor.

This happens as the metal under ground water piping system is bonded at many points.
 
Where there is a common underground metal water piping system, it is common to find 20% or more of the grounded conductor current flowing on the water pipe as a result of the code required bonding, how ever this can also be an indication of a high resistance connection on the service grounded conductor. I assume this is not the case here as you would have noticed symptoms when you disconnect the ground. If there is in fact a problem with the service neutral, then there will be hazardous voltage on the disconnected ground...just like there is on the load side of an open neutral. If you check for voltage between the disconnected grounding conductor and the water pipe and only have a few volts everything is ok, but if you have a lot more than that you have a problem with the service neutral.
Don
 
Often times when this occurs the local utility water company will install a insulated coupling (at least in some jurisdictions)to avoid the metal to metal service to service connection between buildings. At this point the utility water pipe connection is no longer a grounding electrode, but becomes your interior water bond connection. If no other electrodes exist for this service the NEC would mandate you install the prescribed electrodes.

This current can result in PQ issues due to EMF, IMO or per another post IMHHO (In My Hard Headed Opinion), this issue should be rectified.

Additionally if you have downstream grounds on neutral this "spark" can occur as the metallic water piping system is carrying neutral/ground current and the grounding electrode conductor is part of the return path to the service. This can desensitize GFP protection during a fault and if the current is high enough and the GFP setting low enough result in tripping of the GFP.
 
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don_resqcapt19 said:
Where there is a common underground metal water piping system, it is common to find 20% or more of the grounded conductor current flowing on the water pipe as a result of the code required bonding, how ever this can also be an indication of a high resistance connection on the service grounded conductor. I assume this is not the case here as you would have noticed symptoms when you disconnect the ground. If there is in fact a problem with the service neutral, then there will be hazardous voltage on the disconnected ground...just like there is on the load side of an open neutral. If you check for voltage between the disconnected grounding conductor and the water pipe and only have a few volts everything is ok, but if you have a lot more than that you have a problem with the service neutral.
Don
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Don
What would you consider (a number value) as OK?

What would you think is a safe amperage value on the same path?
 
Pierre:

We strive for "0", when we are involved in projects with this issue, we test for and if found clear any neutral ground issues, if it is a metallic to metallic water pipe connection exist we recommend a dielectric coupling. Though we have had buildings that share a common under ground parking garage were re-bar and other metallic components of the building carried minimal current at this point there is little I can think of that would resolve the issue with so many metallic paths.

I have measured up to 5 VAC and 15 amps on buildings that do not have neutral to ground issues. I have measured 225-350 amps on a building with a neutral to ground connection downstream of the main service. GFP was set at 320 Amps which is what brought the problem to light.

DSGC (Downstream Ground Connection) One more for the list.
 
cschmid said:
Thank you gentlemen. I have another question would a galvanized pipe caring an unbalanced neutral load have any structural issues on the galvanized pipe itself?
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Electrolysis? I guess this is not a large issue as long as there is not a DC offset to the current (not balanced around 0 volts) but someone else probably has a much more definitive answer....
 
Pierre,
In my opinion it really doesn't matter....the code requires us to create this parallel path for grounded conductor current, so it must be ok:D

Sorry, I didn't read your question correctly. The voltage you are reading between the disconnected grounding electrode conductor and the water pipe, is for the most part the voltage drop on the service grounded conductor(s). This number should only be a couple of volts at most. When the voltage is higher than this, you should investigate the service grounded conductor....one problem is that the grounded conductor with the problem may not be the grounded conductor for the building that you are working on. Also note that in the case of an open or very poor connection on the service grounded conductor, the voltage between the water pipe and the GEC will at or near line voltage and could be lethal.
Don
 
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Good morning all. The voltage on the old water main actually does originate from the other building. it is 75 years old and wired properly for its time. Than it looks like someone came through and decided they could do some modifications and save some costs. I would assume they knew not of grounding. Let me explain one of the modifications. It is old cloth insulated wiring. the wire consists of two conductors and a woven aluminum ground wire around the conductors which is under the outer sheathing. They have turned the woven aluminum into the neutral and connected to the galvanized pipe for the ground with a new conductor. That is how they expanded the electrical system. They used the cable to run sub panels. I have been upgrading this system systematically every year due to costs. I see a ground wire yet have not dug to find ground rod. Yet I am under the assumption that if the ground Rod is working. I should not be caring current on the bond water line. The building I was playing with the spark in (call it what it was) was ungrounded. I have now grounded the building and after separation of the pipe from other building I do not get a voltage on bonded water line. I have one more panel to upgrade in the other building. This is a little history on the water pipe issue. The building is owned by a non profit organization and money is always a concern.
 
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