# Current flow in main neutral vs. current through water meter

• posted on November 27, 2009, 5:10 pm

Awl --
The current in the main neutral *should* be the difference in current between the main hot legs, right? However, it is usually off by between 1 and 1.5 amps, which seems to correspond to the current flow through/around the water meter. This would seem to be a *necessary* relationship, right?
My impression is that prior to the utility replacing the old wires along the poles and to my house, this current flow through/around the water meter was a lot higher -- 3-5 amps.
So the Q is: What is "acceptable" ito current flow through the water meter to the street?
My assumption is that if I took out the water meter, then all of the neutral current would necessarily flow through the main neutral, and it is just that apparently the water plumbing ground is "good enough" to share some of the return load -- which doesn't seem like such a terrible thing, esp. given the aluminum conductors used by the utility, vs. the copper plumbing to the street, and perhaps farther.
But again, what are acceptable limits ito of current flow through grounds? Is there an NEC ratio, a percentage? Mine seems to be pretty constant at this 1-1.5 A.
--
EA

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• posted on November 27, 2009, 6:05 pm
That is a very interesting observation!
And I wonder if you were to turn your main power off, if you would get a reading of a current flow at your water meter?
My thinking being that your ground is connected to your neighbor's grounds, and it might then flow "backwards" through your water pipes and to your neutral and back to the electric pole.
As to the answer to your question, might want to ask at the following electrical forum. Some pretty sharp people there... http://forum.doityourself.com/electrical-c-d-c-9
"Existential Angst" wrote in message

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• posted on November 27, 2009, 6:54 pm
wrote:

My gut reaction is that no freakin' way should you be seeing anything like an amp going through your water pipes. I'm thinking milliamps would be cause for investigation.
The aluminum conductors have immeasurably low resistance back to the utility transformer, unless there's a bad splice or connection somewhere. The utility company is not going to install service conductors that have higher resistance than water pipe and damp earth.
Bill may be onto something about current leaking in from nearby properties, but it would still mean something's wrong (it just may not be on your property).
How are you measuring this current... clamp-on ammeter? Have you put this thing around the ground wire that goes to the water pipes? If you put it around all three of the service conductors (two hots and the neutral) it ought to read zero. If it does read zero around all three, but the numbers don't add up when you measure each one separately, then it's some kind of AC current measurement artifact.
Do you have a ground rod, apart from the connection to the water pipes?
Chip C Toronto
Chip C

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• posted on November 27, 2009, 7:11 pm
wrote:

Doesnt that mean you have a short, that is wasting-loosing 1.5a.

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• posted on November 28, 2009, 2:40 am
wrote:

Seems to me current flow through a water meter is not at all permitted. In fact, our local code calls for a heavy copper braid bypass around the meter connecting copper supply line to house copper plumbing. In addition, a 4 ga wire connects the input copper line to the ground/neutral lug in the meter base. Of course, there is also the usual long ground rod with 4 ga to the meter base. I get a nice 124.5 V both sides of the line on my Fluke 27. If I disconnect the wire at the input water line, then I could be measuring current in the fashion OP describes without bothering the meter, right? This might be some measure of the ground rod/neutral efficiency. Maybe its just academic but interesting.
Joe

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• posted on November 28, 2009, 6:32 pm
Existential Angst wrote:

Hmmm, Sounds like ground loop problem.

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• posted on November 28, 2009, 7:01 pm
Tony Hwang wrote:

Electricity will take all available paths, so some current flow between the ground at the pole and your ground rods and / or water pipes is to be expected. This is the reason that jumpers are required around water meters so the meter guys don't get fried removing the meter.

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• posted on November 28, 2009, 7:18 pm

Tony, didn't you EE for NASA or sumpn? Man, it was a miracle that moon shot didn't just crash....
Yeah, I got loads of 60 cycle hum in both hots and the neutral. What *shall* I do????
--
EA

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• posted on November 28, 2009, 8:08 pm
Existential Angst wrote:

NASA uses tricycle gear to eliminate ground loops.
Speaking of elimination, that's what I needed to do while I was monitoring my water meter the other day. When I got back, there was current going through it.
I, too, have loads of hum between my hots and neutral. I discovered a way to get rid of it, but then my stereo wouldn't work.

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• posted on November 28, 2009, 10:54 pm
Existential Angst wrote:

Hmmm I only worked on NASA computer systems. Highest ground current I ever read was 1.2 Amp. on a 250KW M-G UPS system which we could bring down to near zero Amp after sorting things out.

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• posted on November 29, 2009, 12:16 am
wrote:

If you have wye distribution you can get some strange ground readings with some quite high. If you have a metal water distribution system the pipe might be an excellent path back to the neutral, particularly if the poles are near the water line since they drive a rod under every transformer.

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• posted on November 28, 2009, 7:40 pm

If there are no other return paths, that is correct. Although as you have observed, in communities with interconnected water supply piping, the water supply piping may be a very good return path (via the various neighbors' neutral to grounding system bonds).

Again, if those are the only two return paths. However, there may be more or less current on the metallic water supply, contributed by your neighbors.

That makes sense. If the service drop was higher resistance, less current goes on the service drop neutral, more current on the water supply ground to your neighbors' neutrals.

[Depending on the local practices for your water serive, you could take steps to eliminate the return current on the water supply. For example, here the water meters are in shallow vaults in the sidewalk; if you install a non-conductive coupling on the house side of the water meter, then you disrupt the return path, while retaining the buried water lateral as a grounding electrode. But be careful about disrupting the return path, see below.]

Yes, but you would have to be very careful about doing this, since as soon as you disconnect the water meter, there will be a voltage difference between the two sides of the water supply, representing the voltage that was driving the current. You could be injured or killed if you get across the two sides of the water piping. This can happen even if your main breaker is off, since a neighbor's neutral could be faulty and could be using your neutral as the principal return path, via this water pipe bond.

Nope, the NEC doesn't directly provide a ratio or say to what extent this is acceptable. It is, however, a side effect of the NEC requirements on grounding and bonding.
Cheers, Wayne