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A voltage to ground mystery.

F

Fred Bloggs

Jan 1, 1970
0
Larry said:
My readings of the OP's description gave either 1000', 100' or 900'
of parallel pipe and power. My remarks apply to any of them. For
sake of discussion, suppose the power flows thru a pair of wires,
one located 11 inches from the pipe and the other 12 inches. (an
assumption corresponding to Romex with about 2 inch diameter)
For the moment, assume they maintain these distances along their
length. (no twisting) Assume a current +I at 11 inches, -I at 12.
The magnetic field in free space encircling one wire at radius r is:
B(r) = u0 * I / (2 pi r)
for an infinite straight wire where u0 = 1.26e-6 and r is in meters.
(Except near the ends of the run, this *closely* approximates the
situation given the assumed geometry.)
Evaluating for +I at 11/39.37 m and -I at 12/39.37 m, yields
B = (1.26e-6 * I / (2 * pi)) * (39.37 / 11 - 39.37 / 12)
B = I * 5.98e-8
Considering I to be the peak value of a 60 Hz AC current, and
so taking B(t) = sin(2 * pi * 60 * t) * I * 5.98e-8 , then
d(B(t))/dt = 2 * pi * 60 * cos(2 * pi * 60 * t) * I * 5.98e-8
= I * 2.25e-5 cos(...) Tesla/Second
This converts directly to Volts/Meter induced along the pipe.
(Doubters can start from F = q V x B, noting that the B field
changing in and out w.r.t. the wire pair is equivalent to the
V x B term. This is too basic to be spelled out here in detail.)
Taking the parallel run as somewhere between 30.5 and 305
meters, the induced peak voltage is 685 uV to 6.85 mV per
Amp of current flow.

With any twisting, that number will go down. If a twist were
applied to one end and the intermediate cable were follow in
proportion along its length, the coupling would be multiplied
by sinc(a), where a was the twist in radians.

Unless they are using thousands of Amps at that construction
site, the 30 VAC observed by the OP clearly has to be due
to some other effect or a markedly different geometry.

Some may opine or proclaim that only the integral form
of the induction law can be validly applied, or that twist
could be non-uniform, or the spacing may vary in that
trench. Except for the latter, none of it changes the
result because my use of the differential form already
assumes the worst possible return path (whereas the
real return path is coincident with the pipe, reducing
the net coupling between earth and pipe). Twisting
of any kind can only reduce the coupling; uniformity
simply causes more reduction, on average. If the OP
buried separate conductors willy-nilly with respect
to the pipe, that could be a problem. In Washington
state, that would never pass muster with the inspector
and I doubt local codes on this issue vary much.

If the OP's problem arose from mixing the power and
pipe badly, the result shows (in part) why that code
exists, and he has some digging to do. But I think it
much more likely that there is an exposed portion of
a hot power conductor leaking *a lot* of power into
ground and the pipe. That is an unstable situation,
dangerous as I've stated, and one the power company
will want fixed, if only because their meter is going to
be downstream from a ground-heating fault.

Given the OP's assertion that the 1000' pipe is buried
in red clay, I don't see any way for it to be anything
but a fault. Driving a well grounded conductor like
that to 25 VAC would take more power than even
an accidental air core transformer could deliver.

Typical horse-manure response that proves once again you can't even
understand what the OP wrote- and also that you love to shoot your mouth
off on subject matter about which you are clueless.
 
L

Larry Brasfield

Jan 1, 1970
0
Fred Bloggs said:
Typical horse-manure response that proves once again you can't even understand what the OP wrote- and also that you love to shoot
your mouth off on subject matter about which you are clueless.


I note that Mr. Bloggs appears unable to point out any
specific fact I have misunderstood from the OP's posts,
nor has he specified any particular flaw in my analysis.
He is fond of emitting noise without substance, mainly
for love of viewing his own spew, I think.
 
F

Fred Bloggs

Jan 1, 1970
0
Larry said:
I note that Mr. Bloggs appears unable to point out any
specific fact I have misunderstood from the OP's posts,
nor has he specified any particular flaw in my analysis.
He is fond of emitting noise without substance, mainly
for love of viewing his own spew, I think.

Maybe in your world- but as usual- you're a worthless crock of excrement
when judged against reality- and your posts convey nothing of any use or
value. It's a sorry-sack of manure who reaches nearly 60 yrs of age and
still fails at communication as badly as you do. But you don't worry
about that- just keep pecking away at your sickening and pompous
garbage- it's all about some fantasy you entertain where people just
fall over admiring your pretense of expertise..
 
G

Glenn Ashmore

Jan 1, 1970
0
Are you saying that this service buried a bare conductor and an
insulated conductor along side the pipe? If the service has a high
leakage current from the primary side to the supposedly isolated
service, it may be dumping quite a bit of current into the Earth
through that bare neutral wire. The power company should check that
out at the pole, to determine how much AC current it is passing to the
neutral with no load connected at your end. This may well be the
problem. And if it is, they would want ot know about it, because it
is an unmetered power consumer they are carrying.

The power line is up about 30' on poles.

Just called the power company. When they figure it out I will report back.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com
 
J

John Popelish

Jan 1, 1970
0
Roger said:
You meant ohm instead of milliohm here, didn't you?
(snip)

I will blame the thousand to one error on sitting here dissolving with
the flue.
But I think the point about the voltage not telling him what the
ground current is made an impression.
 
R

Roger Johansson

Jan 1, 1970
0
Glenn Ashmore said:
The power line is up about 30' on poles.

There has been a lot of misunderstanding in this thread, and I am not
sure where it started. I think you started the confusion yourself, by
talking about induction. That would only be remotely possible if the
conductors were very close to each other and buried together.

The only important part of the thread was that you were made aware of how
serious the situation is and that you need get it fixed by competent
people.
 
M

Michael A. Terrell

Jan 1, 1970
0
Glenn said:
Well this is in the Piedmont of Georgia so the pipe is definitely burried in
1,000' of red clay. :)

The thing I can't figure out is the copper pipe comes out of the ground
right at the puddle so it should be well grounded but if you use a VOM
between the faucet and a nail stuck into the mud a foot from the base it
reads 25V!


Move the nail further ot to see if the voltage goes up even more. if
you can get 100 to 120 volts if you can and connect a 20 watt or higher
light bulb and see if it lights. There are still a few outdated power
distribution systems that use "Earth return", meaning they feed the one
side of the transformer primary and ground the other side and let the
return current flow through the ground. These were used in rural areas
and have mostly been replaced due to this kind of problem.
 
T

Terry

Jan 1, 1970
0
Fred Bloggs said:
The power grid is circulating current through the GND returns at the two
different points of connection to the grid- one at the origin of the
copper pipe and the other at the construction site. You have created a
nice short-circuit with that pipe and the circulating current can be very
large. You will have no option except to install a section of
non-conducting plastic pipe at the construction site, make the faucet and
its T-section riser plastic also.
I agree with Fred. It sounds as though with an o'head single phase power
system there is voltage difference between the ground at the power
transformer and other power system grounds. The copper pipe is providing a
convenient path for some of the ground current?
Have seen that before when a neighbour's buried power service became damaged
and had a bad leak to ground. Our ground and basement appliances became
noticeably 'tingly' due to current leaking through the ground to our
grounded neutral. It disappeared when his service was repaired.
 
M

Michael A. Terrell

Jan 1, 1970
0
Jamie said:
i have a friend, his neighbor had problems when the furnace was running.
my friend would get a mile shock when touching his sink!


WOW! A whole mile? ;)
 
J

Jamie

Jan 1, 1970
0
Terry said:
I agree with Fred. It sounds as though with an o'head single phase power
system there is voltage difference between the ground at the power
transformer and other power system grounds. The copper pipe is providing a
convenient path for some of the ground current?
Have seen that before when a neighbour's buried power service became damaged
and had a bad leak to ground. Our ground and basement appliances became
noticeably 'tingly' due to current leaking through the ground to our
grounded neutral. It disappeared when his service was repaired.
i have a friend, his neighbor had problems when the furnace was running.
my friend would get a mile shock when touching his sink!

there was a ground problem due to the soil around there.
 
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