Bad Ufer?

[Ursahouse]

New construction. Background: Ufer grounding system for remote subpanel some 200 feet away from service entrance and meter main panel from transformer. Single phase power. Three wire from service entrance 200 amp main panel to 200 subpanel buried in 3-inch PVC conduit. I am using a plug-in type circuit tester which indicates a good ground at less than 10 ohms (not sure how the tester does that). Anyway, the plug-in circuit tester shows a green light indicating a properly wired circuit and ground to earth when testing the receptacles at the service entrance meter panel. There is a 8' or 10' ground rod buried next to and long with the timber service pole. This has all passed inspections. I have also installed the Ufer ground in the foundation of the building some 200 feet away. This passed inspection prior to foundation pour. Its been a few years and I am now completing the work at the subpanel. When I test a receptacle at the subpanel, I get a flash of green light and then it goes to dim red light mode. If I use this same plug-in circuit tester on receptacles located in another older house it gives a green light indicating the circuit and ground are good. I have the Earth ground (Green) and the Neutral conductor bonded together at the service entrance (inspected). I have the Earth ground (Green-Bare) and the Neutral wires separate at the subpanel. We are in a drought here. The ground is very dry now. The founding native ground upon which the Ufer ground foundation rests is fractured to sold high resistive rock. In some places there is clay in fractured zones. In places, there are dikes of granite stone which I had to use a backhoe mounted jackhammer to excavate the foundation upon which the Ufer ground is located. Now that I think about it, the concrete used has a REOMIX admixture that helps prevent water from passing through foundation. This is an earthen-bermed house and I wanted to keep moisture out of the slab. I think I have a very dry foundation and soil profile under the foundation (fractured to solid rock).

I want a proper grounding system for this house. I am not interested in doing only that which is required under NEC.

Questions:

1. Is it likely I have a "Bad Ufer Grounding System".
2. Given that I can not just drive rods into the rock substrate anywhere near the subpanel, is it advisable to go sum 50 feet away where the soil profile is similar to that which provides a good ground for the transformer and service entrance main panel?
3. Other options?

I understand the basic properties I am up against after reading at this site and other grounding issues where shallow or other poor soils conditions exists.

What say you?

Should I be concerned that the plug-in circuit tester

 

[Dennis Alwon]

Questions:

1. Is it likely I have a "Bad Ufer Grounding System".

Not really but even if it were that is not the issue you are having

2. Given that I can not just drive rods into the rock substrate anywhere near the subpanel, is it advisable to go sum 50 feet away where the soil profile is similar to that which provides a good ground for the transformer and service entrance main panel?

I doubt that there is a need for rods

3. Other options?

I would not trust a plug in tester totally. See what you get with a meter and if there is an issue then it is in the wiring

 

[GoldDigger]

In theory, even high resistance base rock can provide a decent ground electrode if the total surface area of the concrete is high enough. That is one of the limitations and strengths of a CEE (Ufer.)
An actual ground electrode resistance measurement (if you can find a usable remote ground) may clarify this. It is not clear to me the extent to which the additive you mention can actually affect the resistivity of the concrete itself.

 

[Curious nerd]

>I get a flash of green light and then it goes to dim red light mode.

As if you were charging a capacitor. The other strength of a Ufer is that the large surface area means a relatively large capacitance to ground. That's a useful contribution to lightning protection even when the DC resistance is high.

I'm not qualified to advise you on what to do here, but it couldn't hurt to research putting in a field of radials.

 

[jim dungar]

I am using a plug-in type circuit tester which indicates a good ground at less than 10 ohms (not sure how the tester does that).

There is absolutely no way that a 'plug-in' tester is measuring the resistance to earth.
At best it is measuring the grounding conductor up to its connection to the neutral.

 

[Smart $]

There is absolutely no way that a 'plug-in' tester is measuring the resistance to earth.
At best it is measuring the grounding conductor up to its connection to the neutral.

I agree with first sentence.

Second sentence... wouldn't such a non-loop measurement require a TDR device? Perhaps measuring neutral to EGC impedance at plug-in location.

 

[Ursahouse]

Bad Ufer

Bad Ufer

Thanks for the replies thus far. I have never used one of these plug-in testers before. I have always just used my Multimeter.

Readings from the multimeter are:
120.4 Volts Leg1 to Neutral,
121.2 Volts Leg2 to Neutral,
120.4 Volts Leg1 to Ufer Ground,
121.2 Volts Leg2 to Ufer Ground.
And 0.14 Volts between Neutral and Ufer Ground--all at subpanel.
Most remote 110 V receptacles read same basic volts, very little difference.
At the service entrance/meter readings are:
120.7 Volts Leg1,
121.6 Volts Leg2,
Of course the neutral and Earth Ground are bonded and the potential difference is zero as measure with the mulitimter.
I am not sure if the 0.14 Volts of potential difference between the isolated Neutral and Ufer Earth Ground at the subpanel is causing the red light?
I have enough romex cable a friend just gave me to run a line over to the service entrance ground rods if that would help conduct a test.

I am ok ignoring the plug-in tester but I it would be nice to know why it is indicating green when the neutral and ground are bonded at the service entrance but red at the subpanel, assuming the Ufer is an adequate earth grounding system at this location. I am interested in establishing a proper grounding system regardless.

Also, this plug-tester does have a capacitor, light stays on for a few seconds after unplugging.

Here is what the manufacturer's representative from Sperry Instruments wrote.
"The tester tests 7 common wiring conditions; I haven?t seen a place where it says 7 ohms. The tester is testing the immediate ground connected to the socket that it?s plugged into. If the ground resistance is greater than 10 ohms, this unit will illuminate a red indicator light to warn of a bad ground at the outlet. It is not designed to test the ground rod, just the ground at the outlet it?s testing. Sometimes there isn?t a ground at all."

Note: The 7 ohms is referenced in the instructions I have for the plug-in tester. Makes no difference to me 7 ohms or 10 ohms. I am not against hiring a grounding expert to help in this but I am more concerned about understanding the problem first.

I should be able to run that romex back to the grounding rods at the service entrance/meter, use all three wires, connect to the neutral wire at the subpanel, and use the plug-in tester. If the light goes green, then I think the plug-in tester is just measuring the potential difference between the neutral and the earth ground.


Is there an issue with 0.14 Volts between Neutral and Ufer Ground at the subpanel?


I apologize if I am writing too much.

 

[starbolin]

...
I want a proper grounding system for this house. I am not interested in doing only that which is required under NEC.

Questions:

1. Is it likely I have a "Bad Ufer Grounding System".
2. Given that I can not just drive rods into the rock substrate anywhere near the subpanel, is it advisable to go sum 50 feet away where the soil profile is similar to that which provides a good ground for the transformer and service entrance main panel?
3. Other options?

I understand the basic properties I am up against after reading at this site and other grounding issues where shallow or other poor soils conditions exists.

What say you?

Should I be concerned that the plug-in circuit tester

Don't guess, instrument. You're an engineer, inject a current into your ground system and measure the induced voltage.

 

[starbolin]

...
Bunch of stuff I don't care about.
...

Is there an issue with 0.14 Volts between Neutral and Ufer Ground at the subpanel?


I apologize if I am writing too much.

Induced voltage, tells you nothing. First question: Is there any indication of a functional problem with the grounding or bonding of your installation?

If you are bored or just want a jolly, using safe wiring practices and under engineering supervision, connect a 60W light bulb between a de-energized non-grounded branch circuit conductor and your Ufer bonding conductor. Temporarily disconnect your Ufer from the GEC. For the purpose of measurement, temporarily energize the branch circuit. Monitor the induced voltage on the earth system. Calculate resistance. Takes longer to write it than it does to do it.

 

[Smart $]

...

Is there an issue with 0.14 Volts between Neutral and Ufer Ground at the subpanel?

...

Depends on whether there was any system current on the neutral conductor. Could just be voltage drop.

The difference in your voltage measurements at subpanel and service indicate that there may be system current on the subpanel feeder neutral: |(120.7-120.4)-(121.6-121.2)|=0.1V... but I realize with one meter you did not take the measurements simultaneously.

Your line voltage measurements have different resolutions (tenths versus hundredths) and indicate no difference among themselves. It appears potential reading error is greater at that range, as they should indicate at least 0.1V difference you measured N-G... and they do not. For viable readings at the low level of difference you are asking about, the meter best be calibrated and accuracy verified.

 

[Ursahouse]

Bad Ufer

Bad Ufer

Thanks for the interest.
I had no reason to believe there was a grounding issue until a purchased the $12 plug-tester.
Is the plug-tester's response what is to expected in this situation?
I understand the potential difference 0.4 v between the N and EG(ufer) when I had the lights on to read the multimeter.
It sounds like I may have an adequate grounding system and a lack of knowledge concerning the plug-in tester.
The soil profile at the site is not conducive to a good ground, that is why I went down this path.

 

[fisherelectric]

Did you say you ran 3 wires to sub-panel and then separated the neutrals and grounds at the sub-panel, using only the ufer as an equipment grounding method? Do you have any connection of your EG to neutral?

 

[Dennis Alwon]

Did you say you ran 3 wires to sub-panel and then separated the neutrals and grounds at the sub-panel, using only the ufer as an equipment grounding method? Do you have any connection of your EG to neutral?

I missed that also. That is a violation. You need 4 wires to the sub panel and then the neutrals and equipment grounding conductor are separated and the grounding electrode conductor gets connected to the equipment grounding conductor bar. It sounds like you are using the grounding electrode conductor as a ground-- that's a no-no

 

[jim dungar]

I agree with first sentence.

Second sentence... wouldn't such a non-loop measurement require a TDR device? Perhaps measuring neutral to EGC impedance at plug-in location.

It is not a no-loop measurement. The plug-in tester connects between the neutral and the ground, which creates a loop if there is the upstream neutral-ground bound which I mentioned.

 

[GoldDigger]

It is not a no-loop measurement. The plug-in tester connects between the neutral and the ground, which creates a loop if there is the upstream neutral-ground bound which I mentioned.

But the tester cannot tell the difference between a local bond, and upstream bond or a downstream bond. If the resistance is too low it may be able to say it is a local bond (but a $12 tester will not have this capability) or it can tell you if the resistance is too high (which a plug-in tester might be able to do), indicating no bond or a high resistance bond.

 

[Smart $]

It is not a no-loop measurement. The plug-in tester connects between the neutral and the ground, which creates a loop if there is the upstream neutral-ground bound which I mentioned.

Okay, that's what I thought. Perhaps I misinterpreted you comment...

Or being a moderator you changed it without an "edited" notation. I could have swore it read different than it does now... :angel:

 

[Ursahouse]

Bad Ufer

Bad Ufer

ok, lots of dialogue.
I was told by the County to run three wire from service entrance to subpanel, this is distance of nearly 200 feet. There are no metal connections other than the three conducting wires from service entry panel to the subpanel..
The Neutral and equipment ground are NOT Bonded at the subpanel as they are at the service enterance; i believe this is right. If this is wrong or it is the issue, I can bond the Neutral to the Ufer ground at the subpanel.

 

[Smart $]

ok, lots of dialogue.
I was told by the County to run three wire from service entrance to subpanel, this is distance of nearly 200 feet. There are no metal connections other than the three conducting wires from service entry panel to the subpanel..
The Neutral and equipment ground are NOT Bonded at the subpanel as they are at the service enterance; i believe this is right. If this is wrong or it is the issue, I can bond the Neutral to the Ufer ground at the subpanel.

3-wire is a violation of recent Code editions. Used to be permitted for new installations. Recent editions require 4 (3 + 1 EGC). Pre-existing is still okay under recent codes.

If the county will let you get by, bond the neutral and ground at the subpanel. That's what we did under older Code. Otherwise, you'll have to pull an EGC.

 

[fisherelectric]

It sounds to me as though you have no EG at the subpanel other than the UFER (GEC) which would account for your not reading a decent ground at your receptacles. If the county told you to run only 3 wires, bond the UFEr and the equipment grounds to the neutral at the subpanel and you should be OK. It's not that your Ufer is "bad", it's that it's not supposed to serve as an equipment ground.

 

[jim dungar]

But the tester cannot tell the difference between a local bond, and upstream bond or a downstream bond. If the resistance is too low it may be able to say it is a local bond (but a $12 tester will not have this capability) or it can tell you if the resistance is too high (which a plug-in tester might be able to do), indicating no bond or a high resistance bond.

A common plug-in tester can tell you the resistance of the conductors creating the loop, they can not tell you the resistance of the loop to the earth/dirt, as the OP described one doing.