Stumped by ground/neutral voltage

[gar]

100720-1241 EST

Petrosa:

Check the line to line voltage at the main panel. If the difference between the two is closer to 0 V instead of the expected 240 V, then both legs have the same phase relative to neutral. If both were the same phase, then a 5 V rise on both relative to earth would be more reasonable.

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[PetrosA]

Update

Update

I finally got back to the customer's house today and found the following:

Voltage from transformer pole ground rod (bonded to primary and secondary neutrals - no neutral blocker) to test rod readings were as high as 95V with heavy load turned on. There were no "culprit" circuits that would eliminate the voltage - as the general load increased, so did the voltage. Voltage disappeared when main was shut off. Voltage did not occur with main disconnect off and whole house on generator power. Resistance from pole ground rod to main disconnect neutral block was 0.1 ohm. There was not enough current available to light a 12V 10W "ambiance" type bulb between pole rod and test rod, but tingling is definitely noticeable. Running the house on one leg did not produce a voltage drop on that leg that would indicate a bad neutral between house and transformer.

A secondary issue discovered today was extreme low voltage - as low as 208 between legs. I've notified and filed a report with the POCO. At this point I feel pretty certain that there's a high resistance connection somewhere in the primary neutral and possibly a bad transformer somewhere down the line.

If any of you feel that I'm on the wrong track, please let me know so I can learn. Thank you all for your excellent assistance with this! I'll let you know what the POCO comes up with.

 

[gar]

100727-2054 EST

PetrosA:

I do not believe you have a power company problem.

208 looks like a line to line voltage for a Y secondary. With no load at the house, disconnect to power company open, measure at the disconnect line to line voltage, and each line to neutral. Close the disconnect and put on a substantial load. Again check the voltages. This relates to your 208 question.

Next measure the voltage difference between direct contact on the power company ground rod and the neutral and EGC terminations in the house main panel with substantial load on one side of neutral only. Preferably with no load on the other side. Should be small, a volt or 2 maybe. If this is the result, then relative to the transformer ground rod as the reference start probing the ground working toward the highest voltage. Hopefully this takes you in a defined direction.

Note: if the voltage drop on the neutral is low, as I expect, based upon your 0.1 ohm or less neutral measurement, then your ground potential relative to the transformer ground rod should drop off as your approach either the transformer ground rod or the grounding electrode at the house.

I expect that some place, maybe a long pipe in the ground is connected to a hot wire from the house, but not from the service wires.

Report back.

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[LarryFine]

A secondary issue discovered today was extreme low voltage - as low as 208 between legs. I've notified and filed a report with the POCO. At this point I feel pretty certain that there's a high resistance connection somewhere in the primary neutral and possibly a bad transformer somewhere down the line.

That's starting to sound correct, and familiar; the same issue came up here (in the forum) a week or two ago.

 

[PetrosA]

100727-2054 EST

PetrosA:

I do not believe you have a power company problem.

208 looks like a line to line voltage for a Y secondary. With no load at the house, disconnect to power company open, measure at the disconnect line to line voltage, and each line to neutral. Close the disconnect and put on a substantial load. Again check the voltages. This relates to your 208 question.

Next measure the voltage difference between direct contact on the power company ground rod and the neutral and EGC terminations in the house main panel with substantial load on one side of neutral only. Preferably with no load on the other side. Should be small, a volt or 2 maybe. If this is the result, then relative to the transformer ground rod as the reference start probing the ground working toward the highest voltage. Hopefully this takes you in a defined direction.

Note: if the voltage drop on the neutral is low, as I expect, based upon your 0.1 ohm or less neutral measurement, then your ground potential relative to the transformer ground rod should drop off as your approach either the transformer ground rod or the grounding electrode at the house.

I expect that some place, maybe a long pipe in the ground is connected to a hot wire from the house, but not from the service wires.

Report back.

.

208 happened to be the absolute lowest voltage I recorded today. The highest was 229 between legs with no load at all. L to N was anywhere from 104V to 114-115V.

Voltage to the pole ground rod was within a few volts whether I probed 6 feet away from it or 30 feet away (both in line with the poles/house and at a 90 degree angle to them. I would have to establish a single, known load to map it out exactly. The reason I don't think it's something leaking in the house is that there isn't one circuit I can shut off that will eliminate the potential between the ground and earth other than the main breaker and a leak would imply that there should be one. The voltage is even measurable between the metal pipe of the floor drain in the basement and any of the copper water pipes or electrical boxes.

 

[PetrosA]

Update

Update

POCO was out last night and confirmed a voltage issue on their end (other customers were also affected). They've referred the ground voltage to another tech who will probably be out today.

 

[gar]

100728-1149 EST

PetrosA:

The low line voltage for the most part is a power company problem. When looking at changes in line voltage it is important to know the corresponding current changes. Your additional information indicates the source is a single phase center tapped transformer. Let's assume the total loop impedance at the main panel and looking toward the power company is 0.1 ohms for neutral, the transformer, and one hot line, then if you placed a 10 A load on this circuit at the main panel the voltage should drop 1 V, and 100 A would cause a drop of 10 V. So a 1500 W 120 V heater can be a useful test tool. It is about 12 A.

Let's review your ground voltage problems.

With the main panel disconnect switch off you measure near 0 V from the transformer ground rod (presumably the same point as the transformer center tap) to any point in the soil or water pipes around the home. My interpretation of this is that there are no stray power company ground currents of any large magnitude.

When the main disconnect is closed, then large voltages are measured in the earth, on water pipes, and on drain pipes. This means if there is no large voltage drop on the neutral to the main panel from the transformer, then the neutral at the main is not bonded to the water system. Therefore, I believe the water piping system, etc. is floating and somewhere there is voltage leaking from one 120 V hot line to the earth and/or the water piping system. If there is an electric hot water heater, then check it.

If I have current in the earth flowing in a north south direction, then two probes aligned in a north south direction should produce a maximum voltage. In an east west direction voltage should be a minimum.

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[hurk27]

That's starting to sound correct, and familiar; the same issue came up here (in the forum) a week or two ago.

Yes this sounds like the problem that was found in this thread:
Trouble shooting customer getting shocked at hose bib

and I did state in that thread that this dangerous problem can happen on pole mounted transformers, but this one does sound like the MGN is lost upstream from the transformer, and may be affecting more then just one transformer, because of this statement:

(other customers were also affected)

The quencher that tells me its the primary neutral of the transformer, is the voltage was measured at the pole ground rod to Earth, this voltage on the grounding always has to come from upstream from the grounding that is measured, and the only thing upstream is the primary neutral/MGN

 

[PetrosA]

Yes this sounds like the problem that was found in this thread:
Trouble shooting customer getting shocked at hose bib

and I did state in that thread that this dangerous problem can happen on pole mounted transformers, but this one does sound like the MGN is lost upstream from the transformer, and may be affecting more then just one transformer, because of this statement:

The quencher that tells me its the primary neutral of the transformer, is the voltage was measured at the pole ground rod to Earth, this voltage on the grounding always has to come from upstream from the grounding that is measured, and the only thing upstream is the primary neutral/MGN

Just for clarity, the problem known to be affecting other customers was the low voltage one.

My gut and the fact that the only way to shut this down is by turning off the whole house is telling me this is a bad neutral on the primary side. I walked a part of it (about 6 poles) and found one splice on that section. The lines run another 8-10 poles along the road through trees before reaching the next customer's cutoff and what looks like a splice to a newer set of lines.

The way I'm imagining the issue at this point is like a partially clogged drain - the faucets work fine and water can flow in, but can't flow out fast enough and has to overflow somewhere. The "overflow" is doing that through the ground system looking for a way back to the last good pole ground.

 

[hurk27]

Just for clarity, the problem known to be affecting other customers was the low voltage one.

My gut and the fact that the only way to shut this down is by turning off the whole house is telling me this is a bad neutral on the primary side. I walked a part of it (about 6 poles) and found one splice on that section. The lines run another 8-10 poles along the road through trees before reaching the next customer's cutoff and what looks like a splice to a newer set of lines.

The way I'm imagining the issue at this point is like a partially clogged drain - the faucets work fine and water can flow in, but can't flow out fast enough and has to overflow somewhere. The "overflow" is doing that through the ground system looking for a way back to the last good pole ground.

Just keep in mind this grounding is what is keeping the voltage in check, if you were to remove this grounding the voltage will go much higher, and if all grounding is removed then it can go as high as the primary, this is the same thing if you take neutrals apart without turning off the circuit, you will have 120 volts between the neutrals, in the primary case, the Earthing is like a resistor placed between the neutrals and keeping the voltage down, this is why I caution anyone who comes upon voltage on the grounding to exercise caution to not take any Earth grounding connections apart or they can find themselves with primary voltage between the connection, and a building on fire. in your case you still have pole Earthing that will keep the voltage down also but even then as you remove more and more parallel paths to Earth the voltage will rise, and the situation will become much more dangerous.

 

[PhaseShift]

Just keep in mind this grounding is what is keeping the voltage in check, if you were to remove this grounding the voltage will go much higher, and if all grounding is removed then it can go as high as the primary, this is the same thing if you take neutrals apart without turning off the circuit, you will have 120 volts between the neutrals, in the primary case, the Earthing is like a resistor placed between the neutrals and keeping the voltage down, this is why I caution anyone who comes upon voltage on the grounding to exercise caution to not take any Earth grounding connections apart or they can find themselves with primary voltage between the connection, and a building on fire. in your case you still have pole Earthing that will keep the voltage down also but even then as you remove more and more parallel paths to Earth the voltage will rise, and the situation will become much more dangerous.

What do you mean when you refer to " the same thing if you take neutrals apart". Are you refering to seperating multiple neutrals with a circuit energized or are you just refering to the fact that when you disconnect any neutral from its load your body will now have a greater resistance then the load and thus the voltage will drop across your body?

So your saying since current is flowing through the ground in this case if you disconnect the ground your body will have a higher resistance then the ground and thus more voltage will drop across your body?

 

[hurk27]

ByhaseShift What do you mean when you refer to " the same thing if you take neutrals apart". Are you referring to separating multiple neutrals with a circuit energized or are you just referring to the fact that when you disconnect any neutral from its load your body will now have a greater resistance then the load and thus the voltage will drop across your body?

So your saying since current is flowing through the ground in this case if you disconnect the ground your body will have a higher resistance then the ground and thus more voltage will drop across your body?

Anytime you open the return conductor in a circuit, the voltage on the load side of this conductor will be at the potential of the other conductor feeding the load, in this case the ungrounded hot conductor.
if the circuit conductor feeding the load has a 120 volt potential to ground, then the open neutral conductor from the load will now have a 120 volt potential to ground.

The same goes for the POCO transformer, its just a load to the primary, and if the primary system is a Y based system this transformer will be connected between a ungrounded conductor and the grounded conductor (MGN) if you loose the MGN connection the voltage on the grounded side of the transformer will be at the ungrounded potential, now if it is connected to the house grounding through the cross connection from primary to secondary neutral bond the voltage will rise on the house grounding proportionally to the resistance of the Earth bond connection, if you remove this connection you will have removed the return path the transformer is now using which in turn will raise the voltage on the neutral as high as the ungrounded conductor feeding the transformer, in my area that would be 7200 volts.

Now in the OP case he has the extra grounding at each pole that adds a parallel resistance to the MGN since the MGN is bad somewhere up stream from his customers transformer, and possibly upstream from his neighbors transformer, so even the neighbors house grounding electrodes will also help keep the voltage down as added parallel resistance, but as these resistance to Earth is removed, the voltage will climb.

 

[PhaseShift]

The same goes for the POCO transformer, its just a load to the primary, and if the primary system is a Y based system this transformer will be connected between a ungrounded conductor and the grounded conductor (MGN) if you loose the MGN connection the voltage on the grounded side of the transformer will be at the ungrounded potential,.

What are you referring to as the MGN. Is this the neutral wire (grounded wire) on the transformer primary that is traveling back to the utility source with the ungrounded conductor?


Are you refering to the secondary neutral (grounded conductor) on the secondary of the transformer when you talk about the grounded side fo the transformer being at ungrounded potential?

now if it is connected to the house grounding through the cross connection from primary to secondary neutral bond the voltage will rise on the house grounding proportionally to the resistance of the Earth bond connection,

What are you referring to as the resistance of the earth bond connection here? Is this the connection between the house ground and remote earth ground through the grounding electrode?

So the voltage on the borken primary neutral is bonded to the transformer secondary which is then connected to house ground and then bonded to earth which provides a path back to the utility source. Is this correct?

So the problem then seems to be a broken neutral on the primary of the utility transformer?


[/QUOTE]

 

[gar]

100730-0659 EST

PetrosA:

Your post #22 refers to a 95 V difference from the pole ground rod to an earth test probe with a heavy load with a 6 to 30 ft distance range. If this voltage drop is from current flow from the transformer neutral, which I expect it is, then closer to the pole ground rod the voltage should be less.

Assuming you can repeat this condition, then pick some point, maybe a 100 ft or more away from the house, then place two test probes in the ground 12 to 30 ft apart at this point. Measure the voltage difference with the heavy house load connected, and with the main disconnect on and off. Move the angle of one probe by 45 deg and repeat, then to 90 deg and repeat. What are the results from the three angular positions of the residual voltages and the voltage changes?

The AC voltage readings in my front yard this morning were 12, 9, and 28 millivolts E-W, NE-SW, N-S. I did not try to find the maximum and minimum orientations.

What I use for distance measurement on each side of the meter is the length of a Fluke test lead plus an extension lead. In this case the total span is about 22 ft.

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[PhaseShift]

The same goes for the POCO transformer, its just a load to the primary, and if the primary system is a Y based system this transformer will be connected between a ungrounded conductor and the grounded conductor (MGN) if you loose the MGN connection the voltage on the grounded side of the transformer will be at the ungrounded potential,

I thought about this one some more. I there was a connection on the secondary through the house ground wont the majority of the voltage drop across the primary transformer winding and therfore the grounded side of the winding wont be at the full ungrounded potential?

Or are you giving an example of the full ungrounded potential on the ground if somone where to break the connection to the house grounding or earth grounding?

 

[gar]

100818-1907 EST

PetrosA:

What have you learned about this problem? Is it the power company or something else that is the source of the ground current?

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[PetrosA]

Sorry for taking so long to get back to this. The POCO was out at the end of last week and their "super tech" confirmed that the neutral was suffering from a high resistance splice about 6 poles from the customer's drop. The line had been broken at some point and they used some kind of spring splicer (I don't remember the exact name of it) that went bad. They redid the splice on the neutral and the problems went away. After the fix, the maximum voltage read from the ground rod was about 5V, which the technician claimed is acceptable (to the POCO) unless there are horses on the property. No one is getting buzzed anymore from the ground system, so we're considering the problem to be fixed. Thank you all for your help!

 

[PhaseShift]

After the fix, the maximum voltage read from the ground rod was about 5V

Was this the voltage measured between the EGC or system ground and the remote ground rod?

 

[PetrosA]

Was this the voltage measured between the EGC or system ground and the remote ground rod?

From the ground rod at the pole where the transformer is located to a wire/screwdriver/rod driven into the ground a few feet away. The same voltage was running throughout the system ground to earth.

 

[hurk27]

while 5 volts doesn't seem like a lot, and it probably won't kill anyone, (not immersed in water) it can be felt if a person is bare foot with a wet ground, hands, clothes, or standing in a shower on a concrete tile floor, if a pool or lake is present then 5 volts would raise a red flag, then you have the possibility to kill someone, because of the inability of a person not being able to get out of the water under this much voltage, but as long as this voltage does not get to far above 10 volts it would not be considered a shock hazard without a pool or lake involved.