GROUND ROD IN CONCRETE

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PWRQUAL

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GROUND RODS TO BE MEASURED ARE DOWN 4 FEET INTO CONCRETE TIED TO A RBAR MESH. i WILL BE DOING A 3POINT IOF POTENTIAL DROP TEST.SINCE MY CURRENT STAKE AND VOLTAGE STAKE WILL NOT PENETRATE THE CONCRETE, I HAVE TAKEN A 1FT WIDE PIECE OF FLAT BAR FOR BOTH THE STAKES TO CLIP TO. i WILL BE PUTTING WATER UNDER THE FLAT BAR TO ENSURE GOOD CONTINUITY. SHOULD THIS TYPE OF ARRANGEMENT WORK.

R/
BEN HALL
 
PWRQUAL said:
GROUND RODS TO BE MEASURED ARE DOWN 4 FEET INTO CONCRETE TIED TO A RBAR MESH. i WILL BE DOING A 3POINT IOF POTENTIAL DROP TEST.SINCE MY CURRENT STAKE AND VOLTAGE STAKE WILL NOT PENETRATE THE CONCRETE, I HAVE TAKEN A 1FT WIDE PIECE OF FLAT BAR FOR BOTH THE STAKES TO CLIP TO. i WILL BE PUTTING WATER UNDER THE FLAT BAR TO ENSURE GOOD CONTINUITY. SHOULD THIS TYPE OF ARRANGEMENT WORK.

R/
BEN HALL
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No. The current distribution will not be controlled and uniform as required for the fall of potential test.
The rebar will form an equipotential plane in the concrete and mess things up even more. And the electrode under test will not be localized. To do a proper fall potential your two test electrodes would have to be many times the slab dimension away.
Use a current clamp ground impedance meter instead if you can find a decent additional ground system for it.
 
Ground rod in concrete

Ground rod in concrete

How can I know how far I would have to set the current stake and voltage stake for fall of potential. Is the 25 ohms to be read when the current rod is at 75 ft and the voltage stake at 62.5% of the distance of the Current rod. I know I need to be out of the flux field
I have a clamp on device, but the switchgear has not been installed, so, no path back. Only a rod a rod out of concrete 4 feet thick and then to rbar mess in soil. I know I need to be out of the flux field of the grounding rod. The building is only about 100 long and 75 ft wide. Again, using a three point measurement

Thanks
 
PWRQUAL said:
How can I know how far I would have to set the current stake and voltage stake for fall of potential. Is the 25 ohms to be read when the current rod is at 75 ft and the voltage stake at 62.5% of the distance of the Current rod. I know I need to be out of the flux field
I have a clamp on device, but the switchgear has not been installed, so, no path back. Only a rod a rod out of concrete 4 feet thick and then to rbar mess in soil. I know I need to be out of the flux field of the grounding rod. The building is only about 100 long and 75 ft wide. Again, using a three point measurement

Thanks
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Since the slab will be at most 100 by 75, you could go about 1000 feet away across undisturbed soil and set your current rod there.
Who is requiring you to make the ground measurement? If the concrete meets the requirements for a CEE/Ufer, the NEC does not care what the measured value is.
 
GoldDigger said:
Who is requiring you to make the ground measurement? If the concrete meets the requirements for a CEE/Ufer, the NEC does not care what the measured value is.
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I second the question and even if the concrete does not meet the requirements for a CEE, since there is more than one rod the NEC still doesn't care.


Roger
 
PWRQUAL said:
...I know I need to be out of the flux field of the grounding rod....
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To clarify, you need to be outside the zone of influence of anything conductive connected to the electrode.

This includes Ufer rebar, water mains, gas pipes, or substation fences if they exist. Otherwise these will short-circuit your test.
 
Measuring ground rod reistance.

Measuring ground rod reistance.

Our earth ground measuring meter has relatively short leads. max 75 ft for the current probe. I have made some current probes with a distance of 500 ft for the current probe, voltage probe, 330 ft and ground rod probe is 166 ft. I have measured the resistance of the cabling and since I am measuring a series es voltage drop, I should be able to deduct the actual cabling 14 gauge wiring resistance from the outcome. The building that I am taking measurements has a concrete slabe, 75 by 100 and with a r-bar grid. Trying to get a way from the ground rod and equipotential has me making up extra long cables. Someone on the forum said, that if a mesh, metal or re-bar is welded together and form one plate in regards to mother earth, that the NEC does not require the 25 ohm measurement. If that is so, where do I find it. I have 2011 code. That would be a blessing. I am somewhat skepitical of running conductors out to 500 ft or more. The meter says it has a potential of 50 VAC. Seems kinda weak. (6) 1.5 vdc batteries

Thanks for brain storming this one with me. I am appreciative in advance. It is a federal government job.

r/
Ben
 
You cannot test this with Dead Fall Potential as the distances involved are to great, and there is no way you can take it from multiple angles without crossing buried metallic structures like water pipes Telephone cables, ect.

However there is a much easier way and more accurate that takes less than 5 minutes. Use a Ground Loop Tester Clamp Meter like an AEMC 3731 Ground Resistance Tester.

3731.jpg
 
ground rod in concrete.

ground rod in concrete.

dereckbc said:
You cannot test this with Dead Fall Potential as the distances involved are to great, and there is no way you can take it from multiple angles without crossing buried metallic structures like water pipes Telephone cables, ect.

However there is a much easier way and more accurate that takes less than 5 minutes. Use a Ground Loop Tester Clamp Meter like an AEMC 3731 Ground Resistance Tester.

View attachment 10647
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the ground rod is not connected yet to neutral and so no complete path for using a clamp on. However, thank you for the suggestion. I have come many miles on grounding education since I started on the forum. Thanks a lot, team.

r/
Ben
 
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