cold water grounding electrode.

[jes25]

The plumber removed the jumper wire and water meter. When he put the meter back in he got a little spark. He was alarmed and called me right over. I told him it was because he removed the jumper.

I got to thinking about this. The spark is because of a small load on the GEC. This "spark" would vary depending on the 120volt load ond the electrodes (water pipe) resistance back to the source. I am understanding about right? This spark is normal, correct?

 

[tonyi]

Re: cold water grounding electrode.

Probably someone in the area has a loose service neutral and is feeding return current back through the city's piping and causing it to get distributed around to all the places that have solid neutral connections

Not much you can do about this sort of thing...

 

[jes25]

Re: cold water grounding electrode.

Just so that I am clear. You are suggesting the neighbor has a high resistance neutral so some of thier neutral cuurent is flowing thru thier GEC through the dirt and my GEC to my neutral.

Since this is an exisisting older house maybe I should check my service neutral. Thanks

 

[tonyi]

Re: cold water grounding electrode.

The city's underground water lines, if metal, will allow current to flow from house to house. Out one's GEC, through the city water pipes, in other's GEC(s), and out their neutral's.

It could be this place's neutral, it could be one (or more) somewhere else. If it were this place's neutral, then you'd see some heavy current on the GEC with some unbalanced loads running(maybe turn on a microwave and everything else off in the place). If its somewhere else, then you'll probably only ampprobe a modest amount on this place's neutral

 

[jes25]

Re: cold water grounding electrode.

Now I am with you. I forgot that the citys water piping is continous house to house. Thanks

 

[hbiss]

Re: cold water grounding electrode.

It's not even necessarily a bad neutral connection some where. If you think about it the water main is in parallel with the POCO neutral conductor on the street. The water main and the neutral are connected together (like the rungs of a ladder) at each service by the grounding conductor. Any voltage drop on the POCO neutral will be imposed on the water main so there is a good chance there will be some kind of current on each grounding conductor. See for yourself, check it with an Amprobe.

-Hal

 

[al hildenbrand]

Re: cold water grounding electrode.

The unbalance current from the load in one dwelling will take all possible paths back to the transformer.

When multiple buildings are tied together, electrically, by the metal water pipes, a percentage, likely a significant percentage of the unbalance current will find its way back to the PoCo transformer via the pipe.

The resistance of the water pipe route to the PoCo transformer can be lower than the resistance of the neutral conductors between the transformer and the service disconnect. A lot depends on the physical layout of the systems.