Voltage in Ground

Silverstang12287

New User
Location
Green Lane, PA
Occupation
Electrician
This one has me perplexed as well as my electric company…

I live in a subdivision with 5 homes on one transformer…I was installing a light in my drop ceiling in my basement and when I grabbed the ground wire I got a shock. From the drop ceiling track to ground was 13 volts. I have metal studs in my basement, and I assumed I had a “knicked” wire causing the voltage to my drop ceiling. I started turning off breakers, and I still had the voltage. I then decided to shut off the main, and I was shocked when I still had voltage. I started checking other things in my basement. From a metal door frame to ground, I had 13 volts. Even from bare concrete floor to ground I had 13 volts. I then went out to the meter (200 amp underground service) and ground rod. I stuck a screwdriver in the ground and held one lead from my meter onto the screwdriver and the other lead on the ground rod. I got 13 volts across that. I pulled the meter and went from neutral (utility side) to the ground rod, and get nothing. I called the electric company, and then they showed up. They deemed it a broke neutral, and installed a phase saver. That did not fix the problem. They even went out to the street, and shut the power off at the street to the transformer. That did not fix it. They then thought maybe it was the cable company line causing it. They disconnected the feed to my house for the cable, and then it stopped. Wow! So it was my cable company causing this?? We thought the problem was solved. The electric company started reconnecting the neutral in the meter, and bam! I have the voltage back. Keep in mind, the cable company feed is still disconnected. I then convinced them to check my neighbors homes around me (1/4 mile away in each direction), they came back and told me they have the same voltage readings from ground to ground rod. There suggestion is to put me on an isolated transformer and isolate the neutral. Does that seem like the best solution? I also asked them if they think they should do that for all the neighbors, and they said “they didn’t report and issue”, even though they now know it is present. Do you think it is the cable company?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The utility has a problem with the primary neutral that serves the transformers in the area. The utility connects the primary and secondary neutrals together at transformers that supply a grounded system. The primary neutral has a high resistance or is open. The primary neutral current is flowing via the grounding electrode systems at each house through the earth. The voltage is the voltage drop on this path for the primary neutral current.

The cable shield is connected to the grounding system at each house, so if they opened your service neutral, the voltage would still come in via the cable that is connected to the grounding system at your house.

If they install a transformer where the primary and secondary neutrals are not connected, the can make the problem go away at your property, but they still have a problem and it will not get better by itself. They really need to find the actual source of the problem.
 

romex jockey

Senior Member
Location
Vermont
Did any of them give you the correct answer?
yes & no Don

the technically code related correct answer would be ECG's , GEC's and all 'bare metal' things considered groundING should not be returning current.

the answer in terms of electrical theory, however, is that this is often not the reality.

that said, the smart ones end up here>>>https://en.wikipedia.org/wiki/Earthing_system

~RJ~
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
yes & no Don

the technically code related correct answer would be ECG's , GEC's and all 'bare metal' things considered groundING should not be returning current.

the answer in terms of electrical theory, however, is that this is often not the reality.

that said, the smart ones end up here>>>https://en.wikipedia.org/wiki/Earthing_system

~RJ~
Assuming you are connecting the GEC to the metal underground water pipe and that the main bonding jumper has been installed, and you have a common underground metal water pipe that connects to multiple buildings in the area, the spark or arc is because you are creating a parallel path for the grounded conductor current and the current will flow on all of the possible paths.
In older areas with copper water service lines and cast iron water mains that have physical connections between the sections of main, it is not uncommon to find 20% of more of the grounded conductor current flowing on the water line via the GEC and the MBJ.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Unless the service is drawing an unusually high amount of power I would think that any arcing along the parallel path that Don describes is a sign that the grounded conductor also has some issues.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Unless the service is drawing an unusually high amount of power I would think that any arcing along the parallel path that Don describes is a sign that the grounded conductor also has some issues.
Nope....it is a parallel path and the current will divide based on the impedance's of the paths. In my area, the impedance of the path via water pipe is low enough that you will have 20% or more of the grounded conductor current flowing via the water pipe.

You can see a arc when you make and break a connection with current flows less than one amp.
 

GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
Nope....it is a parallel path and the current will divide based on the impedance's of the paths. In my area, the impedance of the path via water pipe is low enough that you will have 20% or more of the grounded conductor current flowing via the water pipe.

You can see a arc when you make and break a connection with current flows less than one amp.
But can you still see an arc if the parallel path is keeping the voltage down to a couple of volts? Probably.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
But can you still see an arc if the parallel path is keeping the voltage down to a couple of volts? Probably.
Yes, you can see an arc when you short out a D cell.

Typically unless there is a problem with the service neutral, the voltage drop will be only a couple of volts. This is just a current divider circuit, when you connect the grounded conductor via the MBJ and GEC to the common metal underground water pipe system.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
This one has me perplexed as well as my electric company…

I live in a subdivision with 5 homes on one transformer…I was installing a light in my drop ceiling in my basement and when I grabbed the ground wire I got a shock. From the drop ceiling track to ground was 13 volts. I have metal studs in my basement, and I assumed I had a “knicked” wire causing the voltage to my drop ceiling. I started turning off breakers, and I still had the voltage. I then decided to shut off the main, and I was shocked when I still had voltage. I started checking other things in my basement. From a metal door frame to ground, I had 13 volts. Even from bare concrete floor to ground I had 13 volts. I then went out to the meter (200 amp underground service) and ground rod. I stuck a screwdriver in the ground and held one lead from my meter onto the screwdriver and the other lead on the ground rod. I got 13 volts across that. I pulled the meter and went from neutral (utility side) to the ground rod, and get nothing. I called the electric company, and then they showed up. They deemed it a broke neutral, and installed a phase saver. That did not fix the problem. They even went out to the street, and shut the power off at the street to the transformer. That did not fix it. They then thought maybe it was the cable company line causing it. They disconnected the feed to my house for the cable, and then it stopped. Wow! So it was my cable company causing this?? We thought the problem was solved. The electric company started reconnecting the neutral in the meter, and bam! I have the voltage back. Keep in mind, the cable company feed is still disconnected. I then convinced them to check my neighbors homes around me (1/4 mile away in each direction), they came back and told me they have the same voltage readings from ground to ground rod. There suggestion is to put me on an isolated transformer and isolate the neutral. Does that seem like the best solution? I also asked them if they think they should do that for all the neighbors, and they said “they didn’t report and issue”, even though they now know it is present. Do you think it is the cable company?
Cable company lines don’t cause this.
you never said if it was overhead lines or underground lines.
It’s definitely a POCO issue.
It doesn’t have the entire company perplexed, just the ones that are inexperienced and don’t understand electricity.
Call again and ask for an engineer. Explain your problem and what the linemen found at your place and the neighbors.
The recommendation to install an isolation XF is just stupid.
If it’s overhead lines they need to check the connections at all the double dead ends or taps back to the three phase.
If it’s underground and unjacketed CN cable the CN could be degraded and non existent. We had this happen and give a strong shock to everyone exiting a pool.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I pretty much stand by my statement. Maybe I'd chang 'any arcing' to 'any arcing that matters'. I mean, how does a meter bypass work?
 

romex jockey

Senior Member
Location
Vermont
Assuming you are connecting the GEC to the metal underground water pipe and that the main bonding jumper has been installed, and you have a common underground metal water pipe that connects to multiple buildings in the area, the spark or arc is because you are creating a parallel path for the grounded conductor current and the current will flow on all of the possible paths.
In older areas with copper water service lines and cast iron water mains that have physical connections between the sections of main, it is not uncommon to find 20% of more of the grounded conductor current flowing on the water line via the GEC and the MBJ.
the MBJ in our TN-C-S system being the fundamental flaw Don.

That one can legally install multiple MBJ's within any given structure , then legally dispense with them via 250.6

The NEC literally lines one up for failure , while insisting itself 'not a design' manual

~RJ~
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
the MBJ in our TN-C-S system being the fundamental flaw Don.

That one can legally install multiple MBJ's within any given structure , then legally dispense with them via 250.6

The NEC literally lines one up for failure , while insisting itself 'not a design' manual

~RJ~
Without that there is no fault clearing path unless you get the utility to run an additional conductor from their transformer.

You can install multiple MBJs, only if you have multiple service disconnects, and 250.6 never permits you to eliminate a code required MBJ.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I pretty much stand by my statement. Maybe I'd chang 'any arcing' to 'any arcing that matters'. I mean, how does a meter bypass work?
Just like any other switch, and there is arcing on making and breaking the connection, just like touching GEC to the metal water pipe.
 

romex jockey

Senior Member
Location
Vermont
Without that there is no fault clearing path unless you get the utility to run an additional conductor from their transformer.

You can install multiple MBJs, only if you have multiple service disconnects, and 250.6 never permits you to eliminate a code required MBJ.
And most ahj's would agree with you Don , despite the vagueness of 250.6

That said, the power quality EE's pick it right on out

Having been the EC caught between the two factions , i can honestly say this is where NEC code, and electrical theory collide

~RJ~
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
And most ahj's would agree with you Don , despite the vagueness of 250.6

That said, the power quality EE's pick it right on out

Having been the EC caught between the two factions , i can honestly say this is where NEC code, and electrical theory collide

~RJ~

While removing a grounding electrode may reduce stray current, IMO it increases the odds of something remaining energized like building steal or a water pipe while simultaneously increasing the dangers of an open neutral.

In most places around the globe where a property is fed via overhead supply TT earthing is chosen by default.

All grounding electrodes present, but the MBJ substituted for one or more RCDs.
 
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