One Wire

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quogueelectric

Senior Member
Location
new york
mivey said:
I'm guessing 10-100 milliamps through the earth. So I'm guessing 19.9 to 19.99 amps on the grounded conductor and 0.01 to 0.1 amps through the earth.
Did you pull this number from between your buttocks??? I have been told current only returns to the source many times on this forum. Please elaborate.
 

mthead

Senior Member
Location
Long Beach,NY
One Wire

quogueelectric said:
Did you pull this number from between your buttocks??? I have been told current only returns to the source many times on this forum. Please elaborate.

His Buttocks???????????

Was that you in the front row at "Spamalot" last nite.??????????
 

mivey

Senior Member
quogueelectric said:
Did you pull this number from between your buttocks??? I have been told current only returns to the source many times on this forum. Please elaborate.
The earth is a parallel conductor back to the source. While the earth has a low resistance, the connections to it through ground rods make it a relatively high impedance path as compared to the neutral, but it is still a path.
 

domnic

Senior Member
Occupation
Electrical Contractor
djohns6 said:
20 amps on the primary ? I'm assuming you pulled that number out of the air .
primary 19 amps on hot 1 amp on grounded conductor .single phase these # came from the lineman checking to see why a pool is shocking home owner .i checked pool water witch is bonded to home and i get 1.6 to 3.1 when the load on the increases the voltage increases from water to earth.
 

mivey

Senior Member
domnic said:
primary 19 amps on hot 1 amp on grounded conductor .single phase these # came from the lineman checking to see why a pool is shocking home owner .i checked pool water witch is bonded to home and i get 1.6 to 3.1 when the load on the increases the voltage increases from water to earth.
I think a sketch of where the measurements were taken and how the conductors run to the transformer would help.

If you measured 19 amps on the primary and 1 amp on the neutral, then you obviously have neutral problems and your current is running on the grounding conductor instead of the grounded conductor like it should.
 

domnic

Senior Member
Occupation
Electrical Contractor
mivey said:
I think a sketch of where the measurements were taken and how the conductors run to the transformer would help.

If you measured 19 amps on the primary and 1 amp on the neutral, then you obviously have neutral problems and your current is running on the grounding conductor instead of the grounded conductor like it should.
sorry. 20 amp on hot and 19 amp on grounded conductor.
 

mivey

Senior Member
domnic said:
sorry. 20 amp on hot and 19 amp on grounded conductor.
Sounds better. How were the readings taken? Did they use a device that measured the current simultaneously or did they use a clamp-on meter and move from one wire to the other? How accurate was the meter?

Another concern might be that the lineman put a clamp-on meter on the primary and read 20 amps. By the time he moved the meter to the grounded conductor, the load could have dropped. Why did you not measure the grounding conductor?

Considering that the ground rod resistance is essentially one or two or more orders of magnitude higher than the neutral, you should get practically the same reading on the primary and neutral.

Read gar's post #18 and zog's #11 and report back.

Could you give us a general description/sketch of how the service pole, primary back-span, pool, house and other services are oriented with each other?
 

brian john

Senior Member
Location
Leesburg, VA
primary 19 amps on hot 1 amp on grounded conductor .single phase these # came from the lineman checking to see why a pool is shocking home owner .i checked pool water witch is bonded to home and i get 1.6 to 3.1 when the load on the increases the voltage increases from water to earth.


Durn I love getting the complete story at the start of a thread.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
080622-1933 EST

domnic:

I was confused between this thread and another one.

From your very first post it appears that there is one hot primary wire, and one primary neutral on the pole, and by implication that the primary neutral is grounded thru a rod with 15 ohms resistance to ground. I believe you have an 8 foot rod and not 8 inches. And I assume it is vertical.

You said it was a camp site, then later you talk about a pool and home owner.

Does this transformer sevice only one home? Is the transformer between other pole transformers or is it at the end of the primary line?

Do you know what is the meaning of "one order of magnitude"? This would be a factor 10 times, 2 orders is 100, 3 is 1000, and so on.

It seems clear that ideally there should be no primary current flowing in the earth. Since we are lacking information suppose this transformer is at the end of the primary line, that the primary wire is #6 copper, that the distance to the next pole ground rod is 500 ft. The neutral resistance between the pole ground rods would be 0.23 ohms (500 ft of #6 copper). At 20 A that is a voltage drop of 4.6 volts. Thus the approximate voltage gradient in the earth is about 9 MV per foot. Close to the ground rods the gradient will be higher,

A poor connection in the neutral on the poles could cause a much higher gradient.

If the neutral on the poles is good, meaning resistance on the order of what I am assuming, then the gradient in the ground would never be greater than my above estimate.

A voltage field map in various directions will tell you a lot.

.
 

jghrist

Senior Member
How much current flows in the ground and how much in the neutral is complicated. It depends on the mutual inductance between the neutral and earth, between the neutral and the phase wire, the ground resistance of every ground on the multigrounded neutral, and the distance to the source substation, as well as the impedance of the phase wire and neutral.

Phase to ground fault currents generally flow mostly in the neutral close to the fault and close to the substation, but mostly in the earth in the middle part of the line. This is the case for long lines; for short lines almost all of the current stays in the neutral.

Another complicating matter for load currents is that the current in the neutral only has to flow until it is balanced by loads on the other phases. When the three phases are balanced, there is no neutral current (or ground current).
 

mivey

Senior Member
jghrist said:
How much current flows in the ground and how much in the neutral is complicated. It depends on the mutual inductance between the neutral and earth, between the neutral and the phase wire, the ground resistance of every ground on the multigrounded neutral, and the distance to the source substation, as well as the impedance of the phase wire and neutral.

Phase to ground fault currents generally flow mostly in the neutral close to the fault and close to the substation, but mostly in the earth in the middle part of the line. This is the case for long lines; for short lines almost all of the current stays in the neutral.

Another complicating matter for load currents is that the current in the neutral only has to flow until it is balanced by loads on the other phases. When the three phases are balanced, there is no neutral current (or ground current).
But it does not have to be complicated for our rough estimate.

Short transmission lines are generally less than 50 miles. Since we are talking about 7.2 kV, we are nowhere near that distance.

Hopefully, we will be able to get some information on the feeder type and general site layout.
 

glene77is

Senior Member
Location
Memphis, TN
to Mivey,

At 7200V and 20A, I see 144 KW.
At 240V and 144 KW, I see 600A.
I see Some Big Campsite House!

What concerns me is that there is great concern
about missing specifications,
good guesses,
some measurements.

The pool is shocking someone, and needs to be fixed!

If the Service Primary Voltage is 7.2 KV, single phase,
and the Service Primary is 20 Amps, and the Secondary is only 19 Amps ,
and that calculates to 144 KW,
then there is 7.2 KW running somewhere else, perhaps through Earth.

Which brings me back to
The pool is shocking someone, and needs to be fixed!

It sounds like the pool is at some good distance from the house Neutral,
and requires better neutral return to the house Neutral.

Would it be appropriate to measure the Voltage from the pool to earth.
Would it be appropriate to raise the size of the wiring to the pool,
in order to decrease resistance in the Neutral Return Conductors?
Then Measure voltage again?

Would it be appropriate to measure the Voltage from the pool to ground(earth) and try a ground rod at the pool.
Then Measure votage again?

I used to be the electrician at a university hospital, and I measured micro-amps leakage in equipment, which was attached intravenously into patients. The JCAH requires very low available current in patient areas.
Similarly, persons in a pool of ionized (chlorine) water can be subject to shocking experiences at levels lower than the 5 mA. Even tingling shocks can be enough to make swimming difficult, and drowning possible.

For an example, since I did research on this at the university, a persons normal skin resistance (DRY) varies from 10 K ohm to 1 Meg ohm, depending on the person, the calouse layer, the level of perspiration, the after-shave lotion applied by hand, etc. Skin Saturated in chlorine (ionized) water can possibly drop to 1 K ohm.

Continuing the example, let's say there is a pool lamp underwater,
with faulting leakage to the drain (earth).
Let's say the voltage gradient from the lamp to the earth is 30 Volts.
Let's say the distance from the lamp to drain is 12 feet.
Let's say that a persons WET skin resistance is down to 10 K ohm.
Let's say the finger tip to foot distance is 6 feet.
= The voltage gradient from finger to toe is 6/12 * 30 Volts.
= That places 1.5 mA through the human system.
= That tingling shock can make swimming difficult.

This is the real problem at the pool.

Any suggestions on how to resolve the problem,
other than waiting for more measurements and information?
 

mivey

Senior Member
glene77is said:
to Mivey,

At 7200V and 20A, I see 144 KW.
At 240V and 144 KW, I see 600A.
I see Some Big Campsite House! or multiple houses. we can only guess.

What concerns me is that there is great concern
about missing specifications,
good guesses,
some measurements. how do you help solve a problem without information?

The pool is shocking someone, and needs to be fixed! that is the goal

If the Service Primary Voltage is 7.2 KV, single phase,
and the Service Primary is 20 Amps, and the Secondary is only 19 Amps ,
and that calculates to 144 KW,
then there is 7.2 KW running somewhere else, perhaps through Earth. Not correct.

Which brings me back to
The pool is shocking someone, and needs to be fixed! agree again

It sounds like the pool is at some good distance from the house Neutral,
and requires better neutral return to the house Neutral. based on what info?

Would it be appropriate to measure the Voltage from the pool to earth.
Would it be appropriate to raise the size of the wiring to the pool,
in order to decrease resistance in the Neutral Return Conductors?
Then Measure voltage again?

Would it be appropriate to measure the Voltage from the pool to ground(earth) and try a ground rod at the pool.
Then Measure votage again?
I think it would be appropriate to get more information needed to make a diagnosis, which you also seem to agree with.

I used to be the electrician at a university hospital, and I measured micro-amps leakage in equipment, which was attached intravenously into patients. The JCAH requires very low available current in patient areas.
Similarly, persons in a pool of ionized (chlorine) water can be subject to shocking experiences at levels lower than the 5 mA. Even tingling shocks can be enough to make swimming difficult, and drowning possible.

For an example, since I did research on this at the university, a persons normal skin resistance (DRY) varies from 10 K ohm to 1 Meg ohm, depending on the person, the calouse layer, the level of perspiration, the after-shave lotion applied by hand, etc. Skin Saturated in chlorine (ionized) water can possibly drop to 1 K ohm.

Continuing the example, let's say there is a pool lamp underwater,
with faulting leakage to the drain (earth).
Let's say the voltage gradient from the lamp to the earth is 30 Volts.
Let's say the distance from the lamp to drain is 12 feet.
Let's say that a persons WET skin resistance is down to 10 K ohm.
Let's say the finger tip to foot distance is 6 feet.
= The voltage gradient from finger to toe is 6/12 * 30 Volts.
= That places 1.5 mA through the human system.
= That tingling shock can make swimming difficult.

This is the real problem at the pool.

Any suggestions on how to resolve the problem,
other than waiting for more measurements and information?
If cutting off the pool load at the breaker removes the problem, why would you call a lineman out to check into the problem? If it does remove the problem, then the pool has a problem, not the service or primary. I don't think we have the information needed to make that determination, and we are trying to get more information. You are making guesses like everybody else and also requesting more information, so I don't get this:
glene77is said:
What concerns me is that there is great concern
about missing specifications,
good guesses,
some measurements
 

glene77is

Senior Member
Location
Memphis, TN
Gentlemen,
Thank you for the comments.

<If cutting off the pool load at the breaker removes the problem,
<why would you call a lineman out to check into the problem?
<If it does remove the problem,
<then the pool has a problem, not the service or primary.

Good comment, Mivey.
I think Dominc called the Lineman,
and he did not emphasize the Safety Problem at the Pool.

I was only pointing out an obvious trouble-shooting technique.
We all sub-divide our problems, make measurements, and collect info.

<I don't think we have the information needed
<to make that determination,
<and we are trying to get more information.
<You are making guesses like everybody else
<and also requesting more information,
<so I don't get this:
Quote:
Originally Posted by glene77is
What concerns me is that there is great concern
about missing specifications, good guesses, some measurements...

Good comment, Mivey.
As you say, I am guessing, also, just to play out a scenario.
The scenario I laid out shows the possible Safety Problems & dangers.
I was developing a 'rationale' for refocusing the discussion.

The imperative is the safety concern for people involved.
I do hope Dominc gets a solution before somebody is hurt.
 

brian john

Senior Member
Location
Leesburg, VA
Not sure where Dominic is from but in all the years I have done trouble shooting I have yet to investigate a pool stray voltage issue. Willing to look if he is close.

DOMINIC?
 
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