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Old 05-30-2018, 06:10 PM   #1
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Default fall of potential grounding testing

is fall of potential testing practical for outside processing plants, i'm guessing larger than 20 acres.

all of the structures have ground rings and they are all connected

by my understanding of fall of potential testing you should be 8 to 10 times the largest diagonal of the ring away from the ring with your injector

so say a new structure is built inside the existing facility and a new ring installed.

1-if you tie the new ring to the existing stuff and do the fall of potential test don't you need to test outside of the facility? 8 to 10 times further away from entire facilities interconnected rings. your green rod at the ring , injector 8 to 10 x away and measurement probe in the 60% area(multiple spots)

2- even if you leave the new ring unhooked from existing do you know anything by testing outside of only the new ring (the existing is going to influence (lower) the readings right?)

3-is there a better option for testing the grounding system in this scenario?
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Old 05-30-2018, 07:02 PM   #2
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You could do the Intersecting Curves Method.
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Old 05-30-2018, 07:18 PM   #3
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Why are you testing ground rings? FOP is for rods. If your ground ring is above 25 ohms, a "supplemental" ain't going to help.

http://en-us.fluke.com/products/eart...und-clamp.html
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Old 05-30-2018, 07:30 PM   #4
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Why are you testing ground rings? FOP is for rods. If your ground ring is above 25 ohms, a "supplemental" ain't going to help.

http://en-us.fluke.com/products/eart...und-clamp.html
you can use fop for rings as well you go out from ring with your injector 8 to 10 times the largest diagonal of the ring


we aren't measuring for 25 more like we have to be below 1 ohm in substations and 5 ohms everywhere else

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Old 05-30-2018, 07:34 PM   #5
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You could do the Intersecting Curves Method.
http://accelconf.web.cern.ch/accelco...rs/tups062.pdf

found this article on your method, along with slope and the problems with using FOP in a similar situation to my question

thank you very much, i have never heard of this before. do you know if this is accepted by ieee in any way?

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Old 05-30-2018, 07:45 PM   #6
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looks like star-delta method might be better for testing the smaller systems, anyone know much about this method or used it? or another good one for my scenario?
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Old 05-30-2018, 08:04 PM   #7
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you can use fop for rings as well you go out from ring with your injector 8 to 10 times the largest diagonal of the ring
You can, but why? What are you expecting to find? Ground rings by their nature have about the most soil contact of all the methods, and there isn't much you could do to improve it.
"8 to 10 times the largest diagonal of the ring"? What if it's 500 feet, as in a warehouse? You'd need 4,000 to 5,000 feet of lead wire.
Make your maintenance supervisor spring for the Fluke.
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Old 05-30-2018, 08:07 PM   #8
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You can, but why? What are you expecting to find? Ground rings by their nature have about the most soil contact of all the methods, and there isn't much you could do to improve it.
"8 to 10 times the largest diagonal of the ring"? What if it's 500 feet, as in a warehouse? You'd need 4,000 to 5,000 feet of lead wire.
Make your maintenance supervisor spring for the Fluke.
yep


ieee standards actually require below 1 ohm resistance in substations, so you have to test, and if you test correctly you might actually find more than one ohm believe it or not



we have to below 5 ohms everywhere else


this star delta method reduces the footage you are concerned about(as was i)

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Old 05-30-2018, 08:09 PM   #9
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http://accelconf.web.cern.ch/accelco...rs/tups062.pdf

found this article on your method, along with slope and the problems with using FOP in a similar situation to my question

thank you very much, i have never heard of this before. do you know if this is accepted by ieee in any way?
I remember reading about this from the Megger manual on testing large ground systems when researching problems in a expansive antenna farm.
see http://www.weschler.com/_upload/site...owntoearth.pdf
Section III and appendix IV

Megger always has neat stuff to learn about.
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Old 05-30-2018, 08:11 PM   #10
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http://www.electricenergyonline.com/...of-Testing.htm

http://www.weschler.com/_upload/site...owntoearth.pdf
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Old 05-30-2018, 09:07 PM   #11
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Beyond 8-10 electrodes the resistance decrease is insignificant. In cases where I get high readings it's because the soil conductivity is awful. At that point the choices are to fix the soil or go Ufala. Filling your trench with bags of concrete or a couple yards from a truck is generally the cure. Concrete is hygroscopuc so it sucks up moisture and keeps the ground moist. Only trouble with it is corrosion issues.

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Old 05-30-2018, 11:24 PM   #12
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Beyond 8-10 electrodes the resistance decrease is insignificant. In cases where I get high readings it's because the soil conductivity is awful. At that point the choices are to fix the soil or go Ufala. Filling your trench with bags of concrete or a couple yards from a truck is generally the cure. Concrete is hygroscopuc so it sucks up moisture and keeps the ground moist. Only trouble with it is corrosion issues.

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Paul then if you take into account the concrete slabs that are most likely either intentionally or by design tied into the grounding electrode system and then any metallic utility piping it is hard to imagine you could get the ground resistance any lower for a facility as described.
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Old 05-31-2018, 04:47 PM   #13
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Paul then if you take into account the concrete slabs that are most likely either intentionally or by design tied into the grounding electrode system and then any metallic utility piping it is hard to imagine you could get the ground resistance any lower for a facility as described.
i agree, but you don't know what your resistance is until you measure it.
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Old 05-31-2018, 05:52 PM   #14
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Beyond 8-10 electrodes the resistance decrease is insignificant. In cases where I get high readings it's because the soil conductivity is awful. At that point the choices are to fix the soil or go Ufala. Filling your trench with bags of concrete or a couple yards from a truck is generally the cure. Concrete is hygroscopuc so it sucks up moisture and keeps the ground moist. Only trouble with it is corrosion issues.

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do you know if limestone (crushed stone used in concrete) back-fill is a desirable back-fill? probably corrosive to copper like concrete to though huh?

do you know of a good back-fill that's not corrosive? even with less conductivity adding properties
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Old 05-31-2018, 09:15 PM   #15
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do you know if limestone (crushed stone used in concrete) back-fill is a desirable back-fill? probably corrosive to copper like concrete to though huh?

do you know of a good back-fill that's not corrosive? even with less conductivity adding properties
Limestone is not inherently corrosive. It's basically inert and neutralizes acids. Concrete often has residual lime which is why the pH is high and both are highly buffered but concrete plus rebar in contact with copper sets up galvanic corrosion. Copper by itself is fine. Limestone is fairly well drained. The ideal backfill has some clays for water retention but still packs well like any good base. The good drainage is an advantage though on the top layer in a substation where they intentionally want a well drained insulator between the linemen and the ground grid although granite is preferred for that.

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Old 06-01-2018, 04:55 PM   #16
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Limestone is not inherently corrosive. It's basically inert and neutralizes acids. Concrete often has residual lime which is why the pH is high and both are highly buffered but concrete plus rebar in contact with copper sets up galvanic corrosion. Copper by itself is fine. Limestone is fairly well drained. The ideal backfill has some clays for water retention but still packs well like any good base. The good drainage is an advantage though on the top layer in a substation where they intentionally want a well drained insulator between the linemen and the ground grid although granite is preferred for that.

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ive asked some others and im going to research 75% limestone washings with 25%bentonite clay for the bottom 8' and crushed stone for the top 2 (all just going to be approximated)
dennis alwon let me know bentonite clay is used for chemical ground rods

ive read you dont want only bentonite though incase it drys up

thanks man

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Old 06-01-2018, 05:01 PM   #17
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anyone hear the term "IONIC ELECTRODE ground rod" before, sounds like standard ground rod, ive never heard that term, not coming up well in google

http://www.ground1.com/ground_rod_installation.htm

looks like its ionic because of high ionic content surrounding it?

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Old 06-01-2018, 06:23 PM   #18
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ground testing in difficult installations

https://www.netaworld.org/sites/defa...ips-Jowett.pdf
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