testing grounds
- Thread starter sbyrne
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davidr43229
Senior Member
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- Columbus, Oh
We use a Weaton Bridge that measures down to the .0001 level. I don't hink a Fluke meter or any digital will get that degree of accuracy.
bphgravity
Senior Member
- Location
- Florida
Can you clarify what you are trying to measure? Are you concerned with earth resistance of the electrode system, the surge impedance of the grounding system, or possibly just the resistance of the grounding conuctor to the electrode?
Bob NH
Senior Member
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- The "Live Free or Die" State
I have used a Wheatstone bridge to measure small changes in resistance. Direct measurements of small resistances are often made with a 4-wire system known as a Kelvin bridge.
Google "4-wire resistance measurement kelvin" to get a bunch of links.
Google "4-wire resistance measurement kelvin" to get a bunch of links.
brian john
Senior Member
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- Leesburg, VA
Several manufactures AVO, Fluke, Hioki, AEMC all make an earth ground resistance tester, designed to make two point test (continuity test) 3-point (earth ground resistance) and 4-point (to determine the ohm-meter resistance of a selected area of mother earth).
In the two point test you have to deduct the test cable impedance. In my expierence all these test show <.001 ohms at the selected test current and test voltage.
There is also a test set called a DLRO (micro-ohm meter), this test set uses a higher voltage and current that the typical 2 point test set. This set is normally used for testing contact resistance of switches and circuit breakers, though has other applications such as measuring the resistance of a cable to bus connecion, There are limits on test lead lenghts.
In the two point test you have to deduct the test cable impedance. In my expierence all these test show <.001 ohms at the selected test current and test voltage.
There is also a test set called a DLRO (micro-ohm meter), this test set uses a higher voltage and current that the typical 2 point test set. This set is normally used for testing contact resistance of switches and circuit breakers, though has other applications such as measuring the resistance of a cable to bus connecion, There are limits on test lead lenghts.
I'm trying to determine if the existing ground system in a facility I'm working in can support an intrinsically safe ground system or if i need to modify it in anyway.
all literature i've read says the resistance from any zener barriers to the "main ground electrode" must be 1 ohm or less. It makes no mention of actual earth resistance. Therefore, I'm looking for resistance from panel ground bus to main ground electrode (ring in my specific example).
Am I reading this to literally? Should I consider the earth resistance in the 1 ohm specification? Any input on this subject would be appreciated.
Thanks all.
all literature i've read says the resistance from any zener barriers to the "main ground electrode" must be 1 ohm or less. It makes no mention of actual earth resistance. Therefore, I'm looking for resistance from panel ground bus to main ground electrode (ring in my specific example).
Am I reading this to literally? Should I consider the earth resistance in the 1 ohm specification? Any input on this subject would be appreciated.
Thanks all.
Please don't take this wrong, but you are worried about nothing and don't need to test anything. Here is why:
Assuming your GEC is code compliant of at least a # 8 AWG and no longer than about 900 feet, the resistance is less than 1-ohm. I can't imagine any GEC being more than 1-ohm under any normal code compliant condition. So as long as the GEC is in good repair, meets code, don't sweat it.
As far as a 1-ohm or less earth resistance, that is not ever going to happen, unless someone has a copper mine and corporate financing behind them.
Edited for additional comment:
If this is a distant panel board from the service, there shouldn’t be a problem either as long as a code compliant EGC’s are ran with all circuits. Just make sure everything is AT LEAST code minimum, and in good repair.
Assuming your GEC is code compliant of at least a # 8 AWG and no longer than about 900 feet, the resistance is less than 1-ohm. I can't imagine any GEC being more than 1-ohm under any normal code compliant condition. So as long as the GEC is in good repair, meets code, don't sweat it.
As far as a 1-ohm or less earth resistance, that is not ever going to happen, unless someone has a copper mine and corporate financing behind them.
Edited for additional comment:
If this is a distant panel board from the service, there shouldn’t be a problem either as long as a code compliant EGC’s are ran with all circuits. Just make sure everything is AT LEAST code minimum, and in good repair.
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