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.
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...
"Existential Angst" wrote in message
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
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.
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.
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.
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.
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
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.
There's not a good answer to this question. Cetainly your service
drop neutral should be taking more of the current than your water
supply pipes; if not, there's a problem with your service drop
neutral. Beyond that, it is what it is.
[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.
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